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The Economics and Law of Invasive Species Management in Florida


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THE ECONOMICS AND LAW OF INVASIVE SPECIES MANAGEMENT IN FLORIDA By DAMIAN C. ADAMS A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2007 1

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2007 Damian C. Adams 2

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ACKNOWLEDGMENTS I would like to thank my committee chair, Dr. Michael Olexa for his guidance and encouragement over the last several years. While I was languishing in the intellectual desert that is law school, Dr. Olexa provided a welcome oasi s. Working with him as researcher for the Agricultural Law Center rekindled my interest s in agriculture and inspired me to pursue a Masters degree in the Food and Resource Economi cs Department. Without Dr. Olexa, I might never have headed down the PhD path. For that and for the time he has spent helping me navigate the PhD coursework and dissertat ion red tape, I sincerely thank him. I would also like to thank my committee co-chair, Dr. Donna Lee. Dr. Lee has provided countless hours of input and guida nce on my research into the economics of invasive species. Dr. Lee has had a very big impact on my development as a researcher and an economist. Chapters two and three of this dissertation were wholly inspired by a c ourse that she taught. She also helped me secure grant funding for the aquatic pl ants research, and we have since collaborated on other grant-funded projects. Dr. Lee is a wond erful researcher, a keen thinker, and a friend. I value her advice and admire her outlook on life, and hope to mirror her success. I also thank Dr. Richard Kilmer, who is a wonderful mentor and perhaps the most industrious person I know. I have enjoyed our co nversations on myriad topics very much, and hope to be even half as productive as he has been. I would also like to thank Dr. John VanSickl e. His feedback and his time are greatly appreciated. I benefited from hearing his persp ective on this topic (and others) very much. I also thank Dr. Roy Carriker. Dr. Carriker provided me with my first teaching opportunity, for which I am eternally grateful. He has also been a wonderful source of information on Florida water policy and law issu es over the years. His time and input is appreciated. 3

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I would like to thank Dr. Ricky Telg. Dr. Telg has invaluable feedback on my dissertation and has helped me to greatly improve its quality. Lastly, I would like to that t hose outside of the UF campus w ho have helped me keep my sanity while writing my dissertation. These in clude my mom and other family members who have supported me and provided endless joke mate rial; my friends, who were always there to make sure I did not get too mired in schoolwork; my golden retriever, Glen, a great companion; and Alison Lutz, who provided so much feedback on my dissertation that she should have been on the committee. I am eternally indebted to all of them. 4

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TABLE OF CONTENTS page ACKNOWLEDGMENTS ...............................................................................................................3 LIST OF TABLES ...........................................................................................................................7 LIST OF FIGURES .........................................................................................................................8 ABSTRACT .....................................................................................................................................9 CHAPTER 1 INTRODUCTION................................................................................................................. .11 Zebra Mussels .........................................................................................................................13 Hydrilla, Water Lettuce, and Water Hyacinth ........................................................................14 Legal Basis for State Cont rol of Invasive Species ..................................................................17 Summary .................................................................................................................................18 2 OPTIMAL INVESTMENT IN PREVEN TION AND CONTROL OF A POTENTIAL INVADER: THE CASE OF ZEBRA MU SSELS IN FLORIDA WATERWAYS...............20 Introduction .............................................................................................................................20 Background on Invasive Species in the United States ............................................................21 The Invasive Freshwater Zebra Mussel ..................................................................................21 Will Zebra Mussels Invade Florida? .......................................................................................23 Model of Lake Okeechobee Zebra Mussel Infestation ...........................................................24 Zebra Mussel Spread and Distribution ...................................................................................25 Bioeconomic Model of the Zebra Mussel Threat to Lake Okeechobee .................................29 Empirical Approach .........................................................................................................32 Arrival and Survival ........................................................................................................33 Reproduction and Spread ................................................................................................35 Direct Economic Costs and Damages .............................................................................37 Ecological and Recreational Damages ............................................................................41 Effectiveness of Management Methods ..........................................................................44 Policy Scenarios and Results ..................................................................................................45 Conclusion ..............................................................................................................................52 3 BIOECONOMIC MODEL OF INVAS IVE AQUATIC PLANTS HYDRILLA VERTICILLATA (HYDRILLA), EICHHORNIA CRASSIPES (WATER HYACINTH), AND PISTIA STRATIOTES (WATER LETTUCE) FOR FLORIDA LAKES...................................................................................................................................56 Introduction .............................................................................................................................56 Invasive Species Background .................................................................................................56 Hydrilla, Water Hyacinth, and Water Lettuce Past Management ..........................................58 5

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Invasive Aquatic Plant Control ...............................................................................................61 Bioeconomic Modeling of Invasive Species ..........................................................................62 Empirical Approach ................................................................................................................63 Data Sources and Description .........................................................................................64 Hydrilla and Floating Plants Growth Models ..................................................................66 Aquatic Plant Management Scenarios .............................................................................69 Recreational Fishing Effort Model ..................................................................................72 Hydrilla, Water Hyacinth, and Wa ter Lettuce Treatment Cost Model ............................79 Angler Effort Value Model .............................................................................................80 Economic Effects of Invasive Aquatic Plant Management ....................................................80 Conclusion ..............................................................................................................................86 4 THE LEGAL BASIS FOR REGULATORY CONTROL OF INVASIVE AGRICULTURAL PESTS IN FLORIDA.............................................................................88 Introduction .............................................................................................................................88 Use of Police Power to Take Private Property .......................................................................90 Limitations on Police Power ...................................................................................................92 Substantive Due Process and Procedural Due Process ....................................................92 Just Compensation ...........................................................................................................93 Comparing the Limitations on the Use of Police Power: Spreading Decline versus Citrus Canker ......................................................................................................................93 Spreading Decline ...........................................................................................................93 Citrus Canker ...................................................................................................................94 Lessons for Citrus Greening ..........................................................................................100 Conclusion ............................................................................................................................101 5 SUMMARY AND CONCLUSIONS...................................................................................103 Introduction ...........................................................................................................................103 Summary and Conclusions Regarding the Pote ntial Infestation of Zebra Mussels in Florida ...............................................................................................................................104 Summary and Conclusions Regarding I nvasive Aquatic Plants in Florida ..........................106 Summary and Conclusions Regarding the Re gulatory Basis for Controlling Invasive Agricultural Pests in Florida .............................................................................................108 Conclusion ............................................................................................................................110 APPENDIX A ZEBRA MUSSEL INFORMATION SURVEY..................................................................112 B SENSITIVITY ANALYSIS OF ZEBRA MUSSEL PARAMETERS.................................120 LIST OF REFERENCES .............................................................................................................121 BIOGRAPHICAL SKETCH .......................................................................................................137 6

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LIST OF TABLES Table page 2-1. Lake Okeechobee surface water suppl y by sector and county, year 2000. ............................26 2-2. Zebra mussel model parameter values. ...................................................................................46 2-3. Present value estimates of zebra mussel policy scenarios (20 year, 2006 $ million) .............47 2-4. Simulation results compared to Policy I (Do nothing) (present value, 2006 $ million). ........48 3-1. Hydrilla and floating plants gr owth function parameter estimates. ........................................69 3-2. Model assumptions for policy scenarios. ...............................................................................70 3-3. Date of second herbicide treatments for C20. ........................................................................71 3-4. Angler effort regression model parameters. ...........................................................................77 3-5. Annual economic impact of invasive aquatic plant management on 13 lakes. ......................82 B-1. Sensitivity analysis of zebra mussel parameters. .................................................................120 7

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LIST OF FIGURES Figure page 2-1 2006 US Geological Survey map of zeb ra mussels in the United States. ..........................22 2-2 Lake Okeechobee waterway. .............................................................................................38 2-3 Zebra mussel policy impacts on cumu lative probability of infestation. ............................50 3-1 Simulated hydrilla coverage in Lake Istokpoga. ................................................................73 3-2 Simulated hydrilla cove rage in Lake Kissimmee. .............................................................74 3-3 Simulated hydrilla cove rage in Lake Weohyakapka. ........................................................75 3-4 Daily fishing effort lost to invasive aquatic plants for a 10,000 acre lake in Florida. .......79 3-5 Impact of invasive plant control on fishing effort (Lake Jackson example) ......................83 8

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Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy THE ECONOMICS AND LAW OF INVASIVE SPECIES MANAGEMENT IN FLORIDA By Damian C. Adams May 2007 Chair: Michael T. Olexa Cochair: Donna J. Lee Major: Food and Resource Economics Invasive species impact Florida's ecology a nd economy across multiple dimensions. This dissertation examines the impacts of five invasive species in Florida, and evaluates management responses that follow. It firs t discusses potential infestation of Lake Okeechobee by invasive zebra mussels over twenty years using a bioecono mic model. Next, it estimates invasive aquatic plants impacts on freshwater fishing in Florida. Lastly, it analyzes the legal foundations for state control efforts with respect to invasive species. Zebra mussels are a serious threat to Lake Okeechobee, which is vital to agricultural producers and anglers and provide s numerous ecosystem services. A bioeconomic model in a stochastic dynamic simulation framework estimat es the impact of zebra mussels on recreation, surface water users, and ecosystem services over 20 years. Wit hout state intervention it is $349.34 million. Policy responses were simulated. The cost-minimizing choice is to invest in arrival prevention and early warning, which reduces costs by 70.91% and is the only policy choice with positive returns ($247.71 million) compar ed to no control of zebra mussels. Postestablishment eradic ation yields large losses. This study indicates that investment in arrival prevention is more cost effective than post-arrival eradication. 9

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Invasive plants have significant negative impacts on water-based recreation. Despite the high impacts, little economic research has quantif ied these impacts in a way useful to invasive species managers. Economic research conducted on aquatic invasive species usually focuses on a single lake, or is too abstract for managers. Data are usually unavailable for larger-scale studies. This study uses unpublished data to estimate the impact of plant coverage on fishing activity on 13 Florida lakes using a bioeconomic model. Policy response simulations estimate the impacts over five years. The results sugge st that the optimal management policy is maintenance control with respect to hydrilla, wate r hyacinth, and water lettuce. The dissertation then examines the failure of the states Citrus Canke r Eradication Program (CCEP). The CCEP cases are precedent for subse quent pest eradication program challenges. The State's power to take property, due process, and just compensation are reviewed. Lessons for subsequent eradication programs are provided. 10

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CHAPTER 1 INTRODUCTION The relatively free and rapid movement of pe ople and goods across the globe has led to an increase in the invasion rate of many brittle ecosystems by prolif ic and destructive plants and animals (Vitousek et al., 1996; Mack, 2000). Once introduced to new areas, some of these species become invasive, causing a signifi cant proportion of environmental changes worldwide. Invasive species in the United Stat es pose serious ecological and economic problems (Evans, 2003). An invasive species is define d as a non-native species w hose introduction causes or is likely to cause economic or environmental harm or harm to human health (Executive Order 13112, 1999). Invasive species are a pa rticular problem for the tropi cal and subtropical areas of Florida, where physiographic, climatic and geogr aphic characteristics make it relatively easy for non-indigenous species to establish (Simberl off, 1997; Fox [persona l communication], 2007). Florida has a high rate of non-nativ e species introduction, with the Port of Miami receiving about 85% of non-native plant shipments each year (OTA 1993). For example, the entire United States has about 50,000 established non-native plant and an imal species, with Florida alone having over 25,000 as exotic ornamentals (Pimentel, 2003); ov er 1,300 have established in natural areas, and 124 of these are destructive to natural area s (FLEPPC, 2006). By comparison, Florida only has 2,500 native plant species, and the US has 18,000 native species. Invasive species are a grow ing economic concern. Today, there are an estimated 5,000 to 6,000 invasive species in the Unite d States (Pimentel, 2003; Burnha m, 2004), and invasive plants are invading about 700,000 hectares/year of natural areas in the US (Pim entel et al., 2000). The detrimental problems resulting from invasive species have multiple dimensions. Adverse ecological impacts, such as the disp lacement of native speci es (both related and 11

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unrelated), leading to a reduction in the loss of native bio-diversity may cause severe disruption of complex natural ecosystems. They can have devastating ecological impacts, and may be the primary cause of biodiversity loss (Mack, 2000). Economic impacts can follow close behind such detrimental ecological changes, affecting both the quality (and/or quantity) of public goods, and the interests of private entities. For example, the reduction of recreational benefits de rived from public waterways (and the costs of managing offensive invasive species) highlights the public good dimension. Other effects, such as a reduction in property values and/or incurred mitigation costs, have an impact on private citizens and businesses, as well. Economic damage s from invasive species are estimated to be $137 billion/year excluding ecosystem impact s (Pimentel et al., 2000). About 25% of US agricultural production is lost to non -native pests or to their associ ated control costs (Simberloff, 2002). When considering the well-documented impacts of certain invasive species, such as damages caused by Hydrilla verticillata in Florida, or the zebra mussel in the Great Lakes, it is clear that invasive species can ha ve dire economic consequences. With continuing increases in both global trade and the domestic and international migration of people to Florida, the rate of arri val of non-native species is rising. Invasive species management is fast becoming a high priority fo r the protection of Flor idas agricultural and natural systems (Schardt [personal communicatio n], 2007). Yet, despite th e large economic and ecosystem harms associated with invasive specie s, there exists little empirical analysis of invasive species problems in a way that would help policy makers or resource managers (Schardt [personal communication], 2007). There are very fe w invasive species studies in the economics literature, and most of those are distinctly theo retical and too technical or abstract for use by policy makers or resource managers. Few empirical studies have evaluated the impact of 12

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invasive species. The issue of invasive species is one that much more attention (and perhaps budgetary expenditures) will likely be focused on in the near future. In 2002, the US Governmental Accounting O ffice reported that ex isting studies on the economic impact of invasive species in the Unite d States are of limited use for guiding decision makers formulating policies for preventi on and control (USGAO, 2001). Damages to ecosystems, benefits from alternate controls, risks from future intr oductions, and multi-sector analyses have been lacking. More comprehensive approaches are needed to help decision makers identify potential invaders, quantify prevailing threat, and prioritize resources for mitigating damages. There is a great deal about invasive species growth, transmission, and other important information that is unknown. Perhaps this explains the lack of accessible economic studies on the topic. Unfortunately, despite these unknowns, give n the serious risks to agriculture and natural resources posed by invasive species, policy make rs will be called upon to allocate scare public resources in defense of natural and agricultural systems. Studies such as these, though based on several assumptions that have not yet been tested provide important inform ation to the discourse on invasive species management. The purpose of this research is to examine the economic impacts of selected invasive species in Florida, and evaluate the management responses that follow. The specific objectives of the research are 1) to provide much needed empirical economic research on invasive species management; and 2) to examine the impact of litigation on invasive species management by state agencies. Zebra Mussels Chapter Two discusses the potential infest ation of Lake Okeechobee by a fresh water mollusk, the zebra mussel. Zebra mussels ( Dreissena polymorpha ) are small freshwater mussels native to southeast Europe. They first arrived in the US in the Great Lakes region in the mid13

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1980s, probably as free-swimming larv ae in the ballast water of a tran satlantic ship (Hebert et al., 1989; Griffiths et al., 1991; T horp et al., 2002). Within a fe w years of introduction, zebra mussels (ZM) were in many major rivers and lakes in the eastern US (Hebert et al, 1989). Lacking significant competition or predation (N ew York Sea Grant, 1997) and possessing unique characteristics among freshwater mussels (Borch erding, 1991), the spread of ZM across North America has been rapid (Drake and Bossenbroek, 2004; NationalAtla s.gov, 2007; USGS, 2007). Their spread was greatly acceler ated by recreational and commercial boating in and around the Great Lakes (Johnson and Carlton, 1996). Zebra mussels now inhab it waters in twenty eastern and southern states and continue to spread (USGS, 2007). I construct a bioeconomic model to simulate the expected impact s of the zebra mussel (ZM) on the lake based on assumed transmissi on vectors (recreati onal boating), habitat suitability from a previous study (Hayward a nd Estevez, 1997), and effectiveness of ZM mitigation and prevention methods. I include as sumed lake-related ecological and recreational values to construct an estimate of the total economic impacts with respect to a ZM infestation. I then apply state probabilities (i n a stochastic dynamic simulation fo rmat) to arrive at a long-run economic impact analysis of ZM in Lake Okeec hobee. I report present value results of the expected economic impacts over 20 years, includ ing costs and damages to surface water use, recreational anglers, and users of ecosystem services, as well as budgetary costs. The results from this study indicate that i nvestment in arrival prevention is much more cost effective than attempting to control or eradicate invasive species post-arrival. Hydrilla, Water Lettuce, and Water Hyacinth Chapter Three estimates the impact of the i nvasive aquatic plants hydrilla, water lettuce, and water hyacinth on freshwater fishing in Florid a. Hydrilla is a submerged aquatic plant probably introduced as an aquarium plant in the 1950s, and first detected in Florida water bodies 14

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in 1960 (University of Florida, 2001; Langeland, 1996). Its rapid grow th rate and suitability to Florida waters allowed it to sp read rapidly throughout the state. By the early-seventies, hydrilla could be found in all major drainage basins in Florida. By 1995, hydrilla spread to over 40,000 hectares on 43% of the public lakes in the Stat e (Langeland, 1996). It is believed that 98% of hydrilla is under maintenance control in 193 of th e 288 water bodies where it is found in Florida (FDEP, 2003). Water hyacinth and water lettu ce are floating aquatic plants Water hyacinth, native to South America, was introduced to Florida as an ornamental pond pl ant in 1885. Its rapid reproduction led to it being discarded into th e St. Johns River and it spread quickly to neighboring water bodies (Schmitz et al., 1988). Water lettuce has b een in Florida much longer, perhaps since the 16th century, and is also believed to be a native of South America (Schmitz et al). These plants are believed to be u nder maintenance control in Florida. The problems with hydrilla, water hyacint h and water lettuce are multidimensional ecological, economic, public and private. Ecolog ical impacts include displacing native flora (both submersed and floating), altering habitat of native fauna, and disrupting of ecosystems processes. These invasive plants grow in thic k monoculture mats which block sunlight to and out-compete native plants, especially in the increasingly nutrient-rich lakes and rivers of Florida as population growth increases nitrate and phosph ate runoff. Dense mono cultures can contribute to reduced fish populations, and when large mats of plants decompose, the reduced dissolved oxygen levels in a lake can cause massive fish kills. These plants also harm non-aquatic species by covering nesting and egg layi ng areas, and blocking access to water, shelter, and food sources. 15

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Economic impacts follow close behind ecosyst em loss. Hydrilla, water hyacinth and water lettuce can hinder boating, swimming, and fish ing activities in lakes and rivers. Reduced sport fish populations coupled w ith access problems significantly reduce sport fishing activities. The reduction of recreational benefits derived fr om public waterways (and the cost of managing the weeds) highlights the public loss from invasi ve aquatic plants. They also affect private citizens and businesses, blocking po wer generators and agricultural irrigation water intake pipes, jamming water turbines and dams, and clogging canal s and ditches. Infesta tions in private ponds and poorly managed public water bodies can reduce recreational and aesthetic value of waterfront property. Hydrilla has been diffi cult to eradicate because the plant produces underground tubers which generate new plants each year. Likewise, wa ter hyacinth and water lettuce are extremely prolific, propagating bo th by seeding and by creating daughter plants vegetatively. According to the FDEP (2002), Insufficien t management funding allowed hydrilla to expand from 50,000 to 100,000 acres during the middle 1990s. During this time period there was sufficient funding to continue water hyaci nth (and water lettuce) control, which was considered of primary importance. Various aquatic plant control strategies have been considered, including mechanical removal, la ke draw-down, application of va rious herbicides and biological controlboth with insect and herbivorous fish species. Lake draw-down prevents most recreational use, and biological control remains difficult to control, leaving the use of herbicides as the primary management strategy for most la ke managers (FDEP, 2006). Whatever method of control is chosen, there seems to be consensus that keeping invasive aquatic plant populations very low, known as maintenance control, is the most economically efficient funding strategy (Schardt, 1997). Florida has consid erable experience fighting invasi ve aquatic plants (especially 16

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water hyacinth), yet Langeland (19 96) asserts that lack of ade quate and consistent funding for many invasive plants (especially hydrilla) continues to be th e biggest barrier to effective management and the efficient use of public resources over time. The economics of aquatic plant management in Florida have been examined, but only on one or two lakes at a time (Burruss Institute, 1998; Milon and Welsh, 1989; Milon et al., 1986). This study examines the impact of invasive plants on multiple lakes. I use unpublished data on plant coverage, angler effort, and lake physiogr aphic and amenities to estimate a bioeconomic model of the impact of plant coverage on fi shing activity on 13 Flor ida lakes. Using the bioeconomic model of invasive aquatic plants, I th en simulate the single-y ear costs and benefits of six policy scenarios for aquatic plant control. Over five years, the estimated economic value of the 13 lakes is $76.4 million, and lapses in invasive plant control may jeopardize that value. These results suggest that the op timal management policy is maintenance control with respect to hydrilla, water hyacinth and water lettuce. Legal Basis for State Control of Invasive Species Chapter 4 discusses the legal foundations for stat e control efforts with respect to invasive species. Florida is no stranger to agricultural dise ase, particularly thos e affecting its citrus industry. Florida has twice successfully eradicated the invasive citrus ca nker (Division of Plant Industry, 2006). Citrus canker was first detected in Florida in 1910 and d eclared eradicated in 1947. However, in 1986, a highly aggressive Asian strain of the citrus canker was detected in Florida (Timmer, Graham, and Chamberlain, 2006). In 1995, the Asiatic strain of citrus canker reap peared in Florida. S oon after, the state of Florida, in conjunction with the United States Department of Ag riculture, began a citrus canker eradication program. As part of the program, resi dential owners of citr us trees suspected to harbor canker innoculum were compensated up to $55 per tree destroye d by the state. Angry 17

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homeowners sued to prevent further takings of their trees, and from 2000 to 2004 there were two 18-month lapses in the eradication program. Subsequent to the lapses, ther e were five major hurricanes th at helped spread the canker innoculum throughout the state, potentially cripp ling the commercial citrus industry (Albrigo et al., 2005). The hurricanes that passed over Florid a in 2004 (Charley, Frances, Ivan, and Jeanne) spread citrus canker from these residential trees to such an extent that 80,000 commercial acres of citrus were subsequently slated for dest ruction. Concentrated efforts by governmental officials reduced this to 32,000 acres when Hurri cane Wilma made landfall in 2005. Due to the spread of the citrus canker pat hogen with Wilma, officials fa ced the task of destroying an additional 168,000 to 220,000 acres of commercial citrus (USDA, 2006). The inability of the States canker eradication program to continue unabated meant the USDA canker eradication program was largely ineffective. On January 10, 2006, the federal government stated that citrus canker is so widely distribute d that eradication is impossibl e and pulled the funding for the USDAs citrus canker eradicati on program (USDA, 2006). This change in policy came on the heels of a number of judicial decisions upholding the legality of Floridas citrus canker eradication program, but too late to save the USDA eradicat ion program. Though the CCEP was repealed in January 2006 (Timmer et al., 2006), th ese judicial decisions will be precedential to potential challenges to similar State programs de signed to manage and control pests like citrus canker and citrus greenin g (Salisbury, 2006). This portion of the research examines the legal framework that allowed these lapses, and provide s suggestions for the creation of a program to combat a new invasive threatcitrus greening. Summary This chapter contains a broad overview of the significance and relevance of invasive species in Florida. In addition, the chapte r addresses important background introductory 18

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information for each of the three topics included in this series. The first focus area for this series is the economic impact of invasive species in Florida, and its relationship with management practices and strategies. The second focus in the series exam ines the influence invasive aquatic plants have on the recreation and to urism industry in Florida, specifically in terms of freshwater fishing. Finally, the series concludes with an investigation into the issu e of legal foundations for Floridas control of invasive sp ecies that may threaten agricultu ral production or harm natural areas. An overview of the States use of police power to protect agriculture is addressed in conjunction with legal decisions th at balance the exercise of this power with the constitutional mandates of due process and just compensation. These three issues are clearly germane to Floridas economy, environment, and law. 19

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CHAPTER 2 OPTIMAL INVESTMENT IN PREVENTI ON AND CONTROL OF A POTENTIAL INVADER: THE CASE OF ZEBRA MU SSELS IN FLORIDA WATERWAYS Introduction Zebra mussels are a serious threat to seve ral Florida waterways, particularly Lake Okeechobee. The lake is vitally important to agri cultural producers and recr eational anglers. It also provides numerous ecosystem services. We employ a stochastic dynamic simulation method with a bioeconomic model to estimate the impact of zebra mussels on r ecreation, surface water users, and ecosystem services. We estimate th e present value of zebra mussel-related impacts without state intervention to be $349.34 million over 20 years. We simulated several potential policy responses. The overall cost minimizing choi ce is to invest in arrival prevention and early warning, which would reduce present value costs by 70.91%. This is also the only policy choice that netted positive returns ($247.71 million) as compared with doing nothing to control or prevent zebra mussels in the lake. Policies that include post-establishment eradication yield large losses ($414.98 million, $603.36 million). The results from this study indicate that investment in arrival prevention is much more cost effective th an attempting to control or eradicate invasive species post-arrival. As with many invasive species, a great deal about zebra mussel biology, transmission, and other important variables is unknown. Unfortuna tely, zebra mussels and other invasive species pose serious risks to agricultu re and natural resources Despite the unknowns, policy makers will be called upon to allocate scar ce public resources in defense of natural and agricultural systems. Studies such as this one, though based on several assumptions about zebra mussels that have not yet been tested, provide im portant information to th e discourse on invasive species management. 20

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Background on Invasive Species in the United States The relatively free and rapid movement of pe ople and goods across the globe has led to an increase in the invasion rate of many brittle ecosystems by prolif ic and destructive plants and animals (Vitousek et al., 1996; Mack, 2000). Once introduced to new areas, some of these species become invasive, causing a signifi cant proportion of environmental changes worldwide. Invasive species ar e non-native species that may cause economic, environmental or human health problems (Federal Register, 1999). In the US, producti on losses, control costs, and other associated costs related to invasive spec ies is estimated to exceed $137 billion per year (Pimentel et al., 1999). About 25% of US agricultu ral production is lost to nonnative pests or to their associated control costs (Simberloff, 2002) They can also have devastating ecological impacts, and may be the primary cau se of biodiversity loss (Mack, 2000). In 2002, the US Governmental Accounting O ffice reported that ex isting studies on the economic impact of invasive species in the United States are of limited used for guiding decision makers formulating policies for prevention and control. Damages to ecosystems, benefits from alternative controls, risks from future introduction s, and multi-sector analyses have been lacking. More comprehensive approaches are needed to he lp decision makers identify potential invaders, quantify prevailing threats, and prioritize resources for mitigating damages. This chapter helps quantify the prevailing threat fr om an invasive aquatic mussel to a large Florida lakeLake Okeechobee. We examine four policy responses and report the relative impacts on recreation, surface water use, and ecosystem services. The Invasive Freshwater Zebra Mussel Zebra mussels (Dreissena polymorpha) are sma ll freshwater mussels native to southeast Europe. They first arrived in the US in the Gr eat Lakes region in the mid-1980s, probably as free-swimming larvae in the ballast water of a tran satlantic ship (Hebert et al., 1989; Griffiths et 21

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al., 1991; Thorp et al., 2002). Within a few year s of introduction, zebra mussels (ZM) were in many major rivers and lakes in the eastern US (Hebert et al, 1 989). Lacking significant competition or predation (New York Sea Grant, 1997) and possessing unique characteristics among freshwater mussels (Borcherding, 1991), th e spread of ZM across North America has been rapid (Drake and Bossenbroek, 2004; Natio nalAtlas.gov, 2007; USGS, 2007). Their spread was greatly accelerated by recr eational and commercial boating in and around the Great Lakes (Johnson and Carlton, 1996). Zebra mussels now inha bit waters in twenty eastern and southern states and continue to spr ead (USGS, 2007; Figure 2-1). Figure 2-1. 2006 US Geological Survey map of zebra mussels in the United States. Zebra mussels obstruct and foul man-made st ructures, impair wate r-based recreation, and disrupt aquatic ecosystems. They are often found on natural substrates such as submerged plants, logs, rocks, the shells of other animals, and on manmade structures such as bridge abutments, water intake pipes, and boat hulls. When colonies become large, ZM clog water intake pipes, accelerate corrosion, and sink buoys. In areas of the country where ZM have become established, water users face higher maintenance costs to re move mussels and restore water flows, and 22

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prevention costs, such as applying antifouling pa int to submerged structures. From 1985 to 1995, expenditures for controlling zebra mussels in the United States totaled $69 million, and have since risen to over $60 million per year (Deng, 1996; USGAO, 2002). Zebra mussels also cause ecosystem dama ges by disrupting native flora and fauna. Principally, they compete for food sources and ha bitat, and hamper movement of other species. Their success as invaders can be attributed to their rapid re productionfemales produce between 40,000 and one million eggs per year (USCACE, 2003). Because zebra mussels reproduce in large numbers, natural predators such as turtles, crustaceans, catf ish, drum, and ducks have little effect on populations (Strayer, 1999). In area s invaded by zebra mussels, endangered native mussel species are at risk. By 2010, zebra mussels ar e expected to contribu te to the decline in native mussel populations by 50%. Without furt her control efforts, 140 indigenous mussel species could be lost (USGAO, 2002). Cumulati ve damage from zebra mussels in the US including direct and indirect economic costs is estimated to be $3.1 to $5 billion from 2002 2011 (USGAO, 2002 and USGS, 2000). Will Zebra Mussels Invade Florida? North American ZM distribution forecasts ar e based on various environmental conditions, primarily water temperature (Drake and Bossenbr oek, 2004). Initially, ZM we re not expected to colonize warm waters due to their intolera nce of high water temper atures (McMahon, 1991; Mihuc et al., 1999), but more r ecent studies report that they are able to withstand higher temperatures (Drake and Bossenbroek, 2004; Lewandowski and Ejsmont-Karabin, 1983; Jenner and Jansen-Mommen, 1993; Orlova 2002) and may be adapting to local conditions (Marsden et al., 1996; Muller et al., 2001). ZM recently collected from warm er regions have higher heat tolerance than those from northern lo cations (Elderkin and Klerks, 2005). 23

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ZM are now found in the lower Mississippi Rive r and parts of Alabam a (Allen et al., 1999; USGS, 2007), and are expected to spread to Florida (Hayward and Es tevez, 1997; Drake and Bossenbroek, 2004). Two studies have predicted th e suitability of Florida waters to ZM infestation; both report several lakes and rivers that are highly vulnerable to ZM. Drake and Bossenbroek (2004) use a machine-learning algo rithm to predict spread based on several environmental factors. According to their mode l, North Florida has a high and South Florida a moderate likelihood of being infested by ZM. Ha yward and Estevez (19 97) calculate habitat suitability indices for Florida waters based on biology and demography studies. Several economically significant Florida water bodies are vulnerable to ZM invasion, including the St. Johns River and Lake Okeechobee (Hayward and Estevez, 1997). Early studies also suggested that ZM woul d not colonize southern waters due to the relative lack of hard substrates and ZM inabilit y to colonize soft sediments (Nalepa et al., 1995). Recent studies show that they have adapted well to soft sediments (Strayer and Malcom, 2006; Burlakova et al., 2006) and will colonize sand an d mud if hard substrates are unavailable (Strayer, 1999). Floating and subm ersed aquatic plants also provide suitable hard substrates, but were not considered by earlier ZM distribut ion forecasts. Florida lakes and rivers, and specifically Lake Okeechobee, have abundant plant life that could provide suitable substrate for the invading mussels. Model of Lake Okeechobee Zebra Mussel Infestation Lake Okeechobee is a shallow, 448,000-acre lake lo cated in South Florid a. It is the secondlargest lake wholly contained w ithin the US. The lake is an im portant commercial shipping route, a valuable source of water supply, and a major economic and recreation resource (FDEP, 2001). It is the site of several ma jor fishing tournaments each year and supports commercial fishing operations. Lake Okeechobee draws 1.3 million anglers annually and supports a $117 24

PAGE 25

25 million/year fishing industry (Lakeokeechobee.or g, 2007). Five counties surround the lake, all of which pump lake water for agricultural, industrial, potable, and other uses. Lake Okeechobee supplies a substantial percen tage of freshwater used by municipal, industrial and agricu ltural sectors in the five-county regi on surrounding the lake (Table 2-1). In these counties, surface water makes up a large per centage of the water supply, predominantly for agricultural irrigation. For exampl e, 94.49% of lake withdrawals are for agricultural irrigation, and municipal, power plant, mining, and industrial users make up 2.64%, 1.60%, 0.81%, and 0.42% of lake withdrawals, respectively. A ZM infestation would greatly increase the costs of these water users, as well as impact r ecreational and commercia l fishing, and other environmental services provided by the lake; how ever, ZM would primarily affect agricultural surface water users. Zebra Mussel Spread and Distribution Zebra mussels exhibit three types of spreaddi ffusive (within a lake), advective (within a watershed), and jump dispersal (between wa tersheds) (Johnson and Carlton, 1996; Johnson and Padilla, 1996). Diffusive and advective spread of ZM occurs by free-sw imming planktonic larvae according to population dynamics (Stoeckel et al ., 1996). ZM spread and distribution studies have examined infestation of conn ected riverine areas or lakes with in short distances of infested waters using reaction-diffusion models (Buchan and Padilla, 1999). Reaction-diffusion models allow range expansion of species that disperse and reproduce si multaneously, assuming constant dispersal velocity and intrinsic growth rate. Reaction refers to a ch ange in local population (Holmes, 1993). A reaction-di ffusion model may apply to ZM within a connected river ecosystem, or over short distances, but Lake Oke echobee falls into neither of these categories. The lake is distinctly isolated and would not be col onized by ZM without external assistance.

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26 Table 2-1. Lake Okeechobee surface wate r supply by sector and county, year 2000. Counties Served by Lake Okeechobee Glades Hendry Martin Okeechobee Palm Beach Lake Okeechobee Total Florida Total Population (1000s) 10.58 36.21 126.73 35.91 1131.18 1340.61 12388.42 % population drinking water from surface sources 0.00 79.87 0.00 75.78 15.35 15.92 11.83 Irrigated acres (1000s) 25.21 169.58 59.81 23.14 446.85 724.59 1691.69 % Irrigation water from surface sources 72.07 61.71 87.14 15.71 93.80 80.75 51.41 % power plant, mining and livestock water from surface sources 100.00 100.00 100.00 100.00 69.90 78.06 23.76 % of total freshwater from surface sources 100.00 100.00 100.00 100.00 74.70 83.13 44.47 Source: USGS (2006).

PAGE 27

Critical levels of connectivity help determ ine whether an invasive species will reach suitable habitats (With, 2002). Large gaps in habi tat may be the reason why some species ranges are restricted (Holt et al., 2005). When these ga ps are bridged by external forces, then reactiondiffusion models are insufficient because they fail to account for rare l ong-distance transmission events (Holmes, 1993; Hastings et al., 2005). For many invasive species, humans are the primary vector of transmission (Suarez et al., 2001; Jule s et al., 2002; Buchan and Padilla, 1999). This can lead to species geographic ranges greatly exc eeding their natural disper sal abilities (Holt et al., 2005). For example, Higgins and Richardson (1999) estimate that a 0.01% of seeds moving considerable distances (1 10 km) can increase th e spread rate of a plant species by an order of magnitude. Similarly, a reconstruction of the invasion of the Argentine ant ( Linepithema humile ) over the last century reveals a maximum and fair ly constant local dispersal rate, with annual jump distances three times that rate (Suarez et al., 2001). Human-mediated jump dispersal is a concern that must be addressed by invasive species modelers. The combination of local and human-mediated jump dispersal may result in a lack of agreement between linear models and empi rical data (Hengevel d, 1994; Suarez, 2001). Velocities estimated from linear spread mode ls may appropriately pr ovide an upper bound for species spreading within a homogenous system (Holmes, 1993; Hastings et al., 2005), but will likely underestimate spread when human transporta tion is involved and jump dispersal occurs. Buchan and Padilla (1999) underestimated observe d ZM spread rates by almost half due to a failure to account for long-di stance dispersal. Neubert and Caswell (2000) provide other examples of underestimated spread rates due to human interacti on. The probabilities associated with jump dispersal may be very low and difficult to estimate. Despite these small probabilities, they appear to be the driving factor for migration patterns for many species (Allen et al., 1991; 27

PAGE 28

Lonsdale, 1993; Dwyer et al., 1998 ; Bossenbroek et al., 2001; Suar ez et al., 2001; Hasting et al., 2005), and should not be ignored. Three studies of ZM dispersion specifically addressed the is sue of human-mediated jump dispersal. Bossenbroek et al. ( 2001) developed a ZM gravity mode l based on data on registered recreational boats per county. A similar study used lake surface area as a proxy for relative lake attractiveness in Indiana, Mi chigan, Wisconsin and Illinois (Kraft and Johnson, 2000). They found that small lakes (those with less than 100 hect ares) had lower rates of infestation. Kraft et al. (2002) conducted spatial analysis using Ripleys K statistic to estimate the probability that invaded lakes would be found within a particular distan ce of invaded lakes. ZM-invaded lakes in the United States are found to be aggregated at less than 50 kilometers an d segregated at greater than 200 kilometers (Kraft et al., 2002). Thes e findings confound simple diffusion models and suggest that ZM dispersal is better defined by long-distance dispersion events and subsequent spread within lakes or co nnected lake systems. The likely human-mediated vectors of ZM tr ansmission to lakes ove r long distances are recreational boating, commercial bo ating (of ships not obeying exis ting ballast water procedure laws), and intentional introduc tion (Carlton, 1993). Commercial vessels are required by federal law to empty their ballast water prior to ente ring Lake Okeechobee. These efforts have been effective and are credited with a large slowing of the rate of ZM spread. Here, we assume that ZM spread by commercial vessels will not occur. Intentional introduction is not uncommon with invasive species that are percei ved to improve the productive or recreational value of land and water bodies (e.g., water hyacinth, hydrilla, and Melaleuca ). ZM are known to clarify the water column, so there is a possibility of intentional introduction. However, the probability of such an 28

PAGE 29

introduction is unknown but we assume (and hope) th at current educational efforts will prevent an intentional introduction of ZM to Lake Okeechobee. Recreational boating is the likely overland tr ansmission vector for ZM, and has been shown to be the primary transmission vector of unconnected water bod ies in and around the Great Lakes region (Johnson and Carlton, 1996; Buchan and Padilla, 1999; Bossenbroek et al., 2001). For example, about 25% of recreational bo at trailers leaving ZM infested lakes in Michigan carry adult ZM (Ricciardi et al., 1994 ). Johnson and Carlton (1996) estimated that 7.8 9.2 of trailers at public boat ramps transpor ted entangled vegetation with 2.7 2.0 mussels attached on trailers leaving infested lakes. In addition, they estimat ed that 1/275 trailers inspected entering uninfested lakes had ZM liv ing on entangled macrophytes. ZM are commonly found at 1000 adult mussels per meter of aquatic plant stem length. For the purposes of this study, we assume that any transmission of ZM to Lake Okeechobee will be unintended, and by recreational boaters. Bioeconomic Model of the Zebra Mussel Threat to Lake Okeechobee We use a Markov approach to forecast th e likelihood of ZM infestation in Lake Okeechobee and to estimate the long term expected public and private cost under alternative policy scenarios. Lake Okeechobee is not connect ed to any watershed known to be infested with zebra mussels. The river system in the Florida Panhandle is the closest distance to ZM-invaded waters, but the water chemistry in this system is inhos pitable to ZM. Any ZM invasion to Florida is likely to come in the form of the human-med iated movement of water (with larvae) or submerged objects (with juvenile or adult mussels) over long distances. For ZM to reach Lake Okeechobee, a dispersal barrier of nearly 1200 km must be jumped. The stress of overland transport (Ricciardi et al., 1995) and the low numbers of mussels transported during a single 29

PAGE 30

dispersal event (Johnson and Padilla, 1996) make the overland transmission of ZM a rare event, but one that should not be ignor ed. Here, we use a stochastic dynamic simulation approach to estimate the potential ZM invasion within a grav ity model of jump dispersal based on boater behavior. We assume that new ZM introduction occurs wh en a boater travels to an infested lake and then to Lake Okeechobee within a short enough time for ZM to survive the transmission. ZM become established when the mussels reproduce and populate the lake to carrying capacity. At carrying capacity ZM masses will be sufficien tly large to cause both environmental and economic damage. Thus, there are four distinct st ates regarding zebra mussel masses in the Lake Okeechobee Waterway: not invaded (s 1 ), arrived (s 2 ), growing (s 3 ), and carrying capacity (s 4 ). At present time t = 0, the st ate is not invaded, thus (1) 01 0 0 0 S At time t in the future, St is given by (2) S t = A t S 0 where A is a 4x4 matrix of transition probabilities (3) 11121314 21222324 31323334 41424344aaaa aaaa A aaaa aaaa A is composed of a ij the probability of transitioning from state j to i in a single time period. 30

PAGE 31

At any time t, S t is (4) 104 3 2 1 i t tswhere s s s s S The expected future costs of mitigating the threat and infestation of zebra mussels is C t where C t is a function of the state S t and the choice of management methods X For ZM we consider two types of public management: (1) prevention which entails both screening and education measures to reduce the probability of arrival, and m onitoring to provide local water uses with early warning information ( x 1 = 1); and (2) eradication which involves use of a molluscicide to effectively kill all ZM in the lake ( x 2 = 1). The annual cost of management C t is expressed as the produc t of management ( X ), zebra states in compact form (), and unit cost of management ( q ): (5) C t = X t q Where X, t and q are (6) 2 1x x X (7) t ts s 4 10 0 (8) 2 1c c q Direct use damages from zebra mussel infest ation include losses to recreation uses and increased maintenance costs due to ZM fouling. In equation (9), d i are annual ZM damages in state i 31

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(9) 4 3 20 d d d D Ecosystem service losses from zebra mussel infestation include diminished ecosystem functions such as wildlife habitat and aquatic food supply. In equation (10), e i are annual ZM ecosystem losses in state i (10) 4 3 20 e e e E The management objective is to choose a ma nagement strategy bundle X to minimize Z, the present value of total expected costs from the threat of ZM infestation: (11) T t ttt tEDSSXCrZ0 ')(),()1( In equation (11), r is the annua l discount rate and T is numbe r of years in the planning time horizon. Empirical Approach Parameters of the transition probability matrix (Eq. 3) are estimated using ZM arrival, survival, and population dynamics studies in c onjunction with Lake Okeechobee environmental information and data on boating activity. For exam ple, the probability of a ZM establishment ( a 12 ) is a function of the number of boats arriving at the lake from ZM infested waters, ZM survival during the trip and afte r introduction, and the le ngth of time it takes for ZM to establish a viable colony. Once established and growing, ZM survival, population dynamics, and control efforts define the probabilities of the ZM population becoming endemic and causing high levels 32

PAGE 33

of damages (a 34 ), being established without causing significant harm ( a 33 ) or being effectively nullified ( a 32 ). Large economic and ecological dama ges occur when ZM populations reach carrying capacity in the Lake in state 4. Dete rmining the above parameter values, as well as damage and cost estimates, is a difficult task that requires an exha ustive review of ZM experiments and studies. In the following sections, we present and discuss the parameter estimates and data derived from previous ZM research. Arrival and Survival ZM rate of arrival to Lake Okeechobee is assumed from recreational boating data. While most recreational boating activity is local, a small percentage of freshwater boaters in the United States travel very long distances within short periods of time (Buchan and Padilla, 1999). For example, 26% of Wisconsin boaters visit a lake or river during any give n 2-week period, 8.4% trailer their boats more than 50km, 3.4% mo re than 106km, and 0.8% more than 261km. General boating patterns and number of inters tate fishing trips involving Lake Okeechobee are unknown, but there are several fishing tournaments and circuits that draw participants from the entire US, Canada, and even Japan to parts of Florida and from Florida to parts of the Southeastern US with known ZM populations. We us e fishing tournament data as a proxy for the arrival rate of boats with ZM veligers or adul t mussels. We surveyed angler competition rosters from three national fishing tournaments to determ ine frequency of participation in tournaments by anglers from states known to have ZM. Acco rding to a 2006 USGS ma p of ZM distribution (USGS, 2007), ZM are found in 24 states. Of th e 926 anglers participating in three national tournaments on Lake Okeechobee from 2006 2007, 50.45% were from one of these states (Carson, 2007; Eads, 2007). Resu lts confirm Buchan and Padilla s (1999) findings and indicate that tournament participants travel long distances often within short peri ods of time. We assume 33

