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Inter-Rotational Effects of Fertilization and Weed Control Treatments on the Productivity and Soil Nutrient Availability...

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Title:
Inter-Rotational Effects of Fertilization and Weed Control Treatments on the Productivity and Soil Nutrient Availability in Juvenile Loblolly Pine Plantations
Physical Description:
1 online resource (185 p.)
Language:
english
Creator:
Subedi, Praveen
Publisher:
University of Florida
Place of Publication:
Gainesville, Fla.
Publication Date:

Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Forest Resources and Conservation
Committee Chair:
Jokela, Eric J
Committee Members:
Martin, Timothy A
Vogel, Jason

Subjects

Subjects / Keywords:
biomass -- carbon -- competition -- diversity -- loblolly -- plantation -- respiration -- rotation -- spodosol
Forest Resources and Conservation -- Dissertations, Academic -- UF
Genre:
Forest Resources and Conservation thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract:
On a north Florida Spodosol, the inter-rotational effects of fertilization and weed control treatments on the productivity, understory community dynamics, and soil respiration rates in loblolly pine (Pinus taeda (L.)) stands were investigated using  two replicated,randomized complete block design experiments The first rotation treatments were:control (C), fertilizer (F), weed control (W), and fertilizer+weed control (FW). One experiment was actively retreated as in the previous rotation, while the second was left untreated (CC, CF, CW, and CFW). A common full-sib loblolly pine family was planted in both experiments. After three growing seasons, the second rotation pine growth consistently out-performed the first rotation. The actively retreated FW treatment had 4-fold higher aboveground pine biomass than the C (7.7 Mg.ha-1) treatment; the untreated CF(17.9 Mg.ha-1) treatment had 1.5-fold higher pine biomass than the CFW treatment. Lower growth response in the CFW treatment was associated with lower soil P availability (r = 0.8; pFW treatments reduced the understory diversity (Shannon-Weiner index H’) by 2.7-fold compared to the F and CF treatments. In both experiments, herbicide applications suppressed shrubs, but favored grasses in the FW and CFW treatments.Annual soil respiration rates (Mg.C.ha-1.yr-1) were 1.3fold higher in the F and CF treatments compared to the W (10.7) and CW (11.4) treatments. Results suggest that understory mulching and forest floor incorporation may alleviate the need for P fertilization during stand establishment on flatwoods Spodosols previously fertilized with P.
General Note:
In the series University of Florida Digital Collections.
General Note:
Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility:
by Praveen Subedi.
Thesis:
Thesis (M.S.)--University of Florida, 2013.
Local:
Adviser: Jokela, Eric J.

Record Information

Source Institution:
UFRGP
Rights Management:
Applicable rights reserved.
Classification:
lcc - LD1780 2013
System ID:
UFE0046006:00001

MISSING IMAGE

Material Information

Title:
Inter-Rotational Effects of Fertilization and Weed Control Treatments on the Productivity and Soil Nutrient Availability in Juvenile Loblolly Pine Plantations
Physical Description:
1 online resource (185 p.)
Language:
english
Creator:
Subedi, Praveen
Publisher:
University of Florida
Place of Publication:
Gainesville, Fla.
Publication Date:

Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Forest Resources and Conservation
Committee Chair:
Jokela, Eric J
Committee Members:
Martin, Timothy A
Vogel, Jason

Subjects

Subjects / Keywords:
biomass -- carbon -- competition -- diversity -- loblolly -- plantation -- respiration -- rotation -- spodosol
Forest Resources and Conservation -- Dissertations, Academic -- UF
Genre:
Forest Resources and Conservation thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract:
On a north Florida Spodosol, the inter-rotational effects of fertilization and weed control treatments on the productivity, understory community dynamics, and soil respiration rates in loblolly pine (Pinus taeda (L.)) stands were investigated using  two replicated,randomized complete block design experiments The first rotation treatments were:control (C), fertilizer (F), weed control (W), and fertilizer+weed control (FW). One experiment was actively retreated as in the previous rotation, while the second was left untreated (CC, CF, CW, and CFW). A common full-sib loblolly pine family was planted in both experiments. After three growing seasons, the second rotation pine growth consistently out-performed the first rotation. The actively retreated FW treatment had 4-fold higher aboveground pine biomass than the C (7.7 Mg.ha-1) treatment; the untreated CF(17.9 Mg.ha-1) treatment had 1.5-fold higher pine biomass than the CFW treatment. Lower growth response in the CFW treatment was associated with lower soil P availability (r = 0.8; pFW treatments reduced the understory diversity (Shannon-Weiner index H’) by 2.7-fold compared to the F and CF treatments. In both experiments, herbicide applications suppressed shrubs, but favored grasses in the FW and CFW treatments.Annual soil respiration rates (Mg.C.ha-1.yr-1) were 1.3fold higher in the F and CF treatments compared to the W (10.7) and CW (11.4) treatments. Results suggest that understory mulching and forest floor incorporation may alleviate the need for P fertilization during stand establishment on flatwoods Spodosols previously fertilized with P.
General Note:
In the series University of Florida Digital Collections.
General Note:
Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility:
by Praveen Subedi.
Thesis:
Thesis (M.S.)--University of Florida, 2013.
Local:
Adviser: Jokela, Eric J.

Record Information

Source Institution:
UFRGP
Rights Management:
Applicable rights reserved.
Classification:
lcc - LD1780 2013
System ID:
UFE0046006:00001


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1 INTER ROTATIONAL EFFECTS OF FERTILIZATION AND WEED CONTROL TREATMENTS ON THE PRODUCTIVITY AND SOIL N U TRIENT AVAILABILITY IN JUVENILE LOBLOLLY PINE PLANTATION S By PRAVEEN SUBEDI A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2013

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2 2013 Praveen Subedi

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3 To my parents

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4 ACKNOWLEDGMENTS I would li ke to extend m y sincere thanks to my graduate a dvisor, Dr. Eric J. Jokela, for his constant guidance and support throughout the study. His extensive inputs and helpful comments on the drafts of this thesis helped me develop and improve my way of communicat ing ideas. He has been a good mentor and I wish him all the best in his endeavors. Many thanks go to other members of my graduate committee, Dr. Jason G. Vogel and Dr. Timothy A. Martin, for their constant support during the course of the study and helpful advice that improved this thesis. I am much obliged to Dr. Salvador Gezan for his help with statistical analyses. I am extremely grateful to the Forest Biology and Research Cooperative for supporting my graduate study and funding this research and Rayonie r for maintaining and providing access to the study site. I am especially grateful to the following people for their cooperation and hard work in all stages of th is research : G Lokuta A. Milligan and B. G ottloeb (collecting inventory data understory sa mples and soil samples ); J. McCafferty and B. Caudill (processing understory samples); B Ruffin (collecting soil samples) ; and, W. Wood ( identifying understory species ). I would also like to thank C. Drum, M. Wightman, and A. Garcia for their moral suppo rt in the lab. Many thanks go to my friends, especially Binod, Bina, Pradeep, and Santosh, for their friendship, encouragement, and support through this period. Finally, I would like to thank my family for always being there and encouraging me to pursue m y dream.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENT S ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 8 LIST OF FIGURES ................................ ................................ ................................ ........ 12 ABSTRACT ................................ ................................ ................................ ................... 14 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 16 Background ................................ ................................ ................................ ............. 16 Problem ................................ ................................ ................................ .................. 18 Objectives ................................ ................................ ................................ ............... 20 2 EFFECTS OF FERTILIZATION AND WEED CONTROL TREATMENTS ON THE INTER ROTATIONAL PRODUCTIVITY AND SOIL NUTRIENT AVAILABILITY OF LOBLOLLY PINE STANDS IN NORTH FLORIDA ................... 21 Introduction ................................ ................................ ................................ ............. 21 Methods ................................ ................................ ................................ .................. 24 Study Are a ................................ ................................ ................................ ........ 24 Study Design ................................ ................................ ................................ .... 25 Data Preparation and Analysis ................................ ................................ ......... 28 Results ................................ ................................ ................................ .................... 32 Inter rotational Comparison of Height Response of 3 year old Loblolly Pines .. 32 Total Aboveground Biomass Accumulation Lobloll y Pine .............................. 32 Aboveground component biomass accumulation and dry matter allocation patterns loblolly pine ................................ ............................ 33 Understory and total aboveground biomass accumulation: ....................... 34 Nutrient Accumulation ................................ ................................ ...................... 36 Nutrient accumulation in the aboveground components of loblolly pi ne ..... 36 Nutrient accumulation in the understory vegetation ................................ ... 39 Soil Nutrient Supply ................................ ................................ .......................... 41 Discussion ................................ ................................ ................................ .............. 42 Summary and Conclusions ................................ ................................ ..................... 49 3 INTER ROTATIONAL EFFECTS OF FERTILIZATION AND HERBICIDE ON UNDERS TORY VEGETATION ABUNDANCE, RICHNESS AND DIVERSITY IN JUVENILE LOBLOLLY PINE STANDS ................................ ................................ ... 67 Introduction ................................ ................................ ................................ ............. 67 Methods ................................ ................................ ................................ .................. 70

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6 Study Area ................................ ................................ ................................ ........ 70 Study Design ................................ ................................ ................................ .... 71 Sampling ................................ ................................ ................................ .......... 74 Data Analysis ................................ ................................ ................................ ... 75 Results ................................ ................................ ................................ .................... 78 Species Richness ................................ ................................ ............................. 78 Life form Biomass ................................ ................................ ............................ 79 Species Diversity ................................ ................................ .............................. 81 Understory Vegetation Communities ................................ ................................ 82 Discussion ................................ ................................ ................................ .............. 85 Summary and Conclusions ................................ ................................ ..................... 92 4 INTER ROTATIONAL EFFECTS OF FERTILIZER AND WEED CONTROL TRE ATMENTS ON SOIL RESPIRATION IN YOUNG PINUS TAEDA (L.) STANDS GROWING ON A FLORIDA SPODOSOL ................................ ............. 102 Introduction ................................ ................................ ................................ ........... 102 Methods ................................ ................................ ................................ ................ 105 Study Area ................................ ................................ ................................ ...... 105 Study Design ................................ ................................ ................................ .. 106 Soil Respiration ................................ ................................ .............................. 110 Soil Nutrient Supply ................................ ................................ ........................ 111 Aboveground Biomass Measurement ................................ ............................ 111 Decomposition of O rganic Matter ................................ ................................ ... 112 Data Analysis ................................ ................................ ................................ 112 Results ................................ ................................ ................................ .................. 114 Soil Respiration ................................ ................................ .............................. 114 Mean soil respiration ................................ ................................ ................ 114 Annual soil respiration ................................ ................................ .............. 115 Soil Temperature and Soil Moisture ................................ ............................... 116 Decomposition of a Common Substrate among Treatments .......................... 117 Discussion ................................ ................................ ................................ ............ 117 Summary and Conclusions ................................ ................................ ................... 125 5 CONCLUSIONS ................................ ................................ ................................ ... 137 APPENDIX A ALLOMETRIC EQUATIONS FOR THE ESTIMATION OF ABOVEGROUND BIOMASS COMPONENTS OF LOBLOLLY PINE ................................ ................ 143 B FOLIAR NUTRIENT CONCENTRATIONS OF JUVENILE LOBLOLLY PINE STANDS ................................ ................................ ................................ ............... 144 C UNDERSTORY SPECIES BIOMASS AND NUTRIENT ACCUMULATION .......... 149 D SOIL NUTRIENT SUPPLY ................................ ................................ ................... 163

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7 LIST OF REFERENCES ................................ ................................ ............................. 165 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 185

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8 LIST OF TABLES T able page 2 1 Analysis of variance of total aboveground biomass accumulation by stand age for young loblolly pine stands growing in the actively managed retreated and untreated carryover experiments on Spodosols in north Florida. ................. 51 2 2 Aboveground biomass accumulation among treatments in a second rotation 2 year old loblolly pine stand growing in the actively managed retreated experiment on Spodosols in north Florida. ................................ ......................... 52 2 3 Abovegroun d biomass accumulation among treatments in a second rotation 2 year old loblolly pine stand growing in the untreated carryover experiment on Spodosols in north Florida. ................................ ................................ ........... 53 2 4 Effects of silv icultural treatments on the macro and micro nutrient accumulation in the aboveground biomass of two year old loblolly pine and understory vegetation ................................ ................................ ......................... 54 2 5 Correlation coefficients (r) betwe en soil nutrient supply rates during the growing season and aboveground biomass accumulation in loblolly pine stands ................................ ................................ ................................ ................. 59 3 1 Mean richness, evenness, Shannon, and Simpson species diversity for understory vegetation growing in the actively managed retreated experiment of a second rotation, 2 year old loblolly pine plantation in north Florida. ............ 94 3 2 Mean richness, evenness, Shannon, and Simpson species diversity for understory vegetation growing in the untreated carryover experiment of a second rotation, 2 year old loblolly pine plantation in north Florida. ................... 94 3 3 Signifi cance groupings and agreement statistics (A) of understory vegetation communities in a second rotation, 2 year old loblolly pine plantation in north Florida. ................................ ................................ ................................ ............... 95 3 4 Indicator values (IV) of in dicator species for the understory vegetation communities in a second rotation, 2 year old loblolly pine plantation growing in north Florida. ................................ ................................ ................................ ... 95 3 5 Coefficients of determination (R squared) f or the correlations between ordination distances and distances in the original n dimensional space for the actively managed retreated and the untreated carryover experiments ............... 96 3 6 Pearson cor relation coefficients (r) for environmental variables associated with axes 1 and 2 in the NMS ordination for the actively managed retreated and untreated carryover experiment in north Florida. ................................ ......... 96

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9 3 7 Pearson correlation coefficients (r) of understory species with axes 1 and 2 from the NMS ordination of the actively managed retreated experiment in north Florida. ................................ ................................ ................................ ...... 97 3 8 Pearson corre lation coefficients (r) of understory species with axes 1 and 2 from the NMS ordination of the untreated carryover experiment in north Florida. ................................ ................................ ................................ ............... 98 4 1 Partial ANOVAs for repeated measures anal ysis of soil CO2 efflux rates from November 2010 to April 2012 in two year old loblolly pine stands growing in the actively managed retreated and untreated carryover experiments ............. 127 4 2 Stepwi se regressions of factors influencing soil respiration rates for Spodosols that supported juvenile loblolly pine stands in the actively managed retreated and untreated carryover experiments in north Florida ....... 128 4 3 ANOVA for the decomposition of Betula papyrifera (Marsh.) tongue depressors in 2 year old loblolly pine stands in the actively managed retreated and untreated carryover experiments on Spodosols in north Florida. 129 4 4 Effects of fertilization and weed control on the mass loss of a common organic substrate ( Betula papyrifera (Marsh.) tongue depressors) over a 12 month period ................................ ................................ ................................ ..... 129 4 5 Correlation between soil respiration rates and soil nutrient supply during the growing season for Spodosols supporting juvenile loblolly pine stands in the actively managed retreated and untreated carryover experiments ................... 130 A 1 Allometric equations a for estimating foliage, stemwood with bark, branch and aboveground tree biomass in young loblolly pine stands growing on Spodosols of the southeastern United States. ................................ .................. 143 B 1 Effects of silvicultural treatments on the foliar nutrient concentrations of one year old loblolly pine for the actively managed retreated experiment on Spodosols in north Florida. ................................ ................................ ............... 144 B 2 Effects of silvicultural treatments on the foliar nutrient concentrations of one year old loblolly pine for the untreated carryover experiment on Spodosols in north Florida. ................................ ................................ ................................ .... 145 B 3 Effects of silvicultural treatments on the foliar nutrient concentrations of two year old loblolly pine for the actively managed retreated experiment on Spodosols in north Florida. ................................ ................................ ............... 146 B 4 Effects of silvicultural treatments on the foliar nutrient concentrations of two year old loblolly pine for the untreated carryover experiment on Spodosols in north Florida. ................................ ................................ ................................ .... 147

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10 B 5 Analysis of variance for foliar nutrient concentration of loblolly pine stands in the first and second growing season for the actively managed retreated and untreated carryover experiments in north Florida. ................................ ............ 148 C 1 Aboveground biomass accumulation in the understory species for the actively managed retreated and untreated carryover experiments in north Florida. ................................ ................................ ................................ ............. 150 C 2 Percentage contribution by species to the total understory aboveground biomass in the actively managed retreated and untreated carryover experiments in north Florida. ................................ ................................ ............ 151 C 3 Nitrogen accumulation (kg.ha 1 ) in the understory species for both the actively managed retreated and untreated carryover experiments in north Florida. ................................ ................................ ................................ ............. 152 C 4 Phosphorus accumulatio n (kg.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Florida. ................................ ................................ ................................ ............. 153 C 5 Potassium accumulation (kg.ha 1 ) in the understory sp ecies in both the actively managed retreated and untreated carryover experiments in north Florida. ................................ ................................ ................................ ............. 154 C 6 Calcium accumulation (kg.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Florida. ...... 155 C 7 Magnesium accumulation (kg.ha 1 ) in the understory species in both the actively managed retreated and untreated carryov er experiments in north Florida. ................................ ................................ ................................ ............. 156 C 8 Sulfur accumulation (kg.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Florida. ...... 157 C 9 Boron accumulation (g.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Florida. ...... 158 C 10 Copper accumulation (g.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Florida. ...... 159 C 11 M anganese accumulation (g.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Florida. ................................ ................................ ................................ ............. 160 C 12 Zinc accumulation (g.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Florida. ...... 161

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11 C 13 Macro and micro nutrient accumulation in the belowground biomass of Andropogon spp. for the untreated carryover experiment in north Florida. ....... 162 D 1 Soil nutrient supply rates (micrograms/10cm 2 /8weeks; 0 15 cm) for the actively managed retreatment experiment i n north Florida. .............................. 163 D 2 Soil nutrient supply rates (micrograms/10cm 2 /8weeks; 15 cm) for the untreated carryover experiment in north Florida. ................................ .............. 164

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12 LIST OF FIG URES Figure page 2 1 Layout of the actively managed retreatment and the untreated carryover experiments on Spodosols near Gainesville, FL. ................................ ................ 60 2 2 Heights of the first rotation 3 year old loblolly pines at the original IMPAC study sites compared to those in the second rotation actively managed retreated and untreated carryover experiments ................................ .................. 61 2 3 Total aboveground biomass accumulation for second rotation loblolly pine stands. ................................ ................................ ................................ ................ 62 2 4 Dry matter allocation in the aboveground components of second rota tion, two year old loblolly pine stands ................................ ................................ ......... 63 2 5 Phosphorus, Mn, and Zn supply ................................ ................................ ......... 64 2 6 Relationship between soil P supply and the a boveground pine biomass in the untreated carryover experiment on Spodosols in north Florida. ......................... 64 2 7 Mehlich III extractable P concentrations in the soils of the untreated carryover experiment in north Florida. ................................ ................................ ................ 65 2 8 Aboveground biomass and nutrient accumulation ................................ .............. 66 3 1 Life form biomass for the understory vegetation co mmunity .............................. 99 3 2 Shannon Weiner diversity for the life forms (shrubs and grasses) of the understory community ................................ ................................ ...................... 100 3 3 A two dimensi onal ordination plot derived from NMS ................................ ....... 101 3 4 Yearly abundance of Androp o go n spp. and Dicanthelium spp. in second rotation, loblolly pine plantations in north Florida. ................................ ............. 101 4 1 Effects of fertilization and weed control treatments on the least square mean soil respiration rates (CO 2 efflux), mean soil temperature, and mean volumetric soil moisture content ................................ ................................ ....... 131 4 2 Least square mean soil respiration rates ................................ .......................... 132 4 3 Effects of location (Bed and Inter bed positions) on the least square mean soil respiration rates (C O 2 efflux), mean soil temperature, and mean volumetric soil moisture content ................................ ................................ ....... 133

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13 4 4 Effects of root exclusions (with and without) on the least square mean soil respiration rates (CO 2 efflux), mean soil temperature, and mean volumetric soil moisture content ................................ ................................ ......................... 134 4 5 Effects of fertilization and weed control treatments on total annual soil respiration (Nov 2010 Nov 2011) ................................ ................................ ..... 135 4 6 Effects of fertilization and weed control treatments on the decomposition of Betula papyrifera (Marsh.) tongue depressors ................................ .................. 136

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14 Abstract of Thesis Presented to th e Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Master of Science INTER ROTATIONAL EFFECTS OF FERTILIZATION AND WEED CONTROL TREATMENTS ON THE PRODUCTIVITY AND SOIL N U TRIENT AVAILABILITY IN JUVENILE LOBLOLLY PINE PLANTATION S By Praveen Subedi August 2013 Chair: Eric J. Jokela Major: Forest R esources and C onservation On a north Florida Spodosol, the inter rotational effects of fertilization and weed control treatments on the productivity, understory community dynamics, and soil respiration rates in loblolly pine ( Pinus taeda (L.)) stands were investigated using two replicated, randomized complete block design experiments The first rotation trea tments were: control (C), fertilizer (F), wee d control (W), and fertilizer+weed control (FW). One experiment was actively retreated as in the previous rotation, while the second was left untreated (C C C F, C W and C FW ). A common full sib loblolly pine family was planted in both experiments. After thr ee growing seasons, the second rotation pine growth consistently out performed the first rotation. The actively retreated FW treatment had 4 fold higher aboveground pine biomass than the C ( 7.7 Mg.ha 1 ) treatment; the untreated C F (17.9 Mg.ha 1 ) treatment had 1.5 fold higher pine biomass than the C FW treatment. Lower growth response in the C F W treatment was associated with lower soil P availability (r = 0.8; p<0.01) and historical P movement from the E to Bh/Bt horizons T he FW and C FW treatments reduced th e understory diversity ( Shannon Weiner index fold

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15 compared to the F and C F treatments. In both experiments, herbicide application s suppressed shrubs, but favored grasses i n the FW and C FW treatment s Annual soil respiration rates (Mg.C.ha 1 .yr 1 ) were 1.3 fold higher in the F and C F treatments compared to the W (10.7) and C W (11.4) treatments. Results suggest that understory mulching and forest floor incorporation may alleviate the need for P fertilization during stand establishment on flatwoods Spodosols previously fertilized with P.