PAGE 34

that 900 anglers per year fishing on Lake Okeechobee would have come into contact with ZM prior to fishing on the lake. We must also account for the environmental st resses on ZM during the long-distance trip, as well as seasonal timing. Adult mussels are known to survive out of water for long periods of time, on average 3 5 days under temperate summer conditions (Ricciardi et al., 1994; Griffiths et al., 1991) and up to a few weeks in wet fishi ng nets in Europe (Buc han and Padilla, 1999). Large (21 28mm) mussels can easily survive >5 da ys out of water, and a small percentage of large adult ZM (10%) can withst and 10 days exposure under ideal conditions (Ricciardi et al., 1994). Live wells hold the greatest risk of ZM dispersal. Larv ae are discovered in 83% of boat live wells, with densities of 111 222 (1 sd) larvae/liter. A typical boat has a 38-L live well, for an average transportation potential of 4,200 larvae (Johnson and Carlton, 1996). The timing of dispersal can influence the spr ead rates on invasive species (van den Bosch et al., 1992). Given environmental stressors, ZM may arrive at Lake Okeechobee several times before a successful colonization occurs. This may explain why Johnson et al. (2001) overestimated ZM colonization of Wisconsin lake s, as they assumed suitable lakes would be suitable at all times of the year. Also, they ignored seasonal boating patterns. Boating in the Great Lakes region occurs mostly from April to October, with the wa rm summer months seeing most of the activity (P enaloza, 1991). June August aver ages between 1.25 1.69 million boater-days, while October and April only averages 0.56 and 0.24 million boater-days, respectively. Similar, but seasonally reversed, patterns of boating beha vior may be found in Florida, when hot and humid su mmer months create uncomfortab le conditions for boaters and reduce fish activity. Floridas main fishing tourna ment season begins in February of each year and ends in June (Eads, 2007). Mu ssels are activel y settling or are active as larvae during about 5 34

PAGE 35

months of the year. ZM generally have two spawning periods: 1) fr om April to July, and 2) in August (Haag and Garton, 1992; Griebeler and Seitz, 2006; Jantz and Neumann, 1998). During these times, free-swimming veligers are abundant in water that may be transported to Lake Okeechobee. Only when both boaters and ZM ar e active do they pose a significant threat of infestation to Lake Okeechobee. We apply estimates of Lake Okeechobee habita t suitability to estimate ZM survival upon arrival. Hayward and Estevez (1997) estimated hab itat suitability indices (HSI) for zebra mussels based on seven environmental variables: temperature, dissolved oxygen, pH, Secchi depth, salinity, calcium, and sediment size. They conducted a meta-analysis on ZM life-cycle studies and calculated HSI that ranged from 0.0 (perf ectly unsuitable) 1.0 (optimal) using 281,780 data records from the US Environmental Protec tion Agencys STORET database for 9,028 sites in Florida and calculated composite HSI for each s ite. They estimated that 21% of the sites had composite HSI over 0.5, and 3% of sites had HSI above 0.8. Composite HSI were calculated for western Lake Okeechobee (very shallow, high aq uatic plant density) and for the lake proper (open water). The HSI were 0.91 and 0.83, respec tively, making the lake highly suitable to ZM (Hayward and Estevez, 1997). Based on the above, we assume a 3.5% annual probability of ZM introduction and establishment. This probability is in line with Bossenbroek et al. (2001), who estimated the probability that a single boat woul d cause colonization in states surrounding the Great Lakes to be between 0.0000118 0.0000411 per arrival by infe sted boat, or up to about 3.7% chance when a lake experiences 900 arrivals by boats in contact with ZM -infested waters. Reproduction and Spread An appropriate estimate of the rate of spr ead within a water body depends on assumptions about the population dynamics. The life history of ZM has been reviewed by several studies 35

PAGE 36

(McMahon, 1991; Ackerman et al., 1994; Mackie and Schloesser, 1996; Nichols, 1996). ZM development is very quick. Eggs develop into larvae for 1 day if fertilized (Sprung, 1987; Borcherding, 1991; Ackerman et al., 1994). ZM need between 2.5 and 4 weeks to reach the juvenile stage (Borcherding and de Ruyter van Stevenick, 1992; Grie beler and Seitz, 2006; Sprung, 1987). Several studies estimate ZM survival rates for various life cycle stages (Stoeckel et al., 2004; Orlova, 2002; Spr ung, 1993; Thorp et al., 2002). During the ZM larvae (freeswimming) stage, mortality is high (Orlova, 200 2). Sprung (1993) estimates an egg to adult mortality of 0.999913. Within about two months of spawning, juveniles w ill settle and attach to substrates. Once settled, mussels quickly mature. Females produce between 40,000 and one million eggs per year (USCACE, 2003). Initial invasion studies indicate that ZM reach carrying capacity 2 3 years after detection (Nalepa et al., 1995; Strayer et al., 1996; Burlakova, Karatayev, and Padilla, 2006; Borcherding and Sturm, 2002; Lauer and Sp acie, 2004). Average carrying cap acity is about 10,000 ZM/m 2 over a representative lake (Grieb eler and Seitz, 2006). Once carryi ng capacity is reached, about half of ZM populations will vary from 10 30% each year, while the other half periodically crash and recover, typically in 4-year cycles (R amcharan et al., 1992). Whether stable or cyclic, ZM populations reproduce very quickly. The H udson River experienced 4000/m by the end of 1992 after a first detectio n in May 1991 (Strayer et al., 1996 ). Akcakaya and Baker (1998) report ZM density on the upper Mississippi River from first detection in December 1991 October 1995 in three locations. In December 1991, ZM were at less than .1/m. The populations grew at a steady exponential rate, r eaching about 3000/m by October 1995. Beckett et al. (1997) reported ZM densities on dam locks from 50,000 75,000 individuals per m 2 within three years 36

PAGE 37

of first detection in the Lower Mississippi Rive r. For our calculations, we assume that ZM may reach their carrying capacity with in 2 years of introduction. Direct Economic Costs and Damages ZM is a known hazard that the state of Fl orida has taken steps to curb, including lowpower radio alerts warning trav elers near the Florida border, and criminal finesbringing ZM into Florida is a 2 nd degree misdemeanor with a $500 fine and up to 60 days in jail (University of Florida News, 1999). One federal agencythe US Army Corps of Engineers (USACE) is also working to prevent the introducti on of ZM. In 2003, they proposed a monitoring plan to detect the introduction of zebra mussels in the Okeechob ee Waterway (see Figure 2-2). The monitoring plan would include (1) education materials (alert/identification cards, pamphlets, and posters) distributed to boaters, homeowners, and bus inesses along the waterway to involve the community in detecting zebra mussels when they first arrive, and to enlist boaters help in preventing ZM spread by cleani ng boat live wells and trailers before entering the lake; (2) underwater inspections conducted by divers in conjunction with ex isting inspections of manatee screens and lock gates; and (3) s ubstrate sampling to detect settlement of juvenile zebra mussels four times per year. Dive inspections at each of the 5 major structures to survey for ZM would cost approximately $25,000 per inspection. Th e USACE proposed inspection plan calls for quarterly inspections, costing approximatel y $100,000/yr. Additional costs would be about $700/inspection for USACE labor (Crossland, 2007). We further assume that educational efforts would cost $50,000/yr, for a total monitoring plan cost of $152,800/yr. Early detection measures afford surface water users time to retrofit their equipment pre-invasion, and prevention efforts may be effective at reducing the probability of ZM introductions. Unlike other invasive species commonly found in Florida, th ere may not be a feasible method of controlling the spread of ZM once widely established within a lake system. Control 37

PAGE 38

alternatives include potassium chloride, molluscicide ca rbon dioxide (to reduce dissolved oxygen), chlorine, lower pH, in creasing salinity, dewatering, and copper sulphate (VDGIF, 2007). Of these, only potassium and molluscicide are considered to have ne gligible effects on the long run health of the aquatic e nvironment. Both potassium and molluscicide have similar costs per treatment ($2,028 versus $1,778 per million gall ons, respectively), but potassium levels will provide long-run protection ag ainst ZM whereas molluscicide applications do not. Figure 2-2. Lake Okeechobee waterway. There is only one known instance of ZM eradic ation. The Virginia Department of Game and Inland Fisheries successfully eradicated ZM on Millbrook Quarry using high levels of potassium chloride (98 115 parts per milli on) over several weeks at a cost of $365,000 (VDGIF, 2007). They used 174,000 gallons of th e chemical over three weeks in January and February, 2006, at a concentration of 100 parts per million. This is twice wh at is expected to kill 95% of the ZM, but below what would create seri ous human health or environmental concerns. It is estimated that the potassium levels now found in the quarry will not significantly impact fish 38

PAGE 39

or human health, and will protect the quarry fr om further ZM infestation for approximately 33 years. Millbrook Quarry is a 12-acre, 93-ft deep quarry (approximately 180 million gallons). By contrast, Lake Okeechobee is a 448,000 acre lake with an average depth of 9 feet (approximately 1.31 trillion gallons). Lake Okeechobee is 3,613 tim es larger (in water volume) than Millbrook Quarry. A potassium treatment on Lake Okeechobee similar to Millbrook Quarry would require 628.6 million gallons of potassium at a cost of $1.32 billion based on Millbrook Quarry treatment levels and costs. Recall that almost 95% of surface water withdrawals from Lake Okeechobee are for agricultural irrigation. ZM on Lake Okeechobee would clog surface water intake pipes. Surface water impacts of ZM are more likely to be in form of cost increases rather than lost revenue or production losses. Only 6.3% of respondents to a 1996 study of Great La kes surface water users reported production losses (Hus hak, 1996b), and electric utiliti es and industry report a 0.0045 percent output loss (Hushak and Deng, 1997). Theref ore, we focus on the pot ential increases in maintenance costs rather than calculating produc tion losses to agricultura l surface water users. Several studies report the impacts of ZM on surface water users (ONeill, 1996; Deng, 1996; Park and Hushak, 1996; Phillips et al., 2005). ONeill (1996) reports average costs per water use facility for a wide range of water us ersindustrial, public su pply, power generation, and others. Deng (1996) provides es timates of variable ZM mainte nance and control costs as a function of gallons of water used for five ZM control technologies for private and public water utilities, and other industrial users. Park and Hushak (1999) surveyed large surface water users from 1994 1995 regarding their annual ZM monitori ng, control and research costs. Utility and industry users were classified as small (0 10 million gallons/day), medium (11 300 mgd), or 39

PAGE 40

large (>300 mgd) water users. The average control and monitoring costs to industry facilities were $10,000, $92,000, and $439,000 for small, medi um, and large water us ers, respectively. Hushak (1996b) estimates total ZM expenditure s average $0.43 million/facility over 5 years. Small facilities (<5 million gallons/day) have expected costs <$20,000 pe r year; larg e facilities (>300 million gallons/day) can expect ZM to cost them $350,000/year (Hushak, 1996b). ZMimpacted industries in the US reported mean ZM-related expenditures of $167,030 per facility for 60.3 mgd average capacity. Mean expend itures on prevention were $92,833, on planning were $37,190 per facility, on monitoring were $14,393, on retrofit were $48,200, and on mechanical or other control technologies were $6,406 (ONeill, 1997). Currently, the average maintenance cost for annual cleaning of water intake screens costs $6, 240, but would increase 7fold following ZM infestation (ONeill). Chemical treatment of zebra mussels by industrial facilities has an average cost of $1.13 per million gallons of water treated for the least cost alternativechlorine (Deng, 1996). This method ha s up to 95% effectiveness, but only relatively large surface water users are likely to employ this due to th e technical challenges. Non-industrial surface water users will likely opt for physical an d thermal treatments, which cost $4.90/mgd. Using variable and percentage increase in total costs estimates from ONeill (1996), Deng (1996), Park and Hushak (1996a, 1996b), Hushak (1999), Hushak and Deng (1997), and Phillips (2005), we employ a cost-transfer methodology to estimate the potential impact of a ZM infestation to Lake Okeechobee surface water users (Rosenberger and Loomis, 2001). According to the most recent available data, surface wa ter withdrawals from the lake average 1541.34 million gallons per day (USGS, 2006). We apply an average cost of $4.90 per million gallons for physical and thermal treatments according to Deng (1996) to arrive at an estimated average 40

PAGE 41

maintenance cost increase of $2.76 million per year for agricultural surface water users following a full ZM infestation in Lake Okeechobee. Phillips (2005) reports the estimated ZM pr evention-related costs on hydropower facilities. Application of anti-fouling pain t, including labor, was estimated to cost hydropower facilities $25.56 per square foot in year 2005 dollars. It is not known how long the paint will remain effective against ZM before needing to be reappl ied, but we assume that the paint will remain effective for 10 years. Water use and permit records are maintained by the South Florida Water Management District. We obtained records of the 2003 permit holders, which included permits for 504 surface water intake pipes. We conducted a telephone survey (Appendix A) of these users from May August, 2006 and achieved a 7.1% response rate, largely due to stale contact information. The survey included questions rega rding average annual maintenance costs, surface water use, location, presence of i nvasive aquatic plants (which ar e likely to impact maintenance costs), average daily withdrawal frequency of maintenance ( times per year), whether the maintenance was contracted out or performed inhouse, type of maintenance (physical, chemical, or other removal method), the lo cation of the facility (county), and questions regarding their knowledge of ZM. Mean annual ma intenance costs are reported to be $8,936 (sd = $3,913) and they have average water intake pipe diameter and length of 1.91ft (sd = 0.35) and 50.14 ft (sd = 27.23), respectively. This provides a mean in take pipe surface area of 300.58 ft. Assuming 504 intake pipes for the lake, we estimate a total cost for anti-fouling paint of $3.87 million. Ecological and Recreational Damages In addition to the impacts on surface water user s, a ZM infestation may negatively impact recreation and lake ecology. Following a ZM infestation, lake ecology will change dramatically. ZM can reduce plankton populations by 85% (USACE, 1995), increase water clarity, double phosphate levels, and significantly reduce nati ve mussel populations (Caraco et al., 1997; 41

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Strayer, 1999). In the Upper Mississippi Ri ver, native mussel populations dropped with the introduction of ZM; declines in native mussels in cluded two federally listed species (Whitney et al., 1995). ZM in the Hudson River were >70% of the zoobenthic biomass, filtering the equivalent of the entire water column per day (S trayer et al., 1996). Adult ZM can filter up to 1 gallon of water per mussel/day (USGS, 2000). ZM can remove up to 62% of a lakes primary littoral production (Ram charan et al., 1992), fundamentally altering the aquatic food chain (Caraco et al., 1997). Stoeckmann and Garton (1997) estimate that ZM popul ations in the range of 10,000 to 50,000 mussels/m consume 10% to 50% of summertime primary lake production. Studies of the effects of ZM on fishing are mi xed. On one hand, the number of fishing trips was seen to decline dramatically in the Great La kes following the ZM. In the Great Lakes region, 78.5% of respondents who said that ZM affected the amount of time spent on Lake Erie reported spending less time on the lake, with a decline in fishing trips from 11. 2 to 6.3 from 1990 1992 (Hushak, 1996a). On the other hand, field studies of fi sh stocks in the Hudson and Great Lakes regions report a significant decline in open water fi sh species, but a significant increase in littoral fish species, which are responsible for all of th e recorded recreational fishing activity on Lake Okeechobee. Strayer et al. (2004) examine 26 year s of data on fish populations on the Hudson River to ZM effects on littoral and open water fish species. The median decline in open water fish species was 28%, while littoral species experi enced a median increase of 97% (Strayer et al., 2004). Many of these species were of recrea tional importance. Open water species of recreational importance included he rring, shad, striped bass, a nd perch, and littoral species included carp, shiner, bluegill, smallmouth bass, largemouth bass and darters. Overall biodiversity and fish biomass fell after ZM arrival (Strayer et al., 2004). According to unpublished fishing effort data from the Florida Fish and Wi ldlife Conservation Commission, 42

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there are four recreationally significant fish groups on the lakeblack crappie, catfish, largemouth bass, and pan fish. These sp ecies are all litto ral zone species. For some lake systems, the reduction in phytoplankton accompanying a ZM introduction may increase also mitigate the impacts of eutrophication (Ulanowicz and Tuttle, 1992). We must also consider the pot ential for other invasive spec ies to flourish following a ZM infestation, and the negative impacts that w ould have on fishing effort. Increased water transparency can cause the incr eased abundance of submersed aqua tic plants, as was the case in Lake Huron (Skubinna et al., 1995). This may exacerbate invasive aquatic plant problems on Lake Okeechobee. Snail populations may also signi ficantly increase follow ing a ZM introduction (Strayer, 1999), and may include the invasive apple snail that is threatening Florida waters. Given the above, we assume an increase in fishing effort of 10% following a ZM infestation. The average total hours spent fishing on Lake Okeechobee from 1983 2002 was 4,316 hours/day (FFWCC, 2003). Assuming that effort has a direct and linear relationship to available fish species, we expect an increase in fishing effort by 431.6 hours/day. According to the Florida Fish and Wildlife Conservation Commissi on, freshwater anglers on Florida lakes spent an average of $20.65 in 2002 dollars (FFWCC, 2003). This equates to a $3.25 million gain per year. There is also the poten tial for fundamental changes to aqua tic plant life that would hamper the functioning of wetlands. Lake Okeechobee has 29,000 acres of Audubon Society wetlands, and a further 31,000 are assumed from visual insp ection of aerial maps. Costanza et al. (2003) estimate a per hectare value of lake services of $8,498. Of this, $439 per hectare was for wetland services. We assume that 60,000 acres of wetlands connected to the lake ar e vulnerable to injury from ZM infestation, and a 2% inflati on rate for the Costanza et al. value. 43

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Effectiveness of Management Methods There are two methods x 1 and x 2 that may be employed singly or jointly to mitigate ZMrelated damages. Investment in prevention is given by x 1 = 1 which includes efforts to detect and prevent the arrival of ZM and pr ovide water users early warning of ZM establishment in the lake. These efforts may include brochures posters and pamphlets alerting the public to the ZM threat, and boating regulations requiring th at hulls be free of mussels and macrophytes, and live wells be empty prior to entering Lake Okeechobee. It also includes the US ACE monitoring program that would provide early warning to surface wa ter users at a cost of $152,800 per year. We assume that the USACE monitoring program will reduce annual probability of arrival by 75%, or from 3.5% to 0.875%. Sensitivity analyses of this parameter are included in the results section. Investment in ZM eradication is given by x 2 = 1. ZM were effectively eradicated from Millbrook Quarry, VA using potassium chloride. The same protocol for Lake Okeechobee would cost $1.32 billion chemicals and labor costs and would provide an additional 30 years of protection from future introductions. A cost mitigating measure is the application of anti-fouling paint on the interior of surface water intake pipes which would effectively reduc e the cost of keeping pipes free of fouling organisms including ZM. Paint and labor costs are $25.56 per square foot of pipe and each application is good for 10 years. We assume wa ter users would apply an ti-fouling paint after they detect ZM which would occur post-establishm ent. With an early warning system in place, water users would apply antifouling paint be fore ZM is established thereby avoiding maintenance expenditure due to ZM clogged pipe s. If ZM are eradi cated, antifouling paint application becomes unnecessary. We assume that once ZM are introduced into Florida waters, the mussels would become established i.e., they begin reproducing in one year. After two years the mussel population 44

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would reach the carrying capacity of the lake. If an early mon itoring program were in place ( x 1 ), then surface water users would have sufficient time to prepare. Without early warning, initial ZM damages will be 10% higher due to a lag in x 3 application similar to the findings of ONeill (1997), Deng (1996) and others. In the Great Lakes region, it took about 6 years following ZM introduction for costs to stabilize, largely due to initial ZM sp read rates and late adoption of retrofitting. Small water users (0 10 million ga llons per day) did not begin retrofitting water intake pipes and other equipment until 3 years afte r ZM were detected, largely due to a lack of appreciation for the potential impacts of the muss els. This lag in uptake of antifouling measures caused ZM-related costs to jump from $2,000 per f acility to about $15,000 per facility from the 3 rd to 4 th years following ZM introduction. Within 2 years after retrofitting began, control costs fell by over 73% (ONeill, 1997). We assume ZM -related maintenance costs will be $2.76 million with antifouling paint applied before ZM reach carrying capacity. Without the early warning system, the lag in application of anti-fouling paint will increase maintenance costs by 27.75%, or $3.37 million. We also assume that once ZM have arrived, monitoring and prevention costs will fall to zer o. A summary of parameter valu es used in the ZM model are reported in Table 2-2. Policy Scenarios and Results At present, there is no State plan in place to m onitor, prevent, or eradicate ZM in Florida. Thus, to examine the widest range of plausi ble options we construc ted the following four scenarios. Policy scenario I is the current policy being pursued by the statedo nothing with respect to ZM. Policy II provides state funding for labor and technology to prevent introduction of ZM to Lake Okeechobee and to monitor the lake and its entry points to detect the presence of live ZM. Policy III foregoes prevention with a plan to eradicate ZM as soon as it is detected. 45

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Table 2-2. Zebra mussel model parameter values. Symbol Definition Value a 11 Annual probability of ZM not arriving to Lake Okeechobee 0.965 a 21 Annual probability of ZM arrival/year without x 1 (arrival prevention and early warning) 0.035 a 21 Annual probability of ZM moving from state 4 ( carrying capacity) to state 1 (not invade d) with eradication 1 a 32 Annual probability of ZM moving from state 2 (arrived) to state 3 (growing) without eradication 1 a 43 Annual probability of ZM moving from state 3 (growing) to state 4 (carrying capacity) w ithout eradication 1 a 44 Annual probability of ZM staying in state 4 without eradication 1 Other a ij Annual probability of ZM movi ng from state j to state i 0 c 1 Annual cost of arrival prev ention and early warning $152,800 c 2 Total cost of eradication $1.32 billion c 3 Total private mitigation (anti-f ouling paint) costs $3.87 million d 2 Annual ZM-related surface water use maintenance costs in state 2 0 d 3 Annual ZM-related surface water use maintenance costs in state 3 0 d 4 Annual ZM-related surface water use main tenance costs in state 4 $2.76 million e 2 Annual per-hectare ZM-related ecologi cal services losse s in state 2 0 e 3 Annual per-hectare ZM-related ecologi cal services losse s in state 3 0 e 4 Annual per-hectare ZM-related ecologi cal services losse s in state 4 $439 Source: USGS (2006) Since no monitoring is in place, detection is most likely to occur after ZM have become established. Policy IV invests in arrival pr evention measures, early warning and eradication measures if necessary. Budgetary and private m itigation costs for the four policy scenarios are reported in Table 2-3. 46

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Table 2-3. Present value estimates of zebra mussel policy scenarios ( 20 year, 2006 $ million) Public policy action Private action Policy Monitor, prevent arrival Eradicate upon detection Budgetary cost of policy Long run mitigation Mitigation costs I no no 0.00 yes 10.83 II yes no 2.33 yes 3.02 III no yes 872.90 no 0.41 IV yes yes 696.36 no 0.11 We estimate cumulative probabilities of ZM being in each of the four states ( S t ) and employ the parameter estimates (Table 2-2) in equation 11 to arrive at the expected present value of ZM infestation in Lake Okeechobee under the four policy scenarios. We assume a 2% discount rate. The state expenditures vary widely by policy. If the state only pursu es arrival prevention and an early warning system, then policy costs are $2.33 million, compared to a very costly $872.90 million for an only eradicate policy, or $696.36 million for a combination of the two. ZM-related maintenance costs borne by surface wa ter users are $10.83 when the state employs long term management only, compared to $3.02 million for the arrival prevention/early warning system is in place, $0.41 million when only erad ication is used, and $0.11 when both are used simultaneously. Policy costs, maintenance costs, recreation losses, and ecosystem gains are reported in Table 2-4 as a comparison to Policy Ido nothing. Introduction of ZM to the lake will improve fishing recreation by $1.09 million, compared with $0.31 for the arrival prevention/early warning system, $0.25 for only eradication, and $0.22 when both are pursued. ZM prevention and control policies will invariably reduce fishing recreation. The losses range from $0.78 to $0.87 million in 47

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present value over 20 years. These gains are very small when compared to the increases in maintenance costs or ecosystem impacts. Table 2-4. Simulation results compared to Poli cy I (Do nothing) (present value, 2006 $ million). II III IV Monitor, prevent arrival, provide early warning of arrival x 1 = 1, x 2 =0 Eradicate upon detection x 1 =0, x 2 =1 Prevention and eradication x 1 =1, x 2 =1 Policy Costs 2.33 872.9 696.36 Reduction in Maintenance Costs 7.81 10.42 10.72 Recreation Impacts -0.78 -0.84 -0.87 Ecosystem Impacts 243.02 259.96 271.54 Maintenance and Recreation Impacts 7.03 9.58 9.85 Maintenance, Recreation and Ecosystem Impacts 250.05 269.54 281.39 Policy, Maintenance and Recreation Impacts 4.7 -863.32 -686.51 All Values 247.71 -603.36 -414.98 Wetland losses and associated damages are $339.61 million when the state does nothing. If the state employs ZM policies, it can prevent si gnificant losses to ecosystem services. When the state invests in arrival preventi on and early warning, the net gains to ecosy stem services are $243.02 million. They are even higher when th e policy includes erad ication. When only eradication is used, ecosystem service gains ar e $259.96, and when both strategies are used jointly, there are gains of $271.54 million. Some policy makers may question the valid ity of including ecosystem service values because the values are too indirect. When only considering direct economic impactsrecreation, 48

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and maintenance coststhe returns to ZM polic ies are all positive. They are $7.03 million for arrival prevention and early warning, $9.58 million for eradication, and $9.85 when both are used together. When ecosystem impacts are included, the returns to ZM control and prevention strategies are very large. Net direct impacts are $250.05 million, $269.54, and $281.39 for arrival prevention and early warning, eradication, a nd a combination of the two, respectively. The impacts of the ZM policies change dr amatically when cons idering the budgetary demands of the ZM policies. When only considering direct impacts and budgetary costs, Policy II (arrival prevention and early warning) provides the only positive return $4.7 million. Eradication is very expensive, with Policy III (eradication) having total direct impacts of $863.32 million, and Policy IV (combination of Polic ies II and III) with ne t direct impacts of $686.51. The relatively small price ta g associated with Policy II is very effective at reducing the present value costs of eradication. If ecosystem service values are included, the results are still not supportive of eradication. When considering the policy, maintenance, recrea tion and ecosystem impact s, Policy II is still the clear favorite, with net benefits of $247.71 million. By comparison, Policy III (eradication) and Policy IV (arrival prevention, early warni ng, and eradication) yield losses of $603.26 and $414.98 when compared with doing nothing. Given our assumptions, the overall cost and da mage-minimizing choice is to invest in Policy II, arrival prevention and early warning. Th e total net costs and damages of this policy are 70.91% less than Policy I (do nothing), 89.34% less than Policy III (eradication), and 86.71% lower than Policy IV (arrival prevention, early wa rning, and eradication). Investing in prevention and early detection also place a smaller budgetary burden on the stateless than 0.03% of the budgetary costs of the other two polic ies. This is due to the very high cost of eradication, and the 49

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large gains realized by delaying the arrival of ZM. A relatively small amount of spending to prevent the arrival of ZM has a large impact on reducing the probability that ZM will infest the lake (See Figure 2-3). Without monitoring and prevention (x 1 ), there is a 45.42% probability of ZM fully infesting Lake Okeechobee by 2026. With monitoring and prevention, this probability is greatly reduced even if eradication is not attempted. 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 024681 01 21 41 61 82 0 YearCumulative Probability Policy Scenario I Policy Scenario II Policy Scenario III Policy Scenario IV Figure 2-3. Zebra mussel policy impacts on cu mulative probability of infestation. From the standpoint of both surface water users and environmental protection groups, Policy IVthe combination of arri val prevention, early warning, and eradicationis preferred. The ZM-related maintenance cost for this poli cy is only 98.99% lower than Policy I, as compared to 72.22% lower than Policy II, and 96.22% lower when only eradication is used (Policy III). Ecological damages to the lake are also lowest when a combination of policies is used, but by much closer margins than with surface water maintenance costs. Ecosystem damages are also much lower under Policy IV as compared with Policy I. Policy II, III and IV provide 71.55%, 76.54%, and 79.99% less ecosy stem services losses than Policy I. 50

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Recreational anglers would prefer that the st ate not prevent or erad icate ZM. Policy I (do nothing) provides 495.45% more fi shing-related benefits than the combination of management tools which is most effective at minimizing ecol ogical and maintenance costs. Arrival prevention and early warning, and eradication respectiv ely provide 140.91% and 113.64% of the fishingrelated benefits of the combination of management practices. We conducted sensitivity tests on key parameters that are expected to have large impacts on policy outcomesarrival rate, fishing-related benef its, ecosystem valuation, and eradication costs. The results are reported in Appendix B. A ssuming that the ZM arrival rate is half of our original assumptions, the total costs and dama ges of a ZM infestation are still minimized by choosing arrival prevention and early warning. Costs and damages under this policy are now $53.18 million instead of $101.64 million when arri val was assumed to be 3.5% without policy intervention. Similar savings ar e found for maintenance costs, but ecosystem losses and fishing gains are reduced to a point where results from Policy I (arrival preven tion and early warning) and Policy IV (arrival prevention, early warning, and eradicati on) are nearly equivalent; the original policy rankings still stand. We then simulated a loss of 10% instead of a gain of 10% in fishing benefits following a ZM infestation. This did not change the original policy rankings. We also estimated what the per-acre ecosystem damage and the eradication costs would have to be to make policy makers ambivalent between preven ting and eradicating ZM. If ecosystem values were 51.25 times higher or if eradication costs were reduced by 97.5% then policymakers would be ambivalent between prevention and eradicat ion. This provides s upport for our original ranking of the policies. These results set up an interesting dilemma for the state. Surface water users and environmental groups are expected to prefer a very costly combinati on of ZM management 51

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methods, while fishermen may prefer to have no state-funded efforts to prevent or mitigate ZM costs. The social planner, howev er, would clearly prefer to invest only in arrival prevention and early warning, but legislators ma y instead prefer to do nothing as that response puts the least budgetary burden on the state. The only Policy th at may be excluded by all groups is the decision to only eradicate. Depending on the relative in fluence that budgetary pressures and interest groups have on legislators, the st ate would choose to do nothing, only invest in arrival prevention and early warning, or provide a combination of the prevention and detection measures as well as eradication. Our estimates of the economic effects of a ZM infestation suggest that pre-planning is essential to reducing the overall impacts of the mussels. Despite the very low probabilities of ZM establishment on the lake, the expected costs and damages of such an infestation are very high up to $349.34 million over 20 years if nothing is done Eradication of ZM on the lake would be extremely expensive, and perhaps more than the state of Florida would want to spend. This would not be uncommon, as there is only one exampl e of ZM eradication, and that was in a very small water body in Virginia of ve ry high recreational si gnificance. Proactive measures, such as an early warning system and arrival prevention efforts can significantly reduce ecosystem damages, maintenance costs, and state expend itures on a policy response to the ZM problem. Compared with the other policy options, the poli cy of arrival preventi on and early warning is 3.43 to 9.37 times more cost effectiv e than other available policy options. Conclusion The Zebra mussel ( Dreissena polymorpha) is a serious threat to recreation, surface water use, and ecosystem services in lakes and rive rs in the United States. The zebra mussel is expected to reach Florida waters, but state and federal agencies currently have no program to deal with zebra mussel a rrival. The United States Army Corp s of Engineers have proposed an 52

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arrival prevention and education program for recreational boaters, as well as a zebra mussel early monitoring and warning system, but these have not been funded. Costly eradication of the mussel post-establishment is also an option. Here, we estimate and compare the impacts of zebra mussel policies on recreation, surface wate r use, and ecosystem services on Floridas largest lakeLake Okeechobee. We construct a bioeconomic m odel to simulate the expected impacts of the zebra mussel (ZM) on the lake. We first estimate ZM in troduction into the lake based on assumed transportation vectors (rec reational boating), habitat suitabili ty from a previous study (Hayward and Estevez, 1997), and effectiveness of ZM m itigation and prevention methods. We surveyed Lake Okeechobee surface water users and applied our results to ex isting estimates of changes in ZM-related maintenance costs for surface wate r users. We include assumed lake-related ecological and recreational values to construct an estimate of the total economic impacts with respect to a ZM infestation. We then apply st ate probabilities (in a stochastic dynamic simulation format) to arrive at a long-run economic impact analysis of ZM in Lake Okeechobee. We report present value results of the expected econom ic impacts over 20 year s, including costs and damages to surface water use, recr eational anglers, and users of ecosystem services, as well as budgetary costs (Table 2-4). Our model of the economic impacts of zebra mussels on Lake Okeechobee, Florida offers some insight into the cost-effective management of this and other invasi ve species threats. A zebra mussel infestation in Lake Okeechobee ha s expected net economic costs and damages of $349.34 million over 20 years if nothing is done. Recommended best practices for managing invasive species threats are prev ention, control, and eradicati on (where economically feasible) (Hulme, 2006). In aquatic systems, eradication and cont rol is particularly difficult (Floerl and 53

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Inglis, 2005). A comparison of ZM policy scenarios reveals that zebra mussel prevention is more desirable than post-invasion efforts given th e high cost of eradication. For example, the present value policy costs of eradication woul d be $872.9 million over 20 years, but with even modest funding on arrival prevention and early wa rning ($2.33 million), significant savings are achieved. With arrival prevention, early warni ng and eradication combined, the present value policy costs fall to $696.36 million. In addition to budgetary costs of a ZM policy, policy makers must balance the expected impacts on surface water use, recreation, and damages to freshwater ecosystems. An active ZM policy of arrival prevention and early warning, er adication, or a combin ation of the two would provide significant reductions in agricultural surface water us ers maintenance costs ($7.81 million $10.72 million) and very high savings to ecosystem services ($243.02 million $271.54 million). Zebra mussels are expected to be nefit fishing on the lake, but angler-related gains from ZM are not expected to be large comp ared to other impacts. With active ZM policies, fishing benefits would fall by $0.78 million $0. 84 million over 20 years. Ecosystem services are difficult to measure, and some policy makers may be wary of using such values. Without considering ecosystem services, the clear cost-minimizing ZM po licy is arrival prevention and early warning, which yields a net gain of $4.7 million. By comparison, large losses are associated with policies that include eradication ($686.51 million, $863.32 million). The inclusion of ecosystem services does not impact the relative performance of ZM policies. With arrival prevention and early warning, net gains are much larger ($247.71 million). Policies that include eradication still yield large losses ($414.98 million, $603.36 million). The results from this study indicate that invest ment in arrival prevention is much more cost effective than attempting to control or eradicat e invasive species post-arrival. As with many 54

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invasive species, there is a great deal about ZM biology, tr ansmission, and other important variables that are unknown. Unfort unately, ZM and other invasive species pose serious risks to agriculture and natural resources, and despite the unknowns, policy makers will be called upon to allocate scare public resources in defense of natura l and agricultural systems. Studies such as this one, though based on several assumptions about ZM that have not yet been tested, provide important information to the discourse on invasive species management. 55

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CHAPTER 3 BIOECONOMIC MODEL OF INVASIVE AQUATIC PLANTS HYDRILLA VERTICILLATA (HYDRILLA), EICHHORNIA CRASSIPES (WATER HYACINTH), AND PISTIA STRATIOTES (WATER LETTUCE) FOR FLORIDA LAKES Introduction Invasive aquatic plants can ha ve significant negative imp acts on water-based recreation, such as fishing, wildlif e viewing, and boating. Despite the hi gh potential impacts, little economic research has attempted to quantify these impacts across spatial scales that would be useful for invasive species management decisions. The li ttle economic research that has been conducted on aquatic invasive species usually focu ses on a single lake, or is too ab stract to be applied. This is the case because often very little data are available for larger scale studies. This study uses unpublished data on plant coverage, angler effort, and lake physiographic and amenities to estimate the impact of plant coverage on fishing activity on 13 Florida lakes. Using the bioeconomic model of invasive aquatic plants, I th en simulate the single-y ear costs and benefits of six policy scenarios for aquatic plant control. I estimate that the total economic value of the 13 lakes over $64.78 million, and lapses in invasive plant control may jeopardize that value. These results suggest that the op timal management policy is maintenance control with respect to hydrilla, water hyacinth and water lettuce. Invasive Species Background Invasive species in the United States pos e serious ecological and economic problems (Evans, 2003). An invasive spec ies is defined as a non-native species whose introduction causes or is likely to cause economic or environmen tal harm or harm to human health (Executive Order 13112, 1999). Invasive species are a particular problem for the tropical and subtropical areas of Florida, where physiographic, climatic and geographic characteristics make it relatively easy for non-indigenous species to establish (Sim berloff, 1997; Fox [personal communication], 56

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2007). Florida has a high rate of non-native sp ecies introduction, with the Port of Miami receiving about 85% of non-native plant ship ments each year (OTA, 1993). For example, the entire United States has about 50,000 established non-native pl ant and animal species, with Florida alone having over 25,000 as exotic or namentals (Pimentel, 2003); over 1,300 have established in natural areas, a nd 124 of these are dest ructive to natural areas (FLEPPC, 2006). By comparison, Florida only has 2,500 native plant species, and the US has 18,000 native species. Invasive species are a growi ng economic concern. Today, there are an estimated 5,000 to 6,000 invasive species in the Unite d States (Pimentel, 2003; Burnha m, 2004), and invasive plants are invading about 700,000 hectares/year of natu ral areas in the US (P imentel et al., 1999). Economic damages from invasive species are estimated to be $137 billion/year excluding ecosystem impacts (Pimentel et al., 1999). When considering the well-documented impacts of certain invasive species, such as damages caused by hydrilla verticillata in Florida, or the zebra mussel in the Great Lakes, it is clear that invasive species can have dire economic consequences. With continuing increases in both global trade and the domestic and international migration of people to Florida, the rate of arriva l of non-native species is rising. Invasive species management is fast becoming a high priority for the protection of Flor idas agricultural and natural systems (Schardt [personal communication], 2007). Yet, despite the large economic and ecosystem harms associated with invasive specie s, there exists little empirical analysis of invasive species problems in a way that would help policy makers or resource managers (Schardt [personal communication], 2007). There are very fe w invasive species studies in the economics literature, and most of those are distinctly theo retical and too technical or abstract for use by policy makers or resource managers. Few empirical studies have evaluated the impact of invasive species, and very few have examined their impact on recreat ion (Singh et al., 1984; 57

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Milon et al., 1986; Milon and Joyce, 1987; Colle et al., 1987; Milon a nd Welsh, 1989; Newroth and Maxnut, 1993; Henderson, 1995; Bell et al., 1998, et al.). The i ssue of invasive species is one that much more attention (and perhaps budget ary expenditures) will likely be focused on in the near future. Hydrilla, Water Hyacinth, and Water Lettuce Past Management The present level of expenditure s devoted to the management of a handful of invasive plant species is inadequate, even for those few bei ng managed. There are 18 invasive aquatic plant species in Florida waters, but very few of thes e are actively managed. Due to their extremely high propagation and growth rates, the Florida Department of Environmental Protection (FDEP) has targeted Hydrilla verticillata (hydrilla), Eichhornia crassipes (water hyacinth) and Pistia stratiotes (water lettuce) as among its t op management priorities. These plant pests have been the focus of management efforts in Florida for decad es; however, additional research is needed to assess economically efficient strategies for managing them. Hydrilla is a submerged aquatic plant introduced as an aquari um ornamental in the 1950s, and first detected in Florida wate r bodies in 1960 (Unive rsity of Florida, 2001; Blackburn et al., 1969). Its rapid growth rate and suitability to Florid a waters allowed it to spread rapidly throughout the state. By the early 1970s, hydrilla could be found in all major drainage basins in Florida. By 1995, hydrilla spread to over 40,000 h ectares on 43% of the public lakes in the state (Langeland, 1996). Hydrilla eradication efforts ha ve not been successful. The high growth rates and other unique characteristics of hydrilla and other invasive plants make them virtually impossible to eradicate. The Bureau of Invasive Plant Manageme nts current official po licy on invasive plants is to achieve maintenance control, defined as keeping the invasive plan t population at very low levels for the foreseeable future. In 2002, 175 Florida public water bodies were infested with 58

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hydrilla, with 1/3 having more than 10 acres. Hy drilla is under maintena nce control in 96% of Florida waters, but most of the hydrilla budget is spent on about 25 lakes (FDEP, 2004). Total spending on hydrilla was $17.3 million in fiscal year 2001-02 (FDEP, 2004). Water hyacinth and water lettuce are floating aquatic plants. Wa ter hyacinth, a native to South America, was introduced to Florida as an ornamental pond pl ant in 1885. Its rapid reproduction led to it being discarded into the St. Johns Rive r, and it spread quickly to neighboring water bodies (Schmitz et al., 1988). Within a few years, it was credited with blocking boat traffic on the St. J ohns River (Schmitz et al.). Wate r lettuce has been in Florida much longer, perhaps since the 16 th century, and is also believed to be a native of South America (Schmitz et al.). In 2002, wate r hyacinth and/or water lettuce were found in 244 public waters inventoried (57%), and were cons idered to be under maintenance control in 95% of Floridas waters (FDEP, 2004). Of these, 71 had over 10 acre s of floating plants ( 37 with water hyacinth, and 34 with water lettuce) (FDEP, 2004). Total state control spendi ng on floating plants in fiscal year 2001-02 was $3.1 million (FDEP, 2004). The problems with hydrilla, water hyacint h and water lettuce are multidimensional ecological, economic, public and private. Ecolog ical impacts include displacing native flora (both submersed and floating), altering habita t of native fauna, and disrupting ecosystem processes (Haller and Sutton, 1975) These invasive plants grow in thick monoculture mats where over half of the plant biomass is found in the upper 0.5m of the water column (Haller and Sutton, 1975). These mats block sunlight to a nd out-compete native plants (Hofstra, Clayton, Green, et al., 1999; Sutton, 1986), es pecially in the increasingly nutri ent-rich lakes and rivers of Florida. Hydrilla may also outcompete other subm erged invasive aquatic plants, such as Elodea densa and Ceratophyllum demersum (De Kozlow ski, 1991; Chambers et al., 1993). Dense 59

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monocultures can contribute to reduced fish populations, and when large mats of plants decompose, the reduced dissolved oxygen levels in a lake can cause massive fish kills (Bowes et al., 1979). These invasive aquatic plants also harm nonaquatic species by c overing nesting and egg laying areas, and blocking access to water, shelter, and food sources (FDEP, 2004). Endangered species are impacted by invasive sabout 400/958 endangered or thr eatened species are at risk primarily due to invasive species competition or pred ation (Wilcove et al., 1998). Economic impacts follow close behind ecosystem losses. Hydrilla, water hyacinth and water lettuce can hinder boating, swimming, and fi shing activities in lake s and rivers, and reduce the aesthetic value of natural areas (Milon and Joynce, 1987; Co lle, Shireman, Haller, et al., 1987). The reduction of recreational benefits derived from public waterways (and the cost of managing the weeds) highlights th e public loss from invasive aqua tic plants. Floridas 454 public lakes and rivers comprise 1.27 million acres (FDEP, 2004). In total, Florida has 1.5 million acres of lakes and rivers, with 7,700 lakes and ponds and 1,400 rivers and streams (FDEP, 2004). Freshwater fishing lures over 34 million particip ants to Florida who spend in excess of $35 billion/year (Lee [personal comm unication], 2006). Reduced sport fi sh populations coupled with access problems significantly reduce sport fishing ac tivities (Colle et al., 1987; Milon and Joyce, 1987; Milon and Welsh, 1989). For example, Colle et al. (1987) reporte d a nearly 85 percent decrease in total angler effort on Orange Lake, when hydrilla coverage increased from near 0 to almost 95% of the historically open-water region of the lake. Populations of several recrea tionally-important fish species, such as largemouth bass, bluegill, redear sunfish, and black crappie b ecome skewed to young indi viduals (Colle et al., 1987; Tate, Allen, Myers, et al., 2003). They also affects private citizens and businesses, 60

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blocking power generators and agri cultural irrigation water intake pipes, jamming water turbines and dams, and clogging canals and ditches (FDE P, 2004). Infestations in private ponds and poorly managed public water bodies can reduce recreational and aes thetic value of waterfront property. Invasive Aquatic Plant Control Florida has considerable experience fighting invasive aquatic plants (especially water hyacinth), yet Langeland (1996) as serts that lack of adequate and consistent funding for many invasive plants, (especially hydril la) continues to be the biggest barrier to effective management and the efficient use of public resources over time. According to the FDEP (2004), insufficient management funding allowed hydrilla to expa nd from 50,000 to 140,000 acres during the middle 1990s. During this time there was sufficient f unding to continue water hyacinth (and water lettuce) control, which was considered of prim ary importance due to their higher growth rates. Lapses in invasive plant contro l are particularly harmful to Floridas natural and agricultural systems because the invasive plants reproduce very quickly, and have prolific seed banks. Hydrilla has been difficult to eradicate because the plant produces underground tubers which generate new plants each year (Spencer, Ks ander, Madsen et al., 2000; Haller, Miller and Garrand, 1976; Van, 1989). Likewise, water hyacint h and water lettuce are extremely prolific, propagating both by seeding and by creating daughter plants vegetatively. Various aquatic plant control strategies ha ve been considered (Bowes et al., 1979; Chambers, Barko and Smith, 1993; Nichols, 1991), including mechanical removal, lake drawdown, application of various herbicides (V an, Steward, and Conant, 1987; Gangstad, 1978; Klaine and Ward, 1984) and biologi cal control, both with insect a nd herbivorous fish species (De Kozlowski, 1991; Hestand and Ca rter, 1978). Lake draw-down prev ents most recreational use, and biological control agents l ack precision, potentially leadin g to a depopulation of native as 61

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well as invasive plants, or not providing enough control. The primary method of controlling aquatic plants today is the us e of herbicides (FDEP, 2004). Wh atever method of control is chosen, there seems to be consensus that keepin g invasive aquatic plan t populations very low and under maintenance control is the preferred state-wide mana gement strategy (Schardt, 1997). Bioeconomic Modeling of Invasive Species Recently, economists and natural resource managers have turned to bioeconomic models to help guide resource managers decisions. Bioeco nomic models relate the biology of invasive speciespopulation growth rates, dispersion, pr edation, etcto their economic impacts. Some recent studies use bioeconomic models in an op timal control framework to analyze invasive species spread and control (Eiswerth and Johnson, 2002; Eiswerth and van Kooten, 2002; Gutierrez and Regev, 2002), while others emphasi ze feeback links between the biological and economic systems (Finoff, Shogren, Leung a nd Lodge, 2005; Settle and Shogren, 2002). Several studies have used bioeconomic models to estimate costs associated with invasion or to evaluate policy alternatives. For example, Knowler and Barbier (2000) model the invasion of an anchovy fishery by comb-jelly and provide estimates of lost profit s due to the invasion. Settle and Shogren (2002) model the impacts of La ke Trout on the native Cutthroat trout, and the subsequent impacts on wildlife viewing, fishing, and indirect values. Buhle, Margolis and Rueslink (2005) examine the relativ e cost-effectiveness of various control methods for invasive species with different reproductive rates and environmental tolerances. Finnoff and Tshirhart (2005) also examine physiological traits to de termine optimal invasive species control and prevention strategies. Other studies have focused on the changing stoc hastic and uncertain nature of invasive species arrival, spread, and damages. For exam ple, Leung, Lodge, Finoff, et al. (2002) compare arrival prevention and damage mitigation under uncertainty. Olson and Roy (2002, 2005) 62

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examine optimal policy responses under uncertainty and with a stochastically changing invasion. Huffaker and Cooper (1995) use a bioeconomic model of rangeland invasive to measure the impact on grazing. Odom, Cacho, Sinden, et al. (2003) develop a similar model with respect to the invasive scotch broom. The economics of aquatic plant management in Florida have been examined by willingness to pay studies on specific lakes (Burruss Institu te, 1998; Milon and Wels h, 1989; Milon et al., 1986). For example, Milon et al. (1986) es timated a $480,000 annual willingness to pay for hydrilla control on Orange and Lochloosa lakes. They also found that a full hydrilla infestation on the lakes would result in a loss over $5 m illion per year. Colle et al. (1987) similarly estimated a total economic impact of $900,000 for invasive weed control on Orange Lake. Milon and Welsh (1989) estimated $176,000 willingness to pay for invasive plant management on Harris and Griffin lakes, with a total recreati on impact of $1.7 million. Bell et al. (1998) estimated almost $20 million annual willingness to pay for invasive plant management on Lake Tarpon. No work has yet examined impact of various control strategi es on budgetary costs. Empirical Approach This study examines the impact of invasive plants on management expenditures and recreational activity on 13 Florida lakes. I estimate lake-specific yearly growth functions for hydrilla and floating plants (wat er hyacinth and water lettuce together) from unpublished FDEP aquatic plant coverage and treatment acreage data. I then quantify the relationship between the invasive plants and fishing activity to capture the economic implications of invasive aquatic plant infestation. In North Florid a, over 65 percent of boat trip activities are for fishing (Thomas and Statis, 2001), therefore cha nges in angler activity will cap ture much of the recreational impact of invasive aquatic plan ts on Florida lakes. A linear re gression model is specified to measure the impact of invasive aquatic plant c overage on angler effort. Included in the model 63

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are lake specific variables that characterize the biological and physical conditions of a lake that also influence angler effort. These include lake trophic state, lake size, season and lake amenities (such boat ramps and parking facilities). Third, I estimate per acre control costs for hydrilla and floating plants based on DEP treatme nt acreage and cost data. Finally, I simulate the impacts of various invasive plant management stra tegies on recreational fishing value and compare the costs and benefits for four potential policy responses to aquatic plant infest ation on the 13 lakes. Data Sources and Description FDEP performs annual aquatic plant surveys and maintains informa tion on the prevalence and coverage of aquatic plants on Floridas pub lic water bodies. Each year, the FDEP conducts grid sampling studies of aquatic plants in which total acreage of each plant discovered is recorded. Unpublished aquatic plant coverage data on 51 Florida lakes from 1983-2002 was obtained from FDEP. The Florida Fish and Wildlife Conserva tion Commission (FFWCC) perform Creel surveys of angler effort and catch on many Fl orida lakes. Unpublished Creel data on 45 lakes collected from 1966-2002 were obtained from five re gional FFWCC offices. Angler effort is an estimation of the number of hours that anglers on a boat spent fishing, times the number of anglers. For example, if 3 angl ers spent 4 hours fishing, the Cr eel survey would record 12 hours of angler effort. Angler effort is used as a proxy for recrea tional activity level on Florida lakes. Each Creel survey was performed either in spring, summer, fall, or winter, lasting an average of 3.0 months for winter, 3.0 months for summer, 3.1 months for sp ring, and 2.9 months for fall. Since Creel surveys reported angl er effort over time periods of different lengths, I standardize the data by computing average angler effort per day over the time period of the Creel survey. I collected data on physical characteristics of the lake that are expected to impact recreation. Included were amenities, lake size, and trophic state. The presence of lake 64

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amenitiessuch as public boat ramps, parking spaces and camping facilitiesmay influence the demand for recreation on particular lakes. The Florida Fish and Wildlife Conservation Commission operates about 1,300 boat ramps on 454 pub lic lakes and rivers throughout the State that are available for public use, some with a dditional features such as parking (Thomas and Stratis, 2001). Data on lake amenities were co llected from the FFWCC website (FFWCC, 2003). Lake size is defined as lake surface area. Da ta on lake surface area were obtained from Florida LAKEWATCH and Florida DEP. Lake acce ss is determined by water level. Water level information were available but excluded from the analysis because Creel surveys often do not occur when water depth is too shallow for boat use. For example, in 2001 there were 46 public waters inaccessible for FDEP pl ant inventories, and in 2002 there were 26 (FDEP, 2004). A lakes trophic state indicates the amount of plant and animal life that a lake can support and is typically measured with a trophic state index (TS I). The biological pr oductivity of a lake is expected to impact fish populations and catch rates. Particular trophic states are known to be more beneficial to sport fish production than others. The FDEP uses a Florida-specific trophic state index developed by Brezoni k (1984) for surveying water qua lity. The Florida-specific TSI is based on total nitrogen (mg/l), total phosphorous ( g/l), chlorophyll a (mg/m 3 ) for planktonic algae, and secchi depth (m) for water transparency (State of Florida, 1996). I computed a longrun Florida-specific trophic stat e index for each lake. The computed TSI values were used to characterize each lake as Oligotrophic, Mesotrophic, Eutrophic, or Hypereutrophic. 1 The data used in the TSI calculations were obtained from the University of Floridas LAKEWATCH program for the period 1991-2002. Data prior to 1991 were unavailable. 1 It is known that trophic state changes with population growth. Future work will test the assumption that trophic state can be held constant in the regression and still yield consistent results. 65

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Expenditures for invasive aquatic plant ma nagement for years 1998 to 2002 were obtained from Florida FDEP (Ludlow, 2005). These data include the number of acres, date, and cost of herbicide treatment for Florida lakes managed by the FDEP. Data prior to this were largely unavailable. Data were compiled into an Excel spread sheet. Included were hydrilla, water hyacinth and water lettuce coverage at the time of the FDEP s annual aquatic plant survey, control costs, lake specific amenities and surface area, and angler effort per day. Excluded were lakes that did not have both Creel survey and invasive plant survey data for the same years, or lakes that lacked calculable trophic state index numbe rs. Of the 45 lakes for which there were Creel data, 38 lakes remained in the spreadsheet. Of these, 13 had FDEP invasive aquatic plant coverage over 100 acres during the 1998-2002 period for which I also have acres treated data (George, Griffin, Harris, Istokpoga, Jackson, Kissimmee, Lochl oosa, Okeechobee, Orange, Osborne, Poinsett, Sampson, and Weohyakapka). Hydrilla and Floating Plants Growth Models The FDEP conducts annual aquatic plant su rveys primarily from July through December, with most surveys occurring in September. Fishing and Creel surveys however take place at various times throughout the year. H ydrilla in warm southern waters of the United States are the typically emerge beginning in mid-August, w ith maximal new plant sprouting in October (Spencer et al., 2000). Hydrilla biomass is generally highest in November (Bowes et al., 1979). Water hyacinth and water lettuce have simila r growth patterns (Wolverton and McDonald, 1979). Since plant coverage cha nges throughout the year, it was necessary to estimate their coverage during the whole year to match pl ant coverage with Creel survey data. Current herbicide applications used to control invasive aqua tic plants are effective at eliminating most of the existing aboveground biomass (Van, Steward, and Conant, 1987), but 66

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after herbicide application these plants regenerate from underground tubers, seeds, and the small percentage of remaining plant material. Most hyd rilla plant biomass can be effectively killed using aquatic herbicides, but hydrilla tubers can not (Steward, 1980; Steward and Van, 1987). It is estimated that hydrilla tubers covered 108,980 acres of public water bodies in 2002, clearly presenting a persistent manageme nt problem (FDEP, 2004). Seeds fr om floating plants are also pervasive (Schardt, 2007). I could not, however, include tuber or fl oating plant seed banks in the model of plant growth as thes e data are unavailable. Assuming static tuber and seed bank numbers, I was able to estimate single year growth rates for hydrilla and floating plants. Hydrilla grows in stages. At the beginning of the calendar year, there are typically no living hydrilla plants remaining from the previous year when th e plants naturally lose their ability to carry out basic phys iological functions. Once water temperatures reach 3 degrees Celsius, new plants sprout leaf material fr om the underground tuber bank. Growth is rapid through about day 270, or early September (Bowes et al., 1979). As the temperature begins to cool, the plants return to th eir senescent state following t uber production (Best and Boyd, 1996). Water hyacinth and water lettuce follow simila r growth stages (Wolverton and McDonald, 1979). Annual plant growth is a func tion of numerous variables, including water temperature, solar radiation, nutrient levels, av ailable space, water turbidity, lake depth, trophic state, plant predation and competition, and many other f actors (Best and Boyd, 1996; Van, Haller, and Garrard, 1978; Bowes, Holaday, and Haller, 1979; Best, Buzzelli, Bartell, et al., 2001). For the purposes of this study, I make several simplifying assumptions. First, I assume that only lake surface area, time, and herbicide ap plications affect plant growth. I tested this assumption using the most recent lake-wide study of hydrilla growth in Florida (Bowes et al.,1979). Bowes et al., 67

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(1979) measured the level of hydrilla bioma ss on Orange Lake, Florida in 1977. Using the Bowes et al. data, I estimated a temporal gr owth function for hydri lla with time as the explanatory variable (statistically significant at p = 0.01, with an adjusted R 2 greater than 0.975, suggesting a good fit). Second, I assume that the date of the FDEP aquatic plant survey was day 270 of each year after several communications with State of Florida invasive pl ant managers (Schardt, 2007, Ludlow, 2005). I also assumed day 270 to be the date of maximum surface area coverage for hydrilla, water hyacinth and wate r lettuce based on the hydrilla l iterature (Best and Boyd, 1996; field studies of water hyacinth and water lettuce growth were not available) and calculations from Bowes et al. (1979). Third, I assume that the date of herbicid e application is day 60 of each year, a time when tubers and seeds have sprouted and the rapid plant gr owth encourages uptake of herbicides (Schardt, 2007; Ludlow, 2005; Ha ller, 2006). I was not able to reach consensus regarding initial tuber an d seed density on the 13 lakes that are the focus of this study. Future work will factor tubers and seeds into both the growth function estimations and the comparison of the economic efficiency of various manageme nt schemes. Here, I assume a static growth function of hydrilla and floating plants, re spectively, for each of the 13 lakes. The growth equations are a function of time, with three distinct gr owing periods, defined as: Equation 1. 365 1)( )(2 1ttmfor eH tmttsfor eH tstfore Htmtb tm tstg ts tg t Where H t is the acreage of the inva sive aquatic plant at day t ; g 1 is the lake-specific growth parameter for time 0-60, g 2 is the lake-specific growth parameter for time 61 270, and b is the lake-specific decay parameter for time 271 365; ts is the assumed day of plant herbicide spray 68

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application (if done), which is assumed to be 60; and tm is the assumed day of plant maximum surface area coverage and FDEP survey date, wh ich is assumed to be 270. The parameter estimates are reported in Table 3-1. Table 3-1. Hydrilla and floating plants growth function parameter estimates. Hydrilla Floating Lake g 1 g 2 b g 1 g 2 b George 0.014 0.014 0.04 0.018 0.018 0.04 Griffin 0.034 0.016 0.009 0.059 0.02 0.033 Harris 0.047 0.016 0.017 0.035 0.02 0.018 Istokpoga 0.122 0.029 0.093 0.12 0.007 0.041 Jackson 0.091 0.023 0.058 0.082 0.02 0.047 Kissimmee 0.131 0.026 0.092 0.102 0.013 0.044 Lochloosa 0.063 0.014 0.023 0.03 0.02 0.015 Okeechobee 0.03 0.03 0.085 0.141 0.014 0.072 Orange 0.095 0.028 0.074 0.085 0.01 0.026 Osborne 0.078 0.014 0.032 0.059 0.02 0.033 Poinsett 0.102 0.02 0.06 0.088 0.012 0.033 Sampson 0.078 0.028 0.063 0.045 0.011 0.003 Weohyakapka 0.133 0.023 0.086 0.072 -0.005 -0.015 Aquatic Plant Management Scenarios Several management scenarios are considered for the treatment of the invasive aquatic plants (Table 3-2). Scenario A is the status quo, which is calculated from the 1998-2002 FDEP aquatic plant acreage treated data. The status quo treatment is estimated from 5-year averages on the 13 lakes. This is the level of treatment actually pursued by the Florida Department of Environmental Protection. Status quo treatment already provides lake access throughout most of the year on Floridas 454 public lakes. As long as the lakes remain relatively free of hydrilla and floating plants, most of the lakes recreati on and ecosystem value will be preserved. 69

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Aquatic plant herbicide application occurs in early to mid-Spring when plants are young and growing vigorously and able to uptake a large percentage of the herbicide (Haller [personal communication], 2006). Treatment in the summer months would result in too much dissolved oxygen depletion due to plant dieoff at a time when dissolved oxygen is already low (Haller). For simplicity and tractability of calculation, I assume that treatment will occur at day 60. Van, Steward, and Conant (1987) found th at aquatic herbicides are up to 95% effective for the Florida variety of dioecious hydrilla, and Langeland and Pesacreta (1985) found similar effectiveness for the monoecious variety in North Carolina. For th e sake of providing cons ervative estimates of expenditures and losses associated with hydrilla c ontrol, I assume a 99% efficacy rate (1% of the plant biomass continues to grow after the herbicide is applied). For scenario A I use the following invasive aq uatic plant coverage function: Equation 2. 365 1)( )(2 1ttmfor eH tmttsfor eH tstfore Htmtb tm tstg ts tg t where is the percentage of living invasive plant acreage left after treatment, which is assumed to be .01. Table 3-2. Model assumptions for policy scenarios. Scenario First treatment (at day 60) Second treatment (at day specific to lake) 2 A All hydrilla and floating pl ant acreage No treatment B0 No treatment No treatment B2 Scenario A, but every other year No treatment C20 Same as Scenario A 20% of hydrilla and floating plants acreage 2 The date of the second treatment is calculated to maxi mize the effectiveness of treatment. The dates of second treatment are reported in Table 3-3. No te: some calculated dates are greater th an 365. In these cases it is assumed that no second treatment occurs. 70

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Table 3-3. Date of second herbicide treatments for C20. C20 Floating C20 Hydrilla George 223 277 Griffin 210 245 Harris 209 245 Istokpoga 511 163 Jackson 210 193 Kissimmee 294 175 Lochloosa 207 269 Okeechobee 267 161 Orange 362 167 Osborne 210 273 Poinsett 312 210 Sampson 337 167 Weohyakapka 279 190 Scenario B0 is no treatment, and has the same growth function as Equation 1. Scenario B2 is treatment every other year, and has the following growth function: Equation 3. 365 12)( )(2 1ttmfor eH tmttsfor eH tstfore Htmtb tm tstg ts tg t It is assumed that the initia l invasive aquatic plant acreage would double from one year to the next absent treatment. It must be stressed that this assump tion has not been tested and may represent unrealistic growth conditions. For scenario C20 the state treats all of the invasive a quatic plant acreage at day 60 plus an additional treatment 20% of the acreage at a later date. The date for second treatment is lake71

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72 365 1)( 2 )( 2 )(22 2 1ttmfor eH tmttsfor eH tsttsfor eH tstfore Htmtb tm tstg ts tstg ts tg t where F is angler effort, H is hydrilla and floating plants cove rage as estimated on the 13 lakes, and X is the matrix of other factors likely to affect fishing effort, includi ng trophic state, season, lake size and lake amenities. Both F and H are per day averages; trophic state, lake size, and amenities are assumed to remain constant. For each of the management scenarios, the corresponding acreages of hydrilla and floating plants were calculated and were used to calculate th e changes in both recreational fishing benefits and control costs. The results are discussed in the Economic Effects of Aquatic Plant Management section. For three of the la kes, I provide examples of the impact of management scenarios on aquatic plant covera ge (Figure 3-1, Figure 3-2, and Figure 3-3). The benefits associated with invasive aquatic plant manageme nt are measured as a change in the amount of hours that anglers spend fishin g on that lakes, times an estimate the average willingness to pay for an hour of fishing (Thomas and Stratis, 2001). I refer to angler effort as the amount of hours an angler spends fishing on a lake, which is a functi on of several factors: Recreational Fishing Effort Model where ts 2 is the date of second treatment. specific and was calculated to maximize the effec tiveness of the treatment. The growth function for scenario C20 is: Equation 4. Equation 5. F = f(H, X)

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0 2000 4000 6000 8000 10000 12000 14000 0 50 100 150 200 250 300 350 400Time (day of year)Hydrilla (acres) STATUS QUO ALTERNATE YEARS NO CONTROL 20% INCREASE IN CONTROL 73 Figure 3-1. Simulated hydrilla coverage in Lake Istokpoga.

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0 2000 4000 6000 8000 10000 12000 14000 0 50 100 150 200 250 300 350 400Time (day of year)Hydrilla (acres) STATUS QUO ALTERNATE YEARS NO CONTROL 20% INCREASE IN CONTROL 74 Figure 3-2. Simulated hydrilla coverage in Lake Kissimmee.

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75 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 0 50 100 150 200 250 300 350 400Time (day of year) Hydrilla (acres) STATUS QUO ALTERNATE YEARS NO CONTROL 20% INCREASE IN CONTROL Figure 3-3. Simulated hydrilla coverage in Lake Weohyakapka.

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A regression analysis was conducted on the a bove variables using data collected on the 13 lakes over 20 years (from 1982 2002). These data are unbalanced panel data (Greene, 2004). I used Limdep 8.0s panel data analysis tool for unbalanced panel data to perform regression analyses. I conducted several specifi cation tests, including 1) to determine whether hydrilla and floating plant acreage variables s hould be raised to a higher power to provide better parameter estimates; 2) to check whether I needed an interac tion variable to capture the combined effects of invasive aquatic plant acreage and lake size; and 3) pooling te sts were conducted to check whether intercept and slope coefficients could be assumed to be the same for all lakes. While there were not enough degrees of freedom to test for lake-specific slope parameters, the partial Ftest for lake-specific intercept terms indicates no statistically significant difference (Greene, 2004). The amenity variables Ramps and Parking we re perfectly co rrelated, and were redefined as one variable (Ramps+Parking). There was no variation in the variable Camping, so it was excluded from the model. The model paramete r estimates are reported in Table 3-4. All variables except Summer are significant at the 95% level of confidence or higher. The model significance was high ( F = 42.02, significance of F = 0.0000), with the regression equation providing a relatively good fit to the sample data (Adj. R 2 = 0.7836). There were no obvious model problems. Neither Wh ites test nor the Breush-Pagan test for heteroscedasticity revealed any problems, and the Durbin-Wats on statistic was 1.96, signifying no significant problem with autoregression. Lake size, and ramps+parking have a positiv e impact on fishing effort. The positive sign on WACRES suggests that angler effort is greater on larger lakes. Larger lakes likely have fewer conflicts between anglers and other recreational boaters, leading to a better fishing experience and perhaps better fishing. More fishing sites, larger fish may explain this phenomenon, and 76

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proximity of large lakes to large population areas are other explanations. I estimate that for each additional 1000 acres of lake surf ace area, there will be 7.01 additi onal hours of fishing effort per Table 3-4. Angler effort regression model parameters. Coefficient P-value Intercept -406.426 0.002525 Hydrilla 2 ** 4.25E-07 0.030062 Floating 2 ** 4.68E-07 0.026767 (Hydrilla+Floating)x(wacres)** -2.90E-07 0.030224 WACRES*** 0.00701 2.36E-33 Ramps+Parking*** 5.305605 7.79E-07 Oligotrophic** 440.4176 0.037645 Eutrophic*** 377.5538 0.005022 Hypereutrophic*** 615.6091 5.08E-05 SPRING*** 504.9197 1.38E-05 WINTER*** 430.8179 0.000372 SUMMER 155.1794 0.205076 significant at the 90% level of confidence ** significant at the 95 % level of confidence ***significant at the 99 % level of confidence day on that lake. This may suggest that larger lakes are a more valuable natu ral resource for recreational use, and may warrant higher priority for funding to cont rol invasive aquatic plants. Likewise, ramps and parking have a positive im pact on fishing effort. The availability of ramps, and safe, maintained parking areas are lik ely to improve the fishing experience. Here, I estimate that the presence of both parking and ra mps adds almost 5 hours of angler effort per day. An interesting interpretation, when taken together with the aquatic weed effects (discussed below), is that building parking spaces a nd providing ramp access may overcome a certain amount of invasive aquatic plant coverage, at least while lake access is possible through the aquatic weeds. 77

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Interpretation of the trophi c state parameters is less obvi ous, perhaps because there are competing forces at work. On the one hand, scien tific findings suggest a re duction in fish species and fish weight for some sport fish with an increase in Florida lake trophic state (Bachmann et al., 1996; Hoyer et al., 2005). On the other hand, lake eutrophication is advanced by increased runoff from larger population cent ers. This model shows mixed results with respect to trophic states effects on fishing effort. The parameters for oligotrophic, eutr ophic and hypereutrophic lakes are positive, while the parameter on the ex cluded variable mesotrophic is interpreted as being negative; Hypereutrophic lake s attract more fishing effort th an eutrophic, which is greater than mesotrophic. One interpretation is that oligot rophic lakes attract angler s for the clarity of the water that may improve the fishing experience. As lake clarity falls w ith the increased trophic state, the dominant force may then be populat ion center effect, i.e. lakes become eutrophic because they are near population centers and receive more nutrient loads. And because the lake is near a population center it is fished more frequently desp ite the higher trophic state. The aquatic plant parameter estimates suggest that invasive aquatic plant coverage has a negative impact on fishing effort when including the interaction effects of lake size. For example, a lake of 10,000 acres that goes from no invasive aquatic plants to 10 acres of hydrilla and 10 acres of floating plants (water hyacinth and water lettuce) would cause the loss of 0.057 hours of angler effort per day. Going from 10 to 50 acres of hydrilla and floating plants, respectively, would cause the lo ss of 0.287 hours of fishing effort per day. Figure 3-4 shows the impacts of increased hydrilla and floating plants coverage (in equal amounts) on fishing effort for a 10,000 acre lake. This finding is consistent with the literature on hydrilla coverage and angler effort. Colle et at. ( 1987) report a significant nega tive correlation between hydrilla coverage and harvestable bluegi ll and redear sunfish populations on Orange Lake, Florida. Colle 78

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et al. also reported an 85% decrease in total angler effort on Orange Lake when hydrilla coverage increased from 0% to 95%. Lost anger effort per day (versus 0 coverage) -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 050010001500200025003000 Plant acres (hydrilla and floating, each)Change in effort per day Figure 3-4. Daily fishing effort lo st to invasive aquatic plants for a 10,000 acre lake in Florida. Hydrilla, Water Hyacinth, and Water Lettuce Treatment Cost Model The lack of common knowledge of hydrilla grow th rates may have contributed to drastic reductions in State funding for invasive plan t control in the mid 1990s. Without adequate funding for control, hydrilla grew rapidly and took over entire lakes. Control of lakes was eventually regained in subsequent years, but at a very high cost The total cost of controlling hydrilla, water hyacinth and water lettuce in any given year is m odeled as a function of acres treated during that year assuming constant costs: Equation 6. C = c 1 Hydrilla + c 2 Floating where C is the total cost of treating invasive plants, c 1 is the per acre cost of treating hydrilla, Hydrilla is the total number of acres treated, c 2 is the per acre cost of treating water hyacinth and water lettuce, and Floating is the total acres of water hyacinth and water lettuce treated. Equation 6 was estimated from the 5 year averages of per acre treatment costs for the 13 lakes included in this study using data obtained from FDEP for 1998-2002 (Ludlow [personal communication], 2005); the five year average for c 1 is $561 and c 2 is $107. 79

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Angler Effort Value Model According to the Florida Fish and Wildlife Conservation Commission, freshwater anglers on Florida lakes spent $18.20 per hour fishing in 1996 or $20. 65 in 2002 dollars (Thomas and Stratis, 2001; FFWCC, 2003). Applying $20.65 a nd assuming a fishing day is 6 hours, the empirical angler value equation is Equation 7. V = p F where V is the value of fishing, p is the per hour angler value in dollars and F is the number of hours spent fishing. Economic Effects of Invasiv e Aquatic Plant Management Using the actual treatment and surveyed acr eage data from FDEP for the 13 lakes, I simulate the economic effects of each of the treatment scenarios ( A status quo, B0 no treatment, B2 treatment every other year, and C20 second treatment at 20%). Recall Equations 1-4, the growth equations for the invasive aquatic plan ts for each treatment scenario. Angler effort, F is a function of invasive aquatic weed acreage, H and other lake characteristics, X (i.e., lake size, parking, trophic state, and season) such that Equation 8. (,) FfHX and the change in angler effort with respect to a change in invasive plant acreage from a particular scenario is Equation 9. (,) F fHX HH Angler effort can be summed over several years as Equation 10. 10(,) fHX F Fd H H and generalized as 80

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Equation 11. 10dFFF The same generalization can be made of treatment costs and invasive aquatic plant acreage as Equation 12. 10dHHH Equation 13. 10. dCCC The net benefit for each scen ario is calculated as Equation 14. 13365 ,, 11 ,(,) ()LtL Lt Lttts Lt LtfHX NBp dHdCH H where NB is net benefit from the treatment strategy, L is the subject lake (George, Griffin, Harris, Istokpoga, Jackson, Kissimmee, Lochloosa, Oke echobee, Orange, Osborne, Poinsett, Sampson, and Weohyakapka), t is the day of the year, p is the per hour value of fishing, H is invasive aquatic plant coverage, and C is treatment costs. The acreage of hydrilla, water hyacinth and wa ter lettuce changes thr oughout the year. In the warm summer months, when the photoperiods are longer, aquatic plants can infest almost all of the available lake acreage absent control. While it is widely accepted that high levels of aquatic plants can block recreat ional access to Florida lakes, only one study has measured the relationship between invasive plant coverage a nd fishing. Colle et al (1987) report an 85% decrease in total angler effort on Orange Lake when hydrilla c overage increased from 0% to 95%. In Florida, many anglers use shallow-draf t fan boats that are not hampered by aquatic plants, which may explain the persistence of some fishing effort at high le vels of plant coverage. Here, I assume that only 15% of the otherwise expected fishing effort would remain when invasive aquatic plant coverage is above 80% of available lake surface area. I simulate the impacts of the invasive plant management scenarios using General Algebraic Modeling System (GAMS) 2.5A software. The results are reported in Table 3-5, with 81

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an example for 4,000-acre Lake Jackson in Figure 35. One very useful resu lt is the estimation of the total value of the 13 lake sover $64.78 million, with about 3.13 million total fishing hours. These results are similar to those found by other studies on Florida lakes. For example, Milon et al. (1986) estimated a $480,000 annual willingness to pay for hydrilla control on Orange and Lochloosa lakes. They also found that a full hydrilla infestation on the lakes would result in a loss over $5 million per year. Colle et al. (1987) similarly estimate d a total economic impact of $900,000 for invasive weed control on Orange Lake. Table 3-5. Annual economic impact of invasi ve aquatic plant management on 13 lakes. A Status quo B2 -Alternate year control B0 -No control C20 -Second treatment at 20% Fishing Effort (hours) 3,135,966 2,426,774 1,369,516 3,359,053 Treated Acres 13,785 31,285 0 16,542 Peak Acres 21,085 43,620 43,620 4,304 Total Value 64,783,832 50,133,107 28,291,923 69,392,436 Total Control Costs 4,828,254 10,938,970 0 5,793,905 Net Benefit 59,955,578 39,194,966 28,291,923 63,598,531 Change in NB 0 -20,761,440 -31,663,655 3,642,954 Value per year, $ 2006 millions Milon and Welsh (1989) estimate $176,000 willingness to pay for invasive plant management on Harris and Griffin lakes, with a total recreati on impact of $1.7 million. Bell et al. (1998) estimated almost $20 million annual willingness to pay for invasive plant management on Lake Tarpon. Compared with the status quo treatment strategy, reducing treatment to every other year, or halting treatment altogether will lead to significant recreational and ecosystem losses, largely due to access problems. Altern ative year control ( B2 ) results in a 23.61% reduction in fishing hours, 82

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0 5,000 10,000 15,000 20,000 25,000 123456789101112 MonthFishing Effort (hours) Status Quo Alternate Years No Control 20% Increase in Control 99Figure 3-5. Impact of invasive plant contro l on fishing effort (Lake Jackson example) and no control (B0 ) yields a 56.33% loss in angler effort. A 20% increase in control ( C20 ) increases fishing hours by 7.11%. Peak and treated acreage of invasive plants vary widely by cont rol policy. Decreasing treatment more than doubles the peak acreage. Alternate year control ( B2 ) and no control ( B0 ) cause annual peak acreage to increase by 106.88% (the lake maximum), and treated acreage to increase by 126.95% for alternate year control. Increasing treatment substantially decreases the peak acreage and the total acres treated. For example, moving from the status quo to strategy C20 reduces the peak acres by 79.59% (see Figure 3-1, Figure 3-2, and Figure 3-3). This may be extremely important to the ecology of the lakes and for the preserva tion of native plant species. Control costs also vary widely by policy. The status quo (A ) control costs are $4,828,254. These costs rise by 126.56% with the alternate year control ( B2 ), and by 20% for the 20% increase in control ( C20 ). 83

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The state of Florida must bala nce the benefits and costs of invasive species-related public policies. The total recreation-related losses associated with no control ( B0 ) are $33,663,655 per year. Using this as a baseline for return on inve stment calculations, I estimate that status quo control ( A ) yields a 655.80% return on the investment of $4,828,254 in invasive aquatic plant investment. In terms of rate of return, status quo ranks the highest, but in terms of absolute net benefit, increasing control is preferred. Increa sing control by 20% from status quo will increase fishing-related benefits by $3,642,953. B2 yields a 609.37% return on investment, which is lower than the 655.80% rate of re turn to the status quo policy. Alternate year control ( B2 ) results in a loss in fishing-related benefits as compared to the status quo, but yield 99.67% rate of return as compared to do nothing ( B0 ). In the mid-1990s, the state of Florida significan tly reduced the FDEPs invasive plant management budget, and hydrilla growth went unchecked. These results confirm the high costs associated with such a lapse in funding. Treatment of invasive aquatic plan ts should be continued, either at their current levels or at slightly increased levels of control, dependi ng on relative demands on state monies. However, these results may be too conservative as they do not consider the impacts of invasive aquatic plant control on seed and tube r bank numbers or ecosystem br ittleness that may result from prolonged aquatic weed monoculture s. These simulations are restri cted to a 5 year period on 13 lakes. Using the FDEP plant coverage data (n = 997), I estimate a mean hydrilla coverage of 9.36%, with a standard error of 0.61%, and a range of 0 to 100% of the lake surface area. I also estimate mean floating plant coverage of 0.07%, with a standard error less than 0.1% and a range of 0 to 51.92% of lake surface area. At these le vels, tuber and seed banks are at relatively low numbers. Given several years of no control, these numbers would be much higher and could vastly increase control costs and recreational loss es in subsequent years. Treatment strategies B0 84

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(no treatment) and perhaps B2 (treatment every other year) c ould produce such an event, at which point a substantial portion of the total benefit of these 13 lake s would be lost for four years or more. The loss of recreation on these 13 lake s may have a devasta ting impact on certain regional economies. Maintenance control of these aquatic species at low levels is more economically efficient than allowing them to grow rampantly or infrequently controlling them. Indeed, the comparison of the status quo scenario A to the every other year treatment scenario B2 it is apparent that control costs rise substantially and net benefits fall substantially due to sporadic control. Even brief lapses in funding, like what occurred dur ing the mid-1990s, are very costly. In Florida there are 1.05 million acres of lake surface ar ea on lakes with over 1,000 acres (FFWCC, 2005). When considering the economic implications on lakes throughout the State, continued and perhaps increased treatment of invasive aquatic plants may be in the pub lics best interest. Lapses in maintenance control may also ha ve long run consequences. In 2000, it was discovered that hydrilla was becoming resistant to flouridone herbicide, apparently due to random mutations (FDEP, 2004). For example, in 2002 the 19,000-acre Lake Tohopekaliga had 15,000 acres of herbicide-tolerant hydrilla. If mu tation rate is a function of population size, then brief lapses in hydrilla contro l that lead to large plant populations may provide for more mutations and higher rates of herbicidal resistance. There is no close substitute to fluoridone for large-scale hydrilla control; lake managers must be vigilant against larg e hydrilla populations. One important final note about the results is th at while they may be robust over the 5-year period and the 13 lakes I examined, they may not be robust for predicting the economic effects of invasive aquatic plant management for future ti me periods. An important impact of consistent treatment of these plants is on reducing their tuber and seed banks. Seed banks indicate the 85

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potential future biomass (Winton and Clayton, 1996). The presence of tuber and seed banks may exacerbate the differences between the various le vels of treatment. Future work will include tuber and seed banks for hydrilla, wa ter hyacinth, and water lettuce. Conclusion Hydrilla verticillata (hydrilla), Eichhornia crassipes (water hyacinth), and Pistia stratiotes (water lettuce) have long been established in Floridas lakes and rivers. The unique characteristics of these plants allow them to gr ow rapidly, displacing na tive flora and fauna, and reducing recreational use and enjoyment of many water bodies. Recreational freshwater fishing in Florida lures over 3 million anglers with annual expenditures exceeding $3.8 billion. Consistent and significant contro l efforts are required to preven t invasive aquatic plants from eroding the value of Floridas lakes to the states economy and ecosystems. Long run cost-effective management of these invasive species requires consistent control efforts, yet the States funding has fallen short in the past. Using data co llected on 13 lakes with more than 100 acres of invasive plant coverage at any point during 1998-2003, I estimate the growth of hydrilla, water hyacinth, and water lett uce for each lake as well as per acre control costs for hydrilla and floating plants. Using fish ing effort data collected over 20 years, I also estimate the effects of hydrilla, wa ter hyacinth, water lettuce, a nd other lake characteristics on fishing effort. I combine plant growth, angler e ffort, and control costs into a bioeconomic model of hydrilla, water hyacinth and wate r lettuce and fishing effort. The bioeconomic model is used to estimate the value of various invasi ve aquatic plant management regimes. Model results show that over 5 years, the valu e of fishing activity on the 13 lakes is in excess of $64.78 million, with about 3.13 million total fishing hours. Compared with the status quo treatment strategy, reducing treatment to ever y other year, or halting treatment altogether will lead to significant recreational and ecosyst em losses, largely due to access problems. The 86

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status quo ( A ) control costs are $4,828,254. These costs rise by 126.56% with the alternate year control ( B2 ), and by 20% for the 20% increase in control ( C20 ). Peak and treated acreage of invasive plants vary widely by cont rol policy. Decreasing treatment more than doubles the peak acreage. Increasing treatment substantially decreases the peak acreage and the total acres treated. The total recreation-related losses associated with no control ( B0 ) are high$33,663,655 per year. By comparison, status quo control yi elds 655.80% return on investment for control expenditures of $4,828,254 per year. In terms of absolute net benefits, increasing control by 20% will increase fishing-re lated benefits by $3,642,953, but at a lower rate of return 609.37%. Alternate year control ( B2 ) results in a loss in fishing-related benefits as compared to the status quo, but yield 99.67% rate of retu rn as compared to do nothing ( B0 ). A few clear conclusions follow from the result s: 1) Florida lakes have very high economic values that are at risk from i nvasive aquatic plants; 2) maintena nce control of invasive aquatic plants is the preferred cost-minimizing control polic y; and 3) lapses in maintenance control, even if brief, can significantly increase subsequent invasive aq uatic plant control costs. 87

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CHAPTER 4 THE LEGAL BASIS FOR REGULATORY CONTROL OF INVASIVE AGRICULTURAL PESTS IN FLORIDA Introduction Florida is no stranger to agricultural disease, pa rticularly those affecti ng its citrus industry. Florida has twice successfully er adicated citrus canke r (Division of Plan t Industry, Florida Department of Agriculture and Consumer Servic es, 2006). Citrus canker was first detected in Florida in 1910 and declared eradicated in 1947. However, in 1986, a highly aggressive Asian strain of the citrus canke r was detected in Florida 3 (Timmer, Graham, and Chamberlain, 2006). Some speculate that the 1986 stra in was not a reintroduction but a perennial holdover from the 1910 Xanthomonas axonopodis pv. citri introduction (Schubert and Sun, 2001). The 1986 strain was declared eradicated in 1994, but was found again in 1995 in residential and commercial sites, including the Miami International Airpor t in Miami-Dade County (Gottwald et al., 2002). Florida has a high rate of non-nativ e species introduction, with the Port of Miami receiving about 85% of non-native plant shipments en tering the US each year (OTA, 1993). Facing potentially devastating e ffects to the citrus industry as well as Floridas economy, the US Department of Agriculture and the State of Florida implemented major dual-track citrus canker eradication programs (CCEP). Both program s required the removal of all trees within 1,900 feet (initially 125 feet) of an infected tree. The USDA administered and provided compensation to commercial citrus growers whose trees were taken, while the state of Florida administered and provided compensation to resi dential tree owners whose trees were taken. Under the USDA program, commerci al growers were compensated $26 per tree. Residential tree owners were provided $55 per tree, and some counties supplemented this compensation. For 3 Haire v. Florida Dept. Of Agriculture And Consumer Services, 870 So.2d 774 (Fla. 2004). 88

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example, in Broward County tree owners were give n $45 Wal-Mart gift cer tificates for the first tree taken (good for Garden Center purchases only ). Legal challenges to the state and federal eradication programs happened almost immediately after the first tree was taken (Regina, Olexa, and McGovern, 2004) In 2000, residential citrus tree owners of suspicious trees were granted temporary injunctions against the States canker eradicat ion program. From 2000 to 2004, there were two 18-month gaps during which the State was enjoin ed from cutting down healthy trees within 1,900 feet of infected trees and canker innoc ulum increased and was largely undetected on residential trees. Since that time, Florida expe rienced five major hurricanes (Albrigo et al., 2005). The hurricanes of 2004, Charley, Frances, Ivan, and Jeanne, spread citrus canker from these residential trees to such an extent that 80,000 commercial acres of citrus were subsequently slated for destruction. Con centrated efforts by governmental officials reduced this to 32,000 acres when Hurricane Wilma hit in 2005. Due to the spread of the citrus canker pathogen with Wilma, officials faced the task of destr oying an additional 168,000 to 220,000 acres of commercial citrus (USDA, 2006). The inability of the States canker eradication program to continue unabated meant the USDA canker eradi cation program was largely ineffective. On January 10, 2006, the federal government stated that citrus canker is so wi dely distributed that eradication is impossible and pulled the fundi ng for the USDAs citrus canker eradication program (USDA, 2006). This change in policy came on the heels of a number of judicial decisions upholding the legality of Floridas citrus canker eradicat ion program, but too late to save the USDA eradication program. Though the CCEP was repealed in January 2006 (Timmer et al., 2006), these judicial decisi ons will be precedential to pote ntial challenges to similar State 89

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programs designed to manage and control pests like citrus canker and citrus greening (Salisbury, 2006). The State of Florida, as other states in the US, has a duty to protec t its agricultural and natural resource interests from invasive plant, anim als, and other species. The power to exercise protective measures originates from the polic e power inherent in Floridas sovereignty. 4 5 The use of police power to protect Floridas agricultur al interests is delegated by the Legislature to the Director of the Division of Plant Industry within the Department of Agriculture and Consumer Services. 6 This chapter provides an overview of the State s use of police power to protect agriculture in conjunction with legal decisions that balance th e exercise of this power with the constitutional mandates of due process and just compensation. These cases demonstrate how the courts apply these constitutional limitations in challenges to measures involving a burrowing nematode (spreading decline) in comparison with the measures taken in controlling an aggressive strain of citrus canker. Use of Police Power to Take Private Property The State of Florida has the power to take private property for a public purpose as an incident to its sovereignty and requires no constitutional recognition. 7 One form of this power is when Florida uses its police power to take proper ty for the purpose of protecting public safety, public welfare, public morals, or public health. 8 Police power is sometimes used to only 4 Boom Co. v. Patterson, 25 L.Ed 206, 98 U.S. 403 (U.S. 1878). 5 Department of Agriculture and Consumer Services v. Bonanno, 568 So.2d 24 (Fla. 1990). 6 Fla. Stat. 81.031(7) (2002). 7 See infra note 3; see also note 4. 8 Sweat v. Turpentine & Rosin Factors, Inc., 15 So.2d 267 (Fla. 1943). 90