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16 CHAPTER 1 INTRODUCTION Background Southern pine plantations cover more than 18% of the 85 million ha of the forested area in the southern United States (Hartsell and Conner, 2013). These pine plantations predominant ly consist of loblolly pine ( Pinus taeda (L.)) that has a wide natural range and covers vast areas of the Atlantic and Gulf Coastal Plain (Schmidtling, 2001). On well drained productive sites, loblolly pine grows more rapidly than the other southern pine s pecies. However, many of the loblolly pine stands growing in this region occur on nutrient poor soils. Within the lower Coastal Plain region, for example, soils are generally nitrogen (N) and phosphorus (P) limited and are characterized by being poorly dra ined Spodosols with fluctu ating and shallow water tables. Over the past six decades, pine plantations in the U.S. South have increased from 0.7 million ha in the 1950s to almost 15.4 million ha in the 2000s (Zhang and Polyakov, 2010).With an ever increasin g demand for forest products and a dwindling forest land base for production, southern pine plantations will continue to play a major addition, intensive forest management systems aimed at ameliorating site conditions and improving pine productivity are critical to the success of these plantations. Southern pine plantations in the lower Coastal Plain are now among the most intensively managed forests in the world. Technologi cal advancements in silvicultural techniques during the past few decades have resulted in increased productivity over a wide array of southern pine sites (Fox et al. 2007 a ). Mechanical site preparation, competing vegetation control,

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17 fertilization, and pla nting of genetically improved nursery stock have all enhanced the productive potential and yield of these forests (Colbert et al. 1990; Jokela et al. 2004; Carter and Foster, 2006). The potential growth rates of intensively managed loblolly pine forests on some sites in the southern U.S. now exceed 29 m 3 ha 1 yr 1 (Borders and Bailey, 2001), and their rotation lengths have been reduced by nearly 50% compared to intensive management systems for loblolly pine plantations are high, financial returns from these short rotation and high yielding systems are promising (Allen et al. 2005). As a result, more than 800 million loblolly pine seedlings are planted annually in the sout hern U.S. (McKeand et al. 1999). Fertilizer additions and weed control treatments are the common silvicultural practices used in southern pine stands that grow on nutrient limited soils (Fox et al. 2007 a ). Gains in pine yield following such treatments ar e primarily due to increased overall soil nutrient availability (Colbert et al. 1990). The spatial extent of annual fertilizer additions in southern pine plantations has increased by almost 5 fold when compared to the early 1990s (Albaugh et al. 2007). A lmost 0.5 million ha of loblolly pine stands were fertilized annually after 1999; 90% and 64% of which included P and N, respectively (Albaugh et al. 2007). In addition, fertilizer prices have increased by almost 3 fold in the last decade, due to changing global supply and demand (USDA, 2012). In that context, understanding the role that historical silvicultural treatments like fertilizer additions and understory competition control have on growth dynamics, soil nutrient availability, cycling, and other so il and ecosystem processes represents an important

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18 and pressing scientific opportunity for improving our understanding and development of intens ive forest management systems. Problem Previous research conducted on sandy Spodosols in the U.S. lower Coastal Plain have documented that N and P additions are critical for improving the productivity and survival of southern pine stands (Pritchett and Comerford, 1982; Allen, 1987; Jokela and Stearns Smith, 1993). When coupled with genetically improved planting stoc k, almost two to four fold gains in pine productivity have been attained (Jokela and Martin, 2000; Fox et al. 2007 a ). Since higher nutrient demands associated with these rapidly growing stands have the potential to induce micro nutrient deficiencies (Jok ela et al. 1991a; Allen et al. 2005) and limit growth (Vogel and Jokela, 2011), fertilization on some sites now includes micronutrients in addition to N and P (Albaugh et al. 2007; Vogel and Jokela, 2011). A few studies have suggested the potential for l ong term nutrient (e.g., P) re cycling and fertilizer carryover effects on growth in subsequent rotations (Polglase et al. 1992a; Comerford et al. 2002; Everett and Palm Leis, 2009). At the same time, concerns over the sustainability of intensively manag ed forests is increasing as a result of possible site nutrient depletion from frequent harvests (Hatchell et al. 1970 ), alteration of physical and chemical properties of soils ( Tiarks, 1990 ; Powers 199 9 ), and reductions in soil carbon (C) from sustained control of competing vegetation (Rifai et al. 2010; Vogel et. al., 2011). Considering the relatively short history of intensive forest management systems in the U.S. South, additional knowledge regarding their long term effects on the growth dynamics of l oblolly pine plantations in suc cessive rotations is warranted.

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19 Understanding vegetation responses, plant diversity and community dynamics is also central for defining and developing sustainable forest management systems for the future (Brown et al. 2001). Our understanding of the effects of nutrient amendments on the understory plant community dynamics in forested ecosystems is limited. Understory vegetation has varying ecological roles ranging from facilitation of seedling regeneration to organic matter d ecomposition and nutrient cycling (Nilsson and Wardle, 2005). conditions (Tilman and Downing, 1994), silvicultural treatments like fertilizer additions and sustained control of competing vegetation could influence the long term productivity of a site. Clearly, studies conducted over more than a single rotation are necessary for understanding and developing sustainable management systems for the future that also include elements of maintaining plant biodiversity. Global concerns for increasing atmospheric CO 2 concentrations and associated climate change has placed an emphasis on ways to sequester C (Jandl et al. 2007). While intensive forest management practices have expedited g ains in yield in southern pine plantations, making them an important C sink (Maier and Kress, 2000), the effects of these practices on CO 2 release via soil respiration (SR) are still inconclusive. For example, fertilization has been reported to either incr ease (Tyree et al. 2006), decrease (Maier and Kress, 2000), or result in no net change (Samuelson et al. 2009) in SR in southern pine stands. In addition, sustained control of competing understory vegetation has been associated with reduced soil C (Rifai et al. 2010; Vogel et al. 2011). On nutrient limited sites, where decomposition of soil organic C facilitates mineralization of N and P, reductions in soil organic C could affect long term nutrient supply and

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20 ultimately growth and C sequestration at the site. Again, most studies to date have been limited to a single rotation and inter rotational effects of fertilization and understory competition control treatments on SR and organic matter decomposition processes are not clearly understood and justify fu rther investigation. Objectives In nutrient limited Spodosols ( Ultic A laquods ) of north Florida, two replicated experiments were established using a common genetic source of loblolly pine on sites with a prior history of rotation long fertilizer additions and sustained elimination of competing vegetation. One experiment (actively managed retreated) was retreated as in the first rotation, while the second (untreated carryover) was left untreated to investigate the factors affecting the second rotation growth dynamics, soil nutrient availability, soil respiration, and understory plant community dynamics in a juvenile loblolly pine stand. After three growing seasons, this study examined the inter rotational effects of fertilization and weed control treatments o n: 1. aboveground biomass and nutrient accumulation of the pine and understory components, and soil nutrient supply for an actively managed and untreated carryover experiments (Chapter 2), 2. understory vegetation abundance, diversity, and composition (Chapter 3 ), and 3. soil respiration and decomposition of a common organic substrate ( Betula papyrifera (Marsh.) tongue depressors) (Chapter 4). Findings from this study should aid in closing the gaps in our understanding of site productivity and long term sustainabili ty of intensively managed loblolly pine stands. In addition, the results should improve existing nutrient management strategies for this species in the South.

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21 CHAPTER 2 EFFECTS OF FERTILIZA TION AND WEED CONTRO L TREATMENTS ON THE INTER ROTATIONAL PRODUCT IVITY AND SOIL NUTRI ENT AVAILABILITY OF LOBLOLLY PINE STANDS IN NORTH FLORIDA Introductio n Over the last six decades, plantation silviculture in the southern United States has gone through a series of changes that have enhanced the productive capacity of s outhern pine stands (Jokela et al., 2004; Fox et al., 2007a). Coastal Plain pine forests in the southern U.S. are among the most intensively managed in the world. Fertilization and understory competition control are the common silvicultural practices used, and when combined with suitable site preparation techniques and deployment of genetically improved planting stock, improvements in yield can range from two to four fold compared to extensively managed loblolly pine ( Pinus taeda L.) stands (Allen et al., 1990; Colbert et al., 1990; Neary et al., 1990a; Fox et al., 2007a). As the global population continues to increase, intensive forest management systems will undoubtedly play a major role in the Southeast U.S. and other parts of the world for meeting the ever burgeoning demand for forest product and other related ecosystem services (Sedjo and Botkin, 1997). However, considering the relatively short history and use of intensive forest management systems (since the arise regarding their l ong term sustainability. Concern about s ustainability of intensively managed, short rotation pine plantations generally centers on two areas : long term site productivity (Fox, 2000) and maintenance of biodiversity (Jeffries et al., 2010). Understory plant communities in managed forest stands are often thought of as competitors for above and below ground site resources such as water, nutrients, light, and growing space (Morris et al., 1993; Collet et al., 1996; Zutter et al., 1999; Zhang et

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22 al., 2013 ). Fro m the perspective of ecosystem diversity, however, these plant communities are important elements. They may help support long term site sustainability by increasing species richness and functional diversity of the forest ecosystem, and also aid in ecosyste m adaptation to abiotic and biotic stresses and disturbances through, for example, nutrient cycling processes (Tilman et al., 2001; Zak et al., 2003; Folke et al., 200 4; Nilsson and Wardle, 2005). Although understory competition for available soil nutrient s represents one of the primary causes for lower growth rates in young southern pine stands (Neary et al., 1990b), a study conducted by Smethurst and Nambiar (1995) on the second rotation crop of Pinus radiata (D.) showed that allowing competing vegetation in the understory reduced nitrogen (N) leaching and increased N mineralization upon their senescence. On sandy soils, where soil organic carbon (C) serves an important function in aiding moisture and nutrient retention, understory vegetation may also pla y a role in maintaining both soil organic C and serving as a nutrient sink for elements such as N and phosphorus (P), especially during the early stages of stand development (Boring et al., 1981; Gholz and Fisher, 1982; Gholz et al., 1985; Smethurst and Na mbiar, 1995; Blazier et al ., 2005, Rifai et al., 2010). When sustained understory competition control treatments have been applied on some sites using herbicide applications, however, reductions in soil C and N pools have been reported (Laiho et al., 2003; Echeverria et al., 2004; Sarkhot et al., 2007; Sartori et al., 2007; Rifai et al., 2010; Vogel et al., 2011). In that context, it is important to understand whether the silvicultural treatments used to support short rotation, intensively managed pine plan tations affect understory re initiation a nd soil C and nutrient levels. It follows that as soil organic matter

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23 decomposes, nutrients like N and P are mineralized and made available for pine uptake and biogeoc hemical cycling. Silvicultural treatments that c ould potentially increase or decrease soil organic matter could have the potential to influence long term nutrient supply to the site (Jurgensen et al., 1997). Previous research conducted on sandy Spodosols in the U.S. lower Coastal Plain have documented t hat N and P are both growth limiting nutrient elements, and that fertilization is a cost effective treatment that forest managers can use to enhance growth and financial returns (Pritchett and Llewellyn, 1966; Bengtson, 1979; Pritchett and Comerford, 1982; Allen, 1987; Jokela and Stearns Smith, 1993; Fox et al., 2007b; Albaugh et al., 2009). Since higher nutrient demands associated with these intensively managed stands have the potential to induce micro nutrient deficiencies (Stone 1990; Jokela et al., 1991 a; Allen et al., 2005) and limit growth (Vogel and Jokela, 2011), fertilization on some sites now includes B, Cu, and Mn, in addition to N, P, and K (Jokela et al., 1991b; Albaugh et al. 2007; Vogel and Jokela, 2011). In that context, it is important to un derstand the role of residual nutrients from past fertilization activities, if any, to support the growth of newly planted stands. For example, P has been shown to readily recycle in fertilized pine stands (Polglase et al., 1992a) and the residual P from p ast fertilization has the potential to meet the nutrient demands and early growth requirements of newly planted stands (Ballard, 1978; Comerford et al., 2002; Everett and Palm Leis, 2009). C omparative studies over multiple rotations will enable direct asse ssment of the effects of management practices on long term site productivity. D irect assessment of long term site productivity can be an arduous task, and the examples that exist in the literature have rarely attempted to combine both fertilization

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24 and wee d control assessments (Keeves, 1966; Nambiar, 1996). Moreover d ifferences in site management and the planting stock genetics used between rotations can confoun d the results (Nambiar, 1996). The study described here used a replicated field design to answer two questions: 1. In a nutrient stressed environment, are inter rotational growth responses of juvenile loblolly pine affected by the previous silvicultural treatment history (fertilization and weed control)? 2. Does the historical treatment of the understory ve getation community affect its competitive role in the second rotation relative to soil nutrient availability and growth of loblolly pine? These questions were addressed by examining and comparing aboveground biomass accumulation, distribution, and nutrient content of the overstory and understory species across a range of silvicultural treatment histories that had varying levels of soil nutrient availability. Efforts were made to duplicate as closely as possible the first rotation silvicultural treatments, a nd included using a common genetic source of loblolly pine. Methods Study A rea In order to evaluate the factors that limit the biological growth potential of southern pines, the Intensive Management Practices Assessment Center (IMPAC) at the University of Florida established an experimental study site in 1983 (Swindel et al. 1988). The IMPAC experimental site is located approximately 10 km north of The long term mean an nual temperature (1984 2012) of the study site is 20.6C and it receives an annual rainfall of about 1178 mm (National Oceanic and Atmospheric Administration, 2012). The climate is warm and humid. Poorly drained Pomona fine

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25 sands (sandy siliceous hyperther mic Ultic Alaquods) are the predominant soils at the study site. Study D esign The original IMPAC experiment was designed as a 2x2x2 factorial with treatments of species (loblolly and slash pine), complete and sustained weed control, and annual fertilizati on arranged in a randomized split plot (species as whole plots) design with three replications. This resulted in four treatments within each species: control (C), weed control only (W), fertilizer only (F), and both fertilizer and weed control (FW). The en tire experimental area was site prepared using a single pass bedding treatment. Genetically improved (first generation, open pollinated) 1 0 bareroot stock of both loblolly and slash pine were hand planted in January 1983 (Swindel et al. 1988, Colbert et al. 1990, Martin and Jokela, 2004). After applying a fertilizer regime with balanced levels of macro and micronutrients for the first ten years to the F only and FW treatments, it was stopped in May 1993 and then resumed during the sixteenth to eighteent h growing seasons (1998 2000; Jokela and Martin 2000). Fertilizers were applied in narrow bands (30 cm semicircle) around the base of each tree or planting location. Total nutrient additions over the life of the original study for the F and FW treatments for both species were (kg ha 1 ): 1088 N, 230 P, 430 K, 108 Ca, 72 Mg, 72 S, 4.1 Mn, 5.4 Fe, 0.9 Cu, 4 Zn, and 0.9 B. Competing understory vegetation was controlled in the W and FW treatments annually for the first ten years (1983 1993) using a combinatio n of chemical and mechanical methods (Colbert et al, 1990; Neary et al. 1990b; Dalla Tea and Jokela, 1994). The weed control treatment was stopped after canopy closure because the growth of competing understory vegetation was suppressed in the W and FW pl ots. Early and mid rotation growth dynamics for the

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26 original study were reported by Colbert et al. (1990), Jokela and Martin (2000), and Martin and Jokela (2004). Jokela et al. (2010) summarized the growth dynamics for this original experiment over the 25 year study period. Likewise, Vogel et al. (2011) documented the total C and N pools at the end of the rotation for the original experiment. The original IMPAC study was whole tree harvested in May 2009, with the intent of overlaying a second experiment usi ng the same treatment plots. Harvested trees were processed off the treatment plots to ensure no inputs of nutrients into the soil via harvest residues from the aboveground components of pine trees. Considering the need for long term monitoring of the site to understand the effects of the past management history, the IMPAC II study site was initiated in June 2009. Original plots in the first rotation were re experiment. The IMPAC II experiment now consists of two randomized complete block designs (RCBD; 3 replications each), having four treatments (C, F, FW, and W) for the actively managed retreatment des ign and four treatments for the untreated carryover design (Cc, C F C FW C W ) (Figure 2 1). The carryover experiment was established on the previous slash pine plots and the actively managed retreatment experiment was established on th e previous loblolly pi ne plots. Prior to harvesting, all treatment plot corners were physically monumented and the understory vegetation on the C and F only plots were mulched in place (April 2009) to retain this nutrient pool within the plot boundaries. Mulching was not necess ary for the W and FW plots because of the sustained weed control treatment history from the

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27 previous rotation. Following harvest, the entire study area was later bedded in June, with a second bedding pass conducted in August of the same year. Similar to t he last rotation, loblolly pines were planted in each plot at a 1.8 m by 3.0 m spacing, with measurement plots (0.02 ha) consisting of forty trees per plot (8 trees each in 5 beds). Each of the measurement plots was provided with a treated buffer of three trees and two beds, resulting in a 0.08 ha treatment plot. An untreated buffer of six tree spaces was provided between two adjacent treatment plots. Across the treatment plots, an untreated buffer of four beds was maintained (Figure 2 1). A single, full si b and elite performing loblolly family was used to regenerate the entire study in December 2009 using containerized seedlings. Prior to planting, only the active retreatment plots, which received chemical site preparation and weed control in the first rot ation, were treated using a broadcast application of 0.84 kg a.e. ha 1 imazapyr in the form of Chopper (BASF Corp., Research Triangle Park, NC, USA), 1.12 kg a.e. ha 1 triclopyr in the form of Garlon 4 (Dow AgroSciences LLC, Indi anapolis, IN, USA), and 0 .14 kg. ha 1 of metsulfuron methyl in the form of Escort (E.I. du Pont de Nemours and Company, Inc., Wilmington, DE, USA) in October 2009. In October, 2010 these same plots received a directed spray application of triclopyr (3%) and imazapyr (1%) to cont rol Ilex glabra and other understory competitors. Also, in September 2011 the actively managed F and FW plots received another directed spray of glyphosate (3%) to maintain a weed free environment. All treatments (actively managed retreated and untreated c arryover) received a single application of Fipronil (9.1%) in the form of PTM TM (BASF Corp.,

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28 Research Triangle Park, NC, USA) in March 2010 to control Nantucket pine tip moth ( Rhyacionia frustrana ). The untreated carryover plots did not receive any additio nal chemical treatments (herbicide or fertilizer), with the exception of a banded 0.2 kg a.e. ha 1 imazapyr application in May 2010 to control Dicanthelium spp. and to aid seedling survival in all treatment plots. This same banded herbicide treatment was a lso applied to the actively managed C and F plots. The actively managed retreated (F and FW) experiment received fertilizer at the end of July 2011 and beginning of September 2012. Consistent with the last rotation treatments, the total nutrient additions over the first three growing seasons for the F and FW treatments were (kg ha 1 ): 120 N, 53 P, 99 K, 40 Ca, 19 Mg, 56 S, 1.3 Mn, 0.5 Fe, 0.2 Cu, 0.5 Zn, and 0.2 B. As done in the first rotation experiment, the fertilizer was applied in narrow bands (30 cm s emicircle) around the base of each tree or planting location. Data Preparation and A nalysis Estimation of total aboveground biomass for ages 1 3 years was made using existing allometric equations previously developed for loblolly pine for the same family, ages, and soil type (Adegbidi et al. 2002 and inventory data). The following equation: o 1 Ln(X) ( 2 1 ) where, Y is the biomass component expressed in kilograms dry wt., X is the tree height expressed in meters for ages 1 and 2 and DBH expressed in cm for age 3, o 1 are the coefficients of regression, was utilized to estimate the total aboveground biomass of loblolly pine using height and DBH annual inventory data collected in 2011, 2012 and 2013. For estimation of

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29 component biomass, highly significant allometric e quations of the same form as Eq 2 1 w ere developed using the destructive harvest data for 1 2 and 3 year old loblolly pines collected by Adegbidi et al. (2002) ( Table A 1). data were generated from the same genetic family growing on similar s oils as the curr ent study. Corrections for logarithmic bias were m ade on all estimates of biomass accumulation (Baskerville, 1972; Sprugel, 1983). Nutrient analyses of the pine foliage at age 2 were conducted by collecting fully elongated needles (approximately 25 fascicl es) that were sampled from five random trees in each measurement plot in December 2011. These foliar tissues were then analyzed for macro and micro nutrients at the Micro Macro International Laboratory in Athens, GA, USA. About 0.5 g of ground tissue sam ples was first dry ashed in a muffle furnace and then the samples were brought up to volume with aqua regia (3:1 HNO 3 : HCl). The extracts were then analyzed using inductively coupled plasma atomic emission spectroscopy (ICP AES; MMI Labs, Athens, GA, USA) Total N was analyzed in a CNS analyzer (LECO Corporation, St. Joseph, MI, USA) using the Dumas Method (Campbell, 1992). Stemwood with bark and branch tissues were collected from four randomly selected pine trees in each measurement plot in December 2011. These samples were oven dried at 65C to a constant weight and then ground in a Wiley mill to pass through 1 mm sieve. These tissues were then analyzed for macro and micro nutrients at the Micro Macro International Laboratory in Athens, GA, USA using th e same methods described above. Estimates of aboveground understory biomass were made using a clip plot survey conducted in August and September 2011. Within each plot, six quadrats (1 m 2 )

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30 were randomly established in each measurement plot and stratified e qually between the bed and inter bed positions. All standing vegetation that fell within the quadrats was clipped at ground level and sorted separately by species. For overhanging vegetation, only the portion that fell within the quadrat was clipped. All s amples were oven dried at 65C to a constant weight. The dried leaves, twigs or branches of individual understory species in a plot were ground in a Wiley mill to pass through 1 mm sieve. In addition, six culms (with roots) of Andropogon spp. were manually excavated from both bed and inter bed positions of the C FW and C W treatments of the untreated carryover experiment, where Andropogon spp. was predominant, to estimate nutrient accumulation in roots. Andropogon spp. samples were then separated into shoots and roots. Roots were washed with distilled water to rinse off soil particles. Both shoots and rinsed roots were oven dried at 65C to a constant weight prior to subsampling. The subsamples of shoot and root tissues were also ground in a Wiley mill to pass through 1 mm sieve. All tissues were analyzed for macro and micro nutrients at the Micro Macro International Laboratory in Athens, GA, USA. Soil nutrient availability was assessed in the actively managed and untreated carryover experiments using PRS TM pr obes (Western Ag Innovations, Inc., Saskatoon, SK, Canada), ion exchange membranes. Although th e use of ion exchange membranes in forest ecosystems is not as common as in agricultural ecosystems, they have been widely used to determine nutrient supply rate s in the soil (Hart and Firestone, 1989; Ziadi et al. 1999; Qian and Schoenau, 2002 ). Four cation PRS TM probes capable of adsorbing all nutrient cations and four anion PRS TM probes capable of adsorbing all nutrient anions were buried randomly in the upper 15 cm of the beds of all

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31 measurement plots in August 2011. After eight weeks of burial these probes were removed from the soil and rinsed free of adhering soil particles with de ionized and distilled water. All probes were eluted using a 0.5N Hydrochloric Acid (HCl) solution for 1 hour. The eluate was then analyzed colorimetrically using an automated flow injection analysis system for NO 3 N and NH 4 + N to obtain total N supply. For P, K, Ca, Mg, S, B, Cu, Mn, Zn, and Fe, ICP AES was used. All analyses were done at the Western Ag Innovations, Inc. in Saskatoon, SK, Canada. In order to estimate soil nutrient concentrations in the untreated carryover experiment, soil samples were collected from all plots at the depth intervals of 0 10, 10 20, 20 50, and 50 10 0 cm in November 2012 using a 7.6 cm diameter auger. Eight samples were collected from each treatment plot; four from the bed and four from the inter bed position. The samples from the same depth intervals were thoroughly mixed and weighed. Approximately 1 5% of the mixed sample was then subsampled. Roots were removed from the subsamples. Almost 100g of subsample was then air dried and ground in a mortar and pestle to pass thorough a 2 mm sieve. Soil macro and micro nutrients were extracted using the Mehli ch III extraction procedure (Mehlich, 1984). All samples were analyzed at the Micro Macro International Laboratory in Athens, GA, USA. Analysis of variance (ANOVA) for randomized complete block design was used to test the effects of fertilizer and weed con trol on aboveground biomass, nutrient accumulation and soil nutrient supply rates for both the actively managed retreated and the untreated carryover experiments. In order to ensure that the data met assumptions of normality and homoscedasticity, Kolmogoro v Smirnov and equal variance tests were

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32 utilized, respectively (Massey, 1951). For data not meeting the assumptions of normality and homoscedasticity, appropriate transformations were made prior to conducting dentized range (HSD) test was used to separate differences among treatment means at an alpha level of 0.05, unless noted otherwise. Results Inter rotational Comparison of Height Response of 3 year old L obloll y P ines Comparison of loblolly pine tree heigh ts between rotations indicated that at age 3 years the second rotation stands performed better than the first (Figure 2 2). All actively managed retreated plots in the second rotation had significantly greater tree heights than those in the first rotation. For example, with the FW treatment, average tree height in the second rotation averaged 5.7 m compared to 3.9 m during the first rotation. Likewise for the F, W, and C treatments, average heights in the second vs. the first rotation averaged 5.0 m vs. 3.1 m, 4.5 m vs. 3.0 m, and 3.6 m vs. 1.3 m, respectively. In the untreated carryover experiment, all treatments in the second rotation also had greater average tree heights than the first rotation. However, the trend was different than that observed for the actively managed retreated experiment; the C F treatment had significantly greater average tree height (5.2 m), than the C FW (4.3 m), C C (3.9 m) and C W (3.8 m) treatments (Figure 2 2). Total Aboveground B ioma ss Accumulation Loblolly P ine The effects of fe rtilization and weed control on the total aboveground biomass accumulation of the second rotation loblolly pine stands were quantified annually for the first three years for both the actively managed retreated and untreated carryover experiments (Figure 2 3, Table 2 1). In general, continuation of the fertilization and