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describe activities that do not require compensation. However, the exercise of police power may require compensation. 9 It should be noted that it is difficult to di scern the boundary line between the actions that are compensable under the police power and compensable actions under eminent domain. 10 The distinction is that eminent domain involves ta king a property for a pub lic use, where police power involves the destruction of such property to prevent its use in a manne r that is detrimental to the public intere st (Gottwald, Timmer, and McGuire, 1989). Broadly speaking, the courts will consider six factors when decidi ng whether State action is a valid exercise of police power or a compensable taking: 11 1. Whether the State physically invaded the property. 2. Whether the States actions precludes all ec onomically reasonable use of the property. 3. The extent to which the regulation curtails investment-backed expectations. 4. Whether the regulation confers a public benefit or prevents a public harm. 5. Whether the regulation promotes the health, safety, welfare, or morals of the public. 6. Whether the regulation is arbitrar ily and capriciously applied. In the canker and spreading decline cases, th e determinations that cutting healthy, yet suspect citrus trees were compensable takings largely depended on whether the States action conferred a public benefit or prevented a public harm, and these cases preceded the legislatures 2002 statutory compensation sche me for trees cut after 1995. 12 After Patchen v. Dept. of Agriculture and Consumer Services an owner of a healthy resident ial citrus tree that was cut by 9 Department of Agriculture and Consumer Services v. Mid-Florida Growers, Inc., 521 So.2d 101, 101-4 (Fla. 1988), cert. denied, 488 U.S. 870, 109 S.Ct. 180, 102 L.Ed.2d 149 (1988); see also Department of Agriculture and Consumer Services v. Polk, 568 So.2d 35 (Fla. 1990); see also Graham v. Estuary Properties, Inc., 399 So.2d 1374 (Fla. 1981) cert. denied, 454 U.S. 1083 (1981); see also State Plant Board v. Smith, 110 So.2d 401 (Fla. 1959). 10 16A Am. Jur. 2d Constitutional Law 318 (1998). 11 See infra note 7. 12 See Department of Agriculture and Consumer Services v. Mid-Florida Growers, Inc., 521 So.2d 101, 101-4 (Fla. 1988), cert. denied, 488 U.S. 870, 109 S.Ct. 180, 102 L.Ed.2d 149 (1988); see also Patchen v. Dept. of Agriculture and Consumer Services, 906 So.2d 1005 (Fla. 2005). 91

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the State no longer has to pr ove that the States acti ons constituted a taking. 13 However, the question of whether the statutor y compensation is enough is unres olved. The following section addresses this question. Limitations on Police Power The Florida Constitution limits the use of police power to control agricultural disease. Private property cannot be dest royed without due process of law and just compensation. 14 Substantive Due Process and Procedural Due Process Due process includes both substantive and pro cedural elements (Go ttwald et al., 1989). Substantive due process protects indivi dual rights, such as life, liberty or property and the exercise of a police power that infringes one of th ese rights must bear a reasonable relationship to a legitimate objective. 15 The courts have long held that the protection of agriculture is a legitimate objective for the use of the States police power. 16 So long as the legislative decision bears a reasonable relationship to protecting agriculture, the cour t will not substitute its own judgment. Procedural due process ensures that process is fair when these substantive rights are at issue. 17 A procedural due process consideration rele vant to the control of agricultural disease is the opportunity to be heard on whether the destruction is proper. 18 13 906 So.2d 1005 (Fla. 2005). 14 Fla. Const. Art. I, ; see also Fla. Const. Art. X, 15 See Lochner v. New York, 198 U.S. 145 (1905); see also Griswold v. Connecticut, 381 U.S. 479 (1965). 16 Department of Agriculture and Consumer Services v. Mid-Florida Growers, Inc., 521 So.2d 101, 101-4 (Fla. 1988), cert. denied, 488 U.S. 870, 109 S.Ct. 180, 102 L.Ed.2d 149 (1988). 17 See Herrera v. Collins, 506 U.S. 390 (1993). 18 State Plant Board v. Smith, 110 So.2d 401 (Fla. 1959) 92

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Just Compensation The Florida Supreme Court stated that, the absolute destruct ion of property is an extreme exercise of police power and is justified only within the narrowest limits of actual necessity, unless the state chooses to pay compensation. 19 However, the State is not compelled to compensate for property that is valueless, incap able of any lawful use, and a source of public danger, such as diseased cattle, unwholesome meat s, decayed fruit or fish, infested clothing, obscene books or pictures, or buildings in the path of a conflagration. 20 This provision can be rephrased to say that the state remains obligated to provide just compensation, but that the amount of compensation is a nullity becau se the property is without value. Comparing the Limitations on the Use of Polic e Power: Spreading Decline versus Citrus Canker The following lines of cases demonstrate how the facts of the case play a key role in determining the limitations when agricultural crops are destroyed through the exercise of police power. These cases both deal with the diseases that affect citrus trees, spreading decline and citrus canker. Spreading Decline Spreading decline is caused by the burrowing nematode, Radopholus similis a microscopic worm that damages the feeder r oots of citrus trees (Suit and DuCharme, 1953). Over time, the root system deteriorates, causi ng the trees foliage and produc tivity to deteriorate (Suit and DuCharme, 1953). Infected trees are rendered co mmercially unprofitable under ordinary market conditions. The burrowing nematode tr avels very slowly through the soil. 19 Corneal v. State Plant Boar d, 95 So.2d 1 (Fla. 1957); see also Department of Agriculture and Consumer Services v. Polk, 568 So.2d 35 (Fla. 1990) 20 See infra note 16; see also note 17; see also Department of Agriculture and Consumer Services v. Mid-Florida Growers, Inc., 521 So.2d 101, 101-4 (Fla. 1988), cert. denied, 488 U.S. 870, 109 S.Ct. 180, 102 L.Ed.2d 149 (1988). 93

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The eradication program called for the destruct ion all of the citrus trees affected by the nematode and the first four trees pa st the last visibly affected tree. 21 Because spreading decline spreads so slowly, it is not considered an immedi ate threat and procedural due process requires a hearing before, rather than after, the actual destruction. 22 The destruction of diseased trees does not require compensation. 23 Even though it is justified under the police power as necessary to protect neighbori ng property, destruction of trees only suspected of being affected by the nematode does require compensation. 24 The state does have to give compensation for the destructi on of healthy but suspect trees because, although infected, suspect trees do retain some value. 25 Citrus Canker Florida implemented a more aggressive program in its attempt to eradicate Asian strain of citrus canker. This strain of c itrus canker is caused by the bacterium Xanthomonas axonopodis pathovar citri The bacterium causes defoliation, dieback, blemished fruit, reduced fruit quality, and premature fruit drop (Schubert and Sun, 2001). Unlike the slow spreading decline, citrus canker spreads rapidly by wind driven rain, fl ooding, air currents, in sects, birds, human movement within the groves, and movement of infected plants and seedlings (Schubert et al., 2001). Symptoms may manifest as early as seven to fourteen days after infection 26 (Schubert et al., 2001), but may take up to 60 days or more to appear (Schubert et al.). However, the 21 See infra note 17. 22 See infra note 16. 23 See infra note 17. 24 Id. 25 Id. 26 Florida Department of Agriculture & Consumer Services v. City of Po mpano Beach, 792 So .2d 539 (Fla. 4th DCA 2001); 829 So. 2d 928 (Fla. 4th DCA. 2002). 94

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maximum visualization does not occur until approximately 107 to 108 days after infection (Gottwald et al., 2002). In 2002, the Citrus Canker Law amendmen ts .184 and 933.07(2), Florida Statutes, required the destruction of all ci trus trees within 1,900 feet of an infected tree and allow areawide search warrants. 27 28 This enlarged the existing statutory 125foot buffer zone that was based on a study conducted in Argen tina (Gottwald et al., 2002). De struction of all citrus trees within the 125-foot buf fer had survived a number of cour t challenges. Citrus canker was determined to be an imminent threat, which ju stified destruction of tr ees prior to a hearing. 29 30 In cases that examined the legality of the USDAs eradication program, the courts also determined that all healthy but suspect commercial trees within the 125 feet of an infected tree did not require compensation because they were in capable of any lawful use, it is of no value, and it is a source of public danger. 31 32 A study by Gottwald et al. (2002) determined that the 125-foot radius was inadequate because it only captured 30-41% of infection spr eading from a diseased tree (Gottwald et al., 2002; Gottwald et al., 1989). Ba sed on the Gottwald study, the Florida legislature ultimately concluded that an enlarged 1,900-foot buffe r was necessary and amended section 584.184, Florida Statutes. 33 Procedurally, section 584.184, Florida Statutes requires that owners be 27 Fla. Stat. 33.07(2) (2002). 28 Fla. Stat. 81.184 (2002). 29 Denney v. Conner, 462 So.2d 534 (Fla. 1st DCA 1985). 30 Nordmann v. Florida Department of Agriculture and Consumer Services, 473 So.2d 278 (Fla. 5th DCA 1985). 31 See Department of Agriculture and Consumer Services v. Polk, 568 So.2d 35 (Fla. 1990). 32 State Dept. of Agriculture and Consumer Services v. Varela, 732 So.2d 1146 (Fla. 3rd DCA 1999). 33 See infra note 24. 95

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notified of the impending destruction by order. 34 The owner has the option to ask for a stay of destruction in an appellate cour t where the only issues are whethe r the tree itself is infected and whether the tree is within 1,900 feet of an infected tree. 35 Since the disease spreads at a fast rate, the court held that the state had adequate reason to not conduct a full hearin g prior to eradicating an imminent danger. 36 The owners may opt for a hearing after destruction. 37 The hearing determines if the destruction of exposed but healthy residential trees constitutes a taking and, if so, the amount of compensation required. 38 These hearings will determine if trees within the 1,900-foot buffer zone require compensa tion beyond the $55 provi ded by the statute. 39 The USDA program offered $26 per destroyed commercial tree. Enlarging the buffer zone from 125 to 1,900 feet reignited legal cha llenges. In several citrus canker takings cases, homeowners allege d that the FDACS was conducting unreasonable searches of their property and taking trees within the 1,900-f oot radius without allowing the homeowner any opportunity to be heard. Specifi cally, they alleged 1) th at the 1,900-foot rule established by the legislature di d not establish probable cause of a tree being infected and therefore did not provide any basi s to search a property suspected of harboring an infected tree, and 2) area-wide search warrants requested by the FDACS constituted an unreasonable search of 34 See infra note 26. 35 Id. 36 Id. 37 Id. 38 Id. 39 Id. 96

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properties for which probable cau se was not established. The ar ea-wide search warrants included properties that did not necessarily harbor citrus trees with in 1,900 feet of an infected tree. 40 In Florida Dept. Of Agriculture and Consumer Services v. Haire, the court was asked to determine the constitutionality of sec tion 584.184 and 933.07(2), Florida Statutes 41 (Gottwald et al., 1989). Procedurally, the court upheld previous decisions declar ing that citrus canker was an imminent danger and justified dest ruction prior to an opportunity to be heard for trees within the 1,900-foot zone (Gottwald et al., 2002; Gottwald et al., 2006) but that area-wide warrants were unconstitutional and a violation of the Fourth Amendment to the US Constitutions prohibition against unreasonable searches and seizures. 42 Following these rulings, the FDACS will still be able to seek warrant s to search residential properties, but probable cause must be established for each individually identified property. In its examination of substant ive due process, the court de termined that the 1,900-foot buffer zone bore a reasonable relationship to pr otecting the citrus industry (Gottwald et al., 1989). The court noted that restricting the legislature to acting only in areas of scientific certainty would result in a level of supervision hostile to our basic principles of government (Gottwald et al., 1989). It is the charge of the elected legislativ e representatives, not the courts, to decide the proper course of action to protect the public (Gottwald et al ., 1989). The courts can only overturn a legislative exercise of police power if it lacks a reasonable relationship to the legitimate objective (Gottwald et al., 1989). Here, judicial intervention was not warranted because the legislature based its actions on the advice of a Technical Advisory Committee and a peer-reviewed and published st udy (Gottwald et al., 1989). 40 See infra note 1. 41 See infra note 29. 42 See infra note 1. 97

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While the Haire court found the legislative action valid, th e court reiterated that this did not relieve the State from paying just compensation (Gottwald et al., 1989). The compensation in the statute provided a floor value guaranteed to th e affected owner, even if the tree was valueless (Gottwald et al., 1989). This was valid because the homeowner still had the opportunity to have a judicial determination of wh at was just compensation for the tree beyond this floor value. 43 In Patchen v. Dept. of Agriculture and Consumer Services, the Florida Supreme Court was asked whether healthy but suspect residential trees w ithin 1,900 feet of an infected tree were without value. 44 Previously, in Department of Agriculture and C onsumer Services v. Polk, the court held that healthy commercial trees within a 125foot buffer zone were without value and a source of public danger. 45 The court in Patchen was asked to address wh ether this rationale extended to the 1,900-foot buffer zone, part icularly within a residential context. 46 The court neglected to answer this ques tion, holding that the legislature had already decided that homeowners who met the statutory requirements were entitl ed to a minimum level of compensation, essentially conceding the point of whether cutting healthy trees amounted to a taking. 47 The court again reiterated that this doe s not prevent the homeowner from bringing a judicial action to determine wh ether trees within 1,900 feet ar e of greater value than the $55 floor prescribed by the legislatur e, affirming that what constitutes just compensation was a judicial function which could not be preempted by the legislature. 48 43 Id.; see also Rich v. Dept. of Agriculture and Consumer Services, 898 So.2d 1163 (Fla. 2nd DCA 2005). 44 See infra note 11. 45 See infra note 29. 46 Patchen v. Dept. of Agriculture and Consumer Services, 906 So.2d 1005 (Fla. 2005). 47 Id. 48 See infra note 1; see also note 11. 98

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The control of citrus canker, li ke spreading decline, justifies the exercise of police power. In both instances, the legislature eradication programs were valid because they bore a rational relationship to protecting the citrus industr y. However, the procedural due process requirements are different for citrus canker. Citrus canker, unlik e spreading decline, poses an imminent danger, thus justifying th e lack of a full hearing prior to destruction. It is likely that citrus greening would have a similar status. The one remaining unsettled legal issue regarding the CCEP concerns compensation, even with respect to canker-infected trees. The state does not have to give compensation for canker infected commercial trees because they are without value, but the status of re sidential tree value is still unsettled. However, unlike spreading d ecline, healthy but suspect trees may or may not be subject to compensation under co mmon law, yet it appears that the Florida courts are willing to consider destruction of healthy trees as a compensable taking. Currently, there is an apparent conflict in the law between the 3 rd and 4 th appellate districts. The 3 rd District Court of Appeal has held that trees exposed to canker have no marketable value and therefore, no damages can be awarded. 49 The 4 th District Court of Appeal, which includes Broward, Indian River, Okeechobee, Palm Beach, St. Lucie, Martin counties, has allowed homeowners in Broward County to move forward with a class ac tion suit that contends that the FDACS must provide replacement costs for their mature citrus trees, including all ancillary costs, even for infected trees. 50 Currently there are nine plaintiffs representing a potential class of about 100,000 residen tial citrus owners in Broward County 51 (Parsons, Adorno, and Yoss, 2006). It is still an open question as to whether a healthy but suspect tree within 1,900 49 See infra note 30. 50 See infra note 24. 51 Id. 99

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feet of an infected tree may have value beyond the $55 floor value assigned by the legislature, and whether an infected residential tree has value in the 4 th Appellate District. Lessons for Citrus Greening Like citrus canker, citrus greening (H uanglongbing) is a fast-spreading and highly destructive disease that is of great concern to Florida citrus growers and the FDACS. Citrus greening is caused by the bacteria Candidatus Liberibacter spp. spread by two species of psyllids (Chung and Brlansky, 2006). Unlike citrus canker, citrus greening causes ra pid decline and death of citrus trees within a few y ears rather than a mere drop in productivity (Halbert and Keremane, 2004). To prevent use of residential citrus trees as host plants for psyllid populations in areas testing positive for greening, the state of Florid a may need to begin removing residential trees once again. The spreading decline and citrus canker cases have paved the way for a more effective Citrus Greening Control Program (C GCP) that may not fall prey to costly injunctions. To survive legal challenges, a CGCP must first establish a radius of likely infection based on a scientific study similar to the Gottwald et al. studies ( 2006; 1989). Warrants that list specific property addresses and provide probable cause to search su spect premises will be required. Being within the radius established by the scientific study will suffice fo r probable cause. Since citrus greening is fatal, unlike citrus canker, courts will likely allow FDACS to destroy infected trees without compensation, if indeed the biological justifica tion for tree removal still remains (it may be too little too late). This would be the case even for the 4 th Appellate District. However, suspect trees taken within the designated radius will likely be judged to have value, requiring compensation. The level of compensation can not be legislated. The law regarding agricultural pests and the defensive taking of trees is relatively settled. It is likely that a citrus greening eradication program, should one ever be deemed necessary, would surviv e legal challenges and 100

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help protect the multi-billion dollar citrus i ndustry in Florida. Once the Broward County compensation cases are settled, there will be a better understanding of how Florida courts would assess the value of trees potentially affected by citrus green ing, helping policy makers estimate the potential costs of a ci trus greening program. Conclusion The state is allowed flexibility in its exercise of police power so long as there is a reasonable relationship to protecting agriculture This flexibility was evident in the cases upholding the destruction of all trees within 1,900 f eet of a tree infected w ith citrus canker. One must keep in mind that the constitutional limita tions are just that limitations. Statutes may extend benefits beyond the limitations of the constitution. Many statutory schemes allow for compensation of both diseased and non-diseased tr ees alike. For instance, although courts have held that diseased trees are without value, section 581.1845 of the Florida Statutes requires compensation to homeowners for the destruction of their trees in the amount of $55 per tree. 52 The state, by compensating for diseased trees, extends a benefit beyond what is required by the Florida Constitution. It is still an open question as to whether healthy but suspect trees within 1,900 feet of a tree infected with citrus canker have a value beyond $55, and whether infected residential trees have any value in the 4 th Appellate District, but this issue should be settled in early 2007. The legislature must balance a number of factor s in its decisions to protect agriculture and Floridas economy. While it may be authorized to destroy all trees within 1,900 feet of a tree infected with citrus canker, th e rapid spread of citrus canke r in the 2004-5 hurricane seasons rendered the program impracticable. Faced with a lack of federal funds and a statute calling for 52 Fla. Stat. 581.1845 (2002). 101

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the destruction of 25% of Florid as current citrus crop, the citr us canker eradication program was ended in January, 2006 in favor of a series of best management practices for citrus producers called the Citrus Health Response Plan that do es not require the rem oval of infected trees (Timmer et al., 2006). As the Florida citrus industr y braces itself for a ne w invasive plant pest citrus greeninglessons from the citrus canker cases may help guide policy makers should they decide to create a citrus greening eradication program. 102

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CHAPTER 5 SUMMARY AND CONCLUSIONS Introduction This dissertation focuses on th e economic and legal aspects of controlling invasive species in Florida. Invasive species are fast becoming an important issue for many state and federal agencies charged with protecting ag ricultural and natural systems. The increase in global trade, tourism and emig ration has led to an increase in the invasion rate of many brittle ecosystems by prolific and destructive plants and animals. Once introduced to new areas, roughly 10% of these species b ecome invasive, causing a significant proportion of environmental changes and economic losses worldwide. Florida has about 124 invasive species. In the US, production losses, control costs, and other associated costs relate d to invasive species is estimated to exceed $137 billion per year (Pimentel et al., 1999). About 25% of US agricultural production is lost to nonnative pests or to th eir associated control costs (Simberloff, 2002). They can also have devastating ecologica l impacts, and may be the primary cause of biodiversity loss (Mack, 2000). Despite the large economic and environmental damages associated with exotic species invasion, little empirical economic research has been produced on the topic. Much of the economics literature on invasive species is too abstract or technical for policy application. Unfortunately, zebra mussels, invasive aquatic plan ts, and pathogens like ci trus canker and citrus greening pose serious risks to agriculture and natural resources. Despite the unknowns, policy makers will be called upon to allocate scarce public resources in defense of natural and agricultural systems. These studies provide mu ch needed information to the discourse on invasive species management even though they are based on unteste d assumptions about invasive species biology, propagation, spread, and impacts. 103

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Invasive species are a particul ar problem for tropical and subt ropical states like Florida, given that the physiographic, climatic and geogra phic characteristics of these states make them relatively more vulnerable to the establishment of non-indigenous sp ecies than for other states. When considering the well-documented impacts of certain invasive species, such as damages caused by the zebra mussel, hydrilla, and citrus canker, it is clear that the economic consequences of this issue resound with enormous potentiality. With continuing increases in both global trade and the domestic and international migration of people to Florida, it is reasonable to assume that such transmission pathways will keep contributing to the invasive species problem. This is particularly so with regard to waterborne organisms which are carried in the ballast wa ter of ships plying international trade routes. This dissertation focuses on three aspects of Floridas interact ion with invasive species. The first aspect is the potential economic impli cations of the infestation of Lake Okeechobee by zebra mussels. The second aspect is the impact of invasive species on recreation. Specifically, I estimate the recreation impacts asso ciated with three types of inva sive aquatic species currently found in Florida: water hyacinth, water lettuce, a nd hydrilla. The third asp ect addressed in this series is the legal issues associated with Flor idas control and manageme nt of invasive species. The states handling of citrus canker and spreadin g decline are examined to provide lessons for another pestcitrus greening. This chapter prov ides a summary of the dissertation topics. Summary and Conclusions Regarding the Potential Infestation of Zebra Mussels in Florida Zebra mussels have radically changed ecosystems and increased the cost of surface water withdrawals in the Great Lakes region over the la st two decades. They are prolific reproducers, and possess unique biological characteristics that enable them to spread very quickly via human contact. Recreational boaters can unwittingly aide the spread of zebra mussels over long 104

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distances. This is a particular concern for the state of Florida, which has a multi-billion dollar recreational fishing industry. Zebra mussel arrival prevention and eradication measures have been selectively attempted throughout the United States. The US Army Corp s of Engineers have proposed an arrival prevention and early warning system for zebra mussels in Lake Okeechobee, FL, but have not received funding to support the program. Given the long-distances th at anglers travel to fish on Lake Okeechobee, and the very high potential ec onomic impacts associated with zebra mussels in the Great Lakes, it is worth estimating the ex pected impacts of zebra mussels in Florida to provide information useful to policy making. I constructed a bioeconomic model to simu late the potential damages from a zebra infestation on Lake Okeechobee. I first estima ted the rate of zebra mussel arrival based on transportation vectors (recreational boating), and then estimated survival assuming habitat suitability from a previous study (Hayward and Es tevez, 1997). The result s of my survey of surface water users on Lake Okeechobee were app lied to existing estimates of changes in maintenance costs of water intake pipes from ar eas known to be infested with ZM. I report an expected economic impact of ZM over 20 years, including costs and damages to surface water use, angling, ecosystem services, and budgetary co st. I applied state probab ilities in a Stochastic Dynamic Simulation format to arrive at a long-run analysis of ZM in Lake Okeechobee. I found zebra mussel-related impacts without state intervention to be $349.34 million over 20 years. I simulated several potential policy responses to delay or mitigate zebra mussel infestationarrival prevention and early warning, eradication, and a combination of the two. The arrival prevention and early warning policy that I simulated is the same as proposed by the US Army Corps of Engineers for the lake. Erad ication has only been su ccessfully attempted on 105

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one small pond in the United StatesMillbrook Quarry, VA. Lake Okeechobee is over 3,200 times larger than Millbrook Qua rry, and eradication would be very costly$1.32 billion based on Millbrook Quarry control costs on a volume basis. Arrival prevention and early warning are relatively cheap$152,800 per year. Arrival preventi on reduces the probabil ity of zebra mussels arriving at Lake Okeechobee, and an early warning system provides surface water users with enough advance warning to apply mitigation meas ures (anti-fouling paint) that reduce the economic impact of an infestation. The overall cost minimizing choice is to inve st in arrival prevention and early warning, which would reduce present value costs by 70.91%. This is also the only policy choice that netted positive returns ($247.71 million) as compar ed with doing nothing to control or prevent zebra mussels in the lake. Policies that include post-establishment eradication yield large losses ($414.98 million, $603.36 million). A model of the economic impacts of a poten tial invasion of Lake Okeechobee by zebra mussels offers some insight into management of this and other invasive species threats. Lessons from this study include 1. Invasive species become endemic and virtua lly impossible to eradicate once established 2. Post-establishment eradication is much costlie r than arrival prevention. Zebra mussels have no known cost-effective control me asure, unlike is available fo r controlling aquatic plants. Scarce public resources are much more effectiv ely spent to prevent the establishment and where cost-effective, control the population of invasive species, rather than attempt eradication 3. Much more data and empirical economic studi es are needed to help evaluate invasive species funding demands Summary and Conclusions Regarding In vasive Aquatic Plants in Florida Hydrilla verticillata (hydrilla), Eichhornia crassipes (water hyacinth), and Pistia stratiotes (water lettuce) have been esta blished in Floridas lakes and rivers for over half a century. The 106

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unique characteristics of these plants allow them to grow rapidly, displacing native flora and fauna, and reducing recreational use and enj oyment of many water bodi es. Consistent and significant control efforts are requi red to prevent invasive aquatic plants from eroding the value of Floridas lakes to the stat es economy and ecosystems. Long run cost-effective management of these invasive species requires consistent co ntrol efforts, yet the states funding has fallen short in the past. In this chapter, I evaluate the status quo maintenance contro l policy with other potential hydrilla and floating plant contro l policies. I specify a bioecono mic model of invasive aquatic plants using unpublished data on an gler effort, plant coverage, a nd lake physiographic features and amenities. I first specify plant growth models for hydrilla and floating plants using data collected on 13 lakes with more than 100 acres of invasive plant covera ge at any point during 1998-2003. I then simulate the impact of four different control policies for the plantsno control, 99% erad ication once every other year, 99% er adication once ever y year (status quo maintenance control), and 99% eradication once every year with follow-up partial eradication (20%) later in the year. Next, I estimated the imp act of invasive aquatic plant coverage on angler effort as well as per acre cont rol costs for hydrilla and floati ng plants. The bioeconomic model was used to estimate the value of various i nvasive aquatic plant management regimes. Model results show that over five years, the value of fishing activity on the 13 lakes is in excess of $64.78 million, with about 3.13 million total fishing hours. Compared with the status quo treatment strategy, reducing treatment to ever y other year, or halting treatment altogether will lead to significant recreational and ecosyst em losses, largely due to access problems. The status quo ( A ) control costs are $4,828,254. These costs rise by 126.56% with the alternate year control ( B2 ), and by 20% for the 20% increase in control ( C20 ). 107

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Peak and treated acreage of invasive plants vary widely by cont rol policy. Decreasing treatment more than doubles the peak acreage. Increasing treatment substantially decreases the peak acreage and the total acres treated. The total recreation-related losses associated with no c ontrol (B0) are high$33,663,655 per year. By comparison, status quo control yi elds 655.80% return on investment for control expenditures of $4,828,254 per year. In terms of absolute net benefits, increasing control by 20% will increase fishing-re lated benefits by $3,642,953, but at a lower rate of return 609.37%. Alternate year control ( B2 ) results in a loss in fishing-related benefits as compared to the status quo, but yield 99.67% rate of retu rn as compared to do nothing ( B0 ). A few clear conclusions follow from the results: Florida lakes have very high economic values that are at risk from invasive aquatic plants Maintenance control of invasive aquatic plan ts is the preferred cost-minimizing control policy Lapses in maintenance control, even if brief, can significantly increase the costs associated with subsequent invasive aquatic plant control. Also apparent from the research is the l ack of understanding of the biological and economic relationships involving inva sive plants. Little data is available, and very few models and even fewer empirical economics studies ad dress invasive plants Given the risks to agricultural and natural systems from invasive plants, improvements in data collection and modeling are desperately needed. Summary and Conclusions Regarding the Regulatory Basis for Controlling Invasive Agricultural Pests in Florida The state is allowed flexibility in its exercise of police power so long as there is a reasonable relationship to protecting agriculture This flexibility was evident in the cases upholding the destruction of all trees within 1,900 f eet of a tree infected w ith citrus canker. One 108

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must keep in mind that the constitutional limita tions are just that limitations. Statutes may extend benefits beyond the limitations of the constitution. Many statutory schemes allow for compensation of both diseased and non-diseased trees alike. The state, by compensating for diseased trees, extends a benefit beyond what is re quired by the Florida Constitution. It is still an open question as to whether healt hy but suspect trees within 1,900 f eet of a tree infected with citrus canker have a value beyond wh at they are legally assigned. The legislature must balance a number of factor s in its decisions to protect agriculture and Floridas economy. While it may be authorized to destroy all trees within 1,900 feet of a tree infected with citrus canker, th e rapid spread of citrus canke r in the 2004-5 hurricane seasons rendered the program impracticable. Faced with a lack of federal funds and a statute calling for the destruction of 25% of Florid as current citrus crop, the citr us canker eradication program was ended in January, 2006 in favor of a series of best management practices for citrus producers called the Citrus Health Response Plan that do es not require the rem oval of infected trees (Timmer et al., 2006). Close examination of the litigation surr ounding citrus canker and spreading decline eradication programs can provide valuable lesso ns for regulating other invasive agricultural pests, such as citrus green ing. These lessons include 1. Establish a radius of likely inf ection based on scientific study 2. The radius will provide probable cause for sear ching a property for the pest, but individual search warrants will be needed 3. If the disease or pest that is the subject of erad ication is fatal, it is unlikely that the state will have to compensate residential owners for take n trees. If it is not fatal, the courts may yet support compensation 4. Trees merely suspected of harboring the pest, but not testing positive for it, have value that is determined by the courts 109

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5. Fast-spreading agricultural pest eradication effo rts can be devastated by litigation that leads to injunctions. Instead of delaying litigation, the state should fast-tra ck early challenges by certifying the cases as dealing with issues of high public importance. This will move the court cases to the front of the docket list 6. The state should consider litig ation alternatives and involve citizens in the regulatory process with town meetings or informal hear ings. Homeowners were put aback by their lack of participation in th e regulatory process and their inability to have a hearing about tree removal. This alienation led to anger and ultima tely litigation. Instead the state should have considered educating the citizens about the da ngers of citrus canke r, and provided public forums for citizens to have their say. The stat e should also have consid ered mediation as an alternative to costly litigati on, which may have avoided the CCEP injunctions that allowed canker innoculum to build up prior to the 2004-2005 hurricanes. Conclusion This chapter served as a summation of a series of the three research topicsbioeconomic modeling of zebra mussel impacts on Lake Okeechobee, bioeconomic modeling of invasive aquatic plants on Florida lakes, and the limits to regulatory action to contro l invasive agricultural pests in Florida. Invasive species are an importa nt concern for the state of Florida, yet there exists little useful empirical economics research on the topic. In Chapter Two and Chapter Three, bioeconomic models are used to estimate the im pacts of invasive aqua tic plants and mussels. Simulations were run on potential policy responses, and relative impacts of the invasive species under each policy were reported and discussed. One clear conclusion from the results reported in Chapters Two and Three is that it is much more cost-effective to keep invasive species populations at very low levels or prevent their arrival. Once endemic, economic and ecosystem damages are very large. Chapter Four examin es the regulatory framework for controlling agricultural pests. I first examine two past regimesspreading decline and citrus canker, with primary focus on canker. Recent developments in the law regarding citrus canker are discussed, and lessons for future regulatory control of agri cultural pests are discussed. The citrus canker eradication program failed because it ran afoul of procedural due process and compensation requirements that could have been avoi ded by appropriate le gislative action. 110

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The implications regarding these findings are that the state of Florida has a good chance of designing control efforts that w ould survive legal challenges a nd would work to protect the states significant tourism and recreation industries, specifically in terms of fresh water fishing and state park and public recreational area usage. 111

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APPENDIX A ZEBRA MUSSEL INFORMATION SURVEY University of Florida Food and Resource Economics Department Welcome to the Zebra Mussel Information Survey homepage. The zebra mussel is an invasive species not yet established in Florida, bu t it does have the potential to be a future threat to our state. This survey will confidentially acquire information from selected surface water users in Florida, in order to estimate future costs associated with a potential zebra mussel infestation of Florida waters. To start this survey, all you need is the assigned Personal Id entification Number (PIN) sent to you by mail. We sent each business or public utility asked to participate in this survey a unique identification number (PIN) to establish the confidentiality and validity of this survey. Please enter your PIN in th e space below to begin. SUBMIT Section A This section contains a few questions about some invasive species. Throughout this survey, the term your facility refers to th e private business or public utility that: 1) is your employer; and 2) is under permit to withdraw surface water in Florida. Question #1: Water Hyacinth is an invasive aquatic plant found in many parts of Florida. Have you ever heard of this plant? Yes coded: A1Y No A1N Question #2: Hydrilla is another invasive aqua tic plant that is also found in many parts of Florida. Have you ever heard of this plant? Yes coded: A2Y No A2N 112

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Question #3: Has either of these aquatic plants ever impeded the surface water withdrawal s of your facility, to the degree that it required action from a maintenance crew? Yes coded: A3Y No: click here to skip to Question #5 A3N Question #4: Which of the following aquatic plants is most re sponsible for causing water flow impediments at your facility? Hydrilla coded: A41 Water Hyacinth A42 Other aquatic plant A43 Dont know A44 Question #5: Do you have any knowledge regard ing the presence of zebra mussels in the Great Lakes, the Mississippi River, or elsewh ere in the United States? Yes coded: A5Y No A5N Answering yes to Question #5 will send you to the next page Answering no will send you to Section D SUBMIT Section A Notes: Use radio butt ons to record all responses 113

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Section B This section contains a few questions about attitudes towards zebra mussels. Question #1: Please tell us how you know about zebra mussels in the United States. Check all of the boxes that apply. Trade publication coded: B11 Water management district pub lication or employee B12 Other state agency publicati on or employee B13 Internet website B14 Newspaper or magazine article B15 Family member, friend or neighbor B16 Other source B17 Question #2: Given your knowledge of zebra mussels: what leve l of concern, if any, do you have about the possibility of zebra mussels being introduced into Florida? Very concerned coded: B21 Concerned B22 Slightly concerned B23 Not concerned: click here to sk ip to Question #5 B24 Question #3: The concern you have for zebra mussels is primarily related to: Environmental issues coded: B31 Economic issues B32 Political issues B33 Some other issue B34 Question #4: Do you think the state government should spend money to prevent zebra mussels from being introduced into Florida? Yes coded: B4Y No B4N 114

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Question #5: Do you think the concern for zebra mussels show n by various U.S. Government agencies is primarily related to: Environmental issues coded: B51 Economic issues B52 Political issues B53 Some other issue B54 Question #6: Do you think the concern for zebra mussels shown by the general public of the United States (of those persons aware of the issue) is primarily related to: Environmental issues coded: B61 Economic issues B62 Political issues B63 Some other issue B64 Question #7: Has your facility made any contingency plans for dealing with zebra mussels should they become established in Florida? Yes coded: B7Y No B7N Answering yes to Question #7 will send you to the next page Answering no will send you to Section D SUBMIT 115

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Section B Notes: Use check boxes for Question #1 Use radio buttons to reco rd all other responses Section C The following questions ask you about your conti ngency plans to deal with zebra mussels, should they become established in Florida. Question #1: Please tell us how your facility pl ans to combat zebra mussels if faced with this problem in the future. Check all that apply. Increase routine maintenance coded: C11 Retrofit equipment C12 Chemical treatment C13 Other strategy: please specify below C14 C15 Question #2: As a result of such planning, has your facility ac tually spent money on any of these strategies? Yes coded: C2Y No C2N Question #3: If you answered Yes: please tell us the total am ount of money spent for each type of activity being planned. (example: $10, 000 for purchase of chemicals). Increase routine maintenance __________________ C31 Retrofit equipment __________________ C32 Chemical treatment __________________ C33 Other strategy __________________ C34 SUBMIT 116

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Section D This section asks some questions regarding the maintenance of your facilitys surface water intake structures. Specifically, we us the word maintenance to refer to the routine cleaning and upkeep of water conveyance systems, in order to ensure there are no impediments to the flow of water. Such impediments resulting from the growth of organisms have been referred to as biofouling . Question #1: Does bio-fouling caused by native mussels, and/or ot her native organisms require your facility to perform regularly scheduled maintenance of its surface water intake structures? Yes coded: D1Y No: click here to skip to Question #6 D1N Question #2: How often is such maintenance performed on the su rface water intake structures of your facility, because of the bio-fouling caused by nativ e mussels, and/or other native organisms? Twice a year coded: D21 Once a year D22 Once every two years D23 Other frequency: please specify below D24 D25 Question #3: Which of the following is the main cause of the bio-fouling at your facility? Native mussels D31 Other native organism D32 Not sure D33 Question #4: For maintenance performed to remove the bio-fou ling, does your facility c ontract this work out to another firm? Yes coded: D4Y No: click here to skip to Question #6 D4N 117

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Question #5: Please tell us the method(s) of maintenance that your maintenance crews use to combat the biofouling of surface water intake structures. Check all that apply. Physical removal: scraping coded: D51 Physical removal: pressure washing D52 Chemical treatment(s) D53 Backflushing D54 Other method: please specify below D55 D56 Question #6: In the contact letter we sent by mail informing you of this survey, we included data obtained from your facilitys surface water permit. Please review that information now. Is the data we mailed to you correct? Yes: click here to skip to Question #7 coded: D6Y No D6N If you answered No, please make the a ppropriate corrections in the box below: Permit ID Average Daily Withdrawal Amount Intake Size Intake Location N o. No. (Gallons) (Inches) (County) Example : 00001 01 2000000 12 Hillsborough NOTE: If possible, this box pops up only if respondent answers No to Question #6. 118

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Question #7: Please use the following box to tell us about the maintenance costs for ea ch location of surface water intake structures owned by your facility. Maintenance cost refers to the approximate value of costs incurred each tim e maintenance is performed (Visi t), regardless of whether it was contracted to other firms, or performed by yo ur employees. We would also like to know the approximate length of the intake(s). Permit ID Maint. Cost Frequency Intake Length Surface Water Body No. No. ($ per Visit) (Visits per time frame) (Feet) (i.e., Lake Tarpon, St Johns River, etc.) Example : 00001 01 $1000 1 per 2 yrs 1500 Crystal River SUBMIT (Exit page: reached upon final submission) Thank you very much for participati ng in this survey. A ll information is stri ctly confidential. For more information about zebra mussels, use the following links. 119

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APPENDIX B SENSITIVITY ANALYSIS OF ZEBRA MUSSEL PARAMETERS Table B-1. Sensitivity analysis of zebra mussel parameters. Base Results Policy I (Do nothing) Policy II (Arrival prevention and early warning) Policy III (Eradication) Policy IV (Combination of Policies II and III) Net Losses 349.30 101.60 952.70 764.30 Policy Cost 0.00 2.33 872.90 696.40 Maintenance Impacts -10.83 -3.02 -0.41 -0.11 Ecosystem Impacts -339.6 -96.60 -79.65 -68.07 Recreation Impacts 1.09 0.31 0.25 0.22 Sensitivity Test AReduce arrival rate by half to 0.035/2 Net Losses 174.70 53.19 918.40 518.80 Policy Cost 0.00 2.41 838.50 472.10 Maintenance Impacts -5.41 -1.54 -0.26 -0.04 Ecosystem Impacts -169.80 -49.39 -79.91 -46.86 Recreation Impacts 0.54 0.16 0.25 0.15 Sensitivity Test BLoss (instead of gain) to r ecreational uses = 10% of 3.25 Net Losses 351.50 102.30 953.20 764.80 Policy Cost 0.00 2.33 872.90 696.40 Maintenance Impacts -10.84 -3.02 -0.41 -0.11 Ecosystem Impacts -339.60 -96.60 -79.65 -68.07 Recreation Impacts -1.09 -0.31 -0.25 -0.22 Sensitivity Test CIncrease value ecosystem loss to 51.25x$439/ha in $1994 Net Losses 17,415 4,955 4,955 4,185 Policy Cost 0 2.33 872.90 696.40 Maintenance Impacts -10.84 -3.02 -0.41 -0.11 Ecosystem Impacts -17,405 -4,951 -4,082 -3,489 Recreation Impacts 1.09 0.31 0.25 0.22 Sensitivity Test DReduce eradication costs to 2.5% of $1.32 billion Net Losses 349.30 101.60 101.60 87.65 Policy Cost 0.00 2.33 21.82 19.68 Maintenance Impacts -10.84 -3.02 -0.41 -0.11 Ecosystem Impacts -339.60 -96.60 -79.65 -68.07 Recreation Impacts 1.09 0.31 0.25 0.22 120

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LIST OF REFERENCES Ackerman, J.D., B. Sim, S.J. Nichols, and R. Claudi. A Review of the Early Life History of Zebra Mussels ( Dreissena polymorpha ): Comparisons with Marine Bivalves. Canadian Journal of Zoology 72 (2004):1169 1179. Akcakaya, R., and P. Baker. Zebra Mussel Demography and Modeling: Preliminary Analysis of Population Data from Upper Midwest Rivers Washington, D.C.: US Army Corps of Engineers Report EL-98-1, 1998. Internet site: http://el.erdc.usace.army.mil/elpubs/pdf/crel98-1.pdf (Accessed August 13, 2006). Albrigo, L.G., R.S. Buker, J.K. Burns, W.S. Castle, S. Futch, C.W. McCoy, R.P. Muraro, M.E. Rogers, J.P. Syvertsen, J.P. Timme r, A. John, K. Bowman, K.W. Hancock, M.A. Ritenour, P.D. Spyke, and R.C. Vachon. The Impact of Four Hurricanes in 2004 on the Florida Citrus Industr y: Exeriences and Lessons Learned. Proceedings of the Florida State Horticultural Society 2005. 118:6674. Allen, L.J.S., E.J. Allen, C.R.G. Kunst, and R.E. Sosebee.A Diffusion Model for Dispersal of Opuntia imbricata (cholla) on Rangeland. The Journal of Ecology 79 (1991):1123 1135. Allen, Y.C., B.A. Thompson, and C.W. Ramc haran. Growth and Mortality Rates of the Zebra Mussel, Dreissena polymorpha in the Lower Mississippi River. Canadian Journal of Fisheries and Aquatic Sciences 56 (1999):748 759. Animal and Plant Health Inspection Service. United States Department of Agriculture, Citrus Canker Emergency Program Overview Washington, D.C.: Statement of the Inspector General before th e House Appropriations Committee on Agriculture, Rural Development, F ood and Drug Administration and Related Agencies, 1999. Internet site: http://www.aphis.usda.gov/ppq/ep /citruscanker/background.html (Accessed August 15, 2006). Bachmann, R.W., B.L. Jones, D.D. Fox, M. Hoyer, L.A. Bull, and D.E. Canfield, Jr. Relations Between Trophic St ate Indicators and Fish in Florida (U.S.A.) Lakes. Canadian Journal of Fisheries and Aquatic Sciences 53(1996): 842. Beckett, D.C., B.W. Green, and A.C. Miller. Changes in Zebra Musse l Densities in the Upper Mississippi River: 1995 Update Chicago, IL: Illinois Natural History Survey Triannual Unionid Report No. 11, 1996. Internet site: http://ellipse.inhs.uiuc. edu/FMCS/TUR/TUR11.html#p15 (Accessed May 9, 2006). 121