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33 significantly increased total aboveground biomass accumulation. The FW treatment accumulated almost 28 Mg.ha 1 com pared with 8 Mg.ha 1 for the control (C; 3.5 fold response). Different patterns were observed for the second rotation untreated carryover experiment; growth responses for the C F treatment were almost 1.8 fold greater than the untreated control (18 Mg.ha 1 in C F vs. 10 Mg. ha 1 in C C ). Interestingly, despite the previous history of repeated fertilizer and weed control applications, the carryover C FW treatment (12 Mg. ha 1 ) did not differ significantly in aboveground loblolly pine biomass accumulation compared to the C C and Cw treatments (Table 2 1, Figure 2 3) from ages 1 to 3 years. Aboveground component biomass accumulation and dry matter allocation patterns loblolly pine We utilized the data at age 2 years, as a representative of the first three growing se asons, to report the variation in dry matter allocation patterns, total aboveground nutrient accumulation, and soil nutrient availability in both the actively managed retreated and untreated carryover experiments. Foliage, stemwood (with bark), and branch biomass accumulation followed the same trends as total biomass at age 2 years for the actively managed retreated experiment (Table 2 2). The FW treatment significantly improved the biomass accumulation in foliage (4.6 vs. 1.7 Mg.ha 1 ), stemwood (2.7 vs. 0. 9 Mg.ha 1 ), and branches (3.1 vs. 0.9 Mg.ha 1 ) compared to the C treatment. The proportional biomass allocation patterns were influenced by silvicultural treatments; as management intensity increased, predictable changes associated with accelerated stand d evelopment were observed (e.g., > stemwood and branches, < foliage). For instance, the dry matter

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34 allocation patterns in stemwood and branches were lowest for the C treatment and highest for the FW treatment (e.g. stemwood: 25.2% vs. 25.9%; branch: 26.8% v s. 30.2%); the opposite was observed for foliage (e.g. 47.9% vs. 43.8%) (Figure 2 4). Although allocation of biomass to photosynthetic tissues is typically highest at this stage of stand development, the increase in the stemwood:foliage and branches:foliag e ratios in the FW treatment compared to the C treatment (stemwood:foliage, 0.6 vs. 0.52; branches:foliage, 0.7 vs. 0.53) suggests that stand development patterns were more advanced in the most intensively managed treatments (Miller, 1981). Different dry m atter allocation patterns were observed in the aboveground pine components at age 2 years for the untreated carryover experiment (Table 2 3). Only the C F treatment significantly increased the biomass accumulation in foliage (3.8 Mg.ha 1 vs. 2.2 Mg.ha 1 ), s temwood (2.2 Mg.ha 1 vs. 1.2 Mg.ha 1 ), and branches (2.5 Mg.ha 1 vs. 1.2 Mg.ha 1 ) when compared with the control (C C ). Dry matter allocation patterns were significantly influenced by fertilization. Compared to the C C treatment, the dry matter allocation to stemwood and branches increased significantly with the C F treatment (stemwood: 25.2% in C C vs. 25.7% in C F ; branches: 27% in C C vs. 29.3% in C F ); the opposite was true for foliage (47.6% in C C vs. 44.9% in C F ) (Figure 2 4). Similar to that described for t he actively managed retreated experiment, increases were found in the stemwood:foliage and branches:foliage ratios in the C F treatment compared to the C C treatment (stemwood:foliage, 0.58 vs. 0.54; branches:foliage, 0.66 vs. 0.58). Understory and total abo veground biomass accumulation: As expected, fertilizer additions in the second rotation significantly increased the amount of understory biomass accumulation compared to the weed control treatments (Table 2 2). At age 2 years, the F treatment accumulated a lmost 7.7 Mg.ha 1 of

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35 aboveground understory biomass compared to 1.6 Mg.ha 1 and 1.1 Mg. ha 1 for the W and FW treatments, respectively. However, understory vegetation redevelopment was evident in the second rotation untreated carryover experiment, especiall y in the C FW treatment (Table 2 3). For example, understory biomass accumulation in the C FW treatment (3.4 Mg. ha 1 ) did not differ significantly from either the C C (4.8 Mg. ha 1 ) or C F (4.8 Mg. ha 1 ) treatments. On the contrary, the C W treatment (1.7 Mg.ha 1 ) had the lowest levels of competing vegetation when compared to the C C treatment. Understory vegetation composition was influenced by silvicultural treatment histories. In general, grass like species dominated the understory in the weed control treatment s and shrubby species dominated the understory in the absence of the weed control treatments ( Table C 1 ). Andropogon spp. (0.7 Mg.ha 1 ) and Dicanthelium spp. (0.3 Mg.ha 1 ) together contributed about 96% of the total understory aboveground biomass in the FW treatment. Ilex glabra (3.8 Mg.ha 1 ) and Serenoa repens (0.91 Mg.ha 1 ), in contrast contributed almost 61% of the total understory aboveground biomass in the F treatment. Similar responses in understory composition were observed in the untreated carryove r experiment; Androp ogon spp. (3 Mg.ha 1 ) alone contributed to almost 89% of the total understory aboveground biomass in the C FW treatment, and Ilex glabra (2.0 Mg.ha 1 ) and Serenoa repens (1.1 Mg.ha 1 ) together accounted for nearly 65% of the total unders tory aboveground biomass in the C F treatment. The total aboveground biomass (pine+understory) accumulation in the actively managed experiment followed the trend: F > FW > C > W (Table 2 2). Understory vegetation alone accounted for almost 62%, 53%, 21%, an d 10% of the total aboveground biomass for the C, F, W, and FW treatments, respectively. Pine biomass

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36 accounted for 90% of the total aboveground biomass for the FW and 47% for the F treatment. Similarly, i n the untreated carryover experiment the total abo veground biomass accumulation followed the general trend: C F > C C > C FW > C W (Table 2 3). Pine biomass contributed to almost 64%, 49%, 58%, and 69% of the total aboveground biomass in the C F C C C FW and C W treatments, respectively. The understory vegetat ion accounted for almost 51% of the total aboveground biomass for the C C treatment and 31% for the C W treatment. Nutrient Accumulation Nutrient accumulation in the aboveground components of loblolly pine Estimates of aboveground nutrient accumulations in 2 year old loblolly pine are found in Table 2 4 for both macro and micro nutrients. In general, nutrient accumulations followed the aboveground biomass accumulation results; nutrient accumulation increased with increasing intensity of silvicultural treat ments for the actively managed retreated experiment. Nitrogen, P, and K accumulations in the FW (N, 124.1 kg.ha 1 ; P, 8.5 kg.ha 1 ; K, 38.6 kg.ha 1 ) treatment were almost 3.4 3.9 and 3.4 fold higher, respectively, compared to the C treatment (N, 37.0 kg. ha 1 ; P, 2.2 kg.ha 1 ; K, 11.2 kg.ha 1 ). Similarly, B, Mn, and Zn accumulations in the actively managed FW treatment plots were almost 2.8 4.1 and 3.2 fold higher than the C treatment (B, 62 vs. 22 g.ha 1 ; Mn, 183 vs. 750 g.ha 1 ; Zn, 100 vs. 322 g.ha 1 ) Nutrient accumulation in loblolly pine also followed the same trend as biomass accumulation in the untreated carryover experiment. The C F treatment had significantly higher nutrient accumulation compared with the C C treatment. For instance, almost 1.9 1.8 and 2.1 fold higher N, P, and K content, respectively, were associated with the C F treatment when compared with the C C treatment (N, 92 kg.ha 1 vs. 47.6 kg.ha 1 ; P, 5.4

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37 kg.ha 1 vs. 3.0 kg.ha 1 ; K, 34.2 kg.ha 1 vs. 16.5 kg.ha 1 ). Similarly, B and Zn accumulations were also higher in the C F compared to the C C treatment (B, 51 g.ha 1 vs. 29 g.ha 1 ; Zn, 231 g.ha 1 vs. 117 g.ha 1 ). Nutrient accumulations in the aboveground components of pines were also influenced by silvicultural treatments. For most nutr ients, accumulation in the aboveground pine components increased with increasing intensity of silvicultural treatments (Table 2 4). Nitrogen and P accumulations in the foliage were almost 103 kg.ha 1 and 7 kg.ha 1 in the FW treatment compared with 30 kg.ha 1 and 2 kg.ha 1 in the C treatment (N, 3.2 fold; P, 3.8 fold response), respectively. Similar influences of the FW treatment were observed for foliar micronutrient accumulations (Table 2 4). Foliar B accumulation in the FW treatment was almost 2.5 fold higher than in the C treatment (28 g.ha 1 vs. 11 g.ha 1 ). Likewise, the F treatment increased foliar nutrient accumulation for most nutrients, except K and B, when compared to the C treatment (e.g. N, 2.4 fold response; P, 2.5 fold response). The W treatme nt was associated with increased accumulation of only Ca in the folia ge compared to the C treatment. Nutrient accumulation in stemwood (with bark) was influenced by both the F and FW treatments. While the FW treatment significantly increased the accumulati on of most nutrients (except K, Cu, and Zn), the F treatment significantly increased the accumulation of only P, K, and Zn in stemwood compared to the C treatment. For example, stemwood N and P accumulations in the FW treatment were almost 14.2 kg.ha 1 and 0.8 kg.ha 1 compared with 5.4 kg.ha 1 and 0.2 kg.ha 1 respectively, in the C treatment. Stemwood P and Zn accumulation in the F treatment were almost 4 and 2.3

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38 fold higher when compared with the C treatment (P, 0.8 kg.ha 1 vs. 0.2 kg.ha 1 ; Zn, 235 g.ha 1 vs. 100 g.ha 1 ). Nutrient accumulation in the branches followed a similar trend as stemwood; higher branch wood nutrient accumulations were observed with the most intensive silvicultural treatments in the actively managed experiment (Table 2 4). Nitrogen P, and K accumulations in the branches of pines growing in the F (N, 7.1 kg.ha 1 ; P, 0.6 kg.ha 1 ; K, 2.9 kg.ha 1 ) and FW (N, 8.3 kg.ha 1 ; P, 0.7 kg.ha 1 ; K, 2.9 kg.ha 1 ) treatments were significantly greater than the C (N, 2.3 kg.ha 1 ; P, 0.2 kg.ha 1 ; K, 1.0 kg.ha 1 ) treatment; similar effects were observed for B and Cu (B, 13 g.ha 1 in F and 20 g.ha 1 in FW vs. 6 g.ha 1 in C; Cu, 8 g.ha 1 in F and 11 g.ha 1 in FW vs. 3 g.ha 1 in C). Nutrient accumulation in the aboveground components of loblolly pine in the untreated carryover experiment also followed similar trends. The C F treatment increased the foliar accumulation of all macro and micro nutrients, except Mg (Table 2 4). Almost 2 fold gains in N and 1.7 fold gains in P accumulations were observed fo r the C F treatment when compared with the C C treatment (N, 77 kg.ha 1 vs. 37 kg.ha 1 ; P, 4.3 kg.ha 1 vs. 2.5 kg.ha 1 ). Similar influences in nutrient accumulation were also observed in the stemwood component. The C F treatment increased the stemwood accumul ation of nutrients like P, K, Mg, B, Mn, and Zn when compared with the C C treatment (e.g. P, 0.5 kg.ha 1 in C F vs. 0.3 kg.ha 1 in C C ; Mn, 72 g.ha 1 in C F vs. 31 g.ha 1 in C C ). Nutrient accumulation in the branches was also influenced by the first rotation silvicultural treatments. In general, the C F treatment favored higher nutrient accumulation (except S and Cu) in the branches of pine after two growing seasons. For example, N accumulation in the branches was almost 5.8 kg.ha 1 in the C F treatment compared with

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39 2.9 kg.ha 1 in the C C treatment. Interestingly, no significant influences of the C FW treatment in nutrient accumulation in the aboveground components of the second rotation loblolly pine were observed at age 2 years. Nutrient accumulation in the unde rstory vegetation Nutrient accumulation in the understory of the actively managed experiment was affected by the intensive silvicultural treatments like fertilization and weed control (Table 2 4). As expected, sustained control of competing understory veg etation reduced the nutrient accumulation in the aboveground understory biomass in the FW (N, 9.7 kg.ha 1 ; P, 1.4 kg.ha 1 ; B, 5 g.ha 1 ) and W (N, 15.6 kg.ha 1 ; P, 1.9 kg.ha 1 ; B, 9 g.ha 1 ) treatments compared to the F treatment (N, 68 kg.ha 1 ; P, 7.4 kg.ha 1 ; B, 121 g.ha 1 ). No significant influences of the F treatment on nutrient accumulation in the understory vegetation were found compared to the C treatment (Table 2 4). In the untreated carryover experiment, the C F and C W treatments did not significantly influence the N and P accumulation in the second rotation understory vegetation (Table 2 4). However, the C FW treatment had significantly lower Ca, Cu, and Mn accumulation in the understory compared to the C F treatment (Ca, 5.8 kg.ha 1 vs. 26.3 kg.ha 1 ; C u, 6 g.ha 1 vs. 21 g.ha 1 ; Mn, 370 g.ha 1 vs. 1103 g.ha 1 ). Moreover, when compared with the C C treatment, the C W treatment had significantly lower K, Ca, Cu, and Zn accumulation in the understory, differing by almost 71% (22.3 kg.ha 1 in C C vs. 6.4 kg.ha 1 in C W ) 90% (19.9 kg.ha 1 in C C vs. 2.1 kg.ha 1 in C W ), 76% (21 g.ha 1 in C C vs. 5 g.ha 1 in C W ), and 73% (161 g.ha 1 in C C vs. 44 g.ha 1 in C W ), respectively. This difference was primarily due to lower understory biomass in the C W treatment (~ 63% less ) compared to the C C treatment.

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40 Woody species like Ilex glabra and Serenoa repens were the major accumulators of understory nutrients like N, P, B, Cu, Mn, and Zn in the C and F treatments of the actively managed experiment and the C C and C F treatments of the untreated carryover experiment ( Table C 3 through C 12 ). For example, Ilex glabra alone accumulated almost 30 kg.ha 1 and 20 kg.ha 1 of N and 3.3 kg.ha 1 and 1.7 kg.ha 1 of P, respectively, in the F and C treatments. Similarly, it accumulated almost 43 % (~18.2 kg.ha 1 ) of the total understory N in the C F and 32% (~12.7 kg.ha 1 ) of the total understory N in the C C treatments. Boron, Mn, and Zn accumulation in Ilex glabra accounted for almost 64% (~77 g.ha 1 ), 82% (~959 g.ha 1 ), and 52% (~884 g.ha 1 ) of t he total understory micronutrient pools, respectively, in the F treatment. Almost 17 % (~225 g.ha 1 ) of the total understory Mn pool in the C treatment was contributed by Serenoa repens Ilex glabra (717 g.ha 1 ) and Vitis rotundifolia (147 g.ha 1 ) accumula ted nearly 65% and 13% of the total understory Mn pool, respectively, in the C F treatment. Herbaceous species like Andropogon spp. and Dicanthelium spp. were the major nutrie nt accumulators in the FW, W, C FW and C W treatments ( Table C 3 through C 12 ). Andropogon spp accumulated approximately 93% (8.6 kg.ha 1 ) and 80% (13 kg.ha 1 ) of the total understory N pool and 93% (1.3 kg.ha 1 ) and 89% (2.6 kg.ha 1 ) of the total understory P pool, respectively, in the FW and C FW treatments. Manganese and Zn accumulati on in Andropogon spp. was almost 262 g.ha 1 (~71% of the total understory Mn pool ) and 48 g.ha 1 (~60% of the total understory Zn pool ) in the C FW treatment. Dicanthelium spp. was a major N accumulator in the W treated plots (9.9 kg.ha 1 63% o f the total u nderstory N pool).

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41 Soil N utrient S upply Soil nutrient supply rates in the second rotation loblolly pine stands, measured using ion exchange membranes (PRS; Western Ag Innovations, Inc., Saskatoon, SK, Canada), were significantly higher for nutrients like N, Ca, Mn, Cu, Zn, and S in the Table D 1 ) at g/10 cm 2 / cm 2 / 8 weeks) (Figure 2 5). Strong correlations between aboveground pine biomass and soil nutrient supply rates in the growing season were observed for several nutrients (Table 2 5). For instance, correlations between abovegro und pine biomass and soil supply rates for N and Zn were 0.67 and 0.72, respectively, for the actively managed experiment. In the untreated carryover experiment, the C F treatment significantly improved the supply of nutrients like P, Mn, and Zn in the uppe r soil surface when compared to the C C 2 5; Table D 2 ). Phosphorus supply rate in the C F treatment was almost 2.3 fold higher than the C C treatment (C F 2 / 8 weeks; C C 2 / 8 weeks). Interestingly, the C FW treatment had no significant influence on the surface supply of soil nutrients when compared with the C C treatment, except for Zn. In the untreated carryover experiment, strong correlations were observed between the aboveground loblolly pine biomass and soil P (r = 0.83), Mg (r = 0.61), Mn (r = 0.61), and Cu (r = 0.73) supply rates (Table 2 5). Of these nutrients, only soil P supply could significantly predict total aboveground biomass (Forward stepwise regression: R 2 = 0.68) (Figure 2 6).

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42 Discussion Understanding the long term impacts of inten sive forest management on the productivity of planted pines over successive rotations will inform discussions of forest sustainability (Powers, 1999; Fox, 2000; Wear and Greis, 2002). Productivity and growth of pines are affected by multiple factors such a s age, soil nutrient availability, genetics, and competition (Allen et al. 1990; Neary et al. 1990b; Li et al. 1999; Jokela et al. 2010). The long term replicated experiments in this study incorporated rotation long applications of fertilizer and susta ined understory competition control. This experimental framework provided a unique opportunity to investigate inter rotational silvicultural impacts on growth dynamics and the competitive envir onment in loblolly pine stands. The evolution of forest managem ent practices and availability of improved genetic stock have increased the productivity of southern pine plantations over the past six decades (Fox et al. 2007a). In this study, inter rotational comparisons of loblolly pine growth demonstrated that heigh t and aboveground biomass accumulation were consistently greater in the second rotation compared to the first. This response, in part, was likely due to the deployment of genetically superior pine seedlings (a single full sib pine family in the second rota tion vs. first generation open pollinated pine in the first rotation) (Li et al. 1999; Jansson and Li, 2004), improved site preparation (Miller et al. 1991; Borders and Bailey, 2001; Jones et al. 2009) and bedding techniques (double bedding vs. single be dding) (Lauer and Zutter 2001), control of Panicum spp. (Morris et al. 1993) and tip moth (Williston and Barras, 1977; Cade and Hedden, 1987), and elevation in atmospheric CO 2 concentrations (~ 344 ppm in 1983 vs. 393 ppm in 2011) (Nemani et al. 2003; Mo ore et al. 2006) in the second rotation.

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43 Fertilizer additions and understory competition control have been shown to benefit the growth of loblolly pine on nutrient stressed sites by reducing nutrient deficiencies (Swindel et al. 1988; Colbert et al. 1990 ; Borders et al. 2004; Martin and Jokela, 2004; Roth et al. 2007; Jokela et al. 2010). Results from this study clearly demonstrated that these benefits were extended into the second rotation. Third year estimates of aboveground biomass accumulation (FW tr eatment 28 Mg.ha 1 ), for example, were similar to those reported by Colbert et al. (1990; FW treatment 32 Mg.ha 1 ) at age 4 yr for this same site in the previous rotation. Although this example exemplifies the yield for the highest levels of silvicult ural inputs (FW) for the actively managed experiment, results were similar for the untreated carryover experiment. The C F treatment out performed all other treatments in the untreated carryover experiment. Third year estimates of aboveground biomass accumu lation in the C F treatment (17.8 Mg.ha 1 ) was similar to the value of 19.7 Mg.ha 1 reported by Adegbidi et al. (2005) for intensively managed 3 year old loblolly pine stands growing on similar soils. During the early stages of canopy development, demand for soil nutrients is critical to the development of photosynthetic tissues and both the fertilization and weed control treatments can contribute to increased soil nutrient supply (Miller, 1981; Neary et al. 1990a). Higher N and P contents in the abovegrou nd biomass of pines in the FW treatment were indicative of the general nutrient uptake rates of these rapidly growing stands. Total N (124.1 kg.ha 1 ) and P (8.5 kg.ha 1 ) pools in the aboveground pine biomass for 2 year old loblolly pines in the FW treatmen t of our study closely matched those reported by Adegbidi et al. (2005) for this same family at age 3 yrs growing on similar sites in the lower Coastal Plain of Georgia (117 kg.ha 1 N and 8.3 kg.ha 1 P),

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44 respectively. Despite greater nutrient immobilizatio n in the aboveground pine biomass for the F and FW treatments, high foliar N concentration (22.6 g.kg 1 ) observed in the FW treatment and higher soil nutrient supply rates observed in the upper soil surface (15cm) of the F and FW treatments (Figure 2 5), h ighlight the benefits that long term nutrient additions and competing vegetation control have on soil N and P availability in sandy Spodosols. The potential of fertilizer amendments, especially P, to persist and enhance long term soil nutrient availability and affect inter rotational levels of productivity have been previously documented for pine plantations across different regions (Comerford et al. 2002; Crous et al. 2007; Everett and Palm Lei s, 2009; Kiser and Fox, 2012). The notable differences in res idual soil nutrient availability and second rotation growth rates found between the C F and C FW treatments was unexpected, given that comparable levels of fertilizer additions were made between treatm ents in the previous rotation. A number of factors relate d to differences in soil nutrient pools, nutrient mineralization rates, movement and availability of soil nutrients in the upper solum, and immobilization of soil nutrients in the understory vegeta tion may have been responsible. The higher levels of biomas s accumulation associated with the C F treatment compared to the C FW and C C treatments was likely due to higher background soil nutrient pools as a result of past fertilizer additions, forest floor incorporation and understory mulching prior to stand estab lishment (Figure 2 3 and 2 5). Almost 1.4 Mg.ha 1 of N present in the forest floor and the understory vegetation was incorporated in the C F treatment compared to 0.95 Mg.N.ha 1 in the C FW and 0.9 Mg. N ha 1 in the C C treatment (Vogel et al. 2011). Similar levels of soil nutrient enrichment likely occurred

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45 for P. Using forest floor mass, understory biomass, and P data for this same site (Vogel et al ., 2011, Neary et al 1990 b and Polglase et al ., 1992b ) we estimated that P pools in the forest floor and unde rstory vegetation were also higher in the C F treatment (32.5 kg.ha 1 ) compared to the C FW (26.3 kg.ha 1 ) and C C (8.1 kg.ha 1 ) treatments. The nutrient pools in the forest floor and understory from the first rotation likely served as a nutrient source upon decomposition and subsequent mineralization (Tisdale, 2008; Maier et al. 2012), and thereby supported the greater second rotation loblolly pine growth in the C F treatment. With forest floor incorporation during site preparation, Maier et al. (2012) observ ed 18% higher stand volume compared to the control in a 6 year old loblolly pine plantation in South Carolina. Lower soil P (~ 61% lower) and Mn (~62% lower) supply rates for the C FW treatment in our study supports etween successive rotations, especially in highlighting the role that the understory and forest floor play in this process. Despite higher soil N pools at the end of the first rotation, non significant treatment differences in resin available soil N supply two years after forest floor incorporation and understory mulching suggests a depletion of soil N via leaching or immobilization on these sandy soils (Miller, 1981; Kissel et al. 2009). Nevertheless, the strong correlation between pine growth and soil P supply rates in the upper solum suggests that higher background soil nutrient pools and increased P availability likely improved the growth of loblolly pines in the C F treatment compared to the C FW treatment on this site (Allen et al. 1990; Albaugh et al. 2007; Fox et al. 2007b). Quality of the substrate, along with temperature and soil moisture, influence decomposition of the forest floor and understory mulch and subsequent nutrient

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46 mineralization rates (Polglase et al. 1992a, b; Grierson et al. 1999; Piatek and Allen, 1999; Gonalves and Carlyle, 1994; Scott and Binkley, 1997). Since P in understory vegetation is presumably less recalcitrant than that in the litterfall from the pines (Polglase et al. 1992a), higher soil P supply observed in the C F tre atment was likely due to higher P mineralization rates compared to the C FW and C W treatments. Polglase et al. (1992a) and Grierson et al. (1999) observed higher P mineralization rates in fertilized plots that contained understory vegetation for this same s ite. In addition, Polglase et al. (1992b) reported higher phenolic concentrations in the pine litter associated with the weed control treatment. Because higher phenolic concentrations in litter could have the potential to hinder litter decomposition, eithe r by forming a decomposition resistant complex with proteins (Hagerman et al. 1998) or non proteins (Benoit and Starkey, 1968), or inhibiting microbial activity (Harrison, 1971; Schim el et al. 1996), the potential of P mineralization from the first rotat ion forest floor in the C FW and C W plots was presumably lower. On nutrient poor sandy soils, nutrient loss either through leaching or through volatilization (N) in the absence of understory vegetation is of concern in young pine stands (Outcalt and White, 1980; Smethurst and Nambiar, 1995; Piatek and Allen, 2001; Tessier and Raynal, 2003; Kissel et al. 2009; Zerpa and Fox, 2011). Phosphorus leaching from the E to the aluminum dominant Bh/Bt horizons was observed in the untreated carryover experiment (Figur e 2 7). In the C FW treatment, Mehlich III extractable P concentrations were almost 2 fold higher in the 20 50 (19.7 mg.kg 1 ) and 50 100 cm (27.5 mg.kg 1 ) depths compared to the 0 20 cm depth (11.4 mg.kg 1 ). Since root development of 2 year old loblolly pin es are restricted mainly to the upper 25 cm

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47 (Adegbidi et al. 2004), P present in 20 50 and 50 100 cm depth may have been temporarily inaccessible to the pines at this stage of stand development. As a result, aboveground pine growth at age 2 years was not different between the C FW and C C treatments, despite higher average Mehlich III extractable P concentrations (0 100 cm) in the C FW treatment. However, by the end of the third growing season, the growth response of pines in the C FW treatment, though not sig nificant, was beginning to separate from the C C treatment (Figure 2 3). This response would likely become more pronounced as stand development proceeds and nutrients present in the deeper soil horizons become accessible to the pines upon further root devel opment (Adegbidi et al. 2004). The competitive influence of understory vegetation for soil nutrients represents a major growth limitation in southern pine plantations (Neary et al. 1990a,b; Colbert et al. 1990). With nutrient additions understory vegeta tion growth can be dramatically high (Turner and Long, 1975; Persson, 1981; VanderSchaff et al. 2002) and nutrient immobilization in the understory vegetation, thus, places large demands on soil nutrient availability for pines in aggrading stands. Almost 2.8 and 3.8 fold higher N and P accumulation, respectively, in the aboveground understory vegetation in the F plots were found compared to those reported by Gholz et al. (1985) for unfertilized slash pine plantations on similar soils (N, 24.7 kg.ha 1 ; P, 1.9 kg.ha 1 ). In addition to changes in understory biomass, silvicultural treatments mediated shifts in the understory community composition (Neary et al. 1990a; Miller et al. 1991 ). For this same site, Neary et al. (1990a) reported a shift to a shrub d ominated understory community following fertilizer additions six years after site preparation and planting in

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48 the first rotation; shrub biomass increased by 137% and herbaceous biomass decreased by 76%. The herbaceous community dominance documented in the weed control treatments (both in the actively managed (FW, W) and carryover experiments (C FW C W )) was also consistent with the findings of Jones et al. (2009), who reported a dominance of early seral species on sites established with chemical site prepara tion. Along with changes in community composition, differential nutrient uptake rates of these understory communities influenced nutrient availability. The shrub community, dominated by Ilex glabra and Serenoa repens, had higher nutrient uptake potential a s demonstrated by higher aboveground N and P content for the F treatment compared to the C treatment, which had similar amounts of understory biomass accumulation (Figure 2 8). Nitrogen and P concentrations (content:biomass ratio) in the shrubs of the F tr eatment (N, 9.3 mg.kg 1 ; P, 0.9 mg.kg 1 ) of the actively managed experiment and the C F treatment (N, 9.2 mg.kg 1 ; P, 0.7 mg.kg 1 ) of the untreated carryover experiment were almost twice the values reported by Neary et al. (1990a) for fertilized plots (N, 4 .8 mg.kg 1 ; P, 0.3 mg.kg 1 ) at this site. In that context, elimination of shrubby competition from the FW treatment increased the pine biomass by four fold (p = 0.06), as opposed to a two fold increase in the F treatment (p = 0.07). Dominance of the herba ceous understory species like Andropogon spp. in the C FW plots also represented a significant source of competition for loblolly pine growth. Although the root:shoot ratio of N and P accumulation in Andropogon spp. amounted to 1:4 and 1:10, respectively, i n the C FW treatment ( Table C 1 3 ), lower carbon costs associated with the dense, fibrous root system of Andropogon spp. (Eissenstat, 1997) facilitated an uptake and immobilization of almost 13.3 kg.ha 1 of N and 2.6 kg.ha 1 of P

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49 in the aboveground componen t. Strong competitive influences of Andropogon spp. on loblolly pine growth have been previously documented (Mitchell et al. 1999; Zutter et al. 1999). For example, Zutter et al. (1999) reported a six fold decline in root length density of loblolly pine with as few as four Andropogon spp. plants per square meter of soil surface. In addition, allelopathic effects of Andropogon spp. have been shown to inhibit the nodulation of nitrogen fixing plants and thereby reduce soil N availability (Rice, 1972). Thus strong competition from Andropogon spp. for available soil nutrients in the upper soil surface likely influenced the reduced growth observed for loblolly pine in the C FW treatment. Summary and Conclusions This study was designed to examine the effects of previous forest management activities on inter rotational productivity in young loblolly pine stands. Continued application of fertilizer and sustained elimination of competing vegetation favored the establishment and early growth in the second rotation. G rowth, as measured using aboveground biomass and total average height, was greater in the second rotation for both the actively managed retreatment and untreated carryover experiments. Notably, the carryover C F treatment was significantly more productive t han the C FW C W and C C treatments. Long term fertilization and weed control treatments also contributed to shifts in understory community composition to more competitive shrub (F, C F treatments) or Andropogon spp. (C FW C W treatments) dominated communities that affected nutrient immobilization and loblolly pine growth. While greater growth responses in the second rotation in all treatments might be due to advanced genetics, improved site preparation techniques, Panicum spp. control, tip moth control, and el evated atmospheric CO 2 concentrations, these results also suggest that the forest floor and understory

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50 vegetation from the previous rotation was an important nutrient sink, especially for P, in the untreated carryover plots. Upon harvest and regeneration, this nutrient pool presumably became a nutrient source that helped meet the nutritional and developmental demands of the second rotation stand. Historical P movement from the E to the Bh and Bt horizons, in the absence of understory vegetation, especially for the C FW treatment, could represent an early limitation to growth on P limited sites. Strong correlation between pine growth and resin available P supply (r = 0.83) in the surface soils of the untreated carryover experiment, for instance, highlighted th e important role of P supply in early pine growth on Spodosols. Therefore, from a forest management perspective on flatwoods sites that were previously fertilized with P, the newly regenerated stands could benefit from nutrient management practices like un derstory mulching and forest floor incorporation, which could reduce the need for P fertilization at establishment.

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51 Table 2 1 Analysis of variance of total aboveground biomass accumulation by stand age for young loblol ly pine stands growing in the actively managed retreated and untreated carryover experiments on Spodosols in north Florida. Treatments -----------------Stand age (Years) ------------------1 2 3 Actively managed retreated Control (C) A A A Ferti lizer only (F) AB AB B Fertilizer+ weed control (FW) B B C Weed control only (W) AB A AB p Value 0.048 0.004 <0.001 Untreated carryover Control (C C ) A A A Fertilizer only (C F ) B B B Fertilizer+ weed control (C FW ) A A A Weed contr ol only (C W ) A A A p Value <0.001 0.001 <0.001 05).

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52 Table 2 2 Aboveground bioma ss accumulation among treatments in a second rotation 2 year old loblolly pine stand growing in the actively managed retreated experiment on Spodosols in north Florida. Note: Component aboveground biomass of pines may not sum to the total abovegroun d pine biomass because separate allometric functions were used to estimate the aboveground component and total biomass. For a given component, means followed by the tandard deviations are given in parentheses. Treatments ---------------------------------Aboveground biomass ( kg.ha 1 ) ----------------------------------------Pine --------------------Under story Total aboveground Foliage Stem wood Branch wood Total Actively managed retreated Control (C) 1746 (1026) a 918 (606) a 978 (699) a 3623 (2319) a 5848 (9 56) ab 9472 (1644) ab Fertilizer only (F) 3194 (396) ab 1783 (255) ab 1984 (314) b 6924 (955) ab 7692 (2647) b 14616 (1704) c Fertilizer+Weed control (FW) 4567 (198) b 2700 (127) b 3145 (158) b 10320 (475 ) b 1122 (1466) a 11443 (1895) bc Weed control only (W) 2747 (754) a 1504 (472) a 1649 (569) a 5872 (1780) a 1554 (897) a 7426 (1398) a

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53 Table 2 3 Aboveground biomass accumulation among treatments in a second rotation 2 year old loblolly pine stand growing in the untreated carryover experiment on Spodosols in north Florida. Note: Component aboveground biomass of pines may not sum to the total aboveground pine biomass because separate allometric functions were used to estimate the aboveground component and total biomass. For a given component, means followed by the parentheses. Treatments ---------------------------------Aboveground biomass ( kg.ha 1 ) ------------------------------------Pine ------------------Under story Total aboveground Foliage Stem wood Branch wood Total Untre ated carryover Control (C C ) 2196 (331) a 1165 (194) a 1248 (223) a 4590 (746) a 4833 (1474) a 9423 (2167) ab Fertilizer only (C F ) 3799 (357) b 2181 (234) b 2481 (292) b 8404 (872) b 4781 (1404) a 13185 (2271) b Fertilizer+Weed control (C FW ) 2228 (276) a 1176 (165) a 1254 (193) a 4641 (630) a 3372 (496) ab 8013 (1119) a Weed control only (C W ) 1875 (341) a 966 (198) a 1011 (224) a 3838 (761) a 1729 (548) b 5566 (313) a

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54 Table 2 4 Effects of silvicultural treatments on the macro and micro nu trient accumulation in the aboveground biomass of two year old loblolly pine and understory vegetation for the actively managed retreated and untreated carr yover experiments on Spodosols in north Florida. Nutrients Treatments ------------Actively Man aged Retreated -----------------------------Untreated Carryover ---------------Foliage Stem wood Branches Total (Pine) Under story Foliage Stem wood Branches Total (Pine) Under story -----------------------kg.ha 1 -----------------------------------------kg.ha 1 -----------------------Nitrogen Control 29.6 a 5.4 a 2.3 a 37.0 a* 46.9 ab 37.3 a 7.6 a 2.9 a 47.6 a 39.7 a (17.46) (4.62) (1.50) (17.96) (3.6) (6.45) (4.99) (0.55) (11.53) (17.9) Fertilizer only 71.7 bc 11.0 ab 7.1 b 89.2 b 68.0 a 76.9 b 10.0 a 5.8 b 92.0 b 42.0 a (10.32) (0.96) (0.92) (11.47) (17.9) (12.83) (1.92) (0.49) (15.00) (9.3) Fertilizer+ Weed control 102.7 c 14.2 b 8.3 b 124.1 b 9.7 c 41.2 a 6.4 a 2.7 a 50.0 a 16.8 a (9.43) (1.21) (1.10) (7.38) (12.7) (2.91) (2.95) (0.38) (6.11) (6.7) Weed control only 51.9 ab 6.2 ab 3.6 a 61.4 ab 15.6 bc 31.6 a 5.0 a 2.5 a 38.9 a 9.7 a (16.68) (2.14) (0.94) (19.41) (10.4) (0.29) (2.23) (0.32) (2.7 8) (4.0) Phosphorus Control 1.8 a* 0.2 a 0.2 a 2.2 a* 3.9 ab 2.5 a 0.3 a 0.3 a 3.0 a 3.6 a (1.00) (0.16) (0.16) (1.31) (0.5) (0.23) (0.01) (0.04) (0.22) (1.0) Fertilizer only 5.0 b 0.8 b 0.6 b 6.3 b 7.4 a 4.3 b 0.5 b 0 .5 b 5.4 b 4.0 a (0.53) (0.09) (0.10) (0.51) (2.7) (0.27) (0.04) (0.04) (0.28) (0.1) Fertilizer+ Weed control 6.9 b 0.9 b 0.7 b 8.5 b 1.4 b 2.5 a 0.3 a 0.3 a 3.1 a 3.0 a (1.07) (0.05) (0.07) (0.97) (1.7) (0.39) (0.06) (0.03) (0.42) (2. 0) Weed control only 3.1 ab 0.4 a 0.3 a 3.8 ab 1.9 b 1.9 a 0.2 a 0.2 a 2.3 a 1.4 a (0.43) (0.10) (0.09) (0.58) (1.5) (0.17) (0.08) (0.04) (0.26) (0.9)

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55 Table 2 4. Continued Nutrients Treatments --------------Active ly Managed Retreated --------------------------Untreated Carryover -------------Foliage Stem wood Branches Total (Pine) Under story Foliage Stem wood Branches Total (Pine) Under story -----------------------kg.ha 1 -----------------------------------------kg.ha 1 -----------------------Potassium Control 8.7 a 1.5 a 1.0 a 11.2 a 22.5 a 14.2 a 1.1 a 1.3 a 16.5 a 22.3 a (3.56) (1.06) (0.83) (5.35) (4.9) (2.99) (0.09) (0.39) (3.16) (6.0) Fertili zer only 28.5 ab 3.8 b 2.9 b 35.0 b 36.1 a 28.1 b 3.8 b 2.5 b 34.2 b 23.4 a (3.69) (0.72) (0.41) (4.34) (19.6) (5.48) (0.24) (0.26) (5.55) (5.3) Fertilizer+ Weed control 32.7 b 3.3 ab 2.9 b 38.6 b 6.5 a 9.3 a 1.4 a 1.3 a 11.9 a 11.2 ab (13.02) (0.01) (0.34) (13.06) (9.0) (1.39) (0.15) (0.17) (1.26) (4.0) Weed control only 17.8 ab 1.8 a 1.5 ab 21.0 ab 11.5 a 8.3 a 1.0 a 1.1 a 10.3 a 6.4 b (1.42) (0.66) (0.44) (2.02) (10.2) (4.07) (0.52) (0.22) (4.77) (5.1) Calcium Control 2.0 a 0.8 a 1.6 a+ 4.4 a+ 26.3 a 3.1 a 1.1 a 2.1 a 6.3 a 19.9 ab (1.03) (0.59) (1.18) (2.77) (1.4) (0.13) (0.16) (0.31) (0.24) (10.6) Fertilizer only 3.7 b 1.5 ab 3.1 a 8.2 a 26.8 a 4.7 b 1.9 a 4.1 b 10.6 b 26.3 a (0.27) (0.12) (0.77) (0.91) (10.9) (0.10) (0.45) (0.32) (0.30) (11.3) Fertilizer+ Weed control 5.5 c 2.2 b 5.7 b 13.3 b 1.4 b 3.6 a 1.2 a 2.3 a 7.1 a 5.8 bc (0.59) (0.12) (1.65) (2.18) (1.7) (0.68) (0.38) (0.28) (1.03) (3.3) Weed con trol only 3.5 b 1.4 ab 2.9 a 7.8 a 2.6 b 2.8 a 1.0 a 1.7 a 5.5 a 2.1 c (0.62) (0.52) (1.26) (2.37) (1.2) (0.52) (0.31) (0.56) (1.27) (0.8)

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56 Table 2 4. Continued Nutrients Treatments ------------Actively Managed Retr eated --------------------------Untreated Carryover -------------Foliage Stem wood Branches Total (Pine) Under story Foliage Stem wood Branches Total (Pine) Under story -----------------------kg.ha 1 -----------------------------------------kg.ha 1 -----------------------Magnesium Control 1.0 a+ 0.4 a 0.5 a 1.9 a 14.4 a 1.5 a 0.4 a 0.6 a 2.6 ab 8.1 a (0.62) (0.24) (0.44) (1.28) (3.2) (0.12) (0.03) (0.03) (0.12) (3.7) Fertilizer only 1.4 ab 0.7 ab 1.0 ab 3.0 ab 9.0 ab 1.9 a 0.8 b 1.2 b 3.8 b 7.5 ab (0.14) (0.05) (0.15) (0.13) (3.6) (0.34) (0.17) (0.03) (0.48) (2.7) Fertilizer+ Weed control 2.0 b 0.8 b 1.3 b 4.1 b 0.9 c 1.4 a 0.4 a 0.6 a 2.4 ab 1.5 ab (0.26) (0.06) (0.07 ) (0.25) (1.1) (0.49) (0.10) (0.07) (0.63) (0.8) Weed control only 1.4 ab 0.5 ab 0.7 ab 2.6 ab 1.7 bc 1.3 a 0.4 a 0.5 a 2.1 a 1.2 b (0.16) (0.15) (0.21) (0.47) (0.8) (0.30) (0.11) (0.12) (0.52) (0.6) Sulfur Control 1.9 a 0.2 a 0.1 a* 2.2 a 5.7 a 2.4 ab 0.1 a 0.1 a* 2.6 ab 3.5 a (1.19) (0.09) (0.07) (1.35) (1.3) (0.29) (0.04) (0.08) (0.30) (1.4) Fertilizer only 4.1 b 0.4 ab 0.5 b 4.9 b 5.3 a 4.2 c 0.4 a 0.3 a 4.9 c 4.3 a (0.55) (0.12) (0.06) (0.48) ( 1.6) (0.27) (0.19) (0.28) (0.24) (1.4) Fertilizer+ Weed control 6.4 c 0.6 b 0.7 b 7.7 c 0.7 b 2.8 b 0.2 a 0.3 a 3.3 b 2.3 a (0.67) (0.21) (0.05) (0.78) (0.7) (0.33) (0.06) (0.12) (0.50) (0.8) Weed control only 3.1 ab 0.2 a 0.2 a 3.5 ab 1.9 ab 2.1 a 0.2 a 0.2 a 2.4 a 1.6 a (0.77) (0.07) (0.03) (0.80) (1.0) (0.17) (0.10) (0.11) (0.32) (0.8)

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57 Table 2 4. Continued Nutrients Treatments -------------Actively Managed Retreated -------------------------Untreated Carryover -------------Foliage Stem wood Branches Total (Pine) Under story Foliage Stem wood Branches Total (Pine) Under story -----------------------g.ha 1 ------------------------------------------g.ha 1 -----------------------Boron Control 11 a 5 a 6 a 22 a 114 a 15 a 6 a 8 a 29 a 65 a (6.3) (3.0) (4.5) (13.7) (37) (1.0) (0.7) (0.8) (2.0) (19) Fertilizer only 18 ab 10 ab 13 b 40 ab 121 a 21 b 13 b 17 b 51 b 116 a (2.2) (1.0 ) (2.1) (4.4) (61) (0.8) (3.4) (2.4) (5.8) (79) Fertilizer+ Weed control 28 b 14 b 20 c 62 b 5 b 13 a 6 a 7 a 26 a 19 a (2.8) (0.8) (2.7) (2.1) (6) (1.1) (1.0) (0.8) (2.3) (10) Weed control only 18 ab 8 a 11 ab 37 a 9 b 13 a 6 a 6 a 25 a 7 a (3.9) (3.4) (3.5) (10.4) (5) (1.9) (1.2) (1.3) (3.9) (2) Copper Control 3 a 40 a 3 a 46 a 25 ab 5 a 31 a+ 4 a 40 a+ 21 a (1.7) (38.1) (1.8) (41.2) (2) (1.0) (17.7) (0.6) (17.8) (6) Fertilizer onl y 9 b 110 a 8 bc 127 a 39 a 8 b 72 a 10 a 90 a 21 a (1.1) (23.8) (0.8) (25.4) (24) (0.8) (26.3) (5.4) (30.1) (4) Fertilizer+ Weed control 11 b 111 a 11 c 131 a 5 b 4 a 64 a 3 a 71 a 6 b (0.5) (53.5) (1.5) (54.1) (6) (1.0) (44.0) (1.0) (44.8) (3) Weed control only 5 a 76 a 5 ab 86 a 7 ab 3 a 36 a 3 a 42 a 5 b (0.8) (28.5) (1.7) (29.7) (8) (0.6) (35.1) (0.5) (36.0) (3)

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58 Table 2 4. Continued Nutrients Treatments -------------Actively Managed R etreated --------------------------Untreated Carryover -------------Foliage Stem wood Branches Total (Pine) Under story Foliage Stem wood Branches Total (Pine) Under story -----------------------g.ha 1 ------------------------------------------g.ha 1 -----------------------Manganese Control 95 a 35 a 54 a 183 a 1325 a 165 a 40 a 54 a 258 a 265 a (43.1) (27.8) (54.5) (119.6) (424) (17.5) (2.6) (16.1) (13.2) (88) Fertilizer only 248 b 72 ab 99 ab 417 a 1683 a 336 b 117 b 186 b 634 b 1103 b (79.7) (8.4) (19.3) (96.2) (1258) (10.1) (30.0) (32.3) (59.5) (265) Fertilizer+ Weed control 425 c 115 b 217 b 750 b 171 a 334 b 82 ab 97 a 511 ab 370 a (53.7) (21.6) (48.9) (120. 3) (227) (115.6) (37.7) (29.1) (178.1) (182) Weed control only 196 ab 50 a 75 a 320 a 162 a 181 ab 37 a 49 a 266 a 133 a (15.0) (14.5) (31.1) (59.8) (123) (47.4) (18.1) (7.0) (68.2) (103) Zinc Control 34 a 41 a 25 a 10 0 a 269 ab* 48 ab 34 a+ 35 a 117 a 161 ab* (16.5) (35.2) (21.8) (71.4) (67) (4.7) (11.0) (3.4) (6.8) (68) Fertilizer only 84 b 100 a 52 ab 235 ab 1071 a 89 c 79 b 65 b 231 b 590 a (14.8) (14.6) (8.9) (20.0) (708) (6.5) (9.5) (8.9) (7.4 ) (427) Fertilizer+ Weed control 123 c 116 a 87 b 322 b 41 c 64 a 59 ab 36 a 158 a 80 bc (7.0) (46.5) (22.1) (72.1) (43) (5.8) (32.7) (10.0) (45.3) (12) Weed control only 55 ab 63 a 30 a 147 a 49 bc 42 b 37 a 24 a 102 a 44 c (9.3) (20.0) (12.8) (35.0) (28) (7.0) (28.3) (4.7) (38.3) (25) Note: + block effect significant; ANOVA performed on transformed data. Component nutrient accumulation for pine may not sum to the total nutrient accumulation in pine becau se separate allometric functions were used to estimate the aboveground component and total biomass. For a given component within a nutrient, means followed by the same letter are not significantly different amo ng ndard deviations are given in parentheses

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59 Table 2 5 Correlation coefficients (r) between soil nutrient supply rates during the growing season and aboveground biomass accumulation in loblolly pine stands for the actively man aged retreated and untreated carryover experiments on Spodosols in north Florida. -----Actively managed retreated -------------------Untreated carryover --------Nutrients Correlation coefficient (r) P Value Correlation coefficient (r) P Value N 0.67 0.017 0.30 0.344 P 0.42 0.170 0.83 0.001 K 0.07 0.827 0.37 0.241 Ca 0.73 0.007 0.40 0.198 Mg 0.61 0.037 0.31 0.335 S 0.61 0.034 0.15 0.633 B 0.07 0.840 0.13 0.686 Cu 0.51 0.094 0.73 0.007 Mn 0.62 0.031 0.79 0.002 Zn 0.73 0.007 0.55 0.066 Fe 0.57 0.051 0.10 0.748 Note: Data were combined across treatments prior to analysis (n = 12).

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60 Figure 2 1. Layout of the actively managed retreatment and the untreated carryove r experiments on Spodosols near Gainesville, FL.

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61 Figure 2 2. Heights of the first rotation 3 year old loblolly pines at the original IMPAC study sites compared to those in the second rotation actively managed retreated and untreated carryover experiments on Spodosols in north Florida. The notations C F, FW, and W represent, respectively, the plots that received control, fertilizer only, fertilizer + weed control, and weed control only treatments. Note, the untreated carryover plots received treatments in the previous rotation, but did not receive tre atments in the second rotation. Error bars represent standard errors of the mean.

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62 Figure 2 3. Total aboveground biomass accumulation for second rotation loblolly pine stands growing in A ) the actively managed retreated, and B ) untreated carryover expe riments on Spodosols in north Florida. The notations C, F, FW, and W represent, respectively, the plots that received control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the plots that received control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation. Error bars represent standard deviations.