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Bell, F.W. The Economic Value of Lake Tarpon, Fl orida, and the Impacts of Aquatic Weeds. A.L. Burruss Institute of Public Service, Kennesaw State University, 1998. Best, E.P.H., C.P. Buzzelli, S.M. Bartell, R.L. Wetzel, W.A. Boyd, R.D. Doyle, and K.R. Campbell. Modeling Submersed Macrophytes Growth in Relation to Underwater Light Climate: Modeling Approach es and Applica tion Potential. Hydrobiologia 444(2001): 43-70. Best, E.P.H., and W.A. Boyd. 1996. A Simulation Model for Gr owth of the Submersed Aquatic Macrophyte Hydrilla (Hydr illa verticillata (L. f.) Royle ). Vicksburg, MS: U.S. Army Engineer Waterways Experiment Station Technical Report A-96-8, 1996. Borcherding, J. The Annual Reproduc tive Cycle of the Freshwater Mussel Dreissena phlymorpha Pallas in Lakes. Oecologia 87(1991):208 218. Borcherding, J., and E.D. de Ruyter va n Steveninck. 1992. Abundance and Growth of Dreissena polymorpha Larvae in the Water Column of the River Rhine During Downstream Transportation. The Zebra Mussel Dreisse na polymorpha: Ecology, Biological Monitoring and First Applications in Wa ter Quality Management. D. Neumann, and H.A. Jenner, eds. Stuttgart; New York: G. Fischer, 1992. Borcherding, J., and W. Sturm. The Seasonal Succession of Macroinvertebrates, in Particular the Zebra Mussel ( Dreissena polymorpha ) in the River Rhine and Two Neighboring Gravel-Pit La kes Monitored Using Artificial Substrates. International Review of Hydrobiology 87(2002):165 181. Bossenbroek, J.M., C.E. Kraft, and J.C. Ne kola. Prediction of Long-Distance Dispersal Using Gravity Models: Zebra Muss el Invasion of Inland Lakes. Ecological Applications 11(6)(2001):1778 1788. Bowes, G., A.C. Holaday, and W.T. Haller. Seasonal Variation in the Biomass, Tuber Density and Photosynthetic Metabo lism in Three Florida Lakes . Journal of Aquatic Plant Management 17(1979), 61-65. Brezonik, P.L. 1984. Trophic State Indices: Rational for Multivariate Approaches Knoxville, TN: Lake and Reservoir Mana gement, EPA 440/5-84-001 U.S. E.P.A., 441-445. Buchan, L.A.J., and D.K. Padilla. Estimati ng the Probability of Long-Distance Overland Dispersal of Invading Aquatic Species. Ecological Applications 9(1)(1999): 245 265. Buhle, E.R., M. Margolis, and J.L. Ruesink. Bang for the Buck: Cost Effective Control of Invasive Species with Different Life Histories. Ecological Economics 52(2005):355 366. 122

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Burlakova, L.E., A.Y. Karatayev, and D.K. Padilla. Changes in the Distribution and Abundance of Dreissena polymorpha Within Lakes Through Time. Hydrobiologia 571(2006):133 146. Burnham, M. Front Lines of Battle Against Invaders Increasingly Local. Washington, D.C.: Environmental and Energy P ublishing, 2004. Internet site: http://www.eenews.net/Landletter/Backissues/02120404.htm (Accessed June 23, 2006). Burruss Institute of Public Service. The Economic Value of Lake Tarpon, Florida and the Impact of Aquatic Weeds. Kennesaw State Univers ity and Department of Economics, Florida State University, 1998. Caraco, N.F., J.L. Cole, P.A. Raymond, D.L. Strayer, M.L. Pace, S.E.G. Findlay, and D.T. Fischer. Zebra Mussel Invasion in a Large, Turbid River: Phytoplankton Response to Increased Grazing. Ecology 78(2)(1997):588 602. Carlton, J.T. 1993. Dispersal M echanisms of the Zebra Mussel ( Dreissena polymorpha). Zebra Mussels: Biology, Impacts, and Control T.F. Nalepa and D.W. Schloesser, eds. Boca Raton, LA: Lewis, 1993. Carson, R. Personal Communication. FLW Outdoors, February 2007. Chambers, P.A., J.W. Barko, and C.S. Smith. Workshop SummariesEvaluation of Invasions and Declines of Su bmerged Aquatic Macrophytes. Journal of Aquatic Plant Management 31(1993):218 220. Colle, D.E. et al. Influence of Hydrilla on Harvestable Sport-Fish Populations, Angler Use, and Angler Expenditures on Orange Lake, Florida. North American Journal of Fisheries Management 7(1987):410 417. Chen, D., M.B. Coughenour, D. Eberts, and J. S. Thullen. Interac tive Effects of CO2 Enrichment and Temperature on the Growth of Dioecious Hydril la verticillata. Environmental and Experimental Biology 34(4)(1994):345 353. Chung, K.R., and R.H. Brlansky. Citrus Diseases Exotic to Florida: Huanglongbing (Citrus Greening). Gainesville, FL: Plant Pa thology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, 2005. Internet site: http://edis.ifas.ufl.edu/PP133 (Accessed March 8, 2006). Colle, D.E., J.V. Shireman, W.T. Haller, J.C. Joyce, and D.E. Canfield, Jr. Influence of Hydrilla on Harvestable Sport-Fish P opulations, Angler Use, and Angler Expenditures at Orange Lake, Florida . North American Journal of Fisheries Management 7(1987):410-417. Crossland, J. Personal Communication. US Army Corps of Engineers, South Florida Operations Office, January 2007. 123

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De Kozlowski, S.J. Lake Marion St erile Grass Carp Stocking Project. Aquatics 13(1991):13 16. Deng, Y. Present and Expected Economic Costs of Zebra Mussel Damages to Water Users with Great Lakes Intakes. PhD di ssertation, The Ohio State University, August 1996. Division of Plant Industry. Florida Department of Agricu lture and Consumer Services Comprehensive Report on Citrus Canker Eradication Program in Florida through 14 January 2006. Tallahassee, FL: Florida Department of Agriculture and Consumer Services, pp. 1-25, 2006. Internet site: http://www.doacs.state.fl.us/pi/canker/pdf/cankerflorida.pdf (Accessed April 3, 2006). Drake, J.M., and J.M. Bossenbroek. The Pote ntial Distribution of Zebra Mussels in the United States. BioScience 54(10)(2004): 931 941. Dwyer, G., J.S. Elkinton, and A.E. Hajek. Spatial Scale and the Spread of a Fungal Pathogen of Gypsy Moth. The American Naturalist 152(1998):485 494. Eads, B. Personal Communication. Fisher s of Men Tournament, February 2007. Eiswerth, M.E. and G.C. van Kooten. Uncer tainty, Economics, and the Spread of an Invasive Plant Species. American Journal of Agricultural Economics 84(5)(2002):1317 1322. Eiswerth, M.E. and W.S. Johnson. Managing Nonindigenous Invasive Species: Insights from Dynamic Analysis. Environmental and Resource Economic s 23(2002):319 342. Elderkin, C.L., and P.L. Klerks. Var iation in Thermal Tolerance Among Three Mississippi River Populations of the Zebra Mussel, Dreissena polymorpha . Journal of Shellfisheries Research 24(1)(2005):221 226. Evans, E.A. Economic Dimens ions of Invasive Species. Choices 2nd Quarter(2003): 5 9. Federal Register, Feb 3 1999, Executiv e Order 13112, 64(25):6183-86. 2/8/199. Fegan, R.M., M.T. Olexa, and R.J. McGovern Protecting Agriculture: The Legal Basis of Regulatory Action in Florida. Plant Disease 88 (9)(2004):1040-1043. Finoff, D., J.F. Shogren, G. Leung, and D. Lodge. The Importance of Bioeconomic Feedback in Invasive Species Management. Ecological Economics 52(2005):367 381. 124

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Finoff, D. and J. Tschirhart. Identifying, Preventing, and Controlling Invasive Plant Species Using Their Physiological Traits. Ecological Economics 52(2005):397 416. FLEPPC. Florida Exotic Pest Plant Council Fort Lauderdale, FL : Florida Exotic Pest Plant Council, 2006. Internet site: http://www.fleppc.org (Accessed November 8, 2006). Floerl, O., and G.J. Inglis. Starting the Invasion Pathway: The Interaction Between Source Populations and Hu man Transport Vectors. Biological Invasions 7(2005):589 606. Florida Department of E nvironmental Protection. 2001-2002 Aquatic Plant Management Report. Washington, D.C.: Department of Environmental Protection, 2002. Internet site: http://www.dep.state.fl.us/lands /invaspec/2ndlevpgs/A quaticplnts.htm (Accessed January 27, 2006). Florida Department of E nvironmental Protection. 2003-2004 Aquatic Plant Management Report. Tallahassee, FL: Florida Department of Environmental Protection, 2004. Internet site: http://www.dep.state.fl.us/lands/in vaspec/2ndlevpgs/pdfs/Aquatic%20200304.pdf (Accessed February 6, 2005). Florida Department of E nvironmental Protection. Status of the Aquatic Plant Maintenance Program in Florida Public Waters. Washington, D.C.: Department of Environmental Protec tion. Internet site: http://dep.state.fl.us/lands/invaspec/2ndlevpgs/pdfs/Aquatics 2002-2003.pdf (Accessed January 27, 2006) Florida Department of E nvironmental Protection. Plant Management in Florida Waters: Aquatic Herbicidal Control. Washington, D.C.: Department of Environmental Protection. Internet site: http://plants.ifas.ufl .edu/guide/herbcons.html (Accessed January 27, 2006). Florida Fish and Wildlife Conservation Commission. Florida Lakes, 1000 Acres or Larger. Washington, D.C.: Florida Fish and Wildlife Commission. Internet site: http://www.floridaconservation.org/fishing/lakes.html (Accessed October 15. 2005.). Florida Fish and Wildlife Conservation Commission. Boat Ramps Tallahassee, FL: Florida Fish and Wildlife Conservati on Commission, 2003. Internet site: http://www.floridafisheries.com/ramps/ (Accessed Aug 3, 2003). Florida Department of Environmental Protection, Division of Water Resource Management. Basin Status ReportLake Okeechobee November 2001. 125

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Milon, J.W., J. Yingling, and J.E. Reynolds. An Economic Analysis of the Benefits of Aquatic Weed Control in North-Centra l Florida. Economics Report 113, Food and Resource Economics Department, Univ ersity of Florida, Gainesville, 1986. Milon, J.W. and J.C. Joyce. Sportangle rs Perceptions and Economic Valuation of Aquatic Weed Management. Aquatics 9(4)(1987):8 12. Muller, J., S. Woll, and A. Seitz. Genetic Interchange of Dreissena polymorpha Populations Across a Canal. Heredity 86(2001):103 109. Nalepa, T.F., J.A. Wojcik, D.L. Fanslow, a nd G.A. Lang. Initial Colonization of the Zebra Mussel ( Dreissena polymorpha ) in Saginaw Bay, Lake Huron: Population Recruitment, Density, and Size structure. Journal of Great Lakes Research 21(4)(1995):417 434. NationalAtlas.gov Zebra Mussel Dynamic Map. National Climatic Data Center. Climate Atlas of the United States. Asheville, NC: National Environmental and Sa tellite Information Service, 2005. Internet site: http://gis.ncdc.noaa.gov/webs ite/ims-climatls/index.html (Accessed July 7, 2005). Neubert, M.G., and H. Caswell. Demography a nd Dispersal: Calculation and Sensitivity Analysis of Invasion Speed fo r Structured Populations. Ecology 81(2000):1613 1628. Newroth, P.R., and M.D. Maxnuk. Benefits of the British Columbia Aquatic Plant Management Program. Journal of Aquatic Plant Management 31(1993):210 213. New York Sea Grant. North American Range of the Zebra Mussel. Dreissena 7(6)(1997):5 6. Nichols, S.A. The Interaction between Biology and the Management of Aquatic Macrophytes. Aquatic Botany 41(1991):225 252. Nichols, S.J. Variations in the Reproductive Cycles of Dreissena polymorpha in Europe, Russia, and North America. The American Zoologist 36(1996):311 325. Olson, L.J., and S. Roy. The Economics of Controlling a Stochastic Invasion. American Journal of Agricultural Economic s 84(2002):1311 1316. Olson, L.J., and S. Roy. On Prevention and Control of an Uncertain Biological Invasion. Department of Agricultural and Resour ce Economics, University of Maryland, College Park, WP 05-02, January 2005. ONeill, C.R., Jr. Economic Impact of Zebra Mussels Results of the 1995 National Zebra Mussel Information Clearinghouse Study. Great Lakes Research Review 3(1)(1997):35 42. 130

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Orlova, M.I. Dreissena (D.) polymorpha: Evolutionary Origin and Biological Peculiarities as Prerequisites of Invasion Process. Invasive Aquatic Species of EuropeDistribution, Impact and Management. E. Leppakoski, Gollasch, and S. Olenin, eds. Kluwer, Dordrecht, 2002. Park, J., and L.J. Hushak. Zebra Mussel Control Costs in Surface Water Using Facilities. Technical Summary OHSU-TS-028, Ohio Sea Grant College Program Technical Summary Series, 1999. Parsons, W.R., Adorno, and Yoss, P.A. Personal Communication, August, 2006. Penaloza, L.J. Boating Pressure on Wisconsins Lakes and Rivers: Results of the 1989 1990 Wisconsin Recreational Boating Study, Phase 1 Wisconsin Department of Natural Resources Technical Bulletin No. 174, 1991. Phillips, S., T. Darland, and M. Systsma. Potential Economic Impac ts of Zebra Mussels on the Hydropower Facilities in the Columbia River Basin Pacific States Marine Fisheries Commission Report, 2005. Pimentel, D. Economic and Ecological Costs Associated with Aquatic Invasive Species. Proceedings of the Aquatic Invaders of the Delaware Estuary Symposium Malvern, PA, May 20, 2003, pp. 3 5. Pimentel, D., L. Lach, R. Zuniga, and D. Morrison. Environmental and Economic Costs of Nonindigenous Species in the United States. Bioscience 50(1999):53 65. Ramcharan, C.W., D.K. Padilla, and S.I. Dodson. A Multivariate Model for Predicting Population Fluctuations of Dreissena polymorpha in North American Lakes. Canadian Journal of Fisheries and Aquatic Sciences 49(1992):150 158. Ricciardi, A., R. Serrouya, and F.G. Whoris key. Aerial Exposure Tolerance of Zebra and Quagga Mussels (Bivalvia: Dreisse nidae): Implications for Overland Dispersal. Canadian Journal of Fisheries and Aquatic Sciences 52(1994):470 477. Rosenberger, R., and J. Loomis. Benefit Transfer of Outdoor Recreation Use Values: A Technical Document Supporting the Fo rest Service Strategic Plan (2000 Revision) Gen. Tech. Rep. RMRS-GTR-72 Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, 2001. Salisbury, S. Canker Repeal Tops Legislature' s List of Agriculture Priorities Palm Beach Post, March 05, 2006. Schardt J. 1997. Maintenance Control in Strang ers in Paradise: Impact and Management of Nonindigenous Species in Florida Washington, DC: Island Press, 1997. 131

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Schmitz, D.C., B.V. Nelson, L.E. Nall, and J.D. Schardt. 1988. Exotic Aquatic Plants in Florida: A Historical Perspective and Review of the Present Aquatic Plant Regulation Program. Proceedings of the Symposium on Exotic Pest Plants, pp. 303-326. Schubert, T.S., and X. Sun. Bacterial Citrus Canker Florida Department of Agriculture & Consumer Service Division of Plant Industry Plant Pathology, Circular No. 377, 2001. Schubert, T.S., T.R. Gottwald, S.A. Rizvi, J.H. Graham, X. Sun ,and W.N. Dixon. Meeting the Challenge of Eradicati ng Citrus Canker in FloridaAgain. Plant Disease 85 (4)(2001). Settle, C. and J.F. Shogren. Modeling Native-Exotic Species within Yellowstone Lake. American Journal of Agricultural Economics 84(2002):1323 1328. Simberloff, D. The Economics of Biological Invasions. Biodiversity Conservation 11(2002):553 556. Simberloff, D. The Bi ology of Invasions. S tranger in Paradise: Impact and Management of Nonindigenous Species in Florida. Simberloff, D., D.C., Schmitz, and T.C. Brown, eds. Island Press:Washington, D.C., 1997. Singh, K.P. et al. Economic returns and incen tives of lakes rehabili tation: Illinois case studies. Procedings of the Third Annual C onference of the North American Lake Management Society Washington, D.C., 1984. South Florida Water Manage ment District (SFWMD). Water management districts permitting portal. West Palm Beach, FL: South Florida Management District, 2005. Internet site: http://arcimspub.sjrwmd.com/website/permitportal/default.htm (Accessed March 23, 2005). Spencer, D.F., G.G. Ksander, J.D. Madsen, and C.S. Owens. Emergence of Vegetative Propagules of Potamogeton nodosus, Po tamogeton pectinatus, Vallisneria americanan, and Hydrilla verticillata Based on Accumulated Degree-Days. Aquatic Botany 67(2000):237 249. Sprung, M. Ecological Re quirements of Developing Dreissena polymorpha Eggs. Archiv fr Hydrobiologie, Supplement 79(1987):69 86. Sprung, M. The Other Life: An Account of Present Knowledge of the Larval Phase of Dreissena polymorpha . Zebra Mussels: Biology, Impacts, and Control T.F. Nalepa and D.W. Schloesser, eds. Boca Raton, LA: Lewis, 1993. State of Florida. Water Quality Assessment for the St ate of Florida: Section 305(b). Main Report, Bureau of Water Resources Prot ection, Division of Water Facilities, Florida Department of Environmental Pr otection, Tallahassee, Florida, 1996. 132

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State of Florida. State of Florida Quick Facts Orlando, FL: State of Florida.com, 2005. Internet site: http://www.stateofflorida.com/Portal/DesktopDefault.aspx?tabid=95 (Accessed April 3, 2005). Steward, K.K. Retardation of Hydrilla (Hydrilla verticilla ta) Regrowth through Chemical Control of Vegetative Reproduction. Weed Science 28(1980):245 251. Steward, K.K., and T.K. Van. Comparati ve Studies of Monoecious and Dioecious Hydrilla (Hydrilla verticillata) Biotypes. Weed Science 35(1987):204 210. Steward, K.K. Growth of Hydrilla (Hydrilla verticillata) in Hydrosoils of Different Composition. Weed Science 32(1984):371 375. Stoeckel, J.A., K.D. Camlin, K.D. Blodgett, and R. Sparks. Growth Rates of Zebra Mussel Veligers in the Illinois River: Implications for Larval Dispersal and Settlement Patterns. Illinois Natural Hi story Survey, 1996. Stoeckel, J.A., D.K. Padilla, D.W. Schneider, and C.R. Rehm ann. Laboratory Culture of Dreissena polymorpha Larvae: Spawning Success, A dult Fecundity, and Larval Mortality Patterns. Canadian Journal of Zoology 82(2004):1436 1443. Stoeckmann, A.M., and D.W. Garton. A Seasonal Energy Budget for Zebra Mussels ( Dreissena polymorpha ) in Western Lake Erie. Canadian Journal of Fisheries and Aquatic Sciences 54(1997):2743 2751. Strayer, D.L., J. Powell, P. Ambrose, L.C. Smith, M.L. Pace, and D.T. Fischer.Arrival, Spread, and Early Dynamics of a Zebra Mussel ( Dreissena polymorpha ) Population in the Hudson River Estuary. Canadian Journal of Fisheries and Aquatic Sciences 53(1996):1143 1149. Strayer, D.L. Effects of Alien Species on Freshwater Mollusks in North America. Journal of the North Amer ican Benthological Society 18(1)(1999):74 98. Strayer, D.L., K.A. Hattala, and A.W. Ka hnle. Effects of an Invasive Bivalve (Dreissena polymorpha) on Fish in the Hudson River Estuary. Canadian Journal of Fisheries and Aquatic Sciences 61(2004):924 941. Strayer, D.L. and H.M. Malcom. Long-Term Demography of a Zebra Mussel ( Dreissena polymorpha ) Population. Freshwater Biology 51(2006):117 130. Suarez, A.V., D.A. Holway, and T.J. Case. P atterns of Spread in Biological Invasions Dominated by Long-Distance Jump Disper sal: Insights from Argentine Ants. Proceedings of the National Academy of Sciences 98(3)(2001):1095 1100. Suit, R.F., and E.P. DuCharme. The Burro wing Nematode and Other Plant Parasitic Nematodes in Relation to Spr eading Decline of Citrus. Plant Disease Reptr 37(1953):379-383. 133

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Sutton, D.L. Growth of Hydrilla in Esta blished Stands of Spikerush and Slender Arrowhead. Journal of Aquatic Plant Management 24(1986):16 20. Sutton, D.L. and K.M. Portier. Density of Tubers and Turions of Hydrilla in South Florida. Journal of Aquatic Plant Management 23(1985):64 67. Sutton, D.L., and K.M. Portier. Growth of Dioecious Hydrilla in Sediments from Six Florida Lakes. Journal of Aquatic Plant Management 33(1995):3 7. Sutton, D.L., T.K. Van, and K.M. Portier. Growth of Dioecious and Monoecious Hydrilla from Single Tubers. Journal of Aquatic Plant Management 30(1992):15 20. Tate, W.B., M.S. Allen, R.A. Myers, E.J. Nagid, and J.R. Estes. Relation of Age-0 Largemouth Bass Abundance to Hydrilla Coverage and Water Level at Lochloosa and Orange Lakes, Florida. North American Journal of Fisheries Management 23(2003):251 257. Thomas, M.H., and N. Stratis. Assessing the Economic Impact and Value of Floridas Public Piers and Boat Ramps. Florida Fish and Wildlife Conservation Commission, 2001 Thorp, J.H., J.E. Alexander, and G.A. Cobbs. Coping with Warm er, Large rivers: A Field Experiment on Potential Range E xpansion of Northern Quagga Mussels ( Dreissena bugensis ). Freshwater Biology 47(2002):1779 1790. Timmer, L.W., J.H. Graham and H.L. Chamberlain. Fundamentals of Citrus Canker Management. Institute of Food and Agricultural Sciences, EDIS Fact Sheet PP153. July 2006. Ulanowicz, R.E., and J.H. Tuttle. The Trophic Consequences of Oyster Stock Rehabilitation in Chesapeake Bay. Estuaries 15(3)(1992):298 306. University of Florida. Hydrilla Verticillata Gainesville, FL: Non-Native Invasive Aquatic Plants in the United States (website) of the Center for Aquatic and Invasive Plants, University of Florida. Internet site: http://www.plants.ifas.ufl.edu/seagrant/hydver2.html (Accessed March, 4, 2006) United States Army Corps of Engineers (USACE). Environmental Effects of Zebra Mussel Infestations. Technical Note ZMR-1-14, 1995. United States Department of Agriculture, Letter from Deputy Secretary Chuck Connor to Charles H. Bronson, Commi ssioner of Agriculture, Fl orida Department of Agriculture and Consumer Services dated January 10, 2006. United States General Accounting Office (USGAO). Invasive Species Clearer Focus and Greater Commitment Needed to Effectively Manage the Problems Report to Executive Agency Officials, GAO-03-1, October, 2001. 134

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United States Geological Survey (USGS). Zebra Mussels Cause Economic and Ecological Problems in the Great Lakes GLSC USGS Fact Sheet 2000-6, created August 15, 2000. United States Geological Survey (USGS). USGS Real-Time Water Data for Florida Reston, VA: United States Geologica l Survey, 2006. Internet site: http://waterdata.usgs.gov/fl/nwis/rt (Accessed October 10, 2006). United States Geological Survey (USGS). Non-indigenous Aquatic Species Database Reston, VA: United States Geologica l Survey, 2006. Internet site: http://nas.er.usgs.gov (Accessed February 14, 2007). Van, T.K. Differential Responses to Phot operiods in Monoecious and Diecious Hydrilla verticillata. Weed Science 37(1989):552 556. Van, T.K., K.K. Steward, and R.D. Conant. Responses of Monoecious and Dioecious Hydrilla (Hydrilla verticil lata) to Various Concentr ations and Exposures of Diquat. Weed Science 35(1987):247 252. Van, T.K., W.T. Haller, and L.A. Garrard. T he Effect of Daylight and Temperature on Hydrilla Growth and Tuber Production. Journal of Aquatic Plant Management 16(1978):57 59. Van den Bosch, F., R. Hengeveld, and J.A.J. Metz. Analyzing the Velocity of Animal Range Expansion. Journal of Biogeography 16(1992):503 540. Virginia Department of Game and Inland Fisheries (VDGIF). Millbrook quarry zebra mussel eradication. Richmond, VA: Department of Game and Inland Fisheries., 2006. Internet site: http://www.dgif.state.va.us/zebramussels/ (Accessed February 5, 2007). Vitousek, P.M., C.M. DAntionio, L.L. Loope and R. Westbrooks. B iological Invasions as Global Environmental Change. American Scientist 84(5)(1996):468 478. Whitney, S.D., K.D. Blodgett, and R.E. Sp arks. Update on Zebra Mussels and Native Unionids in the Illinois River. Illino is Natural History Survey. Rep., LTRMP Field Station, 1995. Wilcove, D.S., D. Rothstein, J. Dubow, E. Phillips, and E. Losos. Quantifying Threats to Imperiled Species in the United States. BioScience 48(1998):607 615. Winton, M.D., and J.S. Clayton. The Imp act of Invasive Submerged Weed Species on Seed Banks in Lake Sediments. Aquatic Botany 53(1996):31 45. With, K.A. The Landscape Ecol ogy of Invasive Spread. Conservation Biology 16(2002):1192 1203. 135

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Wolverton, B.C., and R.C. McDonald. Water Hyacinth ( Eichhornia crassipes ) Productivity and Harvesting Studies. Economic Botany 33(1979):1-10. Woods, C. New UF Low-Power Radio Stations On I-75 And I95 Warn Travelers About Zebra Mussels. Gainesville, FL: University of Florida News. Internet site: http://news.ufl.e du/1999/02/19/zebra/ (Accessed April 14, 2006). 136

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BIOGRAPHICAL SKETCH Damian Campbell Adams was born in Naples, Florida and spent most of his life living near Gainesville, Florida. As a child, Damian raised prize-winning chickens. At Oak Hall High School, Damian was senior class president, f ounder of the ecology club, a member of Standing Room Only Players acting troupe, lettered in football and weightlifting, ran track, and was a member of the physics competition team and the Mu Alpha Theta math honor competition team. Damian set the Oak Hall High School reco rd for the triple jump in 1991. Damian almost entered basic training for the US Marines in the summer of 1993, but instead followed his mothers advice to attend co llege. Damian applied to only two schoolsUF and Florida State University. UF responded firs t, and so Damian went on to enroll in the University of Florida in 1993. At UF, Damian was active in several student groups, including College Republicans, Rotaract, Alpha Tau Omega fraternity, and even st arted his own student political party (which came only a few dozen votes short of winni ng the UF student body presidency). Damian was also an active contri butor to the student ne wspaperThe Independent Florida Alligator. While a student at UF, Dami an spent a summer interning in the US Congress for Rep. Cliff Stearns, and also spent several mont hs working as a researcher for Nick Hawkins, MP in the British House of Commons. Damian finished his BS in Business Administration ( Highest Honors ) in December, 1997 and enrolled in UFs law school in 1998. Damian took an agricultural law course from Prof. M.T. Olexa, who would later become chair of both his Master of Ag ribusiness and later his PhD committees. Damian began working as a legal researcher for the Ag ricultural Law Center with Dr. Olexa, and soon enrolled in the Master of Agribusiness program in the F ood and Resource Economics Department. In 2001, Damian graduated from both the College of Agri cultural and Life Sciences and the UF College of Law with both his MAB and JD. In 2001, Damian was recruited into the PhD program in the 137

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Food and Resource Economics Department with a very generous USDA National Needs Fellowship. While a PhD student, Damian explored several research topics. In 2002, Damian was asked to teach a course in natural resource and envi ronmental policy, which he enjoyed immensely. This changed his entire career outlook, and he hoped to someday become a professor. In 2003, Damian left UF to earn a Masters degree from Cambridge University in England. Damian was researching an issue that the UK was mired ing enetically modified cropsand he wanted to get first-hand exposure to those conducting the most exciting research on the issue. Cambridge was an amazing experience and Damian returned to Florida in 2004 with a renewed vigor and drive to write a dissertation on the topic of the welfare effect s associated with different regulatory regimes for genetic drift from genetica lly modified crops. Shortly after his return to the US, Damian was offered a faculty job ( 100% teaching) with the Food and Resource Economics Department, which he began in mid-April, 2005. Due to data problems on organic crop production in the US (that he needed to measure the welfare effects of GM policies), Damian deci ded to change disserta tion topics in 2006. Fortunately, he had been working on several invasi ve species projects with Dr. Donna Lee. With wise counsel from his committee, Damian bega n focusing on the economics and law of invasive species management in October, 2006. About six months later, Damian had finished his dissertation and successfully defended on Ap ril 12, 2007. The journey continues. 138


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Title: The Economics and Law of Invasive Species Management in Florida
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THE ECONOMICS AND LAW OF INVASIVE SPECIES MANAGEMENT IN FLORIDA


By

DAMIAN C. ADAMS














A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

2007







































O 2007 Damian C. Adams









ACKNOWLEDGMENTS

I would like to thank my committee chair, Dr. Michael Olexa for his guidance and

encouragement over the last several years. While I was languishing in the intellectual desert that

is law school, Dr. Olexa provided a welcome oasis. Working with him as researcher for the

Agricultural Law Center rekindled my interests in agriculture and inspired me to pursue a

Master' s degree in the Food and Resource Economics Department. Without Dr. Olexa, I might

never have headed down the PhD path. For that and for the time he has spent helping me

navigate the PhD coursework and dissertation red tape, I sincerely thank him.

I would also like to thank my committee co-chair, Dr. Donna Lee. Dr. Lee has provided

countless hours of input and guidance on my research into the economics of invasive species. Dr.

Lee has had a very big impact on my development as a researcher and an economist. Chapters

two and three of this dissertation were wholly inspired by a course that she taught. She also

helped me secure grant funding for the aquatic plants research, and we have since collaborated

on other grant-funded projects. Dr. Lee is a wonderful researcher, a keen thinker, and a friend. I

value her advice and admire her outlook on life, and hope to mirror her success.

I also thank Dr. Richard Kilmer, who is a wonderful mentor and perhaps the most

industrious person I know. I have enjoyed our conversations on myriad topics very much, and

hope to be even half as productive as he has been.

I would also like to thank Dr. John VanSickle. His feedback and his time are greatly

appreciated. I benefited from hearing his perspective on this topic (and others) very much.

I also thank Dr. Roy Carriker. Dr. Carriker provided me with my first teaching

opportunity, for which I am eternally grateful. He has also been a wonderful source of

information on Florida water policy and law issues over the years. His time and input is

appreciated.









I would like to thank Dr. Ricky Telg. Dr. Telg has invaluable feedback on my dissertation

and has helped me to greatly improve its quality.

Lastly, I would like to that those outside of the UF campus who have helped me keep my

sanity while writing my dissertation. These include my mom and other family members who

have supported me and provided endless joke material; my friends, who were always there to

make sure I did not get too mired in schoolwork; my golden retriever, Glen, a great companion;

and Alison Lutz, who provided so much feedback on my dissertation that she should have been

on the committee.

I am eternally indebted to all of them.











TABLE OF CONTENTS


page

ACKNOWLEDGMENT S ........._.._ ..... ._._ ...............3.....


LI ST OF T ABLE S ........._.. ..... ._ ._ ...............7....

LIST OF FIGURES .............. ...............8.....


AB S TRAC T ..... ._ ................. ............_........9

CHAPTER


1 INTRODUCTION ................. ...............11.......... ......

Zebra M ussels ................ .. ....... .. ...... ........... .............1
Hydrilla, Water Lettuce, and Water Hyacinth ......__....._.__._ ......._._. ...........1
Legal Basis for State Control of Invasive Species. ....__ ......_.___ ..... ...__ ............17
Summary ............ ...... .. ...............18..

2 OPTIMAL INVESTMENT INT PREVENTION AND CONTROL OF A POTENTIAL
INVADER: THE CASE OF ZEBRA MUSSELS INT FLORIDA WATERWAYS ...............20

Introduction.............. .. ................. ...........2
Background on Invasive Species in the United States............... ...............21.
The Invasive Freshwater Zebra Mussel ................. ...............21........... ...
W ill Zebra M ussels Invade Florida? ................... ........... ...............23.....
Model of Lake Okeechobee Zebra Mussel Infestation ................. .............................24
Zebra M ussel Spread and Distribution .............................. ...................2
Bioeconomic Model of the Zebra Mussel Threat to Lake Okeechobee .............. .... .........._..29
Empirical Approach............... ...............32
Arrival and Survival .............. ...............33....
Reproduction and Spread .............. ...............35....
Direct Economic Costs and Damages .............. ...............37....
Ecological and Recreational Damages .............. ...............41....
Effectiveness of Management Methods ................. ....__ ....__ ............4
Policy Scenarios and Results ............ ..... ._ ...............45...
Conclusion ............ ..... ._ ...............52...


3 BIOECONOMIC MODEL OF INVASIVE AQUATIC PLANTS HYDRELLA
VERTICILLATA (HYDRELLA), EICHHORNIA CRASSIPES (WATER
HYACINTH), AND PISTIA STRATIOTES (WATER LETTUCE) FOR FLORIDA
LAKE S .............. ...............56....


Introduction................ ... .. .........5
Invasive Species Background ................... ......._ .......__ ...........5
Hydrilla, Water Hyacinth, and Water Lettuce Past Management .............. .....................5












Invasive Aquatic Plant Control ................. ...............61................
Bioeconomic Modeling of Invasive Species ................. .......................... ..........62
Empirical Approach............... .. ...............6
Data Sources and Description ..................... ...............64.
Hydrilla and Floating Plants Growth Models............... ...............66.
Aquatic Plant Management Scenarios............... ...............6
Recreational Fishing Effort Model .............. ... ... ...._. .................... ...........7
Hydrilla, Water Hyacinth, and Water Lettuce Treatment Cost Model............................79
Angler Effort Value Model ....................... ...... ..........8
Economic Effects of Invasive Aquatic Plant Management ................. ......__. ........._...80
Conclusion ............ _...... ._ ...............86....


4 THE LEGAL BASIS FOR REGULATORY CONTROL OF INVASIVE
AGRICULTURAL PESTS INT FLORIDA ................ ...............88................


Introduction................. .. .. .... ...............8
Use of Police Power to Take Private Property ................. ...............90..............
Limitations on Police Power............... ..... .... .... .. ........9
Substantive Due Process and Procedural Due Process............... ...............92
Just Com pensation................. ... ... .. ....................9
Comparing the Limitations on the Use of Police Power: Spreading Decline versus
Citrus Canker .............. ...............93....

Spreading Decline .............. ...............93....
Citrus Canker............... ...............94.
Lessons for Citrus Greening ................. ...............100...............
Conclusion ................ ...............101................


5 SUMMARY AND CONCLUSIONS ................ ...............103...............


Introduction............... .. ... .. .. ............... .. ... ... .......10
Summary and Conclusions Regarding the Potential Infestation of Zebra Mussels in
Florida .................. .......... ... ........ ..... ... .. ........ 0
Summary and Conclusions Regarding Invasive Aquatic Plants in Florida..........................106
Summary and Conclusions Regarding the Regulatory Basis for Controlling Invasive
Agricultural Pests in Florida .............. ...............108....
Conclusion ................ ...............110................


APPENDIX


A ZEBRA MUSSEL INFORMATION SURVEY ................. ...............112........... ...


B SENSITIVITY ANALYSIS OF ZEBRA MUS SEL PARAMETERS ................. ...............120


LIST OF REFERENCES ............_...... .__ ...............121...


BIOGRAPHICAL SKETCH ............_...... .__ ...............137...













LIST OF TABLES


Table page

2-1. Lake Okeechobee surface water supply by sector and county, year 2000. ............................26

2-2. Zebra mussel model parameter values ................. ...............46......_.._...

2-3. Present value estimates of zebra mussel policy scenarios (20 year, 2006 $ million) .............47

2-4. Simulation results compared to Policy I (Do nothing) (present value, 2006 $ million).........48

3-1. Hydrilla and floating plants growth function parameter estimates............... ...............6

3-2. Model assumptions for policy scenarios. ............. ...............70.....

3-3. Date of second herbicide treatments for C20. ............. ...............71.....

3-4. Angler effort regression model parameters. ............. ...............77.....

3-5. Annual economic impact of invasive aquatic plant management on 13 lakes. ................... ...82

B-1. Sensitivity analysis of zebra mussel parameters ...._.. ................. ........_........12










LIST OF FIGURES


Figure page

2-1 2006 US Geological Survey map of zebra mussels in the United States.. .................. .......22

2-2 Lake Okeechobee waterway. ............. ...............38.....

2-3 Zebra mussel policy impacts on cumulative probability of infestation. ................... .........50

3-1 Simulated hydrilla coverage in Lake Istokpoga ................. ...............73........... ..

3-2 Simulated hydrilla coverage in Lake Kissimmee. ............. ...............74.....

3-3 Simulated hydrilla coverage in Lake Weohyakapka. ............. ...... ............... 7

3-4 Daily fishing effort lost to invasive aquatic plants for a 10,000 acre lake in Florida........79

3-5 Impact of invasive plant control on fishing effort (Lake Jackson example)..............._.__...83









Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

THE ECONOMICS AND LAW OF INVASIVE SPECIES MANAGEMENT IN FLORIDA

By

Damian C. Adams

May 2007

Chair: Michael T. Olexa
Cochair: Donna J. Lee
Maj or: Food and Resource Economics

Invasive species impact Florida's ecology and economy across multiple dimensions. This

dissertation examines the impacts of five invasive species in Florida, and evaluates management

responses that follow. It first discusses potential infestation of Lake Okeechobee by invasive

zebra mussels over twenty years using a bioeconomic model. Next, it estimates invasive aquatic

plants' impacts on freshwater fishing in Florida. Lastly, it analyzes the legal foundations for state

control efforts with respect to invasive species.

Zebra mussels are a serious threat to Lake Okeechobee, which is vital to agricultural

producers and anglers and provides numerous ecosystem services. A bioeconomic model in a

stochastic dynamic simulation framework estimates the impact of zebra mussels on recreation,

surface water users, and ecosystem services over 20 years. Without state intervention it is

$349.34 million. Policy responses were simulated. The cost-minimizing choice is to invest in

arrival prevention and early warning, which reduces costs by 70.91% and is the only policy

choice with positive returns ($247.71 million) compared to no control of zebra mussels. Post-

establishment eradication yields large losses. This study indicates that investment in arrival

prevention is more cost effective than post-arrival eradication.










Invasive plants have significant negative impacts on water-based recreation. Despite the

high impacts, little economic research has quantified these impacts in a way useful to invasive

species managers. Economic research conducted on aquatic invasive species usually focuses on a

single lake, or is too abstract for managers. Data are usually unavailable for larger-scale studies.

This study uses unpublished data to estimate the impact of plant coverage on fishing activity on

13 Florida lakes using a bioeconomic model. Policy response simulations estimate the impacts

over Hyve years. The results suggest that the optimal management policy is maintenance control

with respect to hydrilla, water hyacinth, and water lettuce.

The dissertation then examines the failure of the state' s Citrus Canker Eradication Program

(CCEP). The CCEP cases are precedent for subsequent pest eradication program challenges.

The State's power to take property, due process, and just compensation are reviewed. Lessons for

subsequent eradication programs are provided.









CHAPTER 1
INTTRODUCTION

The relatively free and rapid movement of people and goods across the globe has led to an

increase in the invasion rate of many brittle ecosystems by prolific and destructive plants and

animals (Vitousek et al., 1996; Mack, 2000). Once introduced to new areas, some of these

species become "invasive," causing a significant proportion of environmental changes

worldwide. Invasive species in the United States pose serious ecological and economic problems

(Evans, 2003).

An invasive species is defined as a non-native species whose introduction "causes or is

likely to cause economic or environmental harm or harm to human health" (Executive Order

13112, 1999). Invasive species are a particular problem for the tropical and subtropical areas of

Florida, where physiographic, climatic and geographic characteristics make it relatively easy for

non-indigenous species to establish (Simberloff, 1997; Fox [personal communication], 2007).

Florida has a high rate of non-native species introduction, with the Port of Miami receiving about

85% of non-native plant shipments each year (OTA, 1993). For example, the entire United States

has about 50,000 established non-native plant and animal species, with Florida alone having over

25,000 as exotic ornamentals (Pimentel, 2003); over 1,300 have established in natural areas, and

124 of these are destructive to natural areas (FLEPPC, 2006). By comparison, Florida only has

2,500 native plant species, and the US has 18,000 native species.

Invasive species are a growing economic concern. Today, there are an estimated 5,000 to

6,000 invasive species in the United States (Pimentel, 2003; Burnham, 2004), and invasive plants

are invading about 700,000 hectares/year of natural areas in the US (Pimentel et al., 2000).

The detrimental problems resulting from invasive species have multiple dimensions.

Adverse ecological impacts, such as the displacement of native species (both related and









unrelated), leading to a reduction in the loss of native bio-diversity may cause severe disruption

of complex natural ecosystems. They can have devastating ecological impacts, and may be the

primary cause of biodiversity loss (Mack, 2000).

Economic impacts can follow close behind such detrimental ecological changes, affecting

both the quality (and/or quantity) of public goods, and the interests of private entities. For

example, the reduction of recreational benefits derived from public waterways (and the costs of

managing offensive invasive species) highlights the public good dimension. Other effects, such

as a reduction in property values and/or incurred mitigation costs, have an impact on private

citizens and businesses, as well. Economic damages from invasive species are estimated to be

$137 billion/year excluding ecosystem impacts (Pimentel et al., 2000). About 25% of US

agricultural production is lost to non-native pests or to their associated control costs (Simberloff,

2002). When considering the well-documented impacts of certain invasive species, such as

damages caused by Hydrilla verticillata in Florida, or the zebra mussel in the Great Lakes, it is

clear that invasive species can have dire economic consequences.

With continuing increases in both global trade and the domestic and international

migration of people to Florida, the rate of arrival of non-native species is rising. Invasive species

management is fast becoming a high priority for the protection of Florida' s agricultural and

natural systems (Schardt [personal communication], 2007). Yet, despite the large economic and

ecosystem harms associated with invasive species, there exists little empirical analysis of

invasive species problems in a way that would help policy makers or resource managers (Schardt

[personal communication], 2007). There are very few invasive species studies in the economics

literature, and most of those are distinctly theoretical and too technical or abstract for use by

policy makers or resource managers. Few empirical studies have evaluated the impact of










invasive species. The issue of invasive species is one that much more attention (and perhaps

budgetary expenditures) will likely be focused on in the near future.

In 2002, the US Governmental Accounting Office reported that "existing studies on the

economic impact of invasive species in the United States are of limited use for guiding decision

makers formulating policies for prevention and control" (USGAO, 2001). Damages to

ecosystems, benefits from alternate controls, risks from future introductions, and multi-sector

analyses have been lacking. More comprehensive approaches are needed to help decision makers

identify potential invaders, quantify prevailing threat, and prioritize resources for mitigating

damages. There is a great deal about invasive species growth, transmission, and other important

information that is unknown. Perhaps this explains the lack of accessible economic studies on the

topic. Unfortunately, despite these unknowns, given the serious risks to agriculture and natural

resources posed by invasive species, policy makers will be called upon to allocate scare public

resources in defense of natural and agricultural systems. Studies such as these, though based on

several assumptions that have not yet been tested, provide important information to the discourse

on invasive species management.

The purpose of this research is to examine the economic impacts of selected invasive

species in Florida, and evaluate the management responses that follow. The specific objectives

of the research are 1) to provide much needed empirical economic research on invasive species

management; and 2) to examine the impact of litigation on invasive species management by state

agencies.

Zebra Mussels

Chapter Two discusses the potential infestation of Lake Okeechobee by a fresh water

mollusk, the zebra mussel. Zebra mussels (Dreissena polymorpha) are small freshwater mussels

native to southeast Europe. They first arrived in the US in the Great Lakes region in the mid-









1980s, probably as free-swimming larvae in the ballast water of a transatlantic ship (Hebert et al.,

1989; Griffiths et al., 1991; Thorp et al., 2002). Within a few years of introduction, zebra

mussels (ZM) were in many maj or rivers and lakes in the eastern US (Hebert et al, 1989).

Lacking significant competition or predation (New York Sea Grant, 1997) and possessing unique

characteristics among freshwater mussels (Borcherding, 1991), the spread of ZM across North

America has been rapid (Drake and Bossenbroek, 2004; NationalAtlas.gov, 2007; USGS, 2007).

Their spread was greatly accelerated by recreational and commercial boating in and around the

Great Lakes (Johnson and Carlton, 1996). Zebra mussels now inhabit waters in twenty eastern

and southern states and continue to spread (USGS, 2007).