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63 Figure 2 4. Dry matter allocation in the aboveground components of second rotation, two year old loblolly pine stands growing in the A) actively managed and B) untreated carryover experiments on Spodosols in north Florida. The notations C, F, FW, and W represent, respectively, the plots that rece ived control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the plots that received control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation. Among treatments, components followed by similar letters were not significantly different at alpha= 0.05.

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64 Figure 2 5. Phosphorus, Mn, and Zn supply in a) the actively managed retreated and b) untrea ted carryover experiments on Spodosols in north Florida. Within a nutrient, treatments with same letter indicate no significant differences at alpha of 0.1. Error bars represent standard deviations. Figure 2 6. Relationship between soil P supply and th e aboveground pine biomass in the untreated carryover experiment on Spodosols in north Florida. Error bars represent standard deviations.

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65 Figure 2 7. Mehlich III extractable P concentrations in the soils of the untreated carryover experiment in north Fl orida. The notations C C C F C FW and C W respectively, represent the plots that received control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation. Error bars represent standard errors of the mean

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66 Figure 2 8. Aboveground biomass and nutrient accumulation in A) herbaceous plants and grasses of the actively managed retreated, B) shrubs and vines of the actively managed retreated, C) herbaceous plants and grasses of the untreated carryover, and D ) shrubs and vines of the untreated carryover experiments in north Florida. Means within biomass or nutrient treatments followed by same letter were not significantly different at alpha of 0.1. Error bars represent standard errors of the mean.

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67 CHAPTER 3 I NTER ROTATIONAL EFFECTS O F FERTILIZATION AND HERBICIDE ON UNDERSTORY VEGETATIO N ABUNDANCE, RICHNES S AND DIVERSITY IN JUVENILE LOBLOLLY PI NE STANDS Introduction In nutrient limited terrestrial ecosystems, aboveground net primary productivity often increase s with fertilization (Vitousek and Farrington, 1997; LeBauer and Treseder, 2008). Changes in abundance, richness, and diversity of plant communities have been evident following nutrient amendments in terrestrial ecosystems (Tilman, 1987; Bobbink, 1991, Gou gh et al. 2000; Wassen et al. 2005). Unlike in natural productivity gradients, a consistent decline in diversity has been observed on the most productive sites in fertilization experiments (DiTommaso and Aarssen, 1989). Several competitive exclusion mech anisms have been hypothesized to explain such changes in plant community composition following fertilization: 1) changes in competitive interactions between species, 2) shifts in competition from belowground to aboveground, and 3) creation of less heteroge neous sites that favor species coexistence (Newman, 1973; Grime, 1977; Huston, 1979; Tilman and Pacala, 1993; Rajaniemi, 2003). Although changes in community composition following nutrient additions has been well studied in agricultural and grassland ecos ystems, the effects of fertilization on community composition are still poorly documented in forested ecosystems. In part, this may reflect a strong historical focus on overstory productivity rather than understory species re sponses to nutrient additions. Results from several studies have demonstrated responses ranging from increasing (Prescott et al. 1993; Kellner, 1993; Thomas et al. 1999), decreasing (Lu et al. 2010), or no net changes (Ostertag and Verville, 2002) in understory species abundance and diversity (VanderSchaff et al.

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68 2000). Responses to nutrient additions could possibly favor abundance of species limited by nutrients or diminished understory diversity resulting from accelerated canopy closure and limited access of understory species to l ight (Lamb et al. 2009; Suding et al. 2005; Tilman and Pacala, 1993). Similar to productivity, disturbance al so plays an important role in plant community dynamics. The response of plant communities can be influenced by both the frequency and intensity of disturbance (Miller et al. 2011). Since spatio temporal disturbance patterns create a more heterogeneous environment, species coexistence may be influenced by such heterogeneity (Connell, 1978; Mackey and Currie, 2001). While theoretical models suggest that diversity is highest at intermediate levels of disturbance, there is still no consensus regarding the effects of disturbance on diversity (Wilson and Tilman, 1991; Collins, 1992; Elliott and Swank, 1994). In managed forests, disturbances in the under story vegetation community via competition control are now quite common and generally have short lived negative effects on understory diversity For example, studies have documented a significant reduction in understory species diversity (Jones et al. 200 9; Neary et al. 1990b; Zutter and Zedaker, 198 8), species richness (Swindel et al. 1989) and cover (Jones et al. 2009; Miller et al. 1995) following herbicide applications in southern pine plantations. Although understory communities tend to recover to levels of pre treatment diversity within a few years following a single herbicide application (Miller et al. 1999; Brockway et al. 1998; Boyd et al. 1995), it is still not clear how they reinitiate and respond to sustained control (repeated herbicide a pplications) of competing un derstory vegetation over time.

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69 Understanding vegetation responses, plant diversity and community dynamics are central for defining and developing sustainable forest management systems for the future (Brown et al. 2001). Increas ing demands for forest products and a dwindling global per capita holding of forest area, has contributed to the development of more intensive forest management systems designed to increase productivity without diminishing existing forest resources (FAO, 2 010). One of the challenges for southern pine ecosystems is to enhance both productivity and other services such as maintenance of understory biodiversity. To ensure higher pine yields, fertilization and weed control treatments are periodically applied to nutrient limited sites (Allen et al. 1990; Colbert et al. 1990; Fox et al. 2007 a ). While a general gain in plant diversity may occur at intermediate levels of productivity and disturbance, these relationships will likely deviate in southern pine ecosyst ems that have been intensively managed using fertilization and weed control treatments. We hypothesize that in N and P limited juvenile pine stands, where light is not a limiting factor, long term fertilization treatments will not cause a decline in specie s diversity. Instead, it may favor the abundance of a few nutrient limited understory species. With long term selective weed control, we expect a less diverse understory community due to the removal of functional groups such as hardwoods. The resulting und erstory community would be expected to differ substantially from the fertilized community. In addition, we expect these effects to the understory community to be more pronounced when a combination of fertilization and weed control treatments are applied. T his study focuses on response of the understory vegetation community to long term fertilization and sustained control of competing vegetation using herbicides in

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70 young second rotation loblolly pine ( Pinus taeda L.) stands growing on poorly drained Spodosol s in north central Florida. The study described here utilized long term replicated experiments to answer two questions: 1. Do past silvicultural treatments (fertilization and weed control) have inter rotational effects on the understory community abundance a nd diversity in a N and P limited environment? 2. Do historical treatments of understory vegetation affect their reiniti ating patterns and composition? These questions were addressed by examining and comparing aboveground biomass accumulation, species richnes s, and diversity of the understory vegetation community across a range of silvicultural treatment histo ries that had varying levels of soil nutrient availability. Methods Study A rea The Intensive Management Practices Assessment Center (IMPAC) at the Univer sity of Florida established an experimental study site in 1983 to evaluate factors that limit the potential productivity of southern pines (Swindel et al. 1988). The IMPAC experimental site is located approximately 10 km north of Gainesville, Florida (20 he mean sea level. The climate is warm and humid with mean annual temperature and total annual rainfall of 20.6C and 1178 mm, respectively (National Oceanic and Atmospheric Administration, 2012). The predominant soils in this study site are sandy siliceous hyperthermic Ultic Alaquods (Pomona series). Understory vegetation was typical of lower Coastal Plain flatwoods ecosystems. Wiregrass ( Aristidia strictus (Michx.)), gallberry ( Ilex glabra (L.)), saw palmetto ( Serenoa repens (Bartr.)), fetterbush ( Lyonia ferruginea (Walt.)),

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71 blueberries ( Vaccinium spp.), broomsedges ( Andropogon spp.), panic grasses ( Dicanthelium spp. and Panicum spp.), and wax myrtle ( Myrica cerifera (L.)) were the predomin ant residual understory species found at the study site (Neary et al. 1990 b ). Study D esign The IMPAC experiment was designed as a 2x2x2 factorial consisting of species (loblolly and slash pine ( Pinus elliottii var. elliottii ( Engelm.) ) ), complete and sust ained weed control, and annual fertilization arranged in a randomized split plot (species as whole plots) design. This resulted in four treatments within each species: control (C), weed control only (W), fertilizer only (F), and both fertilizer and weed co ntrol (FW). The entire experimental area was site prepared using a single pass bedding treatment. Genetically improved (first generation, open pollinated) 1 0 bareroot stock of both loblolly and slash pine were hand planted in January 1983 (Swindel et al. 1988; Colbert et al. 1990; Martin and Jokela, 2004). After applying a fertilizer regime with balanced levels of macro and micronutrients for the first ten years to the F only and FW treatments, it was stopped in May 1993 and then resumed during the sixt eenth to eighteenth growing seasons (1998 2000; Jokela and Martin, 2000). Fertilizers were applied in narrow bands (30 cm semicircle) around the base of each tree or planting location. Total nutrient additions over the life of the original study for the F and FW treatments for both species were (kg ha 1 ): 1088 N, 230 P, 430 K, 108 Ca, 72 Mg, 72 S, 4.1 Mn, 5.4 Fe, 0.9 Cu, 4 Zn, and 0.9 B. A combination of chemical and mechanical methods were used annually to control competing understory vegetation in the W a nd FW treatments for the first ten years until canopy closure impeded further understory development (Colbert et al, 1990; Neary et al. 1990 b ; Dalla Tea and Jokela, 1994). The

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72 long term production and stand dynamics of the IMPAC experiment over the 25 yea r study period were summarized by Jokela et al. (2010). The IMPAC study was harvested in May 2009, with the intent of overlaying a second experiment using the same treatment plots. Considering the need for long term monitoring of the site to understand the effects of the past management history on both the productivity of loblolly pine and the diversity of understory vegetation community, the IMPAC II study site was initiated in June 2009. Original plots in the first rotation were re established and those p vegetation community responses in th e second rotation experiment. The IMPAC II experiment now consists of two randomiz ed complete block designs (RCBD; 3 replications each) having four treatments (C, F, FW, and W) for the actively managed retreatment design and four treatments for the untreated carryover design (C C C F C FW C W ) (Figure 2 1). The untreated carryover experi ment was established on the previous slash pine plots and the actively managed retreatment experiment was established on the previous loblolly pine plots. While the actively managed retreated experiment continued to receive similar treatments as the first rotation, the untreated carryover experiment did not receive treatments in the second rotation. Prior to harvesting, all treatment plot corners were physically re monumented The understory vegetation within the C and the F treatments was mulched in place (April 2009) to retain this nutrient pool within the plot boundaries. Mulching was not necessary for the W and FW treatments because of the sustained weed control treatment history from the previous rotation. In order to ensure no inputs of nutrients via

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73 h arvest residues, each plot was whole tree harvested and processed off the treatment plots. Following harvest, the entire study area was later bedded in June, with a second bedding pass conducted in August of the same year. Similar to the last rotation l o blolly pines were planted in each plot at a 1.8 m by 3.0 m spacing, with measurement plots (0.02 ha) consisting of forty trees per plot (8 trees each in 5 beds). A treated buffer consisting of three trees and two beds surrounded each measurement plot resul ting in a 0.08 ha treatment plot. Six tree spaces of untreated buffer were provided between two adjacent treatment plots. Across the treatment plots, an untreated buffer of four beds was maintained (Figure 2 1). In December 2009, the entire study was regen erated using containerized seedlings from a single, full sib loblolly family. Prior to planting, only the active retreatment plots, which received chemical site preparation and weed control in the first rotation, were treated using a broadcast application of 0.84 kg a.e. ha 1 imazapyr in the form of Chopper (BASF Corp., Research Triangle Park, NC, USA), 1.12 kg a.e. ha 1 triclopyr in the form of Garlon 4 (Dow AgroSciences LLC, Indi anapolis, IN, USA), and 0.14 kg. ha 1 of metsulfuron methyl in the form of E scort (E.I. du Pont de Nemours and Company, Inc., Wilmington, DE, USA) in October 2009. In October, 2010 these same plots received a directed spray application of triclopyr (3%) and imazapyr (1%) to control Ilex glabra (L.) and other understory competitor s. All treatments (actively managed retreated and untreated carryover) received a single application of Fipronil (9.1%) in the form of PTM TM (BASF Corp., Research Triangle Park, NC, USA) in March 2010 to control Nantucket pine tip moth ( Rhyacionia frustran a ). Later in September 2011, a directed spray of glyphosate

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74 (3%) was applied to the actively managed F and FW treatments to maintain a weed free environment. The untreated carryover experiment did not receive any additional chemical treatments (herbicide or fertilizer), with the exception of a banded 0.2 kg a.e. ha 1 imazapyr application in May 2010 to control Dicanthelium spp. and to aid seedling survival in all treatment plots. This same banded herbicide treatment was also applied to the actively managed C and F treatments. The actively managed retreated (F and FW) experiment received fertilizer at the end of July 2011 and beginning of September 2012. Consistent with the last rotation treatments, the total nutrient additions over the first three growing s easons for the F and FW treatments were (kg ha 1 ): 120 N, 53 P, 99 K, 40 Ca, 19 Mg, 56 S, 1.3 Mn, 0.5 Fe, 0.2 Cu, 0.5 Zn, and 0.2 B. As done in the first rotation experiment, the fertilizer was applied in narrow bands (30 cm semicircle) around the base of each tree or planting location. Sampling During August and September 2011, the understory vegetation community was assessed by conducting a clip plot survey. Six 1 m 2 quadrats were randomly placed in each measurement plots, stratified equally between the b ed and inter bed positions. All standing vegetation that fell within the quadrats was clipped at ground level and sorted s eparately by species or genus. All samples were oven dried at 65C to a constant weight. All samples were weighed to estimate the prop ortion of biomass accumulated by each species in each measurement plot. The biomass data were used to estimate species diversity in each treatment. In addition, life form biomass was grouped into

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75 three categories: grasses (grasses and grass like species), shrubs (shrubs, vines, and trees), and forbs (forbs and ferns). Soil nutrient availability was assessed in the actively managed and untreated carryover experiments using PRS TM probes (Western Ag Innovations, Inc., Saskatoon, SK, Canada), ion exchange memb ranes. Four cation and four anion PRS TM probes were buried randomly in the beds of all measurement plots in August 2011. After eight weeks of burial these probes were removed from the soil and rinsed free of adhering soil particles with de ionized and dist illed water. All probes were eluted using a 0.5N Hydrochloric Acid (HCl) solution for 1 hour. The eluate was then analyzed colorimetrically using an automated flow injection analysis system for NO 3 N and NH 4 + N to obtain total N supply. For P, K, Ca, Mg, S, B, Cu, Mn, Zn, and Fe, ICP AES was used. All analyses were done at the Western Ag Innovations, Inc. in Saskatoon, SK, Canada. Data A nalysis Understory species biomass was u s ed as a measure of species abundance (Chiarucci et al. 1999). Two indices of di versity were calculated: the Simpson index and the Shannon measure of diversity, and is estimated by the following function: where S is the total number of species and p i is the propo rtion of all individuals in a sample belonging to species i

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76 D represents the probability of two individuals chosen at random from a community to be different. Because the Simpson index of diversity is mostly sensitive to abundant species, th e Shannon Weiner index, which is sensitive to rare species, was also used as the measure of diversity. The Shannon uncertainty in predicting an occurrence of species chosen at random in a community (Shannon and W eaver, 1949), was estimated by the following function: where S is the total number of species and p i is the proportion of all individuals in a sample which belong to species i ty, to 5 or more in diverse communities Analysis of variance (ANOVA) for a randomized complete block design was used to test the effects of fertilizer and weed control on species richness, evenness and diversity for both the actively managed retreated an d the untreated carryover experiments. In order to ensure that the data met assumptions of normality and homoscedasticity, Kolmogorov Smirnov and equal variance tests were utilized, respectively (Massey, 1951). For data not meeting the assumptions of norma lity and homoscedasticity, appropriate transformations were made prior to conducting ANOVA among treatment means at an alpha level of 0.05, unless noted otherwise. In o rder to test if the understory vegetation community in the second rotation, 2 year old loblolly pine plantation differed with respect to long term applications of

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77 herbicide and fertilizer, a multi response permutation procedure (MRPP) (Mielke, 1984) in PC ORD 4.35 (McCune and Mefford, 1999) was used with the species biomass data. Species biomass data were relativized with respect to site prior to analysis. Because rare species and outliers often create noise in the data and influence MRPP results, outliers (samples with biomass greater than two standard deviations from the block means) and rare species occurring in just one (8%) of the twelve plots were removed prior to MRPP analysis (Marchant, 2002; Sickle et al. 2007). This resulted in a reduction of numb er of species from 29 to 21 in the actively managed retreated experiment and 33 to 21 in the untreated carryover experiment. MRPP, unlike MANOVA, does not require the assumptions of normality and homoscedasticity to be met. Sorensen (Bray Curtis) distance measure and natural weighting suggested by Mielke (1984) was used in the MRPP analysis. MRPP calculates within group distance (delta), separation between groups or effect size (T statistic), and within group homogeneity (agreement statistic (A)) in species space, and a P value (probability of smaller or equal delta). When MRPP revealed significant treatment differences, separate post hoc MRPP analyses were done to identify the significantly different treatment pairs. Indicator species (Dufrene and Legendre, 1997) were then identified for treatments after the MRPP revealed significant difference between treatment pairs. Indicator species for each treatment or group were identified using indicator values (IV) which represent the percentage of perfect indicatio n by species. The greatest IV for each species was tested against the random expectation obtained by 10000 Monte Carlo permutations at a 95 % significance level. Indicator species were obtained using the Indicator Species Analysis module in PC ORD 4.35 (Mc Cune and Mefford, 1999).

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78 A non metric multidimensional scaling (NMS) ordination method in PC ORD 4.35 was u s ed to investigate the relationships among the understory vegetation community and environmental gradients such as soil nutrient supply, weed control fertilizer addition, and overstory biomass (loblolly pine biomass). NMS is not only superior to other univariate methods in identifying complex relationships between treatments and numerous environmental variables, but also is well suited to non normal d ata or even to data that are on an arbitrary or discontinuous scale (Clarke, 1993; McCune and Grace, 2002). A Sorensen (Bray Curtis) distance measure was used for ordination in this study. Choice of the number of ordination axes depended both on the Monte Carlo test and the plot of stress vs. iteration for the stability of a solution at the chosen axes (McCune and Grace, 2002). Results Species R ichness Species richness was affected by silvicultural treatments in the actively managed retreated experiment. Th e FW treatment had significantly lower species richness compared to the F and C treatments (Table 3 1). The species richness in the C (13.3) and F (~11.7) treatments were almost three times higher than the FW (~4.3) treatment. The richness of shrubby compo nents (shrubs, vines, and trees) were almost three times lower (p = <0.001) in the FW (~1.5) and W (~2) treatments compared to the C (~5.7) and F (~6) treatments. The richness of both grasses and forbs were not influenced by treatments in the activel y mana ged retreated experiment. In the untreated carryover experiment, nutrient additions and herbicide application from the first rotation did not significantly affect the understory species richness in the second rotation (Table 3 2). However, the effects of t reatments on the

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79 richness of shrubby components approached significance (p = 0.06). The richness of shrubby species was relatively higher in the C C (~6) followed by the CF (~4), C FW (~3.3), and C W (~2.7) treatments. Likewise, the treatment effects on richn ess of grasses were weakly significant (p = 0.08). The richness of grassy species was relatively higher in the C W (~6) followed by the C C (~5), C F (~3.3), and C FW (~3.7) treatments. Unlike richness, treatments did not significantly influence the evenness of understory vegetation in the actively managed retreated experiment (Table 3 1). However, the C FW treatment had significantly lower understory vegetation evenness compared to the C C treatment (0.2 vs. 0.51) (Table 3 2). Life form B iomass Life form bioma ss was affected by nutrient addition and weed control treatments in the actively managed experiment (Figure 3 1 ). Weed control treatments that were applied to eliminate understory vegetation significantly reduced the biomass of shrubb y components in the FW (0.01 Mg. ha 1 ) and W (0.02 Mg. ha 1 ) treatments compared to the C and F treatments. Fertilizer additions, however, did not significantly increase the biomass of shru bby vegetation in the F (5.8 Mg. ha 1 ) trea tment compared to the C (5.3 Mg. ha 1 ) treatment. Grass biomass was also not significantly affected by the fertilizer addition or weed control treatments. However, accumulation of grass biomas s followed the trend: F (1.9 Mg. ha 1 ) > W (1.4 Mg. ha 1 ) > FW (1.1 Mg. ha 1 ) > C (0.5 Mg. ha 1 ). Similarly, forb biom ass, which constituted a small fraction of total understory biomass (7% in the W to 0.2% in the FW), was not affected by silvicultural treatments. While the major contributor of understory biomass in the plots receiving the weed control treatment were the grasses ( 98% in the FW and 91% in the W treatments), shrubby species were the dominant contributors of understory biomass in the C (91%) and the F

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80 (75%) treatments. Of the total understory biomass, grasses like Andropogon spp. and Dicanthelium spp., for i nstance, accumulated almost 65% and 31% in the FW treatment and 48% and 35% in the W treatment, respectively ( Table C 2 ). In contrast, shrubby species like Ilex glabra (L.) and Serenoa repens (Bartr.) accounted for almost 44% and 19% of the total understor y biomass in the C treatment and 49% and 12% in the F treatment, respectively ( Table C 2 ). Like in the actively managed retreated experiment, historical fertilizer and weed control treatments in the untreated carryover experiment significantly influenced t he life form biomass of understory vegetation (Figure 3 1 ). The historical weed control treatment significantly reduced the biomass of shrubby vegetation in the C FW (0.26 Mg. ha 1 ) and C W (0.08 Mg. ha 1 ) treatments compared to the C C treatment (4.2 Mg.ha 1 ). In contrast, historical nutrient addition alone did not increase shrub biomass in the second rotation. For example, shrub biomass in the C F (4 Mg. ha 1 ) treatment was comparable to the C C treatment (4.2 Mg.ha 1 ). The C F treatment also did not significantly increase grass biomass compared to the C C treatment. In contrast, the C FW and C W treatments increased the grass biomass component by about 6 and 3 fold, respectively, compared to the C C treatment. Grass biomass accumulation in the untreated carryover ex periment followed the trend: C FW (3.1 Mg ha 1 ) > C W (1.6 Mg ha 1 ) > C F (0.7 Mg ha 1 ) > C C (0.5 Mg ha 1 ). Forb biomass constituted a small fraction of total understory biomass (2% in the Cc to 0.2% in the C W ) and, as in the actively managed experiment, was not influenced by treatments. While the major contributor of understory biomass in the plots that received historical weed control treatment were the grasses (95% in the C W and 91% in the C FW treatments), shrubby species were the major

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81 contributors of unde rstory biomass in the C C (87%) and the C F (84%) treatments. Andropogon spp. accumulated almost 89% of the total understory biomass in the C FW treatment and 68% in the C W treatment. In the C W treatment, Dicanthelium spp. also accounted for 18% of the total understory biomass. In contrast, shrubby species like Ilex glabra (L.) and Serenoa repens (Bartr.) accounted for approximately 42% and 23% of the total understory biomass in the C F and 49% and 24% in the C C treatments, respectively ( Table C 2 ). Species D iv ersity Second rotation understory diversity in the actively managed experiment was significantly influenced by the fertilization and weed control treatments. Shannon Weiner diversity was almost 2.6 times lower in the FW treatment than the F treatment (Tabl e 3 son 3 2). Although differences in the ts (p = 0.37), treatments) was higher (in absolute values) than the shrubby species divers 0.15 in the FW and 0.51 in the W treatments) for those plots that received the herbicide treatment (Figure 3 2 ). The first rotation silvicultural treatments significantly influenced the second rotation understory vegetation diversity in the untre ated carryover experiment (Table 3

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82 2). The Shannon Weiner diversity in the C FW treatment was reduced by almost three fold compared to the C C treatment. The C F and C W treatments, however, had no significant effect on the understory diversity compared to the C C treatment. Shannon Weiner diversity was highest for the C C F C W FW lower in the C FW treatment compared to all other treatments and followed the same trend as the Shannon Weiner diversity (Table 3 was not significantly affected by treatments (p = 0.38), the C F FW and C W y compared to the C C = 1.04) (p < 0.001) (Figure 3 2 ). Understory V egetation C ommunities Understory vegetation composition in the second rotation, 2 year old loblolly pine plantation differed among the actively managed treatments. Silvicultur al activities like fertilization and weed control treatments favored different understory communities. Pairwise comparisons between treatments revealed that the composition of understory vegetation was influenced more by the W rather than the F treatment. Although understory vegetation composition in the C and F treatments were similar, they differed significantly with the FW and W treatments (Table 3 3). Indicator species analysis revealed that shrubby species were the indicators of sites with no herbicide application. For example, Ilex glabra (L.), Serenoa repens (Bartr.), and Lyonia lucida (Lam.) were the indicators for the C and F treatment. In contrast, grassy species like Andropogon spp. and Dicanthelium spp. were the indicators for the FW and W treatm ents (Table 3 4).

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83 In the untreated carryover experiment, the C W and C FW treatments significantly altered the understory vegetation composition compared to the C C treatment (Table 3 3). Understory vegetation in the C W or C FW treatment shifted to a grass dom inated community when compared with the shrub dominated understory vegetation in the C C treatment. There were also significant understory community differences between the C W and C FW treatments. While Dicanthelium spp and Scleria spp. were the indicator s pecies for the C W treatment, Andropogon spp. was the indicator for the C FW treatment. In contrast, no significant influence of the C F treatment was observed in the understory vegetation composition compared to the C C treatment; no indicator species were, t herefore, identified for the C F and C C treatments (Table 3 4). Non metric multi dimensional scaling (NMS) was used to understand if significant differences in species richness, diversity, abundance, and composition represented a significant ecological diff erence among understory vegetation communities growing under different silvicultural treatments. Almost 89% of the variation in the understory vegetation data set in the actively managed experimental treatments was partitioned to the first two ordination a xes; the first axis explained about 25% and the second explained 64% of the total variation (Table 3 5). In a 2 dimensional species ordination space, the C and F treatments were clustered together compared to the FW and W treatments (Figure 3 3 ). In the ac tively managed retreated experiment, the correlation between the ordination axes and environmental variables such as weed control, fertilizer addition, soil nutrient supply (N, P, K, S, B, Cu, Mn, Zn, and Fe) rate at a 15 cm depth, and overstory biomass re vealed that weed control had the most influence (r = 0.948 with

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84 axis 1 and 0.600 with axis 2). The effect of the biomass of the overstory species, i.e. loblolly pine (r = 0.420 with axis 1 and r = 0.472 with axis 2) on ordination axes was second to wee d control. Although soil supply rates of N, K, and S in the growing season influenced axis 1 (r = 0.512, 0.499, and 0.537), fertilizer addition did not have a strong influence on the ordination axes (Table 3 6). In addition, the correlation between Andropogon spp. and the ordination axes revealed a strong negative relationship with both ordination axes (r = 0.909 with axis 1 and 0.592 with axis 2). In contrast, Ilex glabra (L.) had a strong positive relationship with both axes (r = 0.667 with axis 1 and 0.813 with axis 2). In addition, Rhus copallinum (L.) had a strong positive relationship with axis 1 and Serenoa repens (Bartr.), Gaylussacia dumosa (Andr.), and Lyonia lucida (Lam.) had a strong positive relationship with axis 2 (Table 3 7). These result s demonstrate that grassy species like Dicanthelium spp. and Andropogon spp. were characteristic of the W and FW treatments and shrubby species were characteristic of the C and F treatments. In the untreated carryover experiment, almost 91% of the variatio n in the understory vegetation data set was explained by the two ordination axes; 36% of variation was explained by the first axis and 55% of the variation was explained by the second axis (Table 3 5). A 2 dimensional ordination plot of understory vegetati on showed that the C W and C FW treatments were markedly different from the C F and C C treatments (Figure 3 3 ). The first rotation weed control treatment was the most influential variable for both ordination axes (r = 0.626 with axis 1 and 0.970 with axis 2) Axis 1 was also influenced by both the historical application of fertilizer (r = 0.433) and the growing season soil nutrient supply of S (r = 0.547), P (r = 0.476), and Cu (r =

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85 0.418). Likewise, axis 2 was influenced by the overstory biomass (r = 0.54 3) and soil supply of N (r = 0.651) and P (r = 0.541) (Table 3 6). In addition, Andropogon spp. was positively correlated with axis 1; but, shrubs like Ilex glabra (L.) and Serenoa repens (Bartr.) were negatively correlated with axis 1 (Table 3 8). In cont rast, shrubs like Ilex glabra (L.) (r = 0.878), Serenoa repens (Bartr.) (r = 0.740) and Lyonia ferruginea (Walt.) (r = 0.427) had a strong positive correlation with axis 2. Grasses like Andropogon spp. (r = 0.970), Dicanthelium spp. (r = 0.491) and Scler ia spp. (r = 0.432), however, had a strong negative correlation with axis 2. These results suggest that the historical weed control treatment, which was positively correlated with axis 1 and negatively correlated with axis 2, was strongly linked with the abundance of Andropogon spp. in the C W and C FW treatments. On the contrary, the supply of soil nutrients like N and P, which were positively correlated with axis 2, may have favored the growth of shrubby species like Ilex glabra (L.) and Serenoa repens (Ba rtr.) in the C F treatment. Discussion Addressing the contemporary issues of sustainable forest management systems requires a better understanding of the impacts of intensive forest management practices on the understory community composition and dynamics o ver multiple rotations (Powers, 1999; Fox, 2000; Brown et al. 2001). Understory community response, re initiation, and composition are affected by multiple factors such as stage of stand development, competition, soil nutrient availability, disturbance, a nd climate (Neary et al. 1990 c ; VanderSchaaf et al. 2002; Bernhardt et al. 2011). Long term replicated experiments using rotation long applications of fertilizer and sustained understory competition control, as described in this study, created a unique productivity and

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86 disturbance gradient and provided an opportunity to investigate their effects on the understory community dynamics in loblolly pine stands in a subsequent rotation Understory vegetation richness, abundance and diversity: Results from this study show that rotation long silvicultural treatments like weed control and fertilizer applications in loblolly pine stands can affect understory vegetation richness, abundance, and diversity beyond a single rotation. Inter rotational application of weed control treatments, as expected, reduced the richness of shrubby components but did not influence the richness of herbaceous components like grasses. Also, the suppression of shrubs in the FW and W treatments allowed the grassy components to flourish in t he subsequent rotation In southern pine stands, Miller et al. (1995) and Jose et al. (2010) have previously documented an increase in the abundance or cover of herbaceous components with the control of shrubby understory vegetation using herbicides. Swind el et al. (1989) reported for the same site as the current study a dramatic reduction in understory richness with a sustained weed control treatment, which resulted in a larger growth response of pines in the first rotation. It should, however, be noted th at the treatments used in the first rotation were beyond normal operational silvicultural intensities. They were designed to understand biological growth potential and the production ecology of managed southern pine ecosystems (Swindel et al. 1988). In N and P limited pine stands, inter rotational applications of fertilizer did not influence the measures of understory vegetation diversity in the second rotation. Ostertag and Verville (2002) reported similar results in a N and P limited Hawaiian montane for ests. Gilliam et al. (2006) also observed no changes in plant diversity after 6

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87 years of aerial application of N in a montane hardwood forest in West Virginia. Findings of this study are, however, different from the generally observed trend of diversity de cline in productive ecosystems (Tilman, 19 87 ). Such declines in diversity are thought to be the result of competitive exclusion of nutrient efficient species to light (Newman, 1973; Rajaniemi, 2003). As light is not generally limiting in recently establish ed sites as ours (Morris et al. 1993), declines in understory vegetation diversity following nutrient additions was not observed. However, it is possible that at later stages the non limiting environment created by fertilizer additions could accelerate ca nopy closure in these stands, leading to a change in the understory vegetation response. F ertilizer additions could reduce the understory diversity in pine stands as overstory develops and shades the understory (Thomas et al. 1999; Gilliam, 2006; Lu et al 2010). The potential of the first rotation competition control and nutrient addition treatments to persist and affect the understory abundance and diversity in the early stages of the second rotation highlights the role intensive forest management syste ms play on understory community dynamics. Because only few species can recover following frequent disturbance, reduced understory diversity in the C FW treatment was expected given the extreme nature of disturbance and nutrient additions (Connell, 1978; Hus ton, 1979). In addition, the overall decline in diversity was likely due to a strong dominance of Andropogon spp. (89% of the total understory biomass) over other understory species in the C FW treatment. In a disturbed site, nutrient addition likely exacer bated the decline in understory diversity by creating conditions favorable to a few species, leading to their colonization. For instance, nutrient addition has been shown to

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88 favor an invasion by non native species in a disturbed site in Western Australia ( Hobbs and Atkin, 1988). Understory diversity is generally expected to increase at intermediate levels of disturbance as moderate disturbances create resource (e.g. light) heterogeneity and niche differentiation (Chesson and Huntly, 1997). However, the non significant influence of the C W treatment on understory diversity may be, in part, due to resource homogeneity in this recently established site, where light was not a limiting resource. In addition, lack of niche differentiation through repeated applicati on of selective herbicides for shrubby vegetation control may have contributed to the non significant differences in understory diversity. Nevertheless, repeated control of a functional group, usually hardwoods, has the potential to shift the understory ve getation community by preventing the recovery of understory abundance and diversity (Neary et al. 1990 c ). Compared to this study, most operational weed control treatments in southern pine plantations are less extreme and are applied during the first year of stand establishment. As a result, recovery of understory diversity may be possible within a few years after site preparation or herbicide application (Boyd et al. 1995; Miller et al. 1999). Understory vegetation community: In nutrient limited sandy Sp odosols, both long term nutrient addition and weed control contributed to the shifts in the second rotation understory vegetation community. Irrespective of nutrient additions, the weed control treatments (FW and W treatments) had the greatest influence on the life forms and composition of the understory community. Those treatments were dominated by herbaceous species like Andropogon spp. and Dicanthelium spp., whereas shrubby components such as Ilex glabra (L.), Serenoa repens (Bartr.) and Lyonia lucida (L am.)

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89 were characteristic of plots that did not receive the weed control treatment. For this same site, Neary et al. (1990 a ) observed a dominance of shrubs like Ilex glabra (L.) and Serenoa repens (Bartr.) following six years of nutrient additions. Dominanc e of herbaceous species has been reported by Jones et al. (2009) on chemically prepared sites in southern pine stands of Mississippi, USA. Grass species like Aristida spp. and Rhynchospora spp., observed as the dominant species of the grass community at th is site by Conde et al. (1983), were, however, not observed in the second rotation for all treatments. Likewise, previously dominant forb species like Centella asiatica (L.), Polypremum procumbens (L.), Syngonanthus flavidulus (Michx.), Xyris spp. (Conde e t al ., 1983) were also absent across all treatments. However, a new forb species, Gamochaeta purpurea (L.), not recorded previously by Conde et al. (1983), was recorded in the W treatment of this study. In planted stands, overstory vegetation generally aff ects the responses of understory vegetation communities, usually by limiting the light resource (Harrington and Edward, 1999 ; McGuire et al. 2001; Harrington, 2011). The overstory vegetation, however, had little to no influence on the understory community composition in this study. Because light was non limiting at this stage of stand development, strong correlations observed between overstory biomass and the ordination axes were presumably confounded by the strong influence of the weed control treatments (highly correlated with both ordination axes). For instance, even though the overstory biomass was relatively high in the FW treatments (10.3 Mg.ha 1 ), the lower relative abundance and diversity of understory vegetation associated with these treatments was not apparently due to shading or competition for nutrients. Rather, it was likely due to

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90 sustained elimination of shrubby species by the herbicide applications. This interpretation is further supported by the relatively higher understory abundance and div ersity observed in the F treatment, which had a comparable overstory biomass (6.9 Mg.ha 1 ), and the negligible correlation between fertilizer addition and the ordination axes in the actively managed experiment. The residual effect of the first rotation her bicide applications altered the successional pathway of the understory vegetation in the C W and C FW treatments to that of an earlier seral stage dominated by grasses. These findings were consistent with Jose et al. (2010), who reported a significant reduct ion in shrub abundance following herbicide application in longleaf pine ( Pinus palustris (Mill.)) stands of Florida. In contrast, the C F treatment of our study did not alter the composition of the understory community. Shrubby species like Ilex glabra (L. ), Serenoa repens (Bartr.), Rhus copallinum (L.), and Gaylussacia dumosa (Andr.) were dominant in the C C and C F treatments. Interestingly, pioneer species like Andropogon spp. and Panicum spp., documented by Conde et al. (1983) as the dominant species two years after mechanical site preparation on a flatwoods site in north Florida, were no longer dominant in the C C and C F treatments in this study. Retention of first rotation shrubby understory vegetation in the C C and C F treatment as mulch, while establishi ng the second rotation, might have served as a source of propagules and thereby favored the initiation of shrubby species in those treatments. Though m ulching has the potential to serve as a physical barrier for the establishment of seeds with low reserves (herbaceous species), not only by limiting light below the compensation point, but also by exhausting the energy reserves before these

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91 seedlings penetrated the mulch and duff layer (Teasdale and Mohler 1993 ) the double bedding operation after mulching mi nimized such an effect in our study. Furthermore, understory mulch and the forest floor, which served as an important sink for soil nutrients like N and P in the first rotation (Vogel et al. 2011), could have served as a source of nutrients in this rotatio n, and thereby favored the growth of shrubby species like Ilex glabra (L.) and Serenoa repens (Bartr.) in the C C and C F treatments. This interpretation is supported by a strong positive correlation between soil N and P supply with ordination axis 2, which was positively correlated with Ilex glabra (L.) and Serenoa repens (Bartr.). Even though the understory vegetation shifted to become a grass dominant community in the C W and C FW treatments, the difference in species composition between these treatments can be attributed to the overwhelming dominance of Andropogon spp. in the C FW treatment. The yearly abundance of An dropogon spp. and Dicanthelium spp. suggest that Andropogon spp. was beginning to invade the C W treatment after 2 years (Figure 3 4 ). The percen tage contribution of Andropogon spp. to total understory biomass increased from about 7% at age 1 to almost 68% at age 2, and the contribution of Dicanthelium spp. was reduced from 71% at age 1 to almost 18% at age 2 in the C W treatment. As in the C FW trea tment, Andropogon spp., a nutrient efficient species with an allelopathic interaction with other vegetation (Peters and Lowance, 1974; Rice, 1972), will likely invade the understory community in the C W treatment before the onset of light limitations due to canopy closure. As a result, this transient difference in understory composition between the C W and C FW observed in our study will likely diminish with time.

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92 Summary and C onclusions Our results suggest that common silvicultural practices like fertilizatio n and herbicide control of competing vegetation imposed in the first rotation have a strong influence on the understory vegetation community reinitiation, diversity, and response in the second rotation. In N and P limited sites, long term nutrient amendmen ts had little influence on the second rotation understory community composition, at least during these early stages of stand development. In contrast, long term weed control treatments, commonly adopted in the southern pine stands, have the potential to sh ift the understory community dominated by shrubby vegetation towards a community dominated by herbaceous components, at least until canopy closure. When both herbicide and nutrients were added, the shifts in understory community composition became more pro nounced; shrubby species were suppressed and few herbaceous species like Andropogon spp. were favored. Because silvicultural treatments in this study were more extreme than operational treatments typically used in southern pine forest management, the shift s in understory community composition in response to the herbicide treatment would likely be less pronounced. Nevertheless, these results suggest that long term weed control treatments affect ecosystem resilience by reducing the diversity of understory ve getation in young pine stands. In these nutrient limited environments, both fertilization and understory competition control treatments can increase pine productivity through reductions in competition for soil nutrients; annual fertilization provided the same growth benefits as complete and sustained elimination of under story competition (see chapter 2 ). As such, fertilizer only would accentuate growth responses without modifying understory plant diversity. Weed control only would also increase growth (Col bert et al., 1990), but at the

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93 expense of ecosystem services related to understory plant diversity. Management activities in these nutrient limited environments designed to improve the overall understory diversity without diminishing productivity of the pl anted pines should, thus, focus on fertilization rather than the weed control only treatments.

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94 Table 3 1. Mean richness, evenness, Shannon, and Simpson species diversity for understory vegetation growing in the actively managed retreated experiment of a second rotation, 2 year old loblolly pine plantation in north Florida. Treatments Richness Evenness Shannon's diversity (H') Simpson's diversity (D') Control 13.3 A (2.52) 0.48 A (0.08) 1.23 A (0.21) 0.60 A (0.03) Fertilizer only 11.7 A (1.53) 0.54 A (0.03) 1.33 A (0.15) 0.65 A (0.08) Fertilizer and weed control 4.3 B (2.08) 0.45 A (0.39) 0.50 B (0.42) 0.28 B (0.23) Weed control only 8.0 AB (1.00) 0.48 A (0.06) 0.99 AB (0.06) 0.49 AB (0.02) P value 0.008 0.929 0.008 0.019 Note: Column means follow ed by same letter were not significantly different at alpha=0.05. Table 3 2. Mean richness, evenness, Shannon, and Simpson species diversity for understory vegetation growing in the untreated carryover experiment of a second rotation, 2 year old loblolly pine plantation in north Florida. Treatments Richness Evenness Shannon's diversity (H') Simpson's diversity (D') Control 13.3 (1.15) 0.51 A (0.08) 1.31 A (0.17) 0.60 A (0.08) Fertilizer only 10.0 (1.73) 0.54 A (0.14) 1.24 A (0.39) 0.63 A (0.15) Fert ilizer and weed control 9.0 (3.61) 0.20 B (0.08) 0.45 B (0.24) 0.19 B (0.10) Weed control only 9.7 (3.79) 0.45 A (0.04) 0.99 AB (0.08) 0.48 A (0.03) P value 0.36 0.009* 0.018 0.005 Note: Column means followed by same letter were not significantly differ ent at alpha=0.05. Asterisk (*) after p value indicates analysis performed on square root transformed data.

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95 Table 3 3. Significance groupings and agreement statistics (A) of understory vegetation communities in a second rotation, 2 year old loblolly pi ne plantation in north Florida. Treatment Actively managed retreated Untreated carryover Control A A Fertilizer only A A Fertilizer and weed control B B Weed control only B C P value 0.01 < 0.0 1 Agreement statistics (A) 0.25 0.48 Note: With in a column, treatments followed by same letter were not different at an alpha=0.05. P values denote the response permutation procedure (MRPP). Sorensen distance measure (1 sed for MRPP. Table 3 4. Indicator values (IV) of indicator species for the understory vegetation communities in a second rotation, 2 year old loblolly pine plantation growing in north Florida. Experiment Species Treatment groups Indicator Values (IV) P value Actively managed retreated Ilex glabra (L.) C and F 100 0.001 Serenoa repens (Bartr.) C and F 83 0.015 Lyonia lucida (Lam.) C and F 83 0.016 Dicanthelium spp. FW and W 97 0.013 Andropogon spp. FW and W 85 0.013 Untreated carryover Andropogon spp. C FW 50 0.015 Dicanthelium spp. C W 83 0.013 Scleria spp. C W 81 0.017 Carex spp. C W 70 0.036 Note: Grouping of treatments in the actively managed experiment was based on the MRPP. Treatment pairs that were not significantly different w ere paired together as groups. Indicator values represent the percentage of perfect indication by a given species. P values are based on 10000 Monte Carlo randomizations of species abundance data.

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96 Table 3 5. Coefficients of determination (R squared) for the correlations between ordination distances and distances in the original n dimensional space for the actively managed retreated and the untreated carryover experiments in north Florida. The distance was measured using the Sorensen distance measure for the NMS ordination. Axis Actively managed retreated Untreated carryover Non metric multi dimensional scaling (NMS) R 2 Non metric multi dimensional scaling (NMS) R 2 1 0.255 0.365 2 0.638 0.550 Total 0.893 0.915 Note: R 2 for an axis represents the proportion of variance explained by that ordination axis. Table 3 6. Pearson correlation coefficients (r) for environmental variables associated with axes 1 and 2 in the NMS ordination for the actively managed retreated and untreated carryover experime nt in north Florida. Variables Actively managed retreated Untreated carryover Axis 1 Axis 2 Axis 1 Axis 2 r r r r Weed control 0.600 0.948 0.626 0.970 Overstory vegetation biomass (loblolly pine) 0.420 0.472 0.223 0.543 Soil B supply 0.11 5 0.284 0.099 0.362 Soil S supply 0.537 0.272 0.547 0.395 Soil P supply 0.158 0.269 0.476 0.541 Soil N supply 0.512 0.255 0.387 0.651 Soil Fe supply 0.284 0.205 0.357 0.353 Soil Zn supply 0.166 0.111 0.200 0.115 Soil K supply 0.4 99 0.102 0.200 0.045 Soil Cu supply 0.062 0.034 0.418 0.225 Soil Mn supply 0.167 0.019 0.304 0.060 Fertilizer addition 0.149 0.006 0.433 0.090 Note: Coefficients of correlation (r) > 0.4 represent strong correlation of variables with ordina tion axes 1 or 2.

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97 Table 3 7. Pearson correlation coefficients (r) of understory species with axes 1 and 2 from the NMS ordination of the actively managed retreated experiment in north Florida. Species Axis 1 Axis 2 r r Ilex glabra (L.) 0.667 0.813 Dicanthelium spp. 0.114 0.726 Serenoa repens (Bartr.) 0.112 0.632 Andropogon spp. 0.909 0.592 Gaylussacia dumosa (Andr.) 0.277 0.565 Smilax rotundifolia (L.) 0.005 0.508 Lyonia lucida (Lam.) 0.166 0.471 Rhus copallinum (L.) 0.638 0.445 P ersea palustris (Raf.) 0.035 0.416 Vaccinium myrsinites (Lam.) 0.445 0.387 Eleocharis baldwinii (Torr.) 0.431 0.369 Scleria spp. 0.428 0.355 Lyonia ferruginea (Walt.) 0.124 0.349 Lachnanthes caroliniana (Lam.) 0.322 0.293 Rubus spp. 0.46 3 0.284 Cyperus spp. 0.235 0.282 Vitis rotundifolia (Michx.) 0.071 0.260 Eupatorium spp. 0.291 0.185 Paspalum spp. 0.324 0.148 Quercus nigra* 0.459 0.042 Hypericum spp. 0.122 0.011 Note: Species are ranked by the absolute value of r for axis 2 Species followed by asterisk ( ) are highly correlated (r > 0.4) with axes 1 or 2.

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98 Table 3 8. Pearson correlation coefficients (r) of understory species with axes 1 and 2 from the NMS ordination of the untreated carryover experiment in north Florida Species Axis 1 Axis 2 r r Andropogon spp. 0.766 0.970 Ilex glabra (L.) 0.613 0.878 Serenoa repens (Bartr.) 0.786 0.740 Dicanthelium spp. 0.106 0.491 Eupatorium spp. 0.621 0.435 Scleria spp. 0.031 0.432 Lyonia ferruginea (Walt.) 0.3 12 0.427 Cyperus spp. 0.337 0.359 Erectites hierarcifolia (L.) 0.196 0.349 Juncus spp. 0.054 0.323 Sporobolus curtissii (Small) 0.332 0.289 Pteridium aquilinum (L.) 0.319 0.286 Carex spp. 0.051 0.282 Eleocharis baldwinii (Torr.) 0.083 0.271 Lachnanthes caroliniana (Lam.) 0.329 0.225 Woodwardia virginica (L.) 0.265 0.222 Rhus copallinum (L.) 0.242 0.209 Vaccinium myrsinites (Lam.) 0.037 0.189 Hypericum spp. 0.175 0.169 Quercus nigra (L.) 0.368 0.097 Vitis rotundifolia (Michx.) 0.376 0 .074 Note: Species ranked by absolute value of r for axis 2. Species followed by asterisk ( ) are highly correlated (r > 0.4) with axes 1 or 2.

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99 Figure 3 1. Life form biomass for the understory vegetation community in the A ) actively managed retreated a nd B ) untreated carryover experiments on Spodosols in north Florida. The notations C, F, FW, and W represent, respectively, the plots that received control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the plots that received control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation. Within a given life form, treatments followed by similar l etters were not significantly different at alpha= 0.05.

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100 Figure 3 2. Shannon Weiner diversity for the life forms (shrubs and grasses) of the understory community in the A ) actively managed retreated and B ) untreated carryover experiments on Spodosols in north Florida. The notations C, F, FW, and W represent, respectively, the plots that received control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represe nt the plots that received control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation. Within a given life form treatments followed by similar letters were not significantly at alpha= 0.1.