I construct a bioeconomic model to simulate the expected impacts of the zebra mussel

(ZM) on the lake based on assumed transmission vectors (recreational boating), habitat

suitability from a previous study (Hayward and Estevez, 1997), and effectiveness of ZM

mitigation and prevention methods. I include assumed lake-related ecological and recreational

values to construct an estimate of the total economic impacts with respect to a ZM infestation. I

then apply state probabilities (in a stochastic dynamic simulation format) to arrive at a long-run

economic impact analysis of ZM in Lake Okeechobee. I report present value results of the

expected economic impacts over 20 years, including costs and damages to surface water use,

recreational anglers, and users of ecosystem services, as well as budgetary costs. The results

from this study indicate that investment in arrival prevention is much more cost effective than

attempting to control or eradicate invasive species post-arrival.

Hydrilla, Water Lettuce, and Water Hyacinth

Chapter Three estimates the impact of the invasive aquatic plants hydrilla, water lettuce,

and water hyacinth on freshwater fishing in Florida. Hydrilla is a submerged aquatic plant

probably introduced as an aquarium plant in the 1950s, and first detected in Florida water bodies









in 1960 (University of Florida, 2001; Langeland, 1996). Its rapid growth rate and suitability to

Florida waters allowed it to spread rapidly throughout the state. By the early-seventies, hydrilla

could be found in all maj or drainage basins in Florida. By 1995, hydrilla spread to over 40,000

hectares on 43% of the public lakes in the State (Langeland, 1996). It is believed that 98% of

hydrilla is under maintenance control in 193 of the 288 water bodies where it is found in Florida

(FDEP, 2003).

Water hyacinth and water lettuce are floating aquatic plants. Water hyacinth, native to

South America, was introduced to Florida as an ornamental pond plant in 1885. Its rapid

reproduction led to it being discarded into the St. John's River and it spread quickly to

neighboring water bodies (Schmitz et al., 1988). Water lettuce has been in Florida much longer,

perhaps since the 16th century, and is also believed to be a native of South America (Schmitz et

al). These plants are believed to be under maintenance control in Florida.

The problems with hydrilla, water hyacinth and water lettuce are multidimensional--

ecological, economic, public and private. Ecological impacts include displacing native flora

(both submersed and floating), altering habitat of native fauna, and disrupting of ecosystems

processes. These invasive plants grow in thick monoculture mats which block sunlight to and

out-compete native plants, especially in the increasingly nutrient-rich lakes and rivers of Florida

as population growth increases nitrate and phosphate runoff. Dense monocultures can contribute

to reduced fish populations, and when large mats of plants decompose, the reduced dissolved

oxygen levels in a lake can cause massive fish kills. These plants also harm non-aquatic species

by covering nesting and egg laying areas, and blocking access to water, shelter, and food

sources.









Economic impacts follow close behind ecosystem loss. Hydrilla, water hyacinth and

water lettuce can hinder boating, swimming, and fishing activities in lakes and rivers. Reduced

sport fish populations coupled with access problems significantly reduce sport fishing activities.

The reduction of recreational benefits derived from public waterways (and the cost of managing

the weeds) highlights the public loss from invasive aquatic plants. They also affect private

citizens and businesses, blocking power generators and agricultural irrigation water intake pipes,

jamming water turbines and dams, and clogging canals and ditches. Infestations in private ponds

and poorly managed public water bodies can reduce recreational and aesthetic value of

waterfront property. Hydrilla has been difficult to eradicate because the plant produces

underground tubers which generate new plants each year. Likewise, water hyacinth and water

lettuce are extremely prolific, propagating both by seeding and by creating daughter plants

vegetatively.

According to the FDEP (2002), "Insufficient management funding allowed hydrilla to

expand from 50,000 to 100,000 acres during the middle 1990s." During this time period there

was sufficient funding to continue water hyacinth (and water lettuce) control, which was

considered of primary importance. Various aquatic plant control strategies have been considered,

including mechanical removal, lake draw-down, application of various herbicides and biological

control--both with insect and herbivorous fish species. Lake draw-down prevents most

recreational use, and biological control remains difficult to control, leaving the use of herbicides

as the primary management strategy for most lake managers (FDEP, 2006). Whatever method of

control is chosen, there seems to be consensus that keeping invasive aquatic plant populations

very low, known as maintenance control, is the most economically efficient funding strategy

(Schardt, 1997). Florida has considerable experience fighting invasive aquatic plants (especially









water hyacinth), yet Langeland (1996) asserts that lack of adequate and consistent funding for

many invasive plants (especially hydrilla) continues to be the biggest barrier to effective

management and the efficient use of public resources over time.

The economics of aquatic plant management in Florida have been examined, but only on

one or two lakes at a time (Burruss Institute, 1998; Milon and Welsh, 1989; Milon et al., 1986).

This study examines the impact of invasive plants on multiple lakes. I use unpublished data on

plant coverage, angler effort, and lake physiographic and amenities to estimate a bioeconomic

model of the impact of plant coverage on fishing activity on 13 Florida lakes. Using the

bioeconomic model of invasive aquatic plants, I then simulate the single-year costs and benefits

of six policy scenarios for aquatic plant control. Over Hyve years, the estimated economic value

of the 13 lakes is $76.4 million, and lapses in invasive plant control may j eopardize that value.

These results suggest that the optimal management policy is maintenance control with respect to

hydrilla, water hyacinth and water lettuce.

Legal Basis for State Control of Invasive Species

Chapter 4 discusses the legal foundations for state control efforts with respect to invasive

species. Florida is no stranger to agricultural disease, particularly those affecting its citrus

industry. Florida has twice successfully eradicated the invasive citrus canker (Division of Plant

Industry, 2006). Citrus canker was first detected in Florida in 1910 and declared eradicated in

1947. However, in 1986, a highly aggressive Asian strain of the citrus canker was detected in

Florida (Timmer, Graham, and Chamberlain, 2006).

In 1995, the Asiatic strain of citrus canker reappeared in Florida. Soon after, the state of

Florida, in conjunction with the United States Department of Agriculture, began a citrus canker

eradication program. As part of the program, residential owners of citrus trees suspected to

harbor canker innoculum were compensated up to $55 per tree destroyed by the state. Angry









homeowners sued to prevent further takings of their trees, and from 2000 to 2004 there were two

18-month lapses in the eradication program.

Subsequent to the lapses, there were five maj or hurricanes that helped spread the canker

innoculum throughout the state, potentially crippling the commercial citrus industry (Albrigo et

al., 2005). The hurricanes that passed over Florida in 2004 (Charley, Frances, Ivan, and Jeanne)

spread citrus canker from these residential trees to such an extent that 80,000 commercial acres

of citrus were subsequently slated for destruction. Concentrated efforts by governmental

officials reduced this to 32,000 acres when Hurricane Wilma made landfall in 2005. Due to the

spread of the citrus canker pathogen with Wilma, officials faced the task of destroying an

additional 168,000 to 220,000 acres of commercial citrus (USDA, 2006). The inability of the

State's canker eradication program to continue unabated meant the USDA canker eradication

program was largely ineffective. On January 10, 2006, the federal government stated that citrus

canker "is so widely distributed that eradication is impossible" and pulled the funding for the

USDA' s citrus canker eradication program (USDA, 2006). This change in policy came on the

heels of a number of judicial decisions upholding the legality of Florida' s citrus canker

eradication program, but too late to save the USDA eradication program. Though the CCEP was

repealed in January 2006 (Timmer et al., 2006), these judicial decisions will be precedential to

potential challenges to similar State programs designed to manage and control pests like citrus

canker and citrus greening (Salisbury, 2006). This portion of the research examines the legal

framework that allowed these lapses, and provides suggestions for the creation of a program to

combat a new invasive threat-citrus greening.

Summary

This chapter contains a broad overview of the significance and relevance of invasive

species in Florida. In addition, the chapter addresses important background introductory










information for each of the three topics included in this series. The first focus area for this series

is the economic impact of invasive species in Florida, and its relationship with management

practices and strategies. The second focus in the series examines the influence invasive aquatic

plants have on the recreation and tourism industry in Florida, specifically in terms of freshwater

fishing. Finally, the series concludes with an investigation into the issue of legal foundations for

Florida's control of invasive species that may threaten agricultural production or harm natural

areas. An overview of the State's use of police power to protect agriculture is addressed in

conjunction with legal decisions that balance the exercise of this power with the constitutional

mandates of due process and just compensation. These three issues are clearly germane to

Florida's economy, environment, and law.









CHAPTER 2
OPTIMAL INVESTMENT IN PREVENTION AND CONTROL OF A POTENTIAL
INVADER: THE CASE OF ZEBRA MUSSELS IN FLORIDA WATERWAYS

Introduction

Zebra mussels are a serious threat to several Florida waterways, particularly Lake

Okeechobee. The lake is vitally important to agricultural producers and recreational anglers. It

also provides numerous ecosystem services. We employ a stochastic dynamic simulation method

with a bioeconomic model to estimate the impact of zebra mussels on recreation, surface water

users, and ecosystem services. We estimate the present value of zebra mussel-related impacts

without state intervention to be $349.34 million over 20 years. We simulated several potential

policy responses. The overall cost minimizing choice is to invest in arrival prevention and early

warning, which would reduce present value costs by 70.91%. This is also the only policy choice

that netted positive returns ($247.71 million) as compared with doing nothing to control or

prevent zebra mussels in the lake. Policies that include post-establishment eradication yield large

losses ($414.98 million, $603.36 million). The results from this study indicate that investment in

arrival prevention is much more cost effective than attempting to control or eradicate invasive

species post-arrival. As with many invasive species, a great deal about zebra mussel biology,

transmission, and other important variables is unknown. Unfortunately, zebra mussels and other

invasive species pose serious risks to agriculture and natural resources. Despite the unknowns,

policy makers will be called upon to allocate scarce public resources in defense of natural and

agricultural systems. Studies such as this one, though based on several assumptions about zebra

mussels that have not yet been tested, provide important information to the discourse on invasive

species management.










Background on Invasive Species in the United States

The relatively free and rapid movement of people and goods across the globe has led to an

increase in the invasion rate of many brittle ecosystems by prolific and destructive plants and

animals (Vitousek et al., 1996; Mack, 2000). Once introduced to new areas, some of these

species become "invasive," causing a significant proportion of environmental changes

worldwide. Invasive species are non-native species that may cause economic, environmental or

human health problems (Federal Register, 1999). In the US, production losses, control costs, and

other associated costs related to invasive species is estimated to exceed $137 billion per year

(Pimentel et al., 1999). About 25% of US agricultural production is lost to nonnative pests or to

their associated control costs (Simberloff, 2002). They can also have devastating ecological

impacts, and may be the primary cause of biodiversity loss (Mack, 2000).

In 2002, the US Governmental Accounting Office reported that "existing studies on the

economic impact of invasive species in the United States are of limited used for guiding decision

makers formulating policies for prevention and control." Damages to ecosystems, benefits from

alternative controls, risks from future introductions, and multi-sector analyses have been lacking.

More comprehensive approaches are needed to help decision makers identify potential invaders,

quantify prevailing threats, and prioritize resources for mitigating damages. This chapter helps

quantify the prevailing threat from an invasive aquatic mussel to a large Florida lake--Lake

Okeechobee. We examine four policy responses and report the relative impacts on recreation,

surface water use, and ecosystem services.

The Invasive Freshwater Zebra Mussel

Zebra mussels (Dreissena polymorpha) are small freshwater mussels native to southeast

Europe. They first arrived in the US in the Great Lakes region in the mid-1980s, probably as

free-swimming larvae in the ballast water of a transatlantic ship (Hebert et al., 1989; Griffiths et










al., 1991; Thorp et al., 2002). Within a few years of introduction, zebra mussels (ZM) were in

many maj or rivers and lakes in the eastern US (Hebert et al, 1989). Lacking significant

competition or predation (New York Sea Grant, 1997) and possessing unique characteristics

among freshwater mussels (Borcherding, 1991), the spread of ZM across North America has

been rapid (Drake and Bossenbroek, 2004; NationalAtlas.gov, 2007; USGS, 2007). Their spread

was greatly accelerated by recreational and commercial boating in and around the Great Lakes

(Johnson and Carlton, 1996). Zebra mussels now inhabit waters in twenty eastern and southern

states and continue to spread (USGS, 2007; Figure 2-1).

Zebra Mussel Sightings Ditibution
ssene polyrnorpha

















Zebra musselstcralredoverln
Map produced bythe US I 11 I 13,2005
Figure 2-1. 2006 US Geological Survey map of zebra mussels in the United States.

Zebra mussels obstruct and foul man-made structures, impair water-based recreation, and

disrupt aquatic ecosystems. They are often found on natural substrates such as submerged plants,

logs, rocks, the shells of other animals, and on manmade structures such as bridge abutments,

water intake pipes, and boat hulls. When colonies become large, ZM clog water intake pipes,

accelerate corrosion, and sink buoys. In areas of the country where ZM have become established,

water users face higher maintenance costs to remove mussels and restore water flows, and










prevention costs, such as applying antifouling paint to submerged structures. From 1985 to 1995,

expenditures for controlling zebra mussels in the United States totaled $69 million, and have

since risen to over $60 million per year (Deng, 1996; USGAO, 2002).

Zebra mussels also cause ecosystem damages by disrupting native flora and fauna.

Principally, they compete for food sources and habitat, and hamper movement of other species.

Their success as invaders can be attributed to their rapid reproduction-females produce between

40,000 and one million eggs per year (USCACE, 2003). Because zebra mussels reproduce in

large numbers, natural predators such as turtles, crustaceans, catfish, drum, and ducks have little

effect on populations (Strayer, 1999). In areas invaded by zebra mussels, endangered native

mussel species are at risk. By 2010, zebra mussels are expected to contribute to the decline in

native mussel populations by 50%. Without further control efforts, 140 indigenous mussel

species could be lost (USGAO, 2002). Cumulative damage from zebra mussels in the US

including direct and indirect economic costs is estimated to be $3.1 to $5 billion from 2002 -

2011 (USGAO, 2002 and USGS, 2000).

Will Zebra Mussels Invade Florida?

North American ZM distribution forecasts are based on various environmental conditions,

primarily water temperature (Drake and Bossenbroek, 2004). Initially, ZM were not expected to

colonize warm waters due to their intolerance of high water temperatures (McMahon, 1991;

Mihuc et al., 1999), but more recent studies report that they are able to withstand higher

temperatures (Drake and Bossenbroek, 2004; Lewandowski and Ej smont-Karabin, 1983; Jenner

and Jansen-Mommen, 1993; Orlova, 2002) and may be adapting to local conditions (Marsden et

al., 1996; Muller et al., 2001). ZM recently collected from warmer regions have higher heat

tolerance than those from northern locations (Elderkin and Klerks, 2005).









ZM are now found in the lower Mississippi River and parts of Alabama (Allen et al., 1999;

USGS, 2007), and are expected to spread to Florida (Hayward and Estevez, 1997; Drake and

Bossenbroek, 2004). Two studies have predicted the suitability of Florida waters to ZM

infestation; both report several lakes and rivers that are highly vulnerable to ZM. Drake and

Bossenbroek (2004) use a machine-learning algorithm to predict spread based on several

environmental factors. According to their model, North Florida has a high and South Florida a

moderate likelihood of being infested by ZM. Hayward and Estevez (1997) calculate habitat

suitability indices for Florida waters based on biology and demography studies. Several

economically significant Florida water bodies are vulnerable to ZM invasion, including the St.

Johns River and Lake Okeechobee (Hayward and Estevez, 1997).

Early studies also suggested that ZM would not colonize southern waters due to the

relative lack of hard substrates and ZM inability to colonize soft sediments (Nalepa et al., 1995).

Recent studies show that they have adapted well to soft sediments (Strayer and Malcom, 2006;

Burlakova et al., 2006) and will colonize sand and mud if hard substrates are unavailable

(Strayer, 1999). Floating and submersed aquatic plants also provide suitable hard substrates, but

were not considered by earlier ZM distribution forecasts. Florida lakes and rivers, and

specifically Lake Okeechobee, have abundant plant life that could provide suitable substrate for

the invading mussels.

Model of Lake Okeechobee Zebra Mussel Infestation

Lake Okeechobee is a shallow, 448,000-acre lake located in South Florida. It is the second-

largest lake wholly contained within the US. The lake is an important commercial shipping route,

a valuable source of water supply, and a maj or economic and recreation resource (FDEP, 2001).

It is the site of several maj or fishing tournaments each year, and supports commercial fishing

operations. Lake Okeechobee draws 1.3 million anglers annually and supports a $117









million/year fishing industry (Lakeokeechobee.org, 2007). Five counties surround the lake, all of

which pump lake water for agricultural, industrial, potable, and other uses.

Lake Okeechobee supplies a substantial percentage of freshwater used by municipal,

industrial and agricultural sectors in the five-county region surrounding the lake (Table 2-1). In

these counties, surface water makes up a large percentage of the water supply, predominantly for

agricultural irrigation. For example, 94.49% of lake withdrawals are for agricultural irrigation,

and municipal, power plant, mining, and industrial users make up 2.64%, 1.60%, 0.81%, and

0.42% of lake withdrawals, respectively. A ZM infestation would greatly increase the costs of

these water users, as well as impact recreational and commercial fishing, and other

environmental services provided by the lake; however, ZM would primarily affect agricultural

surface water users.

Zebra Mussel Spread and Distribution

Zebra mussels exhibit three types of spread--diffusive (within a lake), advective (within a

watershed), and jump dispersal (between watersheds) (Johnson and Carlton, 1996; Johnson and

Padilla, 1996). Diffusive and advective spread of ZM occurs by free-swimming planktonic larvae

according to population dynamics (Stoeckel et al., 1996). ZM spread and distribution studies

have examined infestation of connected riverine areas or lakes within short distances of infested

waters using reaction-diffusion models (Buchan and Padilla, 1999). Reaction-diffusion models

allow range expansion of species that disperse and reproduce simultaneously, assuming constant

dispersal velocity and intrinsic growth rate. Reaction refers to a change in local population

(Holmes, 1993). A reaction-diffusion model may apply to ZM within a connected river

ecosystem, or over short distances, but Lake Okeechobee falls into neither of these categories.

The lake is distinctly isolated and would not be colonized by ZM without external assistance.










Table 2-1. Lake Okeechobee surface water supply by sector and county, vear 2000.


Counties Served by Lake Okeechobee
Lake
Okeechobee Florida
Glades Hendry Martin Okeechobee Palm Beach Total Total

Population (1000s) 10.58 36.21 126.73 35.91 1131.18 1340.61 12388.42

% population drinking water from
0.00 79.87 0.00 75.78 15.35 15.92 11.83
surface sources


Irrigated acres (1000s) 25.21 169.58 59.81 23.14 446.85 724.59 1691.69

% Irrigation water from surface
72.07 61.71 87.14 15.71 93.80 80.75 51.41
sources

% power plant, mining and
livestock water from surface 100.00 100.00 100.00 100.00 69.90 78.06 23.76
sources
% of total freshwater from surface
100.00 100.00 100.00 100.00 74.70 83.13 44.47
sources
Source: USGS (2006).









Critical levels of connectivity help determine whether an invasive species will reach

suitable habitats (With, 2002). Large gaps in habitat may be the reason why some species ranges

are restricted (Holt et al., 2005). When these gaps are bridged by external forces, then reaction-

diffusion models are insufficient because they fail to account for rare long-distance transmission

events (Holmes, 1993; Hastings et al., 2005). For many invasive species, humans are the primary

vector of transmission (Suarez et al., 2001; Jules et al., 2002; Buchan and Padilla, 1999). This

can lead to species' geographic ranges greatly exceeding their natural dispersal abilities (Holt et

al., 2005). For example, Higgins and Richardson (1999) estimate that a 0.01% of seeds moving

considerable distances (1 10 km) can increase the spread rate of a plant species by an order of

magnitude. Similarly, a reconstruction of the invasion of the Argentine ant (Linepithema humile)

over the last century reveals a maximum and fairly constant local dispersal rate, with annual

jump distances three times that rate (Suarez et al., 2001). Human-mediated jump dispersal is a

concern that must be addressed by invasive species modelers.

The combination of local and human-mediated jump dispersal may result in a lack of

agreement between linear models and empirical data (Hengeveld, 1994; Suarez, 2001).

Velocities estimated from linear spread models may appropriately provide an upper bound for

species spreading within a homogenous system (Holmes, 1993; Hastings et al., 2005), but will

likely underestimate spread when human transportation is involved and jump dispersal occurs.

Buchan and Padilla (1999) underestimated observed ZM spread rates by almost half due to a

failure to account for long-distance dispersal. Neubert and Caswell (2000) provide other

examples of underestimated spread rates due to human interaction. The probabilities associated

with jump dispersal may be very low and difficult to estimate. Despite these small probabilities,

they appear to be the driving factor for migration patterns for many species (Allen et al., 1991;









Lonsdale, 1993; Dwyer et al., 1998; Bossenbroek et al., 2001; Suarez et al., 2001; Hasting et al.,

2005), and should not be ignored.

Three studies of ZM dispersion specifically addressed the issue of human-mediated jump

dispersal. Bossenbroek et al. (2001) developed a ZM gravity model based on data on registered

recreational boats per county. A similar study used lake surface area as a proxy for relative lake

attractiveness in Indiana, Michigan, Wisconsin and Illinois (Kraft and Johnson, 2000). They

found that small lakes (those with less than 100 hectares) had lower rates of infestation. Kraft et

al. (2002) conducted spatial analysis using Ripley's K statistic to estimate the probability that

invaded lakes would be found within a particular distance of invaded lakes. ZM-invaded lakes in

the United States are found to be aggregated at less than 50 kilometers and segregated at greater

than 200 kilometers (Kraft et al., 2002). These findings confound simple diffusion models and

suggest that ZM dispersal is better defined by long-distance dispersion events and subsequent

spread within lakes or connected lake systems.

The likely human-mediated vectors of ZM transmission to lakes over long distances are

recreational boating, commercial boating (of ships not obeying existing ballast water procedure

laws), and intentional introduction (Carlton, 1993). Commercial vessels are required by federal

law to empty their ballast water prior to entering Lake Okeechobee. These efforts have been

effective and are credited with a large slowing of the rate of ZM spread. Here, we assume that

ZM spread by commercial vessels will not occur. Intentional introduction is not uncommon with

invasive species that are perceived to improve the productive or recreational value of land and

water bodies (e.g., water hyacinth, hydrilla, and M~elaleuca). ZM are known to clarify the water

column, so there is a possibility of intentional introduction. However, the probability of such an









introduction is unknown but we assume (and hope) that current educational efforts will prevent

an intentional introduction of ZM to Lake Okeechobee.

Recreational boating is the likely overland transmission vector for ZM, and has been

shown to be the primary transmission vector of unconnected water bodies in and around the

Great Lakes region (Johnson and Carlton, 1996; Buchan and Padilla, 1999; Bossenbroek et al.,

2001). For example, about 25% of recreational boat trailers leaving ZM infested lakes in

Michigan carry adult ZM (Ricciardi et al., 1994). Johnson and Carlton (1996) estimated that 7.8

& 9.2 of trailers at public boat ramps transported entangled vegetation with 2.7 & 2.0 mussels

attached on trailers leaving infested lakes. In addition, they estimated that 1/275 trailers

inspected entering uninfested lakes had ZM living on entangled macrophytes. ZM are commonly

found at 1000 adult mussels per meter of aquatic plant stem length. For the purposes of this

study, we assume that any transmission of ZM to Lake Okeechobee will be unintended, and by

recreational boaters.

Bioeconomic Model of the Zebra Mussel Threat to Lake Okeechobee

We use a Markov approach to forecast the likelihood of ZM infestation in Lake

Okeechobee and to estimate the long term expected public and private cost under alternative

policy scenarios.

Lake Okeechobee is not connected to any watershed known to be infested with zebra

mussels. The river system in the Florida Panhandle is the closest distance to ZM-invaded waters,

but the water chemistry in this system is inhospitable to ZM. Any ZM invasion to Florida is

likely to come in the form of the human-mediated movement of water (with larvae) or

submerged obj ects (with juvenile or adult mussels) over long distances. For ZM to reach Lake

Okeechobee, a dispersal barrier of nearly 1200 km must be jumped. The stress of overland

transport (Ricciardi et al., 1995) and the low numbers of mussels transported during a single










dispersal event (Johnson and Padilla, 1996) make the overland transmission of ZM a rare event,

but one that should not be ignored. Here, we use a stochastic dynamic simulation approach to

estimate the potential ZM invasion within a gravity model of jump dispersal based on boater

behavior.

We assume that new ZM introduction occurs when a boater travels to an infested lake and

then to Lake Okeechobee within a short enough time for ZM to survive the transmission. ZM

become established when the mussels reproduce and populate the lake to carrying capacity. At

carrying capacity ZM masses will be sufficiently large to cause both environmental and

economic damage. Thus, there are four distinct states regarding zebra mussel masses in the Lake

Okeechobee Waterway: not invaded (sl), arrived (s2), grOwing (s3), and carrying capacity (s4).

At present time t = 0, the state is "not invaded," thus


(1) S1







(2) St = At So

where A is a 4x4 matrix of transition probabilities

az, al2 "13 14

(3) = 21 "22 "23 24
a31 32 3334
a41 a42 a43 44

A is composed of aij, the probability of transitioning from state j to i in a single time period.









At any time t, St is



(4) S, =IU where 0


The expected future costs of mitigating the threat and infestation of zebra mussels is Ct

where Ct is a function of the state St and the choice of management methods X. For ZM we

consider two types of public management: (1) "prevention" which entails both screening and

education measures to reduce the probability of arrival, and monitoring to provide local water

uses with early warning information (xl = 1); and (2) "eradication" which involves use of a

molluscicide to effectively kill all ZM in the lake (x2 = 1). The annual cost of management Ct is

expressed as the product of management (X), zebra states in compact form (0), and unit cost of

management (q):

(5) Cr = X' Or &

Where X, 8t and q are



(6) X =L:X


Ts o
(7) 6, =



(8) q = Lcr


Direct use damages from zebra mussel infestation include losses to recreation uses and

increased maintenance costs due to ZM fouling. In equation (9), di, are annual ZM damages in

state 1












(9) D =
d,


Ecosystem service losses from zebra mussel infestation include diminished ecosystem

functions such as wildlife habitat and aquatic food supply. In equation (10), ei are annual ZM

ecosystem losses in state i



(10) E =



The management obj ective is to choose a management strategy bundle X to minimize Z,

the present value of total expected costs from the threat of ZM infestation:


(11) Z= (1+r) jC,(X,S,)+S;(D+E))


In equation (1 1), r is the annual discount rate and T is number of years in the planning time

horizon.

Empirical Approach

Parameters of the transition probability matrix (Eq. 3) are estimated using ZM arrival,

survival, and population dynamics studies in conjunction with Lake Okeechobee environmental

information and data on boating activity. For example, the probability of a ZM establishment

(al2) is a function of the number of boats arriving at the lake from ZM infested waters, ZM

survival during the trip and after introduction, and the length of time it takes for ZM to establish

a viable colony. Once established and growing, ZM survival, population dynamics, and control

efforts define the probabilities of the ZM population becoming endemic and causing high levels










of damages (a34), being established without causing significant harm (a33) Or being effectively

nullified (a32). Large economic and ecological damages occur when ZM populations reach

carrying capacity in the Lake in state 4. Determining the above parameter values, as well as

damage and cost estimates, is a difficult task that requires an exhaustive review of ZM

experiments and studies. In the following sections, we present and discuss the parameter

estimates and data derived from previous ZM research.

Arrival and Survival

ZM rate of arrival to Lake Okeechobee is assumed from recreational boating data. While

most recreational boating activity is local, a small percentage of freshwater boaters in the United

States travel very long distances within short periods of time (Buchan and Padilla, 1999). For

example, 26% of Wisconsin boaters visit a lake or river during any given 2-week period, 8.4%

trailer their boats more than 50km, 3.4% more than 106km, and 0.8% more than 261km.

General boating patterns and number of interstate fishing trips involving Lake Okeechobee

are unknown, but there are several fishing tournaments and circuits that draw participants from

the entire US, Canada, and even Japan to parts of Florida and from Florida to parts of the

Southeastern US with known ZM populations. We use fishing tournament data as a proxy for the

arrival rate of boats with ZM veligers or adult mussels. We surveyed angler competition rosters

from three national fishing tournaments to determine frequency of participation in tournaments

by anglers from states known to have ZM. According to a 2006 USGS map of ZM distribution

(USGS, 2007), ZM are found in 24 states. Of the 926 anglers participating in three national

tournaments on Lake Okeechobee from 2006 2007, 50.45% were from one of these states

(Carson, 2007; Eads, 2007). Results confirm Buchan and Padilla' s (1999) findings and indicate

that tournament participants travel long distances often within short periods of time. We assume









that 900 anglers per year fishing on Lake Okeechobee would have come into contact with ZM

prior to fishing on the lake.

We must also account for the environmental stresses on ZM during the long-distance trip,

as well as seasonal timing. Adult mussels are known to survive out of water for long periods of

time, on average 3 5 days under temperate summer conditions (Ricciardi et al., 1994; Griffiths

et al., 1991) and up to a few weeks in wet Hishing nets in Europe (Buchan and Padilla, 1999).

Large (21 28mm) mussels can easily survive >5 days out of water, and a small percentage of

large adult ZM (10%) can withstand 10 days exposure under ideal conditions (Ricciardi et al.,

1994). Live wells hold the greatest risk of ZM dispersal. Larvae are discovered in 83% of boat

live wells, with densities of 111 + 222 (1 sd) larvae/liter. A typical boat has a 38-L live well, for

an average transportation potential of 4,200 larvae (Johnson and Carlton, 1996).

The timing of dispersal can influence the spread rates on invasive species (van den Bosch

et al., 1992). Given environmental stressors, ZM may arrive at Lake Okeechobee several times

before a successful colonization occurs. This may explain why Johnson et al. (2001)

overestimated ZM colonization of Wisconsin lakes, as they assumed "suitable" lakes would be

suitable at all times of the year. Also, they ignored seasonal boating patterns. Boating in the

Great Lakes region occurs mostly from April to October, with the warm summer months seeing

most of the activity (Penaloza, 1991). June August averages between 1.25 1.69 million

boater-days, while October and April only averages 0.56 and 0.24 million boater-days,

respectively. Similar, but seasonally reversed, patterns of boating behavior may be found in

Florida, when hot and humid summer months create uncomfortable conditions for boaters and

reduce fish activity. Florida' s main fishing tournament season begins in February of each year

and ends in June (Eads, 2007). Mussels are actively settling or are active as larvae during about 5









months of the year. ZM generally have two spawning periods: 1) from April to July, and 2) in

August (Haag and Garton, 1992; Griebeler and Seitz, 2006; Jantz and Neumann, 1998). During

these times, free-swimming veligers are abundant in water that may be transported to Lake

Okeechobee. Only when both boaters and ZM are active do they pose a significant threat of

infestation to Lake Okeechobee.

We apply estimates of Lake Okeechobee habitat suitability to estimate ZM survival upon

arrival. Hayward and Estevez (1997) estimated habitat suitability indices (HSI) for zebra mussels

based on seven environmental variables: temperature, dissolved oxygen, pH, Secchi depth,

salinity, calcium, and sediment size. They conducted a meta-analysis on ZM life-cycle studies

and calculated HSI that ranged from 0.0 ("perfectly unsuitable") 1.0 (optimal) using 281,780

data records from the US Environmental Protection Agency's STORET database for 9,028 sites

in Florida and calculated composite HSI for each site. They estimated that 21% of the sites had

composite HSI over 0.5, and 3% of sites had HSI above 0.8. Composite HSI were calculated for

western Lake Okeechobee (very shallow, high aquatic plant density) and for the lake proper

(open water). The HSI were 0.91 and 0.83, respectively, making the lake highly suitable to ZM

(Hayward and Estevez, 1997).

Based on the above, we assume a 3.5% annual probability of ZM introduction and

establishment. This probability is in line with Bossenbroek et al. (2001), who estimated the

probability that a single boat would cause colonization in states surrounding the Great Lakes to

be between 0.0000118 0.0000411 per arrival by infested boat, or up to about 3.7% chance

when a lake experiences 900 arrivals by boats in contact with ZM-infested waters.

Reproduction and Spread

An appropriate estimate of the rate of spread within a water body depends on assumptions

about the population dynamics. The life history of ZM has been reviewed by several studies









(McMahon, 1991; Ackerman et al., 1994; Mackie and Schloesser, 1996; Nichols, 1996). ZM

development is very quick. Eggs develop into larvae for 1 day if fertilized (Sprung, 1987;

Borcherding, 1991; Ackerman et al., 1994). ZM need between 2.5 and 4 weeks to reach the

juvenile stage (Borcherding and de Ruyter van Stevenick, 1992; Griebeler and Seitz, 2006;

Sprung, 1987). Several studies estimate ZM survival rates for various life cycle stages (Stoeckel

et al., 2004; Orlova, 2002; Sprung, 1993; Thorp et al., 2002). During the ZM larvae (free-

swimming) stage, mortality is high (Orlova, 2002). Sprung (1993) estimates an egg to adult

mortality of 0.999913. Within about two months of spawning, juveniles will "settle" and attach

to substrates. Once settled, mussels quickly mature. Females produce between 40,000 and one

million eggs per year (USCACE, 2003).

Initial invasion studies indicate that ZM reach carrying capacity 2 3 years after detection

(Nalepa et al., 1995; Strayer et al., 1996; Burlakova, Karatayev, and Padilla, 2006; Borcherding

and Sturm, 2002; Lauer and Spacie, 2004). Average carrying capacity is about 10,000 ZM/m2

over a representative lake (Griebeler and Seitz, 2006). Once carrying capacity is reached, about

half of ZM populations will vary from 10 30% each year, while the other half periodically

crash and recover, typically in 4-year cycles (Ramcharan et al., 1992). Whether stable or cyclic,

ZM populations reproduce very quickly. The Hudson River experienced 4000/m2 by the end of

1992 after a first detection in May 1991 (Strayer et al., 1996). Akcakaya and Baker (1998) report

ZM density on the upper Mississippi River from first detection in December 1991 October

1995 in three locations. In December 1991, ZM were at less than .1/m2. The populations grew at

a steady exponential rate, reaching about 3000/m2 by October 1995. Beckett et al. (1997)

reported ZM densities on dam locks from 50,000 75,000 individuals per m2 within three years









of first detection in the Lower Mississippi River. For our calculations, we assume that ZM may

reach their carrying capacity within 2 years of introduction.

Direct Economic Costs and Damages

ZM is a known hazard that the state of Florida has taken steps to curb, including low-

power radio alerts warning travelers near the Florida border, and criminal fines--bringing ZM

into Florida is a 2nd degree misdemeanor with a $500 Eine and up to 60 days in jail (University of

Florida News, 1999). One federal agency--the US Army Corps of Engineers (USACE) is also

working to prevent the introduction of ZM. In 2003, they proposed a monitoring plan to detect

the introduction of zebra mussels in the Okeechobee Waterway (see Figure 2-2). The monitoring

plan would include (1) education materials (alert/identification cards, pamphlets, and posters)

distributed to boaters, homeowners, and businesses along the waterway to involve the

community in detecting zebra mussels when they first arrive, and to enlist boaters' help in

preventing ZM spread by cleaning boat live wells and trailers before entering the lake; (2)

underwater inspections conducted by divers in conjunction with existing inspections of manatee

screens and lock gates; and (3) substrate sampling to detect settlement of juvenile zebra mussels

four times per year. Dive inspections at each of the 5 maj or structures to survey for ZM would

cost approximately $25,000 per inspection. The USACE proposed inspection plan calls for

quarterly inspections, costing approximately $100,000/yr. Additional costs would be about

$700/inspection for USACE labor (Crossland, 2007). We further assume that educational efforts

would cost $50,000/yr, for a total monitoring plan cost of $152,800/yr. Early detection measures

afford surface water users time to retrofit their equipment pre-invasion, and prevention efforts

may be effective at reducing the probability of ZM introductions.

Unlike other invasive species commonly found in Florida, there may not be a feasible

method of controlling the spread of ZM once widely established within a lake system. Control











alternatives include potassium chloride, molluscicide carbon dioxide (to reduce dissolved

oxygen), chlorine, lower pH, increasing salinity, dewatering, and copper sulphate (VDGIF,

2007). Of these, only potassium and molluscicide are considered to have negligible effects on the

long run health of the aquatic environment. Both potassium and molluscicide have similar costs

per treatment ($2,028 versus $1,778 per million gallons, respectively), but potassium levels will

provide long-run protection against ZM whereas molluscicide applications do not.


..* keechoa Stuart








,.... ,~-.. W s-am ea h



Fort Mnyers ,,,
aus~* Ins. lexrlc* 1ln~sOkeechobee Watenrway


Figure 2-2. Lake Okeechobee wateway

There is ony oneknowninsac of ZM eradiation The Virgini~a Dpatmn oGm
and Inland Fisheries successf~ul~nlyMI eradctdZ n ilro uar sn ig eeso
potassium chloride (98 115 parts per Smillin)oesvrawekatactof$600





Februry, 2006 at aone kontraionsa of 100 pater million. This Vriis twiewartisexpete to kill







95% of the ZM, but below what would create serious human health or environmental concerns. It

is estimated that the potassium levels now found in the quarry will not significantly impact fish










or human health, and will protect the quarry from further ZM infestation for approximately 33

years .

Millbrook Quarry is a 12-acre, 93-ft deep quarry (approximately 180 million gallons). By

contrast, Lake Okeechobee is a 448,000 acre lake with an average depth of 9 feet (approximately

1.31 trillion gallons). Lake Okeechobee is 3,613 times larger (in water volume) than Millbrook

Quarry. A potassium treatment on Lake Okeechobee similar to Millbrook Quarry would require

628.6 million gallons of potassium at a cost of $1.32 billion based on Millbrook Quarry

treatment levels and costs.

Recall that almost 95% of surface water withdrawals from Lake Okeechobee are for

agricultural irrigation. ZM on Lake Okeechobee would clog surface water intake pipes. Surface

water impacts of ZM are more likely to be in form of cost increases rather than lost revenue or

production losses. Only 6.3% of respondents to a 1996 study of Great Lakes surface water users

reported production losses (Hushak, 1996b), and electric utilities and industry report a 0.0045

percent output loss (Hushak and Deng, 1997). Therefore, we focus on the potential increases in

maintenance costs rather than calculating production losses to agricultural surface water users.

Several studies report the impacts of ZM on surface water users (O'Neill, 1996; Deng,

1996; Park and Hushak, 1996; Phillips et al., 2005). O'Neill (1996) reports average costs per

water use facility for a wide range of water users--industrial, public supply, power generation,

and others. Deng (1996) provides estimates of variable ZM maintenance and control costs as a

function of gallons of water used for five ZM control technologies for private and public water

utilities, and other industrial users. Park and Hushak (1999) surveyed large surface water users

from 1994 1995 regarding their annual ZM monitoring, control and research costs. Utility and

industry users were classified as small (0 10 million gallons/day), medium (11 300 mgd), or









large (>300 mgd) water users. The average control and monitoring costs to industry facilities

were $10,000, $92,000, and $439,000 for small, medium, and large water users, respectively.

Hushak (1996b) estimates total ZM expenditures average $0.43 million/facility over 5 years.

Small facilities (<5 million gallons/day) have expected costs <$20,000 per year; large facilities

(>300 million gallons/day) can expect ZM to cost them $3 50,000/year (Hushak, 1996b). ZM-

impacted industries in the US reported mean ZM-related expenditures of $167,030 per facility

for 60.3 mgd average capacity. Mean expenditures on prevention were $92,833, on planning

were $37,190 per facility, on monitoring were $14,393, on retrofit were $48,200, and on

mechanical or other control technologies were $6,406 (O'Neill, 1997). Currently, the average

maintenance cost for annual cleaning of water intake screens costs $6,240, but would increase 7-

fold following ZM infestation (O'Neill). Chemical treatment of zebra mussels by industrial

facilities has an average cost of $1.13 per million gallons of water treated for the least cost

alternative-chlorine (Deng, 1996). This method has up to 95% effectiveness, but only relatively

large surface water users are likely to employ this due to the technical challenges. Non-industrial

surface water users will likely opt for physical and thermal treatments, which cost $4.90/mgd.

Using variable and percentage increase in total costs estimates from O'Neill (1996), Deng

(1996), Park and Hushak (1996a, 1996b), Hushak (1999), Hushak and Deng (1997), and Phillips

(2005), we employ a cost-transfer methodology to estimate the potential impact of a ZM

infestation to Lake Okeechobee surface water users (Rosenberger and Loomis, 2001). According

to the most recent available data, surface water withdrawals from the lake average 1541.34

million gallons per day (USGS, 2006). We apply an average cost of $4.90 per million gallons for

physical and thermal treatments according to Deng (1996) to arrive at an estimated average









maintenance cost increase of $2.76 million per year for agricultural surface water users following

a full ZM infestation in Lake Okeechobee.

Phillips (2005) reports the estimated ZM prevention-related costs on hydropower facilities.

Application of anti-fouling paint, including labor, was estimated to cost hydropower facilities

$25.56 per square foot in year 2005 dollars. It is not known how long the paint will remain

effective against ZM before needing to be reapplied, but we assume that the paint will remain

effective for 10 years. Water use and permit records are maintained by the South Florida Water

Management District. We obtained records of the 2003 permit holders, which included permits

for 504 surface water intake pipes. We conducted a telephone survey (Appendix A) of these

users from May August, 2006 and achieved a 7.1% response rate, largely due to stale contact

information. The survey included questions regarding average annual maintenance costs, surface

water use, location, presence of invasive aquatic plants (which are likely to impact maintenance

costs), average daily withdrawal, frequency of maintenance (times per year), whether the

maintenance was contracted out or performed in-house, type of maintenance (physical, chemical,

or other removal method), the location of the facility (county), and questions regarding their

knowledge of ZM. Mean annual maintenance costs are reported to be $8,936 (sd = $3,913) and

they have average water intake pipe diameter and length of 1.91ft (sd = 0.35) and 50.14 ft (sd =

27.23), respectively. This provides a mean intake pipe surface area of 300.58 ft. Assuming 504

intake pipes for the lake, we estimate a total cost for anti-fouling paint of $3.87 million.

Ecological and Recreational Damages

In addition to the impacts on surface water users, a ZM infestation may negatively impact

recreation and lake ecology. Following a ZM infestation, lake ecology will change dramatically.

ZM can reduce plankton populations by 85% (USACE, 1995), increase water clarity, double

phosphate levels, and significantly reduce native mussel populations (Caraco et al., 1997;









Strayer, 1999). In the Upper Mississippi River, native mussel populations dropped with the

introduction of ZM; declines in native mussels included two federally listed species (Whitney et

al., 1995). ZM in the Hudson River were >70% of the zoobenthic biomass, filtering the

equivalent of the entire water column per day (Strayer et al., 1996). Adult ZM can filter up to 1

gallon of water per mussel/day (USGS, 2000). ZM can remove up to 62% of a lake's primary

littoral production (Ramcharan et al., 1992), fundamentally altering the aquatic food chain

(Caraco et al., 1997). Stoeckmann and Garton (1997) estimate that ZM populations in the range

of 10,000 to 50,000 mussels/m2 COnSume 10% to 50% of summertime primary lake production.

Studies of the effects of ZM on fishing are mixed. On one hand, the number of fishing trips

was seen to decline dramatically in the Great Lakes following the ZM. In the Great Lakes region,

78.5% of respondents who said that ZM affected the amount of time spent on Lake Erie reported

spending less time on the lake, with a decline in fishing trips from 11.2 to 6.3 from 1990 1992

(Hushak, 1996a). On the other hand, field studies of fish stocks in the Hudson and Great Lakes

regions report a significant decline in open water fish species, but a significant increase in littoral

fish species, which are responsible for all of the recorded recreational fishing activity on Lake

Okeechobee. Strayer et al. (2004) examine 26 years of data on fish populations on the Hudson

River to ZM effects on littoral and open water fish species. The median decline in open water

fish species was 28%, while littoral species experienced a median increase of 97% (Strayer et al.,

2004). Many of these species were of recreational importance. Open water species of

recreational importance included herring, shad, striped bass, and perch, and littoral species

included carp, shiner, bluegill, smallmouth bass, largemouth bass and darters. Overall

biodiversity and fish biomass fell after ZM arrival (Strayer et al., 2004). According to

unpublished fishing effort data from the Florida Fish and Wildlife Conservation Commission,









there are four recreationally significant Hish groups on the lake--black crappie, catfish,

largemouth bass, and pan fish. These species are all littoral zone species.