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101 Figu re 3 3. A two dimensional ordination plot derived from NMS for the A ) actively managed retreated and B ) untreated carryover experiments in north Florida using understory abundance data. Figure 3 4. Yearly abundance of Androp o g o n spp. and Dicanthelium spp. in second rotation loblolly pine plantations in north Florida. Note that the C FW and C W treatments, respectively, received a combination of fertilizer addition and sustained weed control and weed control only treatments in the first rotation.

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102 CHAPTER 4 INTER ROTATIONAL EFFECTS O F FERTILIZER AND WEE D CONTROL TREATMENTS ON SOIL RESPIRATION IN YOUNG PINUS TAEDA (L.) STANDS GROWING ON A FLORIDA SPODOSOL Introduction Soil respiration (SR), or soil CO 2 efflux, is the second largest terrestrial flux of carbon in the global carbon cycle behind gross primary production (Raich and Schlesinger, 1992; Raich et al. 2002). The release of CO 2 from the soil derives from either heterotrophic (RH; microbial respiration during decomposition of soil organic matter) or auto trophic (RA; respiration by live roots) sources While changes in soil temperature and moisture have been closely associated with variation in SR (Boone et al. 1998; Fang and Moncrieff, 2001; Qi et al. 2002), the factors that affect allocation of carbon (C) to plant roots and C inputs from litterfall also have the potential to influence SR, especially in forested ecosystems (Bowden et al. 1993; Crow et al. 2009; Chen et al. 2011). Intensive forest management practices such as site preparation, fertiliz ation, competing vegetation control, and deployment of genetically improved planting stock have not only dramatically improved the productivity of southern pine plantations, but also reduced their rotation lengths (Jokela et al. 2004; Carter and Foster 200 6; Fox et al. 2007 a ). While such expedited gains in yield have made these plantations an important carbon sink (Maier and Kress, 2000), the effects of intensive management practices on SR are still inconclusive. For example, studies have documented either an increase (Tyree et al. 2006 ; Contosta et al. 2011), decrease (Maier and Kress, 2000; Olsson et al. 2005), or no net change (Pangle and Seiler, 2000; Samuelson et al. 2009) in SR following nutrient additions. While there is generally no consensus

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103 re garding both the immediate (Haynes and Gow er, 1995; Maier and Kress, 2000 ) and long term effects (Bowden et al. 2004, Tyree et al. 2006) of nutrient additions on SR, the effects have been observed to be species specific (Lee and Jose, 2003). Lee and Jose (2003) documented a decrease in SR following N additions in a seven year old Populus deltoides (Marsh.) stand, but no change in a Pinus taeda (L.) stand growing on well drained sandy loams in northwest Florida. Control of competing vegetation using herbic ides, a common silvicultural practice used in intensively managed southern pine stands, has been shown to reduce soil organic matter (Shan et al. 2001; Sarkhot et al. 2007; Vogel et al. 2011). Because decomposition of soil organic matter (SOM) facilitat es mineralization of N and P, reductions in SOM may have detrimental effects on long term nutrient supply to the site. A similar effect on SR may be possible because controlling competing vegetation may lead to declines in soil organic substrates for micro bial activity (Blazier et al. 2005) and thereby influence RH. In addition, vegetation control has been shown to affect SOM (Ibell et al. 2010), soil microbial biomass and composition (Busse et al. 1996; Ratcliffe et al. 2006), and the soil environment (Devine and Harrington, 2007; Parker et al. 2007), all of which could influence SR (Curiel Yuste et al. 2007). The change in SR resulting from sustained understory competition control is, however, poorly understood in forested ecosystems. For example, B usse et al. (2006) observed that weed control reduced microbial respiration in the uncompacted soils of California, but it stimulated microbial respiration in the soils of Louisiana. Of the 85 million ha of forested area in the southern United States, sout hern pine plantations cover more than 16 million ha (Hartshell and Conner, 2013). In response to

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104 meeting the ever burgeoning demand for wood products, many of these pine plantations will continue to be managed using intensive silvicultural treatments (Siry 2002; Fox et al. 2007 a ). Fertilizer additions and weed control practices will increase in usage (Weir and Greis, 2002) and contribute to increases in productivity that can extend beyond a single rotation (Everett and Palm Leis, 2009). For instance, stud ies have shown that the residual P from past fertilization has the potential to meet the nutrient demands and early growth requirements of newly planted stands (Ballard, 1978; Comerford et al. 2002; Everett and Palm Leis, 2009). Given an increase in inten sive silvicultural practices in southern pine plantations, studies examining the inter rotational effects of fertilization and weed control treatments on SR are necessary to better understand C dynamics and the sustainability of these management systems. T his research was conducted to examine the inter rotational effects of fertilization and sustained understory competition control on SR in a second rotation, 2 year old loblolly pine plantation growing on a Florida Spodosol. Because the study area received rotation long additions of fertilizer and sustained weed control treatments in the first rotation, it provided a unique opportunity to understand how historical land management practices affected SR (a proxy for below ground response). In nutrient poor soi ls, we hypothesize that SR in the second rotation would increase following long term nutrient additions, as aboveground production and root development is rapid during the early stages of stand development. As soil and microbial biomass C may decline follo wing sustained weed control treatments (Rifai et al. 2010; Vogel et al. 2011), we also hypothesize that a decrease in SR would be associated with the historical vegetation

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105 control treatments. Two long term replicated experiments were used to answer two q uestions: 1. In a nutrient stressed environment, do historical nutrient additions and understory competition control treatments suppress SR in a second rotation loblolly pine stand? 2. Does prior silvicultural treatment history (e.g., nutrient addition and under story competition control) affect decomposition of OM on an inherently nutrient limited Spodosol that supports an aggrading loblolly pine stand? These questions were addressed by examining and comparing SR, and exploring its relationship with aboveground b iomass and OM decomposition across a range of silvicultural treatment histories that had varying levels of soil nutrient availability. In addition, efforts were made to duplicate as closely as possible the first rotation silvicultural treatments, and inclu ded using a common genetic source of l oblolly pine as planting stock. Methods Study A rea In 1983, the Intensive Management Practices Assessment Center (IMPAC) at the University of Florida established an experimental study site, approximately 10 km north of Gainesville, in order to evaluate the factors that limit the biological growth potential of southern pines (Swindel et al. 1988). The elevation of the IMPAC experimental site is 45 m from the mean sea level. The long term mean annual temperature (1984 201 2) of the study site is 20.6C and it receives about 1178 mm of precipitation annually (National Oceanic and Atmospheric Administration, 2012). The climate is warm and humid. Poorly drained Pomona fine sands (sandy siliceous hyperthermic Ultic Alaquods) ar e the predominant soils. Understory vegetation was typical of Coastal Plain flatwoods sites, and included: wiregrass ( Aristidia strictus (Michx.)), gallberry ( Ilex glabra (L.)), saw

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106 palmetto ( Serenoa repens (Bartr.)), fetterbush ( Lyonia ferruginea (Walt.)) blueberries ( Vaccinium spp.), broomsedges ( Andropogon spp.), panic grasses ( Dicanthelium spp. and Panicium spp.), and wax myrtle ( Myrica cerifera (L.)) (Neary et al. 1990 b ). Study D esign Originally, the IMPAC experiment was designed as a 2x2x2 factorial consisting of species (loblolly and slash pine), complete and sustained weed control, and annual fertilization arranged in a randomized split plot (species as whole plots) design with three replications. This resulted in four treatments within each specie s: control (C), weed control only (W), fertilizer only (F), and both fertilizer and weed control (FW). The entire experimental area was site prepared using a single pass bedding treatment. Genetically improved (first generation, open pollinated) 1 0 barero ot stock of both loblolly and slash pine were hand planted in January 1983 (Swindel et al. 1988, Colbert et al. 1990, Martin and Jokela, 2004). After applying a fertilizer regime with balanced levels of macro and micronutrients for the first ten years t o the F only and FW treatments, it was stopped in May 1993 and then resumed during the sixteenth to eighteenth growing seasons (1998 2000; Jokela and Martin, 2000). Fertilizers were applied in narrow bands (30 cm semicircle) around the base of each tree or planting location. Total nutrient additions over the life of the original study for the F and FW treat ments for both species were (kg. ha 1 ): 1088 N, 230 P, 430 K, 108 Ca, 72 Mg, 72 S, 4.1 Mn, 5.4 Fe, 0.9 Cu, 4 Zn, and 0.9 B (Jokela et al. 2010). Competin g understory vegetation was controlled in the W and FW treatments annually for the first ten years (1983 1993) using a combination of chemical and mechanical methods (Colbert et al, 1990; Neary et al. 1990 b ; Dalla Tea and Jokela, 1994). The weed control treatment was discontinued after canopy closure due to the suppression and reduced growth of

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107 understory vegetation. Early and mid rotation growth dynamics for the original study were reported by Colbert et al. (1990), Jokela and Martin (2000), and Martin and Jokela (2004). Jokela et al. (2010) summarized the growth dynamics for this original experiment over the 25 year study period. Likewise, Vogel et al. (2011) documented the total C and N pools at the end of the rotation for the original experiment. The original IMPAC study was whole tree harvested in May 2009, with the intent of overlaying a second experiment using the same treatment plots. Harvested trees were processed off the treatment plots to ensure that nutrient inputs into the soil did not occur v ia the harvested residues from the pine trees. Considering the need for long term monitoring of the site to understand the effects of the past management history, the IMPAC II study site was initiated in June 2009. Original plots in the first rotation were re experiment. The IMPAC II experiment now consists of two randomized complete block designs (RCBD; 3 replications each) having four treatments each for the actively managed retreatment (C, F, FW, and W) and untreated carryover designs (Cc, C F C FW C W ) (Figure 2 1). The carryover treatments were established on the previous slash pine plots and the acti vely managed retreatment plots were established on the previous loblolly pine plots. Prior to harvesting, all treatment plot corners were re monumented and the understory vegetation in the C and the F treatments was mulched in place (April 2009) to retain the nutrient pool within the plot boundaries. Mulching was not necessary for the W and FW treatments because of the sustained weed control treatment history from the

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108 previous rotation. Following harvest, the entire study area was later bedded in June, with a second bedding pass conducted in August of the same year. Similar to the last rotation, loblolly pines were planted in each plot at a 1.8 m by 3.0 m spacing, with measurement plots (0.02 ha) consisting of forty trees per plot (8 trees each in 5 beds). Each of the measurement plots was provided with a treated buffer of three trees and two beds, resulting in a 0.08 ha treatment plot. An untreated buffer of six tree spaces was provided between two adjacent treatment plots. Across the treatment plots, an un treated buffer of four beds was maintained. A single, full sib loblolly family was used to regenerate the entire study area in December 2009 using containerized stock. Prior to planting, only the active retreatment plots, which received chemical site prepa ration and weed control in the first rotation, were treated using a broadcast application of 0.84 kg a.e. ha 1 imazapyr in the form of Chopper (BASF Corp., Research Triangle Park, NC, USA), 1.12 kg a.e. ha 1 triclopyr in the form of Garlon 4 (Dow AgroSci ences LLC, Indi anapolis, IN, USA), and 0.14 kg. ha 1 of metsulfuron methyl in the form of Escort (E.I. du Pont de Nemours and Company, Inc., Wilmington, DE, USA) in October 2 009. In October, 2010 these same plots received a directed spray application of tr iclopyr (3%) and imazapyr (1%) to control Ilex glabra (L.) and other understory competitors. Also, in September 2011 the actively managed F and FW plots received another directed spray of glyphosate (3%) to maintain a weed free environment. All treatments (actively managed retreated and untreated carryover) received a single application of Fipronil (9.1%) in the form of PTM TM (BASF Corp.,

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109 Research Triangle Park, NC, USA) in March 2010 to control Nantucket pine tip moth ( Rhyacionia frustrana ). The untreated carryover plots did not receive any additional chemical treatments (herbicide or fertilizer), with the exception of a banded 0.2 kg a.e. ha 1 imazapyr application in May 2010 to control Dicanthelium spp. and to aid seedling survival. This same banded herbi cide treatment was also applied to the actively managed C and F treatments. The actively managed retreated (F and FW) plots received fertilizer at the end of July 2011 and beginning of September 2012. Consistent with the last rotation treatments, the total nutrient additions over the first three growing seasons for t he F and FW treatments were (kg. ha 1 ): 120 N, 53 P, 99 K, 40 Ca, 19 Mg, 56 S, 1.3 Mn, 0.5 Fe, 0.2 Cu, 0.5 Zn, and 0.2 B. As done in the first rotation experiment, the fertilizer was applied in n arrow bands (30 cm semicircle) around the base of each tree or planting location. During September and October of 2009, one root exclusion plot (RE) was randomly selected and installed on the bed and inter bed position in each measurement plot (a total of 24 REs were installed in each experiment). Trenches were dug to a depth of ~ 50 cm by hand to sever roots, and 2 mm thick plastic barriers installed to prevent root growth inside the REs. In these young stands, we assumed that roots did not infiltrate into the REs. Because root development of young loblolly pine stands do not exceed beyond a 50 cm soil depth for the first few years (Adegbidi et al. 2004), root development into the REs from below the trench barriers was presumably low and non cies were smaller in stature than the pine In addition, young roots are

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110 not strong enough to laterally penetrate the plastic barrier. The efficacy of similar plastic RE installations have been compared with small REs (30 cm long PVC collars) for mature bl ack spruce stands in Alaska (Vogel and Valentine, 2005). For this study, we used a 3 way factorial (422) of treatments (control, fertilizer only, fertilizer and weed control, and weed control only), locations (bed and inter bed), and REs (with and withou t) with a split plot design, and three replicates each for the actively managed retreated and untreated carryover experiments. Soil R espiration Monthly measures of SR were conducted from November 2010 through April 2012, with the exception of the growing s eason (from May 2011 to September 2011) when SR measurements were made twice per month. During the growing season, instantaneous SR was measured using a 6400 09 Soil CO 2 Flux Chamber (a portable infrared gas analyzer (IRGA)) attached to the LI 6400 Portabl e Photosynthesis System (Li Cor, Inc., Lincoln, NE). During each measurement, the soil CO 2 flux chamber was placed onto the soil collars that were permanently established within the measurement plots. A total of four soil collars per treatment plot, made f rom PVC pipe (diameter 10.16 cm, height 8 cm), were inserted about 3 cm into the soil surface. Of the four collars, two each were randomly placed on the bed and inter bed positions (with and without RE). In order to minimize the effects of disturbance, the soil collars were installed at least one year prior to the initiation of SR measurements in November 2010. The temperature of the soil surface (~5 to 15cm) was measured at each time period with a soil probe thermocouple inserted within 5 cm of the measure ment collar. Similarly, three measurements of soil moisture (top 12 cm of soil) were made within 10 cm of the collar immediately following each SR measurement using time domain reflectometry

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111 (Hydrosense Soil Water Measurement System (CS 620), Campbell Scie ntific, Inc., Logan, UT). Soil N utrient S upply Soil nutrient supply was assessed in the actively managed and untreated carryover experiments using ion exchange membranes (PRS TM probes, Western Ag Innovations, Inc., Saskatoon, SK, Canada). Four cation and a nion PRS TM probes were buried randomly in the upper 15 cm of soil on the beds of all measurement plots in August 2011. After eight weeks the probes were removed and rinsed free of adhering soil particles with de ionized and distilled water. All probes were eluted using a 0.5N Hydrochloric Acid (HCl) solution for 1 hour. The eluate was then analyzed colorimetrically using an automated flow injection analysis system for NO 3 N and NH 4 + N to obtain total N supply. For P, K, Ca, Mg, S, B, Cu, Mn, Zn, and Fe, in ductively coupled plasma atomic emission spectroscopy (ICP AES) was used. All analyses were done at the Western Ag Innovations, Inc. laboratory in Saskatoon, SK, Canada. Aboveground B i omass M easurement Estimation of total aboveground pine biomass at age 2 years was made using inventory data and existing allometric equations previously developed for loblolly pine for the same family, ages, and soil type (Adegbidi et al. 2002). Corrections for logarithmic bias were made on all estimates of biomass (Baskervill e, 1972; Sprugel, 1983). Estimates of aboveground understory biomass were made using a clip plot survey conducted in August and September 2011. Within each plot, six quadrats (1 m 2 ) were randomly established in each measurement plot and stratified equally between the bed and inter bed positions All standing vegetation that fell within the quadrats was clipped at ground level and sorted separately by species. For overhanging vegetation,

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112 only the portion that fell within the quadrat was clipped. All samples were oven dried at 65C to a constant weight. Decomposition of Organic M atter In March 2011, sixty Betula papyrifera (Marsh.) tongue depressors (15 1.9 cm) were buried in the beds of every treatment plot to understand the effects of silvicultural treatme nts on the decomposition of a homogenous source of organic matter. In order to precisely re locate these depressors, six arrays of 10 depressors each were assembled and connected using monofilament line, and randomly buried in each measurement plot. Both i n July and November 2011, 10 tongue depressors in each measurement plot were removed from the soil to determine the amount of mass loss due to decomposition. The remaining 40 tongue depressors from each measurement plot were removed in March 2012. The tong ue depressors were oven dried at 65C to a constant weight and then gently brushed to remove any adhering soil particles before weighing. Careful attention was made to ensure that no decayed materials were lost during sample preparation. Data A nalysis A th ree factor repeated measures analysis of variance method was used to test the effects of treatment, location, and root exclusion on SR (Littell et al. 2006). The following general repeated measures model for a 3 way factorial with covariates was used: Y ij klmn i j m k l im ik il km lm kl ikm + ilm ikl klm iklm n(i) n(k) n(l) + b 1 ) + b 2 ) + b 3 ijkl.. ijk... ) + c 1 ) + c 2 ) + c 3 i jkl.. ijk... ) + e ijklmn where,

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113 i = 1,2,3,4; j = 1,2,3; k = 1,2; l =1,2; m = 1,2,..,21; i = effect of i th treatment; j = effect of the j th replication; m = effect of m th date; k = effect of k th location; l = effect of l th RE ; im ik il km lm kl ikm ilm ikl klm iklm = interactive effects between treatments, date, locations, and REs; n(i) n(k) n(l) = the subject treatment, subject location, and subject root exclusi on interactive effects (random, independent, N (0 2 )); b 1 ), b 2 ), and b 3 ijkl.. ijk... ) = effects of soil temperature (covariate); c 1 ), c 2 ), and c 3 ijkl.. ijk... ) = effects of soil m oisture (covariate); and e ijklmn = error term (independent, N (0 2 e )). Treatments, locations, REs, date, and their interactions, along with replication and covariates, were considered fixed effects. The PROC MIXED procedure in SAS was used for the stat istical analyses. When a covariate was not significant in the model, it was removed from the final model. The selection of the covariance structure was based on the corrected Akaike information criteria (AIC C ) (Burnham and Anderson, 2002). When assumptions of normality and homoscedasticity were not met, data were square root transformed prior to analysis. Multiple linear regression was utilized to investigate the relationships between SR, soil temperature, and soil moisture. In addition, the effects of trea tments, locations, and REs on soil temperature and soil moisture were also investigated using RM ANOVA for a 3

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114 way factorial design. For this, we assigned a value of 0.001 to volumetric moisture contents with zero values prior to transformation. Zero value s of volumetric soil moisture observed in this study likely indicated that soil moisture at our site was below the measurement resolution (1%) of the TDR sensor (Campbell Scientific, Inc., 2010). Decomposition mass loss of the Betula papyrifera (Marsh.) to ngue depressors was analyzed using the PROC MIXED procedure, with months after burial and treatments otherwise stated. Results Soil R espiration Mean soil respiration I n the actively managed retreated experiment, the fixed effects of date, treatment, and location on SR were significant (Table 4 1). For all treatments, SR rates were generally lower in the winter (December February) than during the growing season (April September) (Figure 4 1 ). Mean daily SR rates ranged from 1.06 mol.m 2 .s 1 in January 2011 to 6.03 mol.m 2 .s 1 in August, 2011. Mean SR rates were significantly higher in the F (3.75 mol.m 2 .s 1 ) and FW (3.71 mol.m 2 .s 1 ) treatments compared to the W treatment (2.94 mol.m 2 .s 1 C = W (Figure 4 2 ). As expected, mean SR rates in the bed were almost 1.4 fold higher than the inter bed position (4.07 mol.m 2 .s 1 in the bed vs. 2.83 mol.m 2 .s 1 in the inter bed) (Figure 4 3 ). The lack of significant differences in mean SR rates obse rved between the root exclusion treatments indicated that SR and RH were similar for this site (Figure 4 4 ). The significant interaction between location and date was possibly due to the greater

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115 difference in SR rates between the bed and inter bed position s during the growing season, and similar SR rates during the winter season. In the untreated carryover experiment, SR rates were affected by measurement date, location and root exclusion treatment (Table 4 1). Mean daily SR rates were lower for all treatme nts during the winter season and higher during the growing season, with values ranging from 1.55 mol.m 2 .s 1 in January, 2011 to 6.28 mol.m 2 .s 1 in June, 2011 (Figure 4 1 ). The treatment differences in mean SR rates approached significance (p= 0.13) and the trends among treatments were similar to the actively managed experiment; C F (3.94 mol.m 2 .s 1 FW (3.77 mol.m 2 .s 1 C (3.14 mol.m 2 .s 1 C W (3.12 mol.m 2 .s 1 ) (Figure 4 2 ). The mean SR rate in the bed (4.09 mol.m 2 .s 1 ) was almost 1.4 fo ld higher compared to the inter bed position (2.89 mol.m 2 .s 1 ; Figure 4 3 ). As expected, the root exclusion treatment reduced the mean SR rate (3.74 mol.m 2 .s 1 without RE vs. 3.24 mol.m 2 .s 1 with RE) (Figure 4 4 ). Interactive effects of location and date were similar to the actively managed experiment. Annual soil respiration Linear interpolations were used between measurement dates to estimate annual SR (Nov 2010 Nov 2011). Annual estimates of SR in the actively managed retreated experiment followe d the trend: F (13.8 Mg.C.ha 1 .yr 1 ) > FW (13.3 Mg.C.ha 1 .yr 1 ) > C (12.8 Mg.C.ha 1 .yr 1 ) > W (10.7 Mg.C.ha 1 .yr 1 ). Annual SR in the F treatment was significantly higher than the W treatment (p = 0.1) (Figure 4 5 ). While no significant difference in annua l SR among treatments were observed for the untreated carryover experiment (p = 0.21), annual SR trends were similar to the actively managed retreated plots, i.e. C F (14.1 Mg.C.ha 1 .yr 1 FW (13.7 Mg.C.ha 1 .yr 1 C (11.5 Mg.C.ha 1 .yr 1 ) W (11.4 Mg .C.ha 1 .yr 1 ) (Figure 4 5 ).

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116 Soil Temperature and Soil M oisture For both experiments, soil temperature differed significantly among measurement dates and ranged from ~14C in February, 2011 to ~38C in May, 2011 (Figure 4 1 ). When averaged across the study period, the soil temperature weakly differed among locations in the actively managed experiment (p = 0.08; ~25C in the bed vs. ~26C in the inter bed position). Treatments, however, had no influence on the mean soil temperature in the actively managed re treated experiment (p = 0.43). In contrast, the C FW (27.0C)and C W (26.4C) treatments significantly increased mean soil temperature by almost 2C compared to the C C (24.5C) and C F (24.9C) treatments in the untreated carryover experiment (p < 0.01) (Figu re 4 1 ). Lower soil temperatures in the C C and C F treatment compared to the C FW and C W was likely due to shading associated with leaves and litter from higher aboveground biomass accumulation (pine + understory) (C F 13.1; C C 9.4; C FW 8.0; C W 5.6 Mg.ha 1 ; see Chapter 2 ). The site was dry over the period of study, with soil volumetric moisture contents ranging from 0 to 18% for both experiments. Significant effects of location and RE were observed in volumetric soil moisture content; moisture content was higher in the inter bed position and the sites with REs than the bed and sites without REs over all measurement dates for both experiments (Figure 4 3 and 4 4 ). Treatments, however, had a significant influence on mean volumetric soil moisture content in th e actively (2.1%)) (Figure 4 3 ). Such differences were unexpected given the higher ab oveground biomass (see Chapter 2 ) and presumably greater moisture loss via transpiration i n the FW and F treatments.