For some lake systems, the reduction in phytoplankton accompanying a ZM introduction

may increase also mitigate the impacts of eutrophication (Ulanowicz and Tuttle, 1992).

We must also consider the potential for other invasive species to flourish following a ZM

infestation, and the negative impacts that would have on fishing effort. Increased water

transparency can cause the increased abundance of submersed aquatic plants, as was the case in

Lake Huron (Skubinna et al., 1995). This may exacerbate invasive aquatic plant problems on

Lake Okeechobee. Snail populations may also significantly increase following a ZM introduction

(Strayer, 1999), and may include the invasive apple snail that is threatening Florida waters.

Given the above, we assume an increase in fishing effort of 10% following a ZM infestation. The

average total hours spent fishing on Lake Okeechobee from 1983 2002 was 4,316 hours/day

(FFWCC, 2003). Assuming that effort has a direct and linear relationship to available fish

species, we expect an increase in fishing effort by 431.6 hours/day. According to the Florida Fish

and Wildlife Conservation Commission, freshwater anglers on Florida lakes spent an average of

$20.65 in 2002 dollars (FFWCC, 2003). This equates to a $3.25 million gain per year.

There is also the potential for fundamental changes to aquatic plant life that would hamper

the functioning of wetlands. Lake Okeechobee has 29,000 acres of Audubon Society wetlands,

and a further 31,000 are assumed from visual inspection of aerial maps. Costanza et al. (2003)

estimate a per hectare value of lake services of $8,498. Of this, $439 per hectare was for wetland

services. We assume that 60,000 acres of wetlands connected to the lake are vulnerable to injury

from ZM infestation, and a 2% inflation rate for the Costanza et al. value.









Effectiveness of Management Methods

There are two methods xl and x2 that may be employed singly or j ointly to mitigate ZM-

related damages. Investment in prevention is given by xl = 1 which includes efforts to detect and

prevent the arrival of ZM and provide water users early warning of ZM establishment in the lake.

These efforts may include brochures, posters and pamphlets alerting the public to the ZM threat,

and boating regulations requiring that hulls be free of mussels and macrophytes, and live wells

be empty prior to entering Lake Okeechobee. It also includes the USACE monitoring program

that would provide early warning to surface water users at a cost of $152,800 per year. We

assume that the USACE monitoring program will reduce annual probability of arrival by 75%, or

from 3.5% to 0.875%. Sensitivity analyses of this parameter are included in the results section.

Investment in ZM eradication is given by x2 = 1. ZM were effectively eradicated from

Millbrook Quarry, VA using potassium chloride. The same protocol for Lake Okeechobee would

cost $1.32 billion chemicals and labor costs and would provide an additional 30 years of

protection from future introductions.

A cost mitigating measure is the application of anti-fouling paint on the interior of surface

water intake pipes which would effectively reduce the cost of keeping pipes free of fouling

organisms including ZM. Paint and labor costs are $25.56 per square foot of pipe and each

application is good for 10 years. We assume water users would apply anti-fouling paint after

they detect ZM which would occur post-establishment. With an early warning system in place,

water users would apply antifouling paint before ZM is established thereby avoiding

maintenance expenditure due to ZM clogged pipes. If ZM are eradicated, antifouling paint

application becomes unnecessary.

We assume that once ZM are introduced into Florida waters, the mussels would become

"established" i.e., they begin reproducing in one year. After two years the mussel population









would reach the carrying capacity of the lake. If an early monitoring program were in place (xl),

then surface water users would have sufficient time to prepare. Without early warning, initial ZM

damages will be 10% higher due to a lag in x3 application similar to the findings of O'Neill

(1997), Deng (1996) and others. In the Great Lakes region, it took about 6 years following ZM

introduction for costs to stabilize, largely due to initial ZM spread rates and late adoption of

retrofitting. Small water users (0 10 million gallons per day) did not begin retrofitting water

intake pipes and other equipment until 3 years after ZM were detected, largely due to a lack of

appreciation for the potential impacts of the mussels. This lag in uptake of antifouling measures

caused ZM-related costs to jump from $2,000 per facility to about $15,000 per facility from the

3rd to 4th years following ZM introduction. Within 2 years after retrofitting began, control costs

fell by over 73% (O'Neill, 1997). We assume ZM-related maintenance costs will be $2.76

million with antifouling paint applied before ZM reach carrying capacity. Without the early

warning system, the lag in application of anti-fouling paint will increase maintenance costs by

27.75%, or $3.37 million. We also assume that once ZM have arrived, monitoring and

prevention costs will fall to zero. A summary of parameter values used in the ZM model are

reported in Table 2-2.

Policy Scenarios and Results

At present, there is no State plan in place to monitor, prevent, or eradicate ZM in Florida.

Thus, to examine the widest range of plausible options we constructed the following four

scenarios. Policy scenario I is the current policy being pursued by the state--do nothing with

respect to ZM. Policy II provides state funding for labor and technology to prevent introduction

of ZM to Lake Okeechobee and to monitor the lake and its entry points to detect the presence of

live ZM. Policy III foregoes prevention with a plan to eradicate ZM as soon as it is detected.









Table 2-2. Zebra mussel model parameter values.
Symbol Definition Value
all Annual probability of ZM not arriving to Lake Okeechobee 0.965

Annual probability of ZM arrival/year without xl (arrival
a21 prevention and early warning) 0.035

Annual probability of ZM moving from state 4 (carrying capacity)
a21 to state 1 (not invaded) with eradication 1

Annual probability of ZM moving from state 2 (arrived) to state 3
a32 (grOwing) without eradication 1

Annual probability of ZM moving from state 3 (growing) to state 4
a43 (carrying capacity) without eradication 1

a44 Annual probability of ZM staying in state 4 without eradication 1

Other a, Annual probability of ZM moving from state j to state i 0

cl Annual cost of arrival prevention and early warning $152,800

c2 Total cost of eradication $1.32 billion

c3 Total private mitigation (anti-fouling paint) costs $3.87 million

d2 Annual ZM-related surface water use maintenance costs in state 2 0

d3 Annual ZM-related surface water use maintenance costs in state 3 0

d4 Annual ZM-related surface water use maintenance costs in state 4 $2.76 million

e2 Annual per-hectare ZM-related ecological services losses in state 2 0

e3 Annual per-hectare ZM-related ecological services losses in state 3 0

e4 Annual per-hectare ZM-related ecological services losses in state 4 $439
Source: USGS (2006)

Since no monitoring is in place, detection is most likely to occur after ZM have become

established. Policy IV invests in arrival prevention measures, early warning and eradication

measures if necessary. Budgetary and private mitigation costs for the four policy scenarios are

reported in Table 2-3.










Table 2-3. Present value estimates of zebra mussel policy scenarios (20 year, 2006 $ million)

Public policy action Private action
Monitor, Eradicate
prevent upon Budgetary cost Long run
Policy arrival detection of policy mitigation Mitigation costs
I no no 0.00 yes 10.83

II yes no 2.33 yes 3.02
III no yes 872.90 no 0.41

IV yes yes 696.36 no 0.11


We estimate cumulative probabilities of ZM being in each of the four states (St) and

employ the parameter estimates (Table 2-2) in equation 11 to arrive at the expected present value

of ZM infestation in Lake Okeechobee under the four policy scenarios. We assume a 2%

discount rate.

The state expenditures vary widely by policy. If the state only pursues arrival prevention

and an early warning system, then policy costs are $2.33 million, compared to a very costly

$872.90 million for an "only eradicate" policy, or $696.36 million for a combination of the two.

ZM-related maintenance costs borne by surface water users are $10.83 when the state employs

long term management only, compared to $3.02 million for the arrival prevention/early warning

system is in place, $0.41 million when only eradication is used, and $0. 11 when both are used

simultaneously.

Policy costs, maintenance costs, recreation losses, and ecosystem gains are reported in

Table 2-4 as a comparison to Policy I--do nothing. Introduction of ZM to the lake will improve

fishing recreation by $1.09 million, compared with $0.31 for the arrival prevention/early warning

system, $0.25 for only eradication, and $0.22 when both are pursued. ZM prevention and control

policies will invariably reduce fishing recreation. The losses range from $0.78 to $0.87 million in










present value over 20 years. These gains are very small when compared to the increases in

maintenance costs or ecosystem impacts.

Table 2-4. Simulation results compared to Policy I (Do nothing) (present value, 2006 $ million).
II III IV
Monitor, prevent
arrival, provide early Eradicate upon Prevention and
warning of arrival detection eradication
x = 1, x2=0 x1=0, x2=l X1=l, X2 1

Policy Costs 2.33 872.9 696.36

Reduction in
Maintenance Costs 7.81 10.42 10.72

Recreation Impacts -0.78 -0.84 -0.87

Ecosystem Impacts 243.02 259.96 271.54

Maintenance and
Recreation Impacts 7.03 9.58 9.85

Maintenance,
Recreation and
Ecosystem Impacts 250.05 269.54 281.39

Policy, Maintenance
and Recreation Impacts 4.7 -863.32 -686.51

All Values 247.71 -603.36 -414.98


Wetland losses and associated damages are $339.61 million when the state does nothing. If

the state employs ZM policies, it can prevent significant losses to ecosystem services. When the

state invests in arrival prevention and early warning, the net gains to ecosystem services are

$243.02 million. They are even higher when the policy includes eradication. When only

eradication is used, ecosystem service gains are $259.96, and when both strategies are used

jointly, there are gains of $271.54 million.

Some policy makers may question the validity of including ecosystem service values

because the values are too indirect. When only considering direct economic impacts--recreation,









and maintenance costs--the returns to ZM policies are all positive. They are $7.03 million for

arrival prevention and early warning, $9.58 million for eradication, and $9.85 when both are

used together. When ecosystem impacts are included, the returns to ZM control and prevention

strategies are very large. Net direct impacts are $250.05 million, $269.54, and $281.39 for arrival

prevention and early warning, eradication, and a combination of the two, respectively.

The impacts of the ZM policies change dramatically when considering the budgetary

demands of the ZM policies. When only considering direct impacts and budgetary costs, Policy

II (arrival prevention and early warning) provides the only positive return- $4.7 million.

Eradication is very expensive, with Policy III (eradication) having total direct impacts of $-

863.32 million, and Policy IV (combination of Policies II and III) with net direct impacts of $-

686.51. The relatively small price tag associated with Policy II is very effective at reducing the

present value costs of eradication.

If ecosystem service values are included, the results are still not supportive of eradication.

When considering the policy, maintenance, recreation and ecosystem impacts, Policy II is still

the clear favorite, with net benefits of $247.71 million. By comparison, Policy III (eradication)

and Policy IV (arrival prevention, early warning, and eradication) yield losses of $603.26 and

$414.98 when compared with doing nothing.

Given our assumptions, the overall cost and damage-minimizing choice is to invest in

Policy II, arrival prevention and early warning. The total net costs and damages of this policy are

70.91% less than Policy I (do nothing), 89.34% less than Policy III (eradication), and 86.71%

lower than Policy IV (arrival prevention, early warning, and eradication). Investing in prevention

and early detection also place a smaller budgetary burden on the state--less than 0.03% of the

budgetary costs of the other two policies. This is due to the very high cost of eradication, and the











large gains realized by delaying the arrival of ZM. A relatively small amount of spending to

prevent the arrival of ZM has a large impact on reducing the probability that ZM will infest the

lake (See Figure 2-3). Without monitoring and prevention (xl), there is a 45.42% probability of

ZM fully infesting Lake Okeechobee by 2026. With monitoring and prevention, this probability

is greatly reduced even if eradication is not attempted.



O 5

045


S035 oiySeai
03 Policy Scenario II

E 025 Policy Scenario Ill

0, Policy Scenario IV


S015


0 05


0 2 4 6 8 10 12 14 16 18 20
Year

Figure 2-3. Zebra mussel policy impacts on cumulative probability of infestation.

From the standpoint of both surface water users and environmental protection groups,

Policy IV--the combination of arrival prevention, early warning, and eradication--is preferred.

The ZM-related maintenance cost for this policy is only 98.99% lower than Policy I, as

compared to 72.22% lower than Policy II, and 96.22% lower when only eradication is used

(Policy III). Ecological damages to the lake are also lowest when a combination of policies is

used, but by much closer margins than with surface water maintenance costs. Ecosystem

damages are also much lower under Policy IV as compared with Policy I. Policy II, III and IV

provide 71.55%, 76.54%, and 79.99% less ecosystem services losses than Policy I.









Recreational anglers would prefer that the state not prevent or eradicate ZM. Policy I (do

nothing) provides 495.45% more fishing-related benefits than the combination of management

tools which is most effective at minimizing ecological and maintenance costs. Arrival prevention

and early warning, and eradication respectively provide 140.91% and 1 13.64% of the fishing-

related benefits of the combination of management practices.

We conducted sensitivity tests on key parameters that are expected to have large impacts

on policy outcomes--arrival rate, fishing-related benefits, ecosystem valuation, and eradication

costs. The results are reported in Appendix B. Assuming that the ZM arrival rate is half of our

original assumptions, the total costs and damages of a ZM infestation are still minimized by

choosing arrival prevention and early warning. Costs and damages under this policy are now

$53.18 million instead of $101.64 million when arrival was assumed to be 3.5% without policy

intervention. Similar savings are found for maintenance costs, but ecosystem losses and fishing

gains are reduced to a point where results from Policy I (arrival prevention and early warning)

and Policy IV (arrival prevention, early warning, and eradication) are nearly equivalent; the

original policy rankings still stand. We then simulated a loss of 10% instead of a gain of 10% in

fishing benefits following a ZM infestation. This did not change the original policy rankings. We

also estimated what the per-acre ecosystem damage and the eradication costs would have to be to

make policy makers ambivalent between preventing and eradicating ZM. If ecosystem values

were 51.25 times higher or if eradication costs were reduced by 97.5% then policymakers would

be ambivalent between prevention and eradication. This provides support for our original

ranking of the policies.

These results set up an interesting dilemma for the state. Surface water users and

environmental groups are expected to prefer a very costly combination of ZM management










methods, while fishermen may prefer to have no state-funded efforts to prevent or mitigate ZM

costs. The social planner, however, would clearly prefer to invest only in arrival prevention and

early warning, but legislators may instead prefer to do nothing as that response puts the least

budgetary burden on the state. The only Policy that may be excluded by all groups is the decision

to only eradicate. Depending on the relative influence that budgetary pressures and interest

groups have on legislators, the state would choose to do nothing, only invest in arrival prevention

and early warning, or provide a combination of the prevention and detection measures as well as

eradication.

Our estimates of the economic effects of a ZM infestation suggest that pre-planning is

essential to reducing the overall impacts of the mussels. Despite the very low probabilities of ZM

establishment on the lake, the expected costs and damages of such an infestation are very high--

up to $349.34 million over 20 years if nothing is done. Eradication of ZM on the lake would be

extremely expensive, and perhaps more than the state of Florida would want to spend. This

would not be uncommon, as there is only one example of ZM eradication, and that was in a very

small water body in Virginia of very high recreational significance. Proactive measures, such as

an early warning system and arrival prevention efforts can significantly reduce ecosystem

damages, maintenance costs, and state expenditures on a policy response to the ZM problem.

Compared with the other policy options, the policy of arrival prevention and early warning is

3.43 to 9.37 times more cost effective than other available policy options.

Conclusion

The Zebra mussel (Dreissena polymorpha) is a serious threat to recreation, surface water

use, and ecosystem services in lakes and rivers in the United States. The zebra mussel is

expected to reach Florida waters, but state and federal agencies currently have no program to

deal with zebra mussel arrival. The United States Army Corps of Engineers have proposed an










arrival prevention and education program for recreational boaters, as well as a zebra mussel early

monitoring and warning system, but these have not been funded. Costly eradication of the mussel

post-establishment is also an option. Here, we estimate and compare the impacts of zebra mussel

policies on recreation, surface water use, and ecosystem services on Florida' s largest lake--Lake

Okeechobee.

We construct a bioeconomic model to simulate the expected impacts of the zebra mussel

(ZM) on the lake. We first estimate ZM introduction into the lake based on assumed

transportation vectors (recreational boating), habitat suitability from a previous study (Hayward

and Estevez, 1997), and effectiveness of ZM mitigation and prevention methods. We surveyed

Lake Okeechobee surface water users and applied our results to existing estimates of changes in

ZM-related maintenance costs for surface water users. We include assumed lake-related

ecological and recreational values to construct an estimate of the total economic impacts with

respect to a ZM infestation. We then apply state probabilities (in a stochastic dynamic simulation

format) to arrive at a long-run economic impact analysis of ZM in Lake Okeechobee. We report

present value results of the expected economic impacts over 20 years, including costs and

damages to surface water use, recreational anglers, and users of ecosystem services, as well as

budgetary costs (Table 2-4).

Our model of the economic impacts of zebra mussels on Lake Okeechobee, Florida offers

some insight into the cost-effective management of this and other invasive species threats. A

zebra mussel infestation in Lake Okeechobee has expected net economic costs and damages of

$349.34 million over 20 years if nothing is done. Recommended best practices for managing

invasive species threats are prevention, control, and eradication (where economically feasible)

(Hulme, 2006). In aquatic systems, eradication and control is particularly difficult (Floerl and










Inglis, 2005). A comparison of ZM policy scenarios reveals that zebra mussel prevention is

more desirable than post-invasion efforts given the high cost of eradication. For example, the

present value policy costs of eradication would be $872.9 million over 20 years, but with even

modest funding on arrival prevention and early warning ($2.33 million), significant savings are

achieved. With arrival prevention, early warning and eradication combined, the present value

policy costs fall to $696.36 million.

In addition to budgetary costs of a ZM policy, policy makers must balance the expected

impacts on surface water use, recreation, and damages to freshwater ecosystems. An active ZM

policy of arrival prevention and early warning, eradication, or a combination of the two would

provide significant reductions in agricultural surface water users' maintenance costs ($7.81

million $10.72 million) and very high savings to ecosystem services ($243.02 million -

$271.54 million). Zebra mussels are expected to benefit fishing on the lake, but angler-related

gains from ZM are not expected to be large compared to other impacts. With active ZM policies,

fishing benefits would fall by $0.78 million $0.84 million over 20 years. Ecosystem services

are difficult to measure, and some policy makers may be wary of using such values. Without

considering ecosystem services, the clear cost-minimizing ZM policy is arrival prevention and

early warning, which yields a net gain of $4.7 million. By comparison, large losses are

associated with policies that include eradication ($686.51 million, $863.32 million). The

inclusion of ecosystem services does not impact the relative performance of ZM policies. With

arrival prevention and early warning, net gains are much larger ($247.71 million). Policies that

include eradication still yield large losses ($414.98 million, $603.36 million).

The results from this study indicate that investment in arrival prevention is much more cost

effective than attempting to control or eradicate invasive species post-arrival. As with many










invasive species, there is a great deal about ZM biology, transmission, and other important

variables that are unknown. Unfortunately, ZM and other invasive species pose serious risks to

agriculture and natural resources, and despite the unknowns, policy makers will be called upon to

allocate scare public resources in defense of natural and agricultural systems. Studies such as this

one, though based on several assumptions about ZM that have not yet been tested, provide

important information to the discourse on invasive species management.









CHAPTER 3
BIOECONOMIC MODEL OF INVASIVE AQUATIC PLANTS HYDRELLA VERTICILLATA
(HYDRELLA), EICHHORNIA CRASSIPES (WATER HYACINTH), AND PISTIA
STRATIOTES (WATER LETTUCE) FOR FLORIDA LAKES

Introduction

Invasive aquatic plants can have significant negative impacts on water-based recreation,

such as fishing, wildlife viewing, and boating. Despite the high potential impacts, little economic

research has attempted to quantify these impacts across spatial scales that would be useful for

invasive species management decisions. The little economic research that has been conducted on

aquatic invasive species usually focuses on a single lake, or is too abstract to be applied. This is

the case because often very little data are available for larger scale studies. This study uses

unpublished data on plant coverage, angler effort, and lake physiographic and amenities to

estimate the impact of plant coverage on Hishing activity on 13 Florida lakes. Using the

bioeconomic model of invasive aquatic plants, I then simulate the single-year costs and benefits

of six policy scenarios for aquatic plant control. I estimate that the total economic value of the

13 lakes over $64.78 million, and lapses in invasive plant control may jeopardize that value.

These results suggest that the optimal management policy is maintenance control with respect to

hydrilla, water hyacinth and water lettuce.

Invasive Species Background

Invasive species in the United States pose serious ecological and economic problems

(Evans, 2003). An invasive species is defined as a non-native species whose introduction "causes

or is likely to cause economic or environmental harm or harm to human health" (Executive

Order 13112, 1999). Invasive species are a particular problem for the tropical and subtropical

areas of Florida, where physiographic, climatic and geographic characteristics make it relatively

easy for non-indigenous species to establish (Simberloff, 1997; Fox [personal communication],










2007). Florida has a high rate of non-native species introduction, with the Port of Miami

receiving about 85% of non-native plant shipments each year (OTA, 1993). For example, the

entire United States has about 50,000 established non-native plant and animal species, with

Florida alone having over 25,000 as exotic ornamentals (Pimentel, 2003); over 1,300 have

established in natural areas, and 124 of these are destructive to natural areas (FLEPPC, 2006). By

comparison, Florida only has 2,500 native plant species, and the US has 18,000 native species.

Invasive species are a growing economic concern. Today, there are an estimated 5,000 to

6,000 invasive species in the United States (Pimentel, 2003; Burnham, 2004), and invasive plants

are invading about 700,000 hectares/year of natural areas in the US (Pimentel et al., 1999).

Economic damages from invasive species are estimated to be $137 billion/year excluding

ecosystem impacts (Pimentel et al., 1999). When considering the well-documented impacts of

certain invasive species, such as damages caused by hydrilla verticillata in Florida, or the zebra

mussel in the Great Lakes, it is clear that invasive species can have dire economic consequences.

With continuing increases in both global trade and the domestic and international

migration of people to Florida, the rate of arrival of non-native species is rising. Invasive species

management is fast becoming a high priority for the protection of Florida' s agricultural and

natural systems (Schardt [personal communication], 2007). Yet, despite the large economic and

ecosystem harms associated with invasive species, there exists little empirical analysis of

invasive species problems in a way that would help policy makers or resource managers (Schardt

[personal communication], 2007). There are very few invasive species studies in the economics

literature, and most of those are distinctly theoretical and too technical or abstract for use by

policy makers or resource managers. Few empirical studies have evaluated the impact of

invasive species, and very few have examined their impact on recreation (Singh et al., 1984;









Milon et al., 1986; Milon and Joyce, 1987; Colle et al., 1987; Milon and Welsh, 1989; Newroth

and Maxnut, 1993; Henderson, 1995; Bell et al., 1998, et al.). The issue of invasive species is

one that much more attention (and perhaps budgetary expenditures) will likely be focused on in

the near future.

Hydrilla, Water Hyacinth, and Water Lettuce Past Management

The present level of expenditures devoted to the management of a handful of invasive plant

species is inadequate, even for those few being managed. There are 18 invasive aquatic plant

species in Florida waters, but very few of these are actively managed. Due to their extremely

high propagation and growth rates, the Florida Department of Environmental Protection (FDEP)

has targeted Hydrilla verticillata (hydrilla), Eichhornia cra~ssipes (water hyacinth) and Pistia

stratiotes (water lettuce) as among its top management priorities. These plant pests have been the

focus of management efforts in Florida for decades; however, additional research is needed to

assess economically efficient strategies for managing them.

Hydrilla is a submerged aquatic plant introduced as an aquarium ornamental in the 1950s,

and first detected in Florida water bodies in 1960 (University of Florida, 2001; Blackburn et al.,

1969). Its rapid growth rate and suitability to Florida waters allowed it to spread rapidly

throughout the state. By the early 1970s, hydrilla could be found in all maj or drainage basins in

Florida. By 1995, hydrilla spread to over 40,000 hectares on 43% of the public lakes in the state

(Langeland, 1996).

Hydrilla eradication efforts have not been successful. The high growth rates and other

unique characteristics of hydrilla and other invasive plants make them virtually impossible to

eradicate. The Bureau of Invasive Plant Management' s current official policy on invasive plants

is to achieve "maintenance control," defined as keeping the invasive plant population at very low

levels for the foreseeable future. In 2002, 175 Florida public water bodies were infested with









hydrilla, with 1/3 having more than 10 acres. Hydrilla is under maintenance control in 96% of

Florida waters, but most of the hydrilla budget is spent on about 25 lakes (FDEP, 2004). Total

spending on hydrilla was $17.3 million in fiscal year 2001-02 (FDEP, 2004).

Water hyacinth and water lettuce are floating aquatic plants. Water hyacinth, a native to

South America, was introduced to Florida as an ornamental pond plant in 1885. Its rapid

reproduction led to it being discarded into the St. John's River, and it spread quickly to

neighboring water bodies (Schmitz et al., 1988). Within a few years, it was credited with

blocking boat traffic on the St. John's River (Schmitz et al.). Water lettuce has been in Florida

much longer, perhaps since the 16th century, and is also believed to be a native of South America

(Schmitz et al.). In 2002, water hyacinth and/or water lettuce were found in 244 public waters

inventoried (57%), and were considered to be under maintenance control in 95% of Florida' s

waters (FDEP, 2004). Of these, 71 had over 10 acres of floating plants (37 with water hyacinth,

and 34 with water lettuce) (FDEP, 2004). Total state control spending on floating plants in fiscal

year 2001-02 was $3.1 million (FDEP, 2004).

The problems with hydrilla, water hyacinth and water lettuce are multidimensional--

ecological, economic, public and private. Ecological impacts include displacing native flora

(both submersed and floating), altering habitat of native fauna, and disrupting ecosystem

processes (Haller and Sutton, 1975). These invasive plants grow in thick monoculture mats

where over half of the plant biomass is found in the upper 0.5m of the water column (Haller and

Sutton, 1975). These mats block sunlight to and out-compete native plants (Hofstra, Clayton,

Green, et al., 1999; Sutton, 1986), especially in the increasingly nutrient-rich lakes and rivers of

Florida. Hydrilla may also outcompete other submerged invasive aquatic plants, such as Elodea

densa and Ceratophyllum demersum (De Kozlowski, 1991; Chambers et al., 1993). Dense









monocultures can contribute to reduced fish populations, and when large mats of plants

decompose, the reduced dissolved oxygen levels in a lake can cause massive fish kills (Bowes et

al., 1979).

These invasive aquatic plants also harm non-aquatic species by covering nesting and egg

laying areas, and blocking access to water, shelter, and food sources (FDEP, 2004). Endangered

species are impacted by invasives--about 400/958 endangered or threatened species are "at risk"

primarily due to invasive species competition or predation (Wilcove et al., 1998).

Economic impacts follow close behind ecosystem losses. Hydrilla, water hyacinth and

water lettuce can hinder boating, swimming, and fishing activities in lakes and rivers, and reduce

the aesthetic value of natural areas (Milon and Joynce, 1987; Colle, Shireman, Haller, et al.,

1987). The reduction of recreational benefits derived from public waterways (and the cost of

managing the weeds) highlights the public loss from invasive aquatic plants. Florida's 454 public

lakes and rivers comprise 1.27 million acres (FDEP, 2004). In total, Florida has 1.5 million acres

of lakes and rivers, with 7,700 lakes and ponds, and 1,400 rivers and streams (FDEP, 2004).

Freshwater fishing lures over 34 million participants to Florida who spend in excess of $35

billion/year (Lee [personal communication], 2006). Reduced sport fish populations coupled with

access problems significantly reduce sport fishing activities (Colle et al., 1987; Milon and Joyce,

1987; Milon and Welsh, 1989). For example, Colle et al. (1987) reported a nearly 85 percent

decrease in total angler effort on Orange Lake, when hydrilla coverage increased from near 0 to

almost 95% of the historically open-water region of the lake.

Populations of several recreationally-important fish species, such as largemouth bass,

bluegill, redear sunfish, and black crappie become skewed to young individuals (Colle et al.,

1987; Tate, Allen, Myers, et al., 2003). They also affects private citizens and businesses,









blocking power generators and agricultural irrigation water intake pipes, jamming water turbines

and dams, and clogging canals and ditches (FDEP, 2004). Infestations in private ponds and

poorly managed public water bodies can reduce recreational and aesthetic value of waterfront

property.

Invasive Aquatic Plant Control

Florida has considerable experience Eighting invasive aquatic plants (especially water

hyacinth), yet Langeland (1996) asserts that lack of adequate and consistent funding for many

invasive plants, (especially hydrilla) continues to be the biggest barrier to effective management

and the efficient use of public resources over time. According to the FDEP (2004), "insufficient

management funding allowed hydrilla to expand from 50,000 to 140,000 acres during the middle

1990s." During this time there was sufficient funding to continue water hyacinth (and water

lettuce) control, which was considered of primary importance due to their higher growth rates.

Lapses in invasive plant control are particularly harmful to Florida' s natural and agricultural

systems because the invasive plants reproduce very quickly, and have prolific seed banks.

Hydrilla has been difficult to eradicate because the plant produces underground tubers which

generate new plants each year (Spencer, Ksander, Madsen et al., 2000; Haller, Miller and

Garrand, 1976; Van, 1989). Likewise, water hyacinth and water lettuce are extremely prolific,

propagating both by seeding and by creating daughter plants vegetatively.

Various aquatic plant control strategies have been considered (Bowes et al., 1979;

Chambers, Barko and Smith, 1993; Nichols, 1991), including mechanical removal, lake draw-

down, application of various herbicides (Van, Steward, and Conant, 1987; Gangstad, 1978;

Klaine and Ward, 1984) and biological control, both with insect and herbivorous fish species (De

Kozlowski, 1991; Hestand and Carter, 1978). Lake draw-down prevents most recreational use,

and biological control agents lack precision, potentially leading to a depopulation of native as









well as invasive plants, or not providing enough control. The primary method of controlling

aquatic plants today is the use of herbicides (FDEP, 2004). Whatever method of control is

chosen, there seems to be consensus that keeping invasive aquatic plant populations very low

and under maintenance control is the preferred state-wide management strategy (Schardt, 1997).

Bioeconomic Modeling of Invasive Species

Recently, economists and natural resource managers have turned to bioeconomic models to

help guide resource managers' decisions. Bioeconomic models relate the biology of invasive

species--population growth rates, dispersion, predation, etc--to their economic impacts. Some

recent studies use bioeconomic models in an optimal control framework to analyze invasive

species spread and control (Eiswerth and Johnson, 2002; Eiswerth and van Kooten, 2002;

Gutierrez and Regev, 2002), while others emphasize feeback links between the biological and

economic systems (Finoff, Shogren, Leung and Lodge, 2005; Settle and Shogren, 2002).

Several studies have used bioeconomic models to estimate costs associated with invasion

or to evaluate policy alternatives. For example, Knowler and Barbier (2000) model the invasion

of an anchovy fishery by comb-j elly and provide estimates of lost profits due to the invasion.

Settle and Shogren (2002) model the impacts of Lake Trout on the native Cutthroat trout, and the

subsequent impacts on wildlife viewing, fishing, and indirect values. Buhle, Margolis and

Rueslink (2005) examine the relative cost-effectiveness of various control methods for invasive

species with different reproductive rates and environmental tolerances. Finnoff and Tshirhart

(2005) also examine physiological traits to determine optimal invasive species control and

prevention strategies.

Other studies have focused on the changing stochastic and uncertain nature of invasive

species arrival, spread, and damages. For example, Leung, Lodge, Finoff, et al. (2002) compare

arrival prevention and damage mitigation under uncertainty. Olson and Roy (2002, 2005)









examine optimal policy responses under uncertainty and with a stochastically changing invasion.

Huffaker and Cooper (1995) use a bioeconomic model of rangeland invasive to measure the

impact on grazing. Odom, Cacho, Sinden, et al. (2003) develop a similar model with respect to

the invasive scotch broom.

The economics of aquatic plant management in Florida have been examined by willingness

to pay studies on specific lakes (Burruss Institute, 1998; Milon and Welsh, 1989; Milon et al.,

1986). For example, Milon et al. (1986) estimated a $480,000 annual willingness to pay for

hydrilla control on Orange and Lochloosa lakes. They also found that a full hydrilla infestation

on the lakes would result in a loss over $5 million per year. Colle et al. (1987) similarly

estimated a total economic impact of $900,000 for invasive weed control on Orange Lake. Milon

and Welsh (1989) estimated $176,000 willingness to pay for invasive plant management on

Harris and Griffin lakes, with a total recreation impact of $1.7 million. Bell et al. (1998)

estimated almost $20 million annual willingness to pay for invasive plant management on Lake

Tarpon. No work has yet examined impact of various control strategies on budgetary costs.

Empirical Approach

This study examines the impact of invasive plants on management expenditures and

recreational activity on 13 Florida lakes. I estimate lake-specific yearly growth functions for

hydrilla and floating plants (water hyacinth and water lettuce together) from unpublished FDEP

aquatic plant coverage and treatment acreage data. I then quantify the relationship between the

invasive plants and fishing activity to capture the economic implications of invasive aquatic

plant infestation. In North Florida, over 65 percent of boat trip activities are for fishing (Thomas

and Statis, 2001), therefore changes in angler activity will capture much of the recreational

impact of invasive aquatic plants on Florida lakes. A linear regression model is specified to

measure the impact of invasive aquatic plant coverage on angler effort. Included in the model









are lake specific variables that characterize the biological and physical conditions of a lake that

also influence angler effort. These include lake trophic state, lake size, season and lake amenities

(such boat ramps and parking facilities). Third, I estimate per acre control costs for hydrilla and

floating plants based on DEP treatment acreage and cost data. Finally, I simulate the impacts of

various invasive plant management strategies on recreational fishing value and compare the costs

and benefits for four potential policy responses to aquatic plant infestation on the 13 lakes.

Data Sources and Description

FDEP performs annual aquatic plant surveys and maintains information on the prevalence

and coverage of aquatic plants on Florida's public water bodies. Each year, the FDEP conducts

grid sampling studies of aquatic plants in which total acreage of each plant discovered is

recorded. Unpublished aquatic plant coverage data on 51 Florida lakes from 1983-2002 was

obtained from FDEP.

The Florida Fish and Wildlife Conservation Commission (FFWCC) perform "Creel"

surveys of angler effort and catch on many Florida lakes. Unpublished Creel data on 45 lakes

collected from 1966-2002 were obtained from five regional FFWCC offices. Angler effort is an

estimation of the number of hours that anglers on a boat spent fishing, times the number of

anglers. For example, if 3 anglers spent 4 hours fishing, the Creel survey would record 12 hours

of angler effort. Angler effort is used as a proxy for recreational activity level on Florida lakes.

Each Creel survey was performed either in spring, summer, fall, or winter, lasting an average of

3.0 months for winter, 3.0 months for summer, 3.1 months for spring, and 2.9 months for fall.

Since Creel surveys reported angler effort over time periods of different lengths, I standardize

the data by computing average angler effort per day over the time period of the Creel survey.

I collected data on physical characteristics of the lake that are expected to impact

recreation. Included were amenities, lake size, and trophic state. The presence of lake









amenities--such as public boat ramps, parking spaces and camping facilities--may influence the

demand for recreation on particular lakes. The Florida Fish and Wildlife Conservation

Commission operates about 1,300 boat ramps on 454 public lakes and rivers throughout the State

that are available for public use, some with additional features such as parking (Thomas and

Stratis, 2001). Data on lake amenities were collected from the FFWCC website (FFWCC, 2003).

Lake size is defined as lake surface area. Data on lake surface area were obtained from

Florida LAKEWATCH and Florida DEP. Lake access is determined by water level. Water level

information were available but excluded from the analysis because Creel surveys often do not

occur when water depth is too shallow for boat use. For example, in 2001 there were 46 public

waters inaccessible for FDEP plant inventories, and in 2002 there were 26 (FDEP, 2004).

A lake' s trophic state indicates the amount of plant and animal life that a lake can support

and is typically measured with a trophic state index (TSI). The biological productivity of a lake

is expected to impact fish populations and catch rates. Particular trophic states are known to be

more beneficial to sport fish production than others. The FDEP uses a Florida-specific trophic

state index developed by Brezonik (1984) for surveying water quality. The Florida-specific TSI

is based on total nitrogen (mg/1), total phosphorous (Cpg/1), chlorophyll a (mg/m3) for planktonic

algae, and secchi depth (m) for water transparency (State of Florida, 1996). I computed a long-

run Florida-specific trophic state index for each lake. The computed TSI values were used to

characterize each lake as Oligotrophic, Mesotrophic, Eutrophic, or Hypereutrophic. The data

used in the TSI calculations were obtained from the University of Florida' s LAKEWATCH

program for the period 1991-2002. Data prior to 1991 were unavailable.




SIt is known that trophic state changes with population growth. Future work will test the assumption that trophic
state can be held constant in the regression and still yield consistent results.










Expenditures for invasive aquatic plant management for years 1998 to 2002 were obtained

from Florida FDEP (Ludlow, 2005). These data include the number of acres, date, and cost of

herbicide treatment for Florida lakes managed by the FDEP. Data prior to this were largely

unavailable.

Data were compiled into an Excel spreadsheet. Included were hydrilla, water hyacinth

and water lettuce coverage at the time of the FDEP' s annual aquatic plant survey, control costs,

lake specific amenities and surface area, and angler effort per day. Excluded were lakes that did

not have both Creel survey and invasive plant survey data for the same years, or lakes that lacked

calculable trophic state index numbers. Of the 45 lakes for which there were Creel data, 3 8 lakes

remained in the spreadsheet. Of these, 13 had FDEP invasive aquatic plant coverage over 100

acres during the 1998-2002 period for which I also have acres treated data (George, Griffin,

Harris, Istokpoga, Jackson, Kissimmee, Lochloosa, Okeechobee, Orange, Osborne, Poinsett,

Sampson, and Weohyakapka).

Hydrilla and Floating Plants Growth Models

The FDEP conducts annual aquatic plant surveys primarily from July through December,

with most surveys occurring in September. Fishing and Creel surveys however take place at

various times throughout the year. Hydrilla in warm southern waters of the United States are the

typically emerge beginning in mid-August, with maximal new plant sprouting in October

(Spencer et al., 2000). Hydrilla biomass is generally highest in November (Bowes et al., 1979).

Water hyacinth and water lettuce have similar growth patterns (Wolverton and McDonald,

1979). Since plant coverage changes throughout the year, it was necessary to estimate their

coverage during the whole year to match plant coverage with Creel survey data.

Current herbicide applications used to control invasive aquatic plants are effective at

eliminating most of the existing aboveground biomass (Van, Steward, and Conant, 1987), but









after herbicide application these plants regenerate from underground tubers, seeds, and the small

percentage of remaining plant material. Most hydrilla plant biomass can be effectively killed

using aquatic herbicides, but hydrilla tubers can not (Steward, 1980; Steward and Van, 1987). It

is estimated that hydrilla tubers covered 108,980 acres of public water bodies in 2002, clearly

presenting a persistent management problem (FDEP, 2004). Seeds from floating plants are also

pervasive (Schardt, 2007). I could not, however, include tuber or floating plant seed banks in the

model of plant growth as these data are unavailable. Assuming static tuber and seed bank

numbers, I was able to estimate single year growth rates for hydrilla and floating plants.

Hydrilla grows in stages. At the beginning of the calendar year, there are typically no

living hydrilla plants remaining from the previous year when the plants naturally lose their

ability to carry out basic physiological functions. Once water temperatures reach 3 degrees

Celsius, new plants sprout leaf material from the underground tuber bank. Growth is rapid

through about day 270, or early September (Bowes et al., 1979). As the temperature begins to

cool, the plants return to their senescent state following tuber production (Best and Boyd, 1996).

Water hyacinth and water lettuce follow similar growth stages (Wolverton and McDonald,

1979).

Annual plant growth is a function of numerous variables, including water temperature,

solar radiation, nutrient levels, available space, water turbidity, lake depth, trophic state, plant

predation and competition, and many other factors (Best and Boyd, 1996; Van, Haller, and

Garrard, 1978; Bowes, Holaday, and Haller, 1979; Best, Buzzelli, Bartell, et al., 2001). For the

purposes of this study, I make several simplifying assumptions. First, I assume that only lake

surface area, time, and herbicide applications affect plant growth. I tested this assumption using

the most recent lake-wide study of hydrilla growth in Florida (Bowes et al.,1979). Bowes et al.,










(1979) measured the level of hydrilla biomass on Orange Lake, Florida in 1977. Using the

Bowes et al. data, I estimated a temporal growth function for hydrilla with time as the

explanatory variable (statistically significant at p = 0.01, with an adjusted R2 greater than 0.975,

suggesting a good fit).

Second, I assume that the date of the FDEP aquatic plant survey was day 270 of each year

after several communications with State of Florida invasive plant managers (Schardt, 2007,

Ludlow, 2005). I also assumed day 270 to be the date of maximum surface area coverage for

hydrilla, water hyacinth and water lettuce based on the hydrilla literature (Best and Boyd, 1996;

field studies of water hyacinth and water lettuce growth were not available) and calculations

from Bowes et al. (1979). Third, I assume that the date of herbicide application is day 60 of each

year, a time when tubers and seeds have sprouted and the rapid plant growth encourages uptake

of herbicides (Schardt, 2007; Ludlow, 2005; Haller, 2006). I was not able to reach consensus

regarding initial tuber and seed density on the 13 lakes that are the focus of this study. Future

work will factor tubers and seeds into both the growth function estimations and the comparison

of the economic efficiency of various management schemes. Here, I assume a static growth

function of hydrilla and floating plants, respectively, for each of the 13 lakes.

The growth equations are a function of time, with three distinct growing periods, defined

as:


Seg'" for l H, = H,,egz' '" for ts < t <; tm

Equation 1. H,,-~-n)Jrt 6

Where Ht is the acreage of the invasive aquatic plant at day t; gl is the lake-specific growth

parameter for time 0-60, g2 is the lake-specific growth parameter for time 61 270, and b is the

lake-specific decay parameter for time 271- 365; ts is the assumed day of plant herbicide spray










application (if done), which is assumed to be 60; and tm is the assumed day of plant maximum

surface area coverage and FDEP survey date, which is assumed to be 270. The parameter

estimates are reported in Table 3-1.

Table 3-1. Hydrilla and floating plants growth function parameter estimates.
Hydrilla Floating
Lake gl 2 b gl 2 b
George 0.014 0.014 0.04 0.018 0.018 0.04
Griffin 0.034 0.016 0.009 0.059 0.02 0.033

Harri s 0.047 0.016 0.017 0.035 0.02 0.018

Istokpoga 0.122 0.029 0.093 0.12 0.007 0.041
Jackson 0.091 0.023 0.058 0.082 0.02 0.047

Kissimmee 0.131 0.026 0.092 0.102 0.013 0.044

Lochloosa 0.063 0.014 0.023 0.03 0.02 0.015

Okeechobee 0.03 0.03 0.085 0.141 0.014 0.072

Orange 0.095 0.028 0.074 0.085 0.01 0.026
Osborne 0.078 0.014 0.032 0.059 0.02 0.033

Poinsett 0.102 0.02 0.06 0.088 0.012 0.033

Sampson 0.078 0.028 0.063 0.045 0.011 0.003

Weohyakapka 0.133 0.023 0.086 0.072 -0.005 -0.015


Aquatic Plant Management Scenarios

Several management scenarios are considered for the treatment of the invasive aquatic

plants (Table 3-2). Scenario A is the status quo, which is calculated from the 1998-2002 FDEP

aquatic plant acreage treated data. The status quo treatment is estimated from 5-year averages on

the 13 lakes. This is the level of treatment actually pursued by the Florida Department of

Environmental Protection. Status quo treatment already provides lake access throughout most of

the year on Florida' s 454 public lakes. As long as the lakes remain relatively free of hydrilla and

floating plants, most of the lakes' recreation and ecosystem value will be preserved.










Aquatic plant herbicide application occurs in early to mid-Spring when plants are young

and growing vigorously and able to uptake a large percentage of the herbicide (Haller [personal

communication], 2006). Treatment in the summer months would result in too much dissolved

oxygen depletion due to plant die-off at a time when dissolved oxygen is already low (Haller).

For simplicity and tractability of calculation, I assume that treatment will occur at day 60. Van,

Steward, and Conant (1987) found that aquatic herbicides are up to 95% effective for the Florida

variety of dioecious hydrilla, and Langeland and Pesacreta (1985) found similar effectiveness for

the monoecious variety in North Carolina. For the sake of providing conservative estimates of

expenditures and losses associated with hydrilla control, I assume a 99% efficacy rate (1% of the

plant biomass continues to grow after the herbicide is applied).

For scenario A, I use the following invasive aquatic plant coverage function:

Ie 't for < t < ts

Equation 2. H, = eH,,egz' '" for ts < t < tm
H,me-b(t-tn) fOr tm < t < 365

where e is the percentage of living invasive plant acreage left after treatment, which is assumed

to be .01.

Table 3-2. Model assumptions for policy scenarios.
Second treatment
Scenario First treatment (at day 60) l, ,;C + 1,\


\a( ay specC~I cV o ae)

No treatment

No treatment

No treatment

20% of hydrilla and floating plants acreage


A

BO

B2

C20


All hydrilla and floating plant acreage

No treatment

Scenario A, but every other year

Same as Scenario A


2 The date of the second treatment is calculated to maximize the effectiveness of treatment. The dates of second
treatment are reported in Table 3-3. Note: some calculated dates are greater than 365. In these cases it is assumed
that no second treatment occurs.












Table 3-3. Date of second herbicide treatments for C20.
C20 C20
Floating Hydrilla
George 223 277
Griffin 210 245

Harri s 209 245

Istokpoga 511 163
Jackson 210 193

Kissimmee 294 175
Lochloosa 207 269

Okeechobee 267 161

Orange 362 167
Osborne 210 273

Poinsett 312 210

Sampson 337 167
Weohyakapka 279 190


Scenario BO is no treatment, and has the same growth function as Equation 1.

Scenario B2 is treatment every other year, and has the following growth function:


S2eg't for1 Equation 3. H, = EH,eg2(t-tS) fOr ts < t < tm
Heme-b't-tm fOr tm < t < 365

It is assumed that the initial invasive aquatic plant acreage would double from one year to

the next absent treatment. It must be stressed that this assumption has not been tested and may

represent unrealistic growth conditions.

For scenario C20, the state treats all of the invasive aquatic plant acreage at day 60 plus an

additional treatment 20% of the acreage at a later date. The date for second treatment is lake-










specific and was calculated to maximize the effectiveness of the treatment. The growth function

for scenario C20 is:


Iegt for < t < ts
EH~eef2r fOr ts Equation 4. H, =~ e'" o m
EH,e-b(t-tm) fOr tm2 < t < 365


where ts2 is the date of second treatment.

For each of the management scenarios, the corresponding acreages of hydrilla and

floating plants were calculated and were used to calculate the changes in both recreational

Eishing benefits and control costs. The results are discussed in the Economic Effects of Aquatic

Plant Management section. For three of the lakes, I provide examples of the impact of

management scenarios on aquatic plant coverage (Figure 3-1, Figure 3-2, and Figure 3-3).

Recreational Fishing Effort Model

The benefits associated with invasive aquatic plant management are measured as a change

in the amount of hours that anglers spend fishing on that lakes, times an estimate the average

willingness to pay for an hour of fishing (Thomas and Stratis, 2001). I refer to "angler effort" as

the amount of hours an angler spends fishing on a lake, which is a function of several factors:

Equation 5. F = f(H, X)

where F is angler effort, H is hydrilla and floating plants coverage as estimated on the 13 lakes,

and Xis the matrix of other factors likely to affect fishing effort, including trophic state, season,

lake size and lake amenities. Both F and H are per day averages; trophic state, lake size, and

amenities are assumed to remain constant.






































0 50 100 150 200 250 300 350
Time (day of year)


Figure 3-1. Simulated hydrilla coverage in Lake Istokpoga.


Hydrilla














Hydrilla


0 50 100 150 200 250 300 350
Time (day of year)


Figure 3-2. Simulated hydrilla coverage in Lake Kissimmee.














Hydrilla (acres)
90000


8000


7000


6000





4000


3000


2000


1000



0 50 100 150 200 250 300 350 400
Time (day of year)

Figure 3-3. Simulated hydrilla coverage in Lake Weohyakapka.









A regression analysis was conducted on the above variables using data collected on the 13

lakes over 20 years (from 1982 2002). These data are unbalanced panel data (Greene, 2004). I

used Limdep 8.0's panel data analysis tool for unbalanced panel data to perform regression

analyses. I conducted several specification tests, including 1) to determine whether hydrilla and

floating plant acreage variables should be raised to a higher power to provide better parameter

estimates; 2) to check whether I needed an interaction variable to capture the combined effects of

invasive aquatic plant acreage and lake size; and 3) pooling tests were conducted to check

whether intercept and slope coefficients could be assumed to be the same for all lakes. While

there were not enough degrees of freedom to test for lake-specific slope parameters, the partial F-

test for lake-specific intercept terms indicates no statistically significant difference (Greene,

2004). The amenity variables Ramps and Parking were perfectly correlated, and were redefined

as one variable (Ramps+Parking). There was no variation in the variable Camping, so it was

excluded from the model. The model parameter estimates are reported in Table 3-4.

All variables except Summer are significant at the 95% level of confidence or higher. The

model significance was high (F = 42.02, significance ofF = 0.0000), with the regression

equation providing a relatively good fit to the sample data (Adj. R2 = 0.7836). There were no

obvious model problems. Neither White' s test nor the Breush-Pagan test for heteroscedasticity

revealed any problems, and the Durbin-Watson statistic was 1.96, signifying no significant

problem with autoregression.

Lake size, and ramps+parking have a positive impact on fishing effort. The positive sign

on WACRES suggests that angler effort is greater on larger lakes. Larger lakes likely have fewer

conflicts between anglers and other recreational boaters, leading to a better fishing experience

and perhaps better fishing. More fishing sites, larger fish may explain this phenomenon, and










proximity of large lakes to large population areas are other explanations. I estimate that for each

additional 1000 acres of lake surface area, there will be 7.01 additional hours of fishing effort per

Table 3-4. Angler effort regression model parameters.
Coefficient P-value

Intercept -406.426 0.002525

Hydrilla2** 4.25E-07 0.030062
Floating2** 4.68E-07 0.026767

(Hy drilla+Floati ng)x(wacre s)**" -2.90E-07 0.03 0224
WACRES*** 0.00701 2.3 6E-3 3

Ramps+Parking*** 5.305605 7.79E-07
Oligotrophic** 440.4176 0.037645
Eutrophic*** 377.5538 0.005022

Hypereutrophic*** 615.6091 5.08E-05
SPRING*** 504.9197 1.38E-05
WINTTER*** 430.8179 0.000372

SUMMER 155.1794 0.205076

* significant at the 90% level of confidence
** significant at the 95% level of confidence
***significant at the 99% level of confidence

day on that lake. This may suggest that larger lakes are a more valuable natural resource for

recreational use, and may warrant higher priority for funding to control invasive aquatic plants.

Likewise, ramps and parking have a positive impact on fishing effort. The availability of

ramps, and safe, maintained parking areas are likely to improve the fishing experience. Here, I

estimate that the presence of both parking and ramps adds almost 5 hours of angler effort per

day. An interesting interpretation, when taken together with the aquatic weed effects (discussed

below), is that building parking spaces and providing ramp access may overcome a certain

amount of invasive aquatic plant coverage, at least while lake access is possible through the

aquatic weeds.









Interpretation of the trophic state parameters is less obvious, perhaps because there are

competing forces at work. On the one hand, scientific findings suggest a reduction in fish species

and fish weight for some sport fish with an increase in Florida lake trophic state (Bachmann et

al., 1996; Hoyer et al., 2005). On the other hand, lake eutrophication is advanced by increased

runoff from larger population centers. This model shows mixed results with respect to trophic

states' effects on fishing effort. The parameters for oligotrophic, eutrophic and hypereutrophic

lakes are positive, while the parameter on the excluded variable mesotrophic is interpreted as

being negative; Hypereutrophic lakes attract more fishing effort than eutrophic, which is greater

than mesotrophic. One interpretation is that oligotrophic lakes attract anglers for the clarity of the

water that may improve the fishing experience. As lake clarity falls with the increased trophic

state, the dominant force may then be population center effect, i.e. lakes become eutrophic

because they are near population centers and receive more nutrient loads. And because the lake is

near a population center it is fished more frequently despite the higher trophic state.

The aquatic plant parameter estimates suggest that invasive aquatic plant coverage has a

negative impact on fishing effort when including the interaction effects of lake size. For

example, a lake of 10,000 acres that goes from no invasive aquatic plants to 10 acres of hydrilla

and 10 acres of floating plants (water hyacinth and water lettuce) would cause the loss of 0.057

hours of angler effort per day. Going from 10 to 50 acres of hydrilla and floating plants,

respectively, would cause the loss of 0.287 hours of fishing effort per day. Figure 3-4 shows the

impacts of increased hydrilla and floating plants coverage (in equal amounts) on fishing effort

for a 10,000 acre lake. This finding is consistent with the literature on hydrilla coverage and

angler effort. Colle et at. (1987) report a significant negative correlation between hydrilla

coverage and harvestable bluegill and redear sunfish populations on Orange Lake, Florida. Colle










et al. also reported an 85% decrease in total angler effort on Orange Lake when hydrilla coverage

increased from 0% to 95%.







t: -4




S-9
S-10

Plant acres (hydrilla and floating, each)

Figure 3-4. Daily fishing effort lost to invasive aquatic plants for a 10,000 acre lake in Florida.

Hydrilla, Water Hyacinth, and Water Lettuce Treatment Cost Model

The lack of common knowledge of hydrilla growth rates may have contributed to drastic

reductions in State funding for invasive plant control in the mid 1990s. Without adequate

funding for control, hydrilla grew rapidly and took over entire lakes. Control of lakes was

eventually regained in subsequent years, but at a very high cost. The total cost of controlling

hydrilla, water hyacinth and water lettuce in any given year is modeled as a function of acres

treated during that year assuming constant costs:

Equation 6. C = clHydrilla czFloating

where C is the total cost of treating invasive plants, cl is the per acre cost of treating hydrilla,

Hydrilla is the total number of acres treated, ct is the per acre cost of treating water hyacinth and

water lettuce, and Floating is the total acres of water hyacinth and water lettuce treated. Equation

6 was estimated from the 5 year averages of per acre treatment costs for the 13 lakes included in

this study using data obtained from FDEP for 1998-2002 (Ludlow [personal communication],

2005); the five year average for cl is $561 and ct is $107.










Angler Effort Value Model

According to the Florida Fish and Wildlife Conservation Commission, freshwater anglers

on Florida lakes spent $18.20 per hour fishing in 1996 or $20.65 in 2002 dollars (Thomas and

Stratis, 2001; FFWCC, 2003). Applying $20.65 and assuming a fishing day is 6 hours, the

empirical angler value equation is

Equation 7. V =p F

where Vis the value of fishing, p is the per hour angler value in dollars and F is the number of

hours spent fishing.

Economic Effects of Invasive Aquatic Plant Management

Using the actual treatment and surveyed acreage data from FDEP for the 13 lakes, I

simulate the economic effects of each of the treatment scenarios (A- status quo, BO- no treatment,

B2- treatment every other year, and C20- second treatment at 20%). Recall Equations 1-4, the

growth equations for the invasive aquatic plants for each treatment scenario. Angler effort, F, is a

function of invasive aquatic weed acreage, H, and other lake characteristics, X(i.e., lake size,

parking, trophic state, and season) such that

Equation 8. F = f (H, X)

and the change in angler effort with respect to a change in invasive plant acreage from a

particular scenario is

aF af (H, X)
Equation 9.
8H 8H

Angler effort can be summed over several years as


Equation 10. F' = F" + d( XdH
8H

and generalized as










Equation 11. dF = F' FO

The same generalization can be made of treatment costs and invasive aquatic plant acreage as

Equation 12. dH = H' HO

Equation 13. dC = C' CO

The net benefit for each scenario is calculated as


Equation 14. NB=ii p6 8f (H ,XL H, C(Lttt


where NB is net benefit from the treatment strategy, L is the subj ect lake (George, Griffin, Harris,

Istokpoga, Jackson, Kissimmee, Lochloosa, Okeechobee, Orange, Osborne, Poinsett, Sampson,

and Weohyakapka), t is the day of the year, p is the per hour value of Eishing, H is invasive

aquatic plant coverage, and C is treatment costs.

The acreage of hydrilla, water hyacinth and water lettuce changes throughout the year. In

the warm summer months, when the photoperiods are longer, aquatic plants can infest almost all

of the available lake acreage absent control. While it is widely accepted that high levels of

aquatic plants can block recreational access to Florida lakes, only one study has measured the

relationship between invasive plant coverage and fishing. Colle et al. (1987) report an 85%

decrease in total angler effort on Orange Lake when hydrilla coverage increased from 0% to

95%. In Florida, many anglers use shallow-draft fan boats that are not hampered by aquatic

plants, which may explain the persistence of some fishing effort at high levels of plant coverage.

Here, I assume that only 15% of the otherwise expected fishing effort would remain when

invasive aquatic plant coverage is above 80% of available lake surface area.

I simulate the impacts of the invasive plant management scenarios using General

Algebraic Modeling System (GAMS) 2.5A software. The results are reported in Table 3-5, with









an example for 4,000-acre Lake Jackson in Figure 3-5. One very useful result is the estimation of

the total value of the 13 lakes--over $64.78 million, with about 3.13 million total fishing hours.

These results are similar to those found by other studies on Florida lakes. For example, Milon et

al. (1986) estimated a $480,000 annual willingness to pay for hydrilla control on Orange and

Lochloosa lakes. They also found that a full hydrilla infestation on the lakes would result in a

loss over $5 million per year. Colle et al. (1987) similarly estimated a total economic impact of

$900,000 for invasive weed control on Orange Lake.

Table 3-5. Annual economic impact of invasive aquatic plant management on 13 lakes.
B2-Alternate C20-Second
A- Status quo year control BO-No control treatment at 20%
Fishing Effort (hours) 3,135,966 2,426,774 1,369,516 3,359,053
Treated Acres 13,785 31,285 0 16,542
Peak Acres 21,085 43,620 43,620 4,304
Total Value l 64,783,832 50,133,107 28,291,923 69,392,436
Total Control Costs'' 4,828,254 10,938,970 0 5,793,905
Net Benefit'' 59,955,578 39,194,966 28,291,923 63,598,531

Change in NB 0 -20,761,440 -31,663,655 3,642,954
" Value per year, $ 2006 millions

Milon and Welsh (1989) estimate $176,000 willingness to pay for invasive plant management on

Harris and Griffin lakes, with a total recreation impact of $1.7 million. Bell et al. (1998)

estimated almost $20 million annual willingness to pay for invasive plant management on Lake

Tarpon.

Compared with the status quo treatment strategy, reducing treatment to every other year, or

halting treatment altogether will lead to significant recreational and ecosystem losses, largely due

to access problems. Alternative year control (B2) results in a 23.61% reduction in fishing hours,











25,000


20,000
r~-~ No Control
o / -+ 20% Increase in Control
S15,000





5,000



1 2 3 4 5 6 7 8 9 10 11 12
Month

99Figure 3-5. Impact of invasive plant control on fishing effort (Lake Jackson example)


and no control (BO) yields a 56.33% loss in angler effort. A 20% increase in control (C20)

increases fishing hours by 7. 11%.

Peak and treated acreage of invasive plants vary widely by control policy. Decreasing

treatment more than doubles the peak acreage. Alternate year control (B2) and no control (BO)

cause annual peak acreage to increase by 106.88% (the lake maximum), and treated acreage to

increase by 126.95% for alternate year control. Increasing treatment substantially decreases the

peak acreage and the total acres treated. For example, moving from the status quo to strategy

C20 reduces the peak acres by 79.59% (see Figure 3-1, Figure 3-2, and Figure 3-3). This may be

extremely important to the ecology of the lakes and for the preservation of native plant species.

Control costs also vary widely by policy. The status quo (A) control costs are $4,828,254.

These costs rise by 126.56% with the alternate year control (B2), and by 20% for the 20%

increase in control (C20).









The state of Florida must balance the benefits and costs of invasive species-related public

policies. The total recreation-related losses associated with no control (BO) are $33,663,655 per

year. Using this as a baseline for return on investment calculations, I estimate that status quo

control (A) yields a 655.80% return on the investment of $4,828,254 in invasive aquatic plant

investment. In terms of rate of return, status quo ranks the highest, but in terms of absolute net

benefit, increasing control is preferred. Increasing control by 20% from status quo will increase

fishing-related benefits by $3,642,953. B2 yields a 609.37% return on investment, which is lower

than the 655.80% rate of return to the status quo policy. Alternate year control (B2) results in a

loss in fishing-related benefits as compared to the status quo, but yield 99.67% rate of return as

compared to do nothing (BO). In the mid-1990s, the state of Florida significantly reduced the

FDEP's invasive plant management budget, and hydrilla growth went unchecked. These results

confirm the high costs associated with such a lapse in funding.

Treatment of invasive aquatic plants should be continued, either at their current levels or at

slightly increased levels of control, depending on relative demands on state monies. However,

these results may be too conservative as they do not consider the impacts of invasive aquatic

plant control on seed and tuber bank numbers or ecosystem brittleness that may result from

prolonged aquatic weed monocultures. These simulations are restricted to a 5 year period on 13

lakes. Using the FDEP plant coverage data (n = 997), I estimate a mean hydrilla coverage of

9.36%, with a standard error of 0.61%, and a range of 0 to 100% of the lake surface area. I also

estimate mean floating plant coverage of 0.07%, with a standard error less than 0. 1% and a range

of 0 to 51.92% of lake surface area. At these levels, tuber and seed banks are at relatively low

numbers. Given several years of no control, these numbers would be much higher and could

vastly increase control costs and recreational losses in subsequent years. Treatment strategies BO










(no treatment) and perhaps B2 (treatment every other year) could produce such an event, at

which point a substantial portion of the total benefit of these 13 lakes would be lost for four years

or more. The loss of recreation on these 13 lakes may have a devastating impact on certain

regional economies.

Maintenance control of these aquatic species at low levels is more economically efficient

than allowing them to grow rampantly or infrequently controlling them. Indeed, the comparison

of the status quo scenario A to the every other year treatment scenario B2, it is apparent that

control costs rise substantially and net benefits fall substantially due to sporadic control. Even

brief lapses in funding, like what occurred during the mid-1990s, are very costly. In Florida

there are 1.05 million acres of lake surface area on lakes with over 1,000 acres (FFWCC, 2005).

When considering the economic implications on lakes throughout the State, continued and

perhaps increased treatment of invasive aquatic plants may be in the public' s best interest.

Lapses in maintenance control may also have long run consequences. In 2000, it was

discovered that hydrilla was becoming resistant to flouridone herbicide, apparently due to

random mutations (FDEP, 2004). For example, in 2002 the 19,000-acre Lake Tohopekaliga had

15,000 acres of herbicide-tolerant hydrilla. If mutation rate is a function of population size, then

brief lapses in hydrilla control that lead to large plant populations may provide for more

mutations and higher rates of herbicidal resistance. There is no close substitute to fluoridone for

large-scale hydrilla control; lake managers must be vigilant against large hydrilla populations.

One important final note about the results is that while they may be robust over the 5-year

period and the 13 lakes I examined, they may not be robust for predicting the economic effects of

invasive aquatic plant management for future time periods. An important impact of consistent

treatment of these plants is on reducing their tuber and seed banks. Seed banks indicate the










potential future biomass (Winton and Clayton, 1996). The presence of tuber and seed banks may

exacerbate the differences between the various levels of treatment. Future work will include

tuber and seed banks for hydrilla, water hyacinth, and water lettuce.

Conclusion

Hydrilla verticillata (hydrilla), Eichhornia cra~ssipes (water hyacinth), and Pistia stratiotes

(water lettuce) have long been established in Florida' s lakes and rivers. The unique

characteristics of these plants allow them to grow rapidly, displacing native flora and fauna, and

reducing recreational use and enj oyment of many water bodies. Recreational freshwater fishing

in Florida lures over 3 million anglers with annual expenditures exceeding $3.8 billion.

Consistent and significant control efforts are required to prevent invasive aquatic plants from

eroding the value of Florida' s lakes to the state's economy and ecosystems.

Long run cost-effective management of these invasive species requires consistent control

efforts, yet the State's funding has fallen short in the past. Using data collected on 13 lakes with

more than 100 acres of invasive plant coverage at any point during 1998-2003, I estimate the

growth of hydrilla, water hyacinth, and water lettuce for each lake as well as per acre control

costs for hydrilla and floating plants. Using fishing effort data collected over 20 years, I also

estimate the effects of hydrilla, water hyacinth, water lettuce, and other lake characteristics on

fishing effort. I combine plant growth, angler effort, and control costs into a bioeconomic model

of hydrilla, water hyacinth and water lettuce and fishing effort. The bioeconomic model is used

to estimate the value of various invasive aquatic plant management regimes.

Model results show that over 5 years, the value of fishing activity on the 13 lakes is in

excess of $64.78 million, with about 3.13 million total fishing hours. Compared with the status

quo treatment strategy, reducing treatment to every other year, or halting treatment altogether

will lead to significant recreational and ecosystem losses, largely due to access problems. The









status quo (A) control costs are $4,828,254. These costs rise by 126.56% with the alternate year

control (B2), and by 20% for the 20% increase in control (C20).

Peak and treated acreage of invasive plants vary widely by control policy. Decreasing

treatment more than doubles the peak acreage. Increasing treatment substantially decreases the

peak acreage and the total acres treated.

The total recreation-related losses associated with no control (BO) are high--$33,663,655

per year. By comparison, status quo control yields 655.80% return on investment for control

expenditures of $4,828,254 per year. In terms of absolute net benefits, increasing control by 20%

will increase fishing-related benefits by $3,642,953, but at a lower rate of return- 609.37%.

Alternate year control (B2) results in a loss in fishing-related benefits as compared to the status

quo, but yield 99.67% rate of return as compared to do nothing (BO).

A few clear conclusions follow from the results: 1) Florida lakes have very high economic

values that are at risk from invasive aquatic plants; 2) maintenance control of invasive aquatic

plants is the preferred cost-minimizing control policy; and 3) lapses in maintenance control, even

if brief, can significantly increase subsequent invasive aquatic plant control costs.









CHAPTER 4
THE LEGAL BASIS FOR REGULATORY CONTROL OF INVASIVE AGRICULTURAL
PESTS IN FLORIDA

Introduction

Florida is no stranger to agricultural disease, particularly those affecting its citrus industry.

Florida has twice successfully eradicated citrus canker (Division of Plant Industry, Florida

Department of Agriculture and Consumer Services, 2006). Citrus canker was first detected in

Florida in 1910 and declared eradicated in 1947. However, in 1986, a highly aggressive Asian

strain of the citrus canker was detected in Florida3 (Timmer, Graham, and Chamberlain, 2006).

Some speculate that the 1986 strain was not a reintroduction but a perennial holdover from the

1910 Xanthomona~s axonopodis py. citri introduction (Schubert and Sun, 2001). The 1986 strain

was declared eradicated in 1994, but was found again in 1995 in residential and commercial

sites, including the Miami International Airport in Miami-Dade County (Gottwald et al., 2002).

Florida has a high rate of non-native species introduction, with the Port of Miami receiving about

85% of non-native plant shipments entering the US each year (OTA, 1993).

Facing potentially devastating effects to the citrus industry as well as Florida' s economy,

the US Department of Agriculture and the State of Florida implemented maj or dual-track citrus

canker eradication programs (CCEP). Both programs required the removal of all trees within

1,900 feet (initially 125 feet) of an infected tree. The USDA administered and provided

compensation to commercial citrus growers whose trees were taken, while the state of Florida

administered and provided compensation to residential tree owners whose trees were taken.

Under the USDA program, commercial growers were compensated $26 per tree. Residential tree

owners were provided $55 per tree, and some counties supplemented this compensation. For

3 Haire v. Florida Dept. Of Agriculture And Consumer Services, 870 So.2d 774 (Fla. 2004).










example, in Broward County tree owners were given $45 Wal-Mart gift certificates for the first

tree taken (good for Garden Center purchases only). Legal challenges to the state and federal

eradication programs happened almost immediately after the first tree was taken (Regina, Olexa,

and McGovern, 2004)

In 2000, residential citrus tree owners of suspicious trees were granted temporary

injunctions against the State's canker eradication program. From 2000 to 2004, there were two

18-month gaps during which the State was enj oined from cutting down healthy trees within

1,900 feet of infected trees and canker innoculum increased and was largely undetected on

residential trees. Since that time, Florida experienced five maj or hurricanes (Albrigo et al.,

2005). The hurricanes of 2004, Charley, Frances, Ivan, and Jeanne, spread citrus canker from

these residential trees to such an extent that 80,000 commercial acres of citrus were subsequently

slated for destruction. Concentrated efforts by governmental officials reduced this to 32,000

acres when Hurricane Wilma hit in 2005. Due to the spread of the citrus canker pathogen with

Wilma, officials faced the task of destroying an additional 168,000 to 220,000 acres of

commercial citrus (USDA, 2006). The inability of the State's canker eradication program to

continue unabated meant the USDA canker eradication program was largely ineffective. On

January 10, 2006, the federal government stated that citrus canker "is so widely distributed that

eradication is impossible" and pulled the funding for the USDA' s citrus canker eradication

program (USDA, 2006). This change in policy came on the heels of a number of judicial

decisions upholding the legality of Florida' s citrus canker eradication program, but too late to

save the USDA eradication program. Though the CCEP was repealed in January 2006 (Timmer

et al., 2006), these judicial decisions will be precedential to potential challenges to similar State










programs designed to manage and control pests like citrus canker and citrus greening (Salisbury,

2006).

The State of Florida, as other states in the US, has a duty to protect its agricultural and

natural resource interests from invasive plant, animals, and other species. The power to exercise

protective measures originates from the police power inherent in Florida's sovereignty.4,5 The

use of police power to protect Florida's agricultural interests is delegated by the Legislature to

the Director of the Division of Plant Industry within the Department of Agriculture and

Consumer Services.6

This chapter provides an overview of the State' s use of police power to protect agriculture

in conjunction with legal decisions that balance the exercise of this power with the constitutional

mandates of due process and just compensation. These cases demonstrate how the courts apply

these constitutional limitations in challenges to measures involving a burrowing nematode

(spreading decline) in comparison with the measures taken in controlling an aggressive strain of

citrus canker.

Use of Police Power to Take Private Property

The State of Florida has the power to take private property for a public purpose as an

incident to its sovereignty and requires no constitutional recognition.' One form of this power is

when Florida uses its police power to take property for the purpose of protecting "public safety,

public welfare, public morals, or public health.8 "Police power" is sometimes used to only


SBoom Co. v. Patterson, 25 L.Ed 206, 98 U.S. 403 (U.S. 1878).

SDepartment of Agriculture and Consumer Services v. Bonanno, 568 So.2d 24 (Fla. 1990).
6 Fla. Stat. #581.031(7) (2002).

SSee infra note 3: see also note 4.

SSweat v. Turpentine & Rosin Factors, Inc., 15 So.2d 267 (Fla. 1943).










describe activities that do not require compensation. However, the exercise of police power may

require compensation.9

It should be noted that it is difficult to discern the boundary line between the actions that

are compensable under the police power and compensable actions under eminent domain. 10 The

distinction is that eminent domain involves taking a property for a public use, where police

power involves the destruction of such property to prevent its use in a manner that is detrimental

to the public interest (Gottwald, Timmer, and McGuire, 1989). Broadly speaking, the courts will

consider six factors when deciding whether State action is a valid exercise of police power or a

compensable taking: "

1. "Whether the State physically invaded the property."
2. Whether the State' s actions "precludes all economically reasonable use of the property."
3. "The extent to which the regulation curtails investment-backed expectations."
4. Whether the regulation "confers a public benefit or prevents a public harm."
5. Whether the regulation "promotes the health, safety, welfare, or morals of the public."
6. Whether the regulation is "arbitrarily and capriciously applied."

In the canker and spreading decline cases, the determinations that cutting healthy, yet

suspect citrus trees were compensable takings largely depended on whether the State's action

conferred a public benefit or prevented a public harm, and these cases preceded the legislature's

2002 statutory compensation scheme for trees cut after 1995.12 After Patchen v. Dept. of

Agriculture and Consumer Services, an owner of a healthy residential citrus tree that was cut by



9 Department of Agriculture and Consumer Services v. Mid-Florida Growers, Inc., 521 So.2d 101, 101-4 (Fla.
1988), cert. denied, 488 U.S. 870, 109 S.Ct. 180, 102 L.Ed.2d 149 (1988); see also Department of Agriculture and
Consumer Services v. Polk, 568 So.2d 35 (Fla. 1990); see also Graham v. Estuary Properties, Inc., 399 So.2d 1374
(Fla. 1981) cert. denied, 454 U.S. 1083 (1981); see also State Plant Board v. Smith, 110 So.2d 401 (Fla. 1959).

'0 16A Am. Jur. 2d Constitutional Law 318 (1998).

11 See in~fra note 7.

12 See Department of Agriculture and Consumer Services v. Mid-Florida Growers, Inc., 521 So.2d 101, 101-4 (Fla.
1988), cert. denied, 488 U.S. 870, 109 S.Ct. 180, 102 L.Ed.2d 149 (1988); see also Patchen v. Dept. of Agriculture
and Consumer Services, 906 So.2d 1005 (Fla. 2005).










the State no longer has to prove that the State's actions constituted a taking. 13 However, the

question of whether the statutory compensation is enough is unresolved. The following section

addresses this question.

Limitations on Police Power

The Florida Constitution limits the use of police power to control agricultural disease.

Private property cannot be destroyed without "due process of law" and "just compensation.1

Substantive Due Process and Procedural Due Process

Due process includes both substantive and procedural elements (Gottwald et al., 1989).

Substantive due process protects individual rights, such as life, liberty or property, and the

exercise of a police power that infringes one of these rights must bear a "reasonable relationship"

to a legitimate obj ective. 1 The courts have long held that the protection of agriculture is a

legitimate obj ective for the use of the State' s police power. 16 So long as the legislative decision

bears a reasonable relationship to protecting agriculture, the court will not substitute its own

judgment. Procedural due process ensures that process is fair when these substantive rights are

at issue. 1 A procedural due process consideration relevant to the control of agricultural disease

is the "opportunity to be heard" on whether the destruction is proper. I







13 906 So.2d 1005 (Fla. 2005).

14 Fla. Const. Art. I, #9: see also Fla. Const. Art. X, #6.

'5See Lochner v. New York, 198 U.S. 145 (1905); see also Griswold v. Connecticut, 381 U.S. 479 (1965).

16 Department of Agriculture and Consumer Services v. Mid-Florida Growers, Inc., 521 So.2d 101, 101-4 (Fla.
1988), cert. denied, 488 U.S. 870, 109 S.Ct. 180, 102 L.Ed.2d 149 (1988).

17 See Herrera v. Collins, 506 U.S. 390 (1993).

1s State Plant Board v. Smith, 110 So.2d 401 (Fla. 1959)










Just Compensation

The Florida Supreme Court stated that, "the absolute destruction of property is an extreme

exercise of police power and is justified only within the narrowest limits of actual necessity,

unless the state chooses to pay compensation."19 However, the State is not compelled to

compensate for property that is "valueless, incapable of any lawful use, and a source of public

danger," such as "diseased cattle, unwholesome meats, decayed fruit or fish, infested clothing,

obscene books or pictures, or buildings in the path of a conflagration."20 This provision can be

rephrased to say that the state remains obligated to provide "just compensation," but that the

amount of compensation is a nullity because the property is without value.

Comparing the Limitations on the Use of Police Power: Spreading Decline versus Citrus
Canker

The following lines of cases demonstrate how the facts of the case play a key role in

determining the limitations when agricultural crops are destroyed through the exercise of police

power. These cases both deal with the diseases that affect citrus trees, spreading decline and

citrus canker.

Spreading Decline

Spreading decline is caused by the burrowing nematode, RRRRRRRRRRRRRRRRRadohohus similis, a microscopic

worm that damages the feeder roots of citrus trees (Suit and DuCharme, 1953). Over time, the

root system deteriorates, causing the tree's foliage and productivity to deteriorate (Suit and

DuCharme, 1953). Infected trees are rendered commercially unprofitable under ordinary market

conditions. The burrowing nematode travels very slowly through the soil.



19 COrneal v. State Plant Board, 95 So.2d 1 (Fla. 1957); see also Department of Agriculture and Consumer Services
v. Polk, 568 So.2d 35 (Fla. 1990)

20 See in~fra note 16: see also note 17: see also Department of Agriculture and Consumer Services v. Mid-Florida
Growers, Inc., 521 So.2d 101, 101-4 (Fla. 1988), cert. denied, 488 U.S. 870, 109 S.Ct. 180, 102 L.Ed.2d 149 (1988).










The eradication program called for the destruction all of the citrus trees affected by the

nematode and the first four trees past the last visibly affected tree.21 Because spreading decline

spreads so slowly, it is not considered an immediate threat and procedural due process requires a

hearing before, rather than after, the actual destruction.22

The destruction of diseased trees does not require compensation. 23 Even though it is

justified under the police power as necessary to protect neighboring property, destruction of trees

only suspected of being affected by the nematode does require compensation. 24 The state does

have to give compensation for the destruction of healthy but suspect trees because, although

infected, suspect trees do retain some value.25

Citrus Canker

Florida implemented a more aggressive program in its attempt to eradicate Asian strain of

citrus canker. This strain of citrus canker is caused by the bacterium Xanthomona~s axonopodis

pathovar citri. The bacterium causes defoliation, dieback, blemished fruit, reduced fruit quality,

and premature fruit drop (Schubert and Sun, 2001). Unlike the slow spreading decline, citrus

canker spreads rapidly by wind driven rain, flooding, air currents, insects, birds, human

movement within the groves, and movement of infected plants and seedlings (Schubert et al.,

2001). Symptoms may manifest as early as seven to fourteen days after infection26 (Schubert et

al., 2001), but may take up to 60 days or more to appear (Schubert et al.). However, the


21 See in~fra note 17.

22 See in~fra note 16.

23 See in~fra note 17.
24 Id.

25 Id.

26 Florida Department of Agriculture & Consumer Services v. City of Pompano Beach, 792 So.2d 539 (Fla. 4th
DCA 2001); 829 So. 2d 928 (Fla. 4th DCA. 2002).









maximum visualization does not occur until approximately 107 to 108 days after infection

(Gottwald et al., 2002).

In 2002, the Citrus Canker Law amendments --584.184 and 933.07(2), Florida Statutes,

required the destruction of all citrus trees within 1,900 feet of an infected tree and allow area-

wide search warrants.27,28 This enlarged the existing statutory 125- foot buffer zone that was

based on a study conducted in Argentina (Gottwald et al., 2002). Destruction of all citrus trees

within the 125-foot buffer had survived a number of court challenges. Citrus canker was

determined to be an imminent threat, which justified destruction of trees prior to a hearing.29'30

In cases that examined the legality of the USDA' s eradication program, the courts also

determined that all healthy but suspect commercial trees tI ithrin the 125 feet of an infected tree

did not require compensation because they were "incapable of any lawful use, it is of no value,

and it is a source of public danger."31,32

A study by Gottwald et al. (2002) determined that the 125-foot radius was inadequate

because it only captured 30-41% of infection spreading from a diseased tree (Gottwald et al.,

2002; Gottwald et al., 1989). Based on the Gottwald study, the Florida legislature ultimately

concluded that an enlarged 1,900-foot buffer was necessary and amended section 584. 184,

Florida Statutes.33 Procedurally, section 584. 184, Florida Statutes requires that owners be



27Fla. Stat. #933.07(2) (2002).

28Fla. Stat. #581.184 (2002).

29 Dennev v. Conner, 462 So.2d 534 (Fla. 1st DCA 1985).

30 Nordmann v. Florida Department of Agriculture and Consumer Services, 473 So.2d 278 (Fla. 5th DCA 1985).

31 See Department of Agriculture and Consumer Services v. Polk, 568 So.2d 35 (Fla. 1990).

32State Dept. of Agriculture and Consumer Services v. Varela, 732 So.2d 1146 (Fla. 3rd DCA 1999).

33See in~fra note 24.










notified of the impending destruction by order.34 The owner has the option to ask for a stay of

destruction in an appellate court where the only issues are whether the tree itself is infected and

whether the tree is within 1,900 feet of an infected tree.35 Since the disease spreads at a fast rate,

the court held that the state had adequate reason to not conduct a full hearing prior to eradicating

an "imminent danger."36 The owners may opt for a hearing after destruction.37 The hearing

determines if the destruction of exposed but healthy residential trees constitutes a taking and, if

so, the amount of compensation required.38 These hearings will determine if trees within the

1,900-foot buffer zone require compensation beyond the $55 provided by the statute.39 The

USDA program offered $26 per destroyed commercial tree.

Enlarging the buffer zone from 125 to 1,900 feet reignited legal challenges. In several

citrus canker takings cases, homeowners alleged that the FDACS was conducting unreasonable

searches of their property and taking trees within the 1,900-foot radius without allowing the

homeowner any "opportunity to be heard." Specifically, they alleged 1) that the 1,900-foot rule

established by the legislature did not establish probable cause of a tree being infected and

therefore did not provide any basis to search a property suspected of harboring an infected tree,

and 2) area-wide search warrants requested by the FDACS constituted an unreasonable search of








34 See in~fra note 26.
35 Id.

36 Id.

r7 Id.

38 Id.

39 Id.










properties for which probable cause was not established. The area-wide search warrants included

properties that did not necessarily harbor citrus trees within 1,900 feet of an infected tree.40

In Florida Dept. OfAgriculture and Consumer Services v. Haire, the court was asked to

determine the constitutionality of section 584.184 and 933.07(2), Florida StatuteS41 (Gottwald et

al., 1989). Procedurally, the court upheld previous decisions declaring that citrus canker was an

"imminent danger" and justified destruction prior to an "opportunity to be heard" for trees within

the 1,900-foot zone (Gottwald et al., 2002; Gottwald et al., 2006), but that area-wide warrants

were unconstitutional and a violation of the Fourth Amendment to the US Constitution' s

prohibition against unreasonable searches and seizures.42 Following these rulings, the FDACS

will still be able to seek warrants to search residential properties, but probable cause must be

established for each individually identified property.

In its examination of substantive due process, the court determined that the 1,900-foot

buffer zone bore a "reasonable relationship" to protecting the citrus industry (Gottwald et al.,

1989). The court noted that restricting the legislature to acting only in areas of scientific

certainty would result in a level of supervision hostile to our basic principles of government

(Gottwald et al., 1989). It is the charge of the elected legislative representatives, not the courts,

to decide the proper course of action to protect the public (Gottwald et al., 1989). The courts can

only overturn a legislative exercise of police power if it lacks a "reasonable relationship" to the

legitimate objective (Gottwald et al., 1989). Here, judicial intervention was not warranted

because the legislature based its actions on the advice of a Technical Advisory Committee and a

peer-reviewed and published study (Gottwald et al., 1989).

40 See in~fra note 1.

41 See in~fra note 29.

42 See in~fra note 1.









While the Haire court found the legislative action valid, the court reiterated that this did not

relieve the State from paying "just compensation" (Gottwald et al., 1989). The compensation in

the statute provided a floor value guaranteed to the affected owner, even if the tree was valueless

(Gottwald et al., 1989). This was valid because the homeowner still had the opportunity to have

a judicial determination of what was "just compensation" for the tree beyond this floor value. 43

In Patchen v. Dept. ofAgriculture and Consumer Services, the Florida Supreme Court was

asked whether healthy but suspect residential trees I irlhil 1, 900 feet of an infected tree were

without value.44 Previously, in Department of Agriculture and Consumer Services v. Polk, the

court held that healthy conanercial trees within a 125-foot buffer zone were without value and a

source of public danger. 45 The court in Patchen was asked to address whether this rationale

extended to the 1,900-foot buffer zone, particularly within a residential context.46 The court

neglected to answer this question, holding that the legislature had already decided that

homeowners who met the statutory requirements were entitled to a minimum level of

compensation, essentially conceding the point of whether cutting healthy trees amounted to a

taking.47 The court again reiterated that this does not prevent the homeowner from bringing a

judicial action to determine whether trees within 1,900 feet are of greater value than the $55

floor prescribed by the legislature, affirming that "what constitutes 'just compensation' was a

judicial function which could not be preempted by the legislature."48



43Id.: see also Rich v. Dept. of Agriculture and Consumer Services, 898 So.2d 1163 (Fla. 2nd DCA 2005).

44See intfia note 11.

45See intfia note 29.

46 Patchen v. Dept. of Agriculture and Consumer Services, 906 So.2d 1005 (Fla. 2005).
47Id.

48See intfia note 1: see also note 11.









The control of citr-us canker, like spreading decline, justifies the exercise of police power.

In both instances, the legislature eradication programs were valid because they bore a "rational

relationship" to protecting the citrus industry. However, the procedural due process

requirements are different for citrus canker. Citrus canker, unlike spreading decline, poses an

imminent danger, thus justifying the lack of a full hearing prior to destruction. It is likely that

citrus greening would have a similar status.

The one remaining unsettled legal issue regarding the CCEP concerns compensation, even

with respect to canker-infected trees. The state does not have to give compensation for canker

infected commercial trees because they are without value, but the status of residential tree value

is still unsettled. However, unlike spreading decline, healthy but suspect trees may or may not

be subj ect to compensation under common law, yet it appears that the Florida courts are willing

to consider destruction of healthy trees as a compensable taking.

Currently, there is an apparent conflict in the law between the 3rd and 4th appellate districts.

The 3rd District Court of Appeal has held that trees exposed to canker have "'no marketable

value' and therefore, no damages can be awarded."49 The 4th District Court of Appeal, which

includes Broward, Indian River, Okeechobee, Palm Beach, St. Lucie, Martin counties, has

allowed homeowners in Broward County to move forward with a class action suit that contends

that the FDACS must provide replacement costs for their mature citrus trees, including all

ancillary costs, even for infected trees.'o Currently there are nine plaintiffs representing a

potential class of about 100,000 residential citr-us owners in Broward Countys1 (Parsons, Adorno,

and Yoss, 2006). It is still an open question as to whether a healthy but suspect tree 0I ilhinl 1,900

49 See in~fra note 30.

so See in~fra note 24.
s' Id.









feet of an infected tree may have value beyond the $55 floor value assigned by the legislature,

and whether an infected residential tree has value in the 4th Appellate District.

Lessons for Citrus Greening

Like citrus canker, citrus greening (Huanglongbing) is a fast-spreading and highly

destructive disease that is of great concern to Florida citrus growers and the FDACS. Citrus

greening is caused by the bacteria Can2didatus Liberibacter spp. spread by two species of psyllids

(Chung and Brlansky, 2006). Unlike citrus canker, citrus greening causes rapid decline and death

of citrus trees within a few years rather than a mere drop in productivity (Halbert and Keremane,

2004). To prevent use of residential citrus trees as host plants for psyllid populations in areas

testing positive for greening, the state of Florida may need to begin removing residential trees

once agamn.

The spreading decline and citrus canker cases have paved the way for a more effective

Citrus Greening Control Program (CGCP) that may not fall prey to costly injunctions. To survive

legal challenges, a CGCP must first establish a radius of likely infection based on a scientific

study similar to the Gottwald et al. studies (2006; 1989). Warrants that list specific property

addresses and provide probable cause to search suspect premises will be required. Being within

the radius established by the scientific study will suffice for probable cause. Since citrus

greening is fatal, unlike citrus canker, courts will likely allow FDACS to destroy infected trees

without compensation, if indeed the biological justification for tree removal still remains (it may

be too little too late). This would be the case even for the 4th Appellate District. However,

suspect trees taken within the designated radius will likely be judged to have value, requiring

compensation. The level of compensation can not be legislated. The law regarding agricultural

pests and the defensive taking of trees is relatively settled. It is likely that a citrus greening

eradication program, should one ever be deemed necessary, would survive legal challenges and


100