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117 Stepwise regression of SR rates revealed that soil temperature accounted for almost 24% of the variation in the actively managed retreated experiment and 21% in the untreated carryover experiment (Table 4 2). Soil moisture, on th e other hand, explained just 6% and 7% of the total variation in SR in the actively managed retreated and untreated carryover experiments, respectively. Decomposition of a Common Substrate among T reatments Silvicultural treatments and time of burial had si gnificant effects on the mass loss of Betula papyrifera (Marsh.) tongue depressors (Table 4 3). Mass loss was higher in the F and C treatments compared to the FW and W treatments (Figure 4 6 Table 4 4). For example, almost 97% and 93% of the original mass was lost during the 12 month period for the F and C treatments, respectively, compared to 86% in the W and 83% in the FW treatments. Similar to the actively managed experiment, significant differences in mass loss were found in the untreated carryover e xperiment (Table 4 3). Mass loss in the C F and C C treatment was significantly higher than the C W treatment over the12 month period (Figure 4 6 Table 4 4); mass loss associated with the C F treatment was approximately 93% compared to 85% for the C W treatmen t. Discussion The need for understanding long term implications of intensive forest management practices on SR or CO 2 release is important relative to the current issues of global climate change (Rustad et al. 2000; Woodbury et al. 2007). Soil respiratio n from pine plantations could be influenced by factors like temperature, moisture, substrate quality, plant biomass allocation, and disturbance regimes, all of which can influence global carbon dynamics (Raich and Schlesinger, 1992; Kirschbaum, 1995; Boone et al. 1998; Fang and Moncrieff, 2001; Busse et al. 2006). Rotation long

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118 application of fertilizer and sustained control of competing vegetation in a long term replicated experiment, as used in this study, provided a unique opportunity to investigate in ter rotational influences of forest management practices on SR and belowground processes. Average daily SR rates in this study were comparable to the reported ranges for loblolly pine plantations under varying management regimes (Gough et al. 2005; Samuel son et al. 2009; Tyree et al. 2008). For instance, in a one year old loblolly pine plantation growing in the Coastal Plain of South Carolina, SR rates ranged from 1.1 mol.m 2 .s 1 to 8.5 mol.m 2 .s 1 (Gough et al. 2005). Samuelson et al. (2009) reported SR rates of 1.9 to 6.3 mol.m 2 .s 1 in seven year old loblolly pine stands in South Carolina growing under irrigation and fertilization treatments. In an 11 year old lo blolly pine plantation growing on excessively well drained sandy Ultisols in North Carolina, SR ranged from a low of 1 mol.m 2 .s 1 in January to greater than 5 mol.m 2 .s 1 in June (Maier and Kress 2000). Estimates of annual soil C loss via SR from 2 yea r old pine stands in this study were within the ranges of 7 to 22 Mg.C.ha 1 .yr 1 reported for early and mid rotation southern pine stands (Ewel et al. 1987; Maier and Kress, 2000; Lee and Jose, 2003, Gough et al. 2005; Samuelson et al. 2009). Annual SR rates in this study were also comparable with the value of 16.7 Mg.C.ha 1 .yr 1 reported by Gough et al. (2005) for one year old loblolly pine stands in South Carolina. In contrast, Pangle and Seiler (2002) estimated a lower annual SR rate of 4.4 Mg.ha 1 .y r 1 for a 2 year old loblolly pine stand growing in the Virginia Piedmont where the site was prepared with a chop and burn treatment.

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119 In the nutrient limited sandy Spodosols of this study, long term fertilization treatments did not suppress SR compared wi th the unfertilized treatments in both experiments. Similar responses have been observed in early to mid rotation pine stands subjected to nutrient additions (Pangle and Seiler, 2002; Lee and Jose, 2003; Tyree et al. 2008; Samuelson et al. 2009). This r esult, however, was not consistent wi th the findings of Maier and Kr ess (2000) and Butnor et al. (2003), who observed a reduction in SR with fertilizer additions. In a meta analysis of N manipulation studies in forest ecosystems, Janssens et al. (2010) als o reported a general decline in SR following nitrogen additions; however, in stands younger than 4 years, such declines in SR were not evident. It is often hypothesized that, in aggrading stands, complementary effects of fertilization on root (positive eff ect) and microbial respiration (negative effect) results in no net change in total SR (Lee and Jose, 2003; Gough and Seiler, 2004; Tyree et al. 2008). In addition, in young harvested stands, where microbial activity may be nutrient limited because of the influx of woody material the suppression effects of fertilization on SR have seldom been observed possibly because fertilization accelerates both root development and microbial activity (Janssens et al. 2010). Sustained control of competing vegetation d ecreased SR rates when compared to long term fertilizer additions. The significantly lower SR rates in the W treatment compared to the F treatment, as observed in this study, was likely due to lower belowground activity (root and microbes) associated with an almost 97% lower aboveground biomass (7.4 Mg.ha 1 in the W vs. 14.6 Mg.ha 1 in the F treatment; Chapter 2 ) and 86% lower levels of C pools in the roots, understory vegetation, and forest floor that was incorporated at the end of the first rotation in th e F treatment (49.3

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120 Mg.C.ha 1 in the W vs. 91.5 Mg.C.ha 1 in the F; Vogel et al. 2011). This interpretation is supported, in part, by a strong correlation between mean SR rates and total aboveground biomass (r = 0.704, p = 0.01) and the significantly lowe r mass loss of the Betula papyrifera (Marsh.) tongue depressors observed in this study after 12 months (86% in the W treatment vs. 97% in the F treatment). Nevertheless, it should be noted that increases in labile C sources either from recently severed roo ts (Hendrickson and Robinson, 1984) or assimilation of carbohydrate rich forest floor materials into the soil (Mallik and Hu, 1997; Irvine and Law, 2002) likely increased SR in our study. Weakly significant differences (p = 0.13) among treatments, and a tr end similar to the actively managed treatments for the second rotation SR rates in the untreated carryover experiment were, in part, due to the differences in C incorporated into the site prior to the establishment of this study, and the belowground activi ty associated with actively growing pine biomass. Soil C pools in the forest floor, roots, and understory vegetation that were incorporated into the C F treatment at the end of the first rotation (97.5 Mg.C.ha 1 ) were almost 1.5 fold higher compared to 66. 5 Mg.C.ha 1 in the C W treatment (Vogel et al. 2011). In addition, the second rotation aboveground pine biomass accumulation was higher in the C F followed by the C FW C C and C W treatments (C F 8.4; C FW 4.6; C C 4.6; C W 3.8 Mg.ha 1 ; Chapter 2 ). Correlati ons between aboveground pine biomass and mean SR rates revealed a positive relationship (r = 0.504, p = 0.09) in the untreated carryover experiment. A significant positive relationship between soil P availability (r = 0.64, p = 0.03, Table 4 5) and mean SR rates was likely due to increased belowground activity (root + microbes) associated with increased aboveground pine biomass. This interpretation is supported by a strong correlation

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121 between aboveground pine biomass and soil P availability (r = 0.83, p < 0 .01; Cha pter 2 ). These results suggest that the carryover effects of the historical fertilization treatments likely increased the abundance of roots of photosynthetically active plants and the availability of soil C, a substrate for microbial activity, whi ch thereby stimulated SR rates (Hgberg et al. 2001; Kuzyakov and Cheng, 2001; Tang et al. 2005). Conversely, the residual effects of the sustained competition control treatments in the first rotation resulted in a decrease SR rates in the second rotatio n. Improved aeration, incorporation of organic matter, and faster growing pines on the beds likely contributed to significantly higher total SR on the bed vs. inter bed position in both experiments. Stimulatory effects of bedding on SR have been previously observed (Carter et al. 2002). In addition, site disturbance, especially following harvest, has been associated with higher SR (Londo et al. 1999; Lee et al. 2002). Significant location and date interactions in both experiments were possibly due to lar ger differences in total SR between the bed and inter bed positions during the growing season, suggesting that below ground processes were more active on the beds. Besides fine root production during the growing season (Lee and Jose, 2003), higher temperat ure and soil moisture likely aided the decomposition of organic matter present in the beds and thereby resulted in the differences observed between the bed and inter bed positions. Heterotrophic respiration is the dominant component of total SR across a wi de range of forest ecosystems (Bowden et al. 1993; Kelting et al. 1998; Buchmann, 2000). In the actively managed experiment, non significant differences between sites with and without REs indicated that RH contributed almost all of the SR. Negligible

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122 con tributions of root respiration (RA) to the total SR was unexpected given the actively growing aboveground vegetation in this experiment. However, it should be noted that the coefficients of variation for SR within the RE treatments were high at all measure ment dates (CV range: 25 54%). Organic matter enrichment during bedding (site establishment) and lack of a steady state environment in our open canopy system likely contributed to the spatial heterogeneity observed and the resultantly high coefficients o f variation. Comparison of SR rates for the RE treatments revealed that microbial activity contributed more than plant roots in the untreated carryover plots. In the current study, the contribution of roots to SR was lower (~ 4% in C C 12% in C F 17% in C F W and 25% in C W ) compared to the range of 30% to 62% reported for mature conifers and hardwoods across temperate regions (Ewel et al. 1987; Bowden et al. 1993; Maier and Kress, 2000; Haynes and Gower, 1995). However, the contributions of root respiratio n could range from 10% to 90%, depending upon the methods used to separate RH and RA variation across vegetation types, and climatic regions (Hanson et al. 2000). N otably the mass loss of the Betula papyrifera (Marsh.) tongue depressors in the C C and C F treatments suggests that microbial activity was greater when compared to the C FW and C W treatments. The role of organic matter in facilitation of microbial activity has been previously reviewed by Kuzyakov et al. (2000). Higher mass loss of the Betula pap yrifera (Marsh.) tongue depressors in the plots not receiving understory competition control in both experiments (actively managed: C and F; untreated carryover: C C and C F ) suggests that the fresh organic matter input from the understory vegetation retaine d in these plots

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123 et al. 1953; Kuzyakov et al. 2000) on soil microbes and thereby enhanced the decomposition process (Fontaine et al. 2003). For this same site, Polglase et al. (1992a) also reported more rapid deco mposition of OM derived from the litter of pine and understory vegetation in the fertilized plots compared to the OM derived from the litter of pines only in the weed control plots. In addition, higher phenolic concentrations were reported for the litter d erived from the weed control plots (Polglase et al, 1992b). Phenolic compounds have the potential to suppress microbial activity (Harrison, 1971; Schimel et al. 1996) and could have contributed to the lower mass loss of the Betula papyrifera (Marsh.) tong ue depressors in the FW, W, C FW C W treatments. Also, microclimate differences observed in the untreated carryover experiment (lower mean soil temperature in the C C and C F compared to the C FW and C W treatments) likely contributed to the observed difference s in the decomposition of the Betula papyrifera (Marsh.) tongue depressors. Because the retention of understory vegetation apparently increased OM decomposition in both experiments, these results highlight the potential role that the long term nutrient add itions and understory retention treatments (C, F and C C C F ) have on increasing nutrient mineralization rates on sandy Spodosols. In this study, the decomposition of the Betula papyrifera (Marsh.) tongue depressors deviated from the generally observed for m of exponential decay (Olson, 1963); rates of decomposition (mass loss:time ratio) increased with time (e.g. 3.9, 6.0, and 7.4 at 4, 8, and 12 months, respectively). Because the beds were drier from March until June (average volumetric moisture content ra nge: 1% and 3%), deviation in decomposition trends were likely due to the effects of diminished soil moisture on both

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124 substrate and microbial community activity (Cheng and Kuzyakov, 2005). Nevertheless, it should be noted that frequent drying and wetting c ycles can increase OM decomposition (Birch, 1958; Jarvis et al. 2007). Across different terrestrial ecosystems, numerous studies have documented a close relationship between soil temperature and SR (Lloyd and Taylor, 1994; Davidson et al. 1998; Fang and Moncrieff, 2001; Lee and Jose, 2003; Gough et al. 2005). In the current study, soil temperature, however, explained only 21 to 24% of the total variation in SR. In young stands and on disturbed sites, as found in this study, larger microsite variation due to localized accumulation of organic matter likely contributed to the weak relationship between soil temperature and SR. Tyree et al. (2008) also reported that soil temperature accounted for only 30% of total variation in SR in 2 year old loblolly pine sta nds growing on Ultisols in Virginia. Gough et al. (2005), however, reported that soil temperature alone explained 50% of the total variation in SR in 1 year old loblolly pine stands in South Carolina, where the soils were much cooler, (ranging from 0.5C t o 27C) compared to our site (5C in December to 48C in August). Large soil temperature ranges over the course of our study and decreased sensitivity of SR at higher temperatures (Luo et al. 2001; Peng et al. 2009) may have contributed to the weak soil temperature respiration relationship observed. Volumetric soil moisture content, although significant in the model, explained only a small portion of the total variation in SR. Weak relationships between soil moisture and SR have also been reported for ear ly to mid rotation loblolly pine stands (Tyree et al. 2008; Gough et al. 2005; Samuelson et al. 2009). Unlike stands having closed canopies, where micro site

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125 organic matter), soil temperature and moisture alone may not accurately predict variation in SR in these relatively young, open canopy systems. Summary and C onclusions This study was primarily designed to investigate the inter rotational effects of silvicultural t reatments on SR in young loblolly pine plantations growing on nutrient limited Spodosols. Our results suggest that the long history of fertilizer additions (F treatment) did not suppress SR, at least during these early stages of stand development. Because long term fertilizer additions increased soil organic matter content, SR was higher in fertilized plots that did not receive understory competition control compared to those that received sustained understory competition control (W treatment). In the untre ated carryover experiment, the effects of prior silvicultural treatment histories on SR were not as strong as in the actively managed experiment. However, the carryover C F treatment increased SR, apparently by increasing OM decomposition potentially the l arger pool of forest floor and soil C that carried over from the last rotation (Vogel et al. 2011), and aboveground biomass. Conversely, SR was lower in plots receiving the historical sustained understory competition control treatment (C W ) which had lower amounts of forest floor C in the previous rotation and slower decomposition in the current rotation In these young, second rotation loblolly pine stands, RH was the dominant component of total SR, even though treatments wi th higher aboveground biomass accumulation had higher SR rates. In addition, facilitation of OM decomposition in the understory retention treatments (C, F, C F and C C ) reinforces the potential role that understory vegetation may have on nutrient cycling an d mineralization processes. Nevertheless, the competitive role of understory vegetation on nutrient immobilization

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126 and its effects on loblolly pine growth potential (see Chapter 2 ) should not be discounted for these treatments, especially on nutrient limit ed sites. Finally, soil temperature and moisture alone were generally weak predictors of SR in these stands, which were characterized by having open canopies and significant microsite variation common to aggrading forest ecosystems.

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127 Table 4 1. Partial ANOV As for repeated measures analysis of soil CO2 efflux rates from November 2010 to April 2012 in two year old loblolly pine stands growing in the actively managed retreated and untreated carryover experiments on Spodosols in north Florida. Source ---Activel y managed retreated ----------Untreated carryover -------Num DF Den DF F value P value Num DF Den DF F value P Value Replication 2 6.29 2.7 0.1402 2 6.05 0.66 0.5505 Date 20 608 19 <.0001 20 604 23.74 <.0001 Treatment 3 6.24 4.3 0.059 3 6.38 2 .63 0.1395 Location 1 128 82 <.0001 1 63.2 40.39 <.0001 Root exclusion 1 93 0.1 0.7307 1 61.8 7.69 0.0073 Treatment Date 60 610 1 0.5577 60 607 0.84 0.8022 TreatmentLocation 3 89.7 2 0.1261 3 58.6 1.76 0.1652 Treatment Root exclusion 3 89.2 0.8 0.5059 3 60.9 0.75 0.5275 LocationDate 20 603 3.1 <.0001 20 603 4.85 <.0001 Location Root exclusion 1 89.4 2.9 0.0907 1 61.3 1.73 0.193 0 Root exclusionDate 20 603 1 0.4619 20 603 0.76 0.7681 TreatmentLocationDate 60 609 0.9 0.758 60 607 0.86 0.7598 TreatmentLocation Root exclusion 3 88.9 1.4 0.2584 3 61 0.24 0.8686 Treatment Root exclusion Date 60 609 0.9 0.6921 60 607 0.41 1 .0000 Location Root exclusion Date 20 603 0.3 0.9997 20 603 0.54 0.9474 TreatmentLocation Root exclusion Date 60 609 0.7 0.9822 60 607 0.68 0.9698 Covariates Soil moisture 1 665 20 <.0001 1 595 10.08 0.0016 Soil temperature 1 517 3.5 0.0633

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128 Table 4 2. Stepwise regressions of factors influencing soil respiration rates for Spodosol s that supported juvenile loblolly pine stands in the actively managed retreated and untreated carryover experiments in north Florida Parameter Parameter estimate Partial R 2 F value P>F Actively managed retreated Soil temperature 0.0277 0.239 332.628 <0. 001 Soil moisture 0.0408 0.055 78.315 <0.001 Untreated carryover Soil temperature 0.0236 0.214 274.184 <0.001 Soil moisture 0.0580 0.0659 91.638 <0.001 Note: Data pooled across date, treatments, location, and root exclusions.

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129 Table 4 3. ANO VA for the decomposition of Betula papyrifera (Marsh.) tongue depressors in 2 year old loblolly pine stands in the actively managed retreated and untreated carryover experiments on Spodosols in north Florida. Source --Actively managed retreated --------Untreated carryover -------Num DF Den DF F value P value Num DF Den DF F value P value Treatment 3 22 23.03 <.0001 3 24 5.67 0.0044 Time 2 22 1697.47 <.0001 2 24 968.06 <.0001 Treatment Time 6 22 2.29 0.072 6 24 1.03 0.4283 Table 4 4. Eff ects of fertilization and weed control on the mass loss of a common organic substrate ( Betula papyrifera (Marsh.) tongue depressors) over a 12 month period in the actively managed retreated and untreated carryover experiments on Spodosols in north Florida. Experiment Treatments HSD at alpha= 0.1) Actively managed retreated Control (C) A Fertilizer only (F) A Fertilizer+ weed control (FW) B Weed control only (W) B Untreated carryover Control (C C ) A Fertilizer only ( C F ) A Fertilizer+ weed control (C FW ) AB Weed control only (C W ) B Note: Within an experiment, treatments with same letter are not significantly different (alpha= 0.1)

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130 Table 4 5. Correlation between soil respiration rates and soil nutrient suppl y during the growing season for Spodosols supporting juvenile loblolly pine stands in the actively managed retreated and untreated carryover experiments in north Florida (n=12). Soil supply rates ---------Actively managed retreated -----------------Unt reated carryover ---------r P value r P value N supply 0.265 0.41 0.127 0.69 P supply 0.463 0.13 0.638 0.03 K supply 0.24 0 0.45 0.347 0.27 Ca supply 0.504 0.10 0.327 0.30 Mg supply 0.573 0.05 0.451 0.14 S supply 0.349 0.27 0.216 0.50 B s upply 0.382 0.22 0.239 0.45 Cu supply 0.568 0.05 0.573 0.05 Mn supply 0.554 0.06 0.571 0.05 Zn supply 0.473 0.12 0.475 0.12

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131 Figure 4 1. Effects of fertilization and weed control treatments on the least square mean soil respiration rates (CO 2 e fflux), mean soil temperature, and mean volumetric soil moisture content in the actively managed retreated ( A through C respectively) and untreated carryover experiments ( D through F respectively) for juvenile loblolly pine stands growing on Spodosols i n north Florida. The notations: C, F, FW, and W represent, respectively, the plots that received the control, fertilizer only, fertilizer + weed control, and weed control only treatments during both rotations. The notations: C C C F C FW and C W respectiv ely, represent the plots that received the control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation. Error bars for soil respiration show the standard error of LS mean Error bars for soil tempera ture and volumetric soil moisture represent the standard error of the mean.

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132 Figure 4 2. Least square mean soil respiration rates in the A ) actively managed retreated and B ) untreated carryover experiments for juvenile loblolly pine stands growing on Spod osols in north Florida. The notations: C, F, FW, and W represent, respectively, the plots that received the control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations: C C C F C FW and C W respec tively, represent the plots that received the control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation. Treatments with similar letters were ). Error bars represent the standard error of the estimate.

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133 Figure 4 3. Effects of location (Bed and Inter bed positions) on the least square mean soil respiration rates (CO 2 efflux), mean soil temperature, and mean volumetric soil moisture content in t h e actively managed retreated (A through C respectively) and untr eated carryover experiments (D through F respectively) for juvenile loblolly pine stands growing on Spodosols in north Florida. Error bars for soil respiration show the standard error of LS mean Error bars for soil temperature and volumetric soil moisture represent the standard error of the mean.

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134 Figure 4 4. Effects of root exclusions (with and without) on the least square mean soil respiration rates (CO 2 efflux), mean soil temperature, and mean volumetric soil moisture content in the actively managed retreated ( A through C respectively) and untreated carryover experiments ( D through F respectively) for juvenile loblolly pine stands growing on Spodosols in north Florida. Error bars for soil respiration show the standard error of LS mean Error bars for soil temperature and volumetric soil moisture represent the standard error of the mean.

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135 Figure 4 5. Effects of fertilization and weed control treatments on total annual soil respirati on (Nov 2010 Nov 2011) in the A ) actively managed retreated and B ) untreated carryover experiments for juvenile loblolly pine stands growing on Spodosols in north Florida. The notations: C, F, FW, and W represent, respectively, the plots that received th e control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations: C C C F C FW and C W respectively, represent the plots that received the control, fertilization only, fertilization + weed control, an d weed control only treatments in the previous rotation. Treatments with similar letter were not significantly of the mean.

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136 Figure 4 6. Effects of fertilization and weed c ontrol treatments on the decomposition of Betula papyrifera (Marsh.) tongue depressors for the A ) actively managed retreated and B ) untreated carryover experiments for juvenile loblolly pine stands growing on Spodosols in north Florida. The notations: C, F, FW, and W represent, respectively, the plots that received the control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations: C C C F C FW and C W respectively, represent the plots that received t he control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation. Error bars represent the standard deviation.

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137 CHAPTER 5 CONCLUSIONS A productivity and disturbance gradient created from the long term application of fertilizer and understory competition control treatments provided an unique opportunity to examine their inter rotational effects on the growth dynamics, soil nutrient availability, understory plant community development, and soil respiratio n responses in a second rotation, juvenile loblolly pine plantation growing on a Spodosol in north Florida. The original IMPAC (Intensive Management Practices Assessment Center) experiment was designed as a 2x2x2 factorial consisting of species (loblolly a nd slash pine), complete and sustained weed control, and annual fertilization arranged in a randomized split plot (species as whole plots) design with three replications. This resulted in four treatments within each species: control (C), weed control only (W), fertilizer only (F), and both fertilizer and weed c ontrol (FW). After 26 years, the original IMPAC experiment was harvested in 2009, with the intent of overlaying a second experiment using the same treatment plots. Prior to harvest, however, the under story vegetation in the F and C plots were mulched in place to retain this nutrient pool within the treatment plot boundaries. Mulching was not necessary in the W and FW treatments because of the historical weed control treatments used in the previous rota tion. The IMPAC II experiment now consists of two randomized complete block designs (RCBD; 3 replications each), having four treatments (C, F, FW, and W) for the actively managed retreatment design and four treatments for the untreated carryover design (Cc C F C FW C W ) (Figure 2 1). The carryover experiment was established on the previous slash pine plots and the actively managed retreatment experiment on the previous loblolly pine plots. In this study, the

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138 actively managed experiment received the same fer tilizer and weed control treatments in the second rotation as in the first. In contrast, the untreated carryover experiment was allowed to grow without additional fertilizer and weed control treatments. A single, full sib and elite performing loblolly fami ly was used to regenerate the entire study area in December 2009 using containerized seedlings. The original planting density remained consistent between r otations for both experiments. Early results, through age 3 yr, showed that loblolly pine growth in t he second rotation consistently out performed the first rotation. Improved cultural practices (e.g., advanced genetics, seedling stock, site preparation) and environmental factors (e.g., elevated atmospheric CO 2 ) may be responsible. Long term application o f fertilizer and sustained elimination of competing vegetation favored the establishment and early growth in the second rotation actively managed experiment (e.g., aboveground biomass: 28 Mg.ha 1 in the FW vs. 8 Mg.ha 1 in the C treatment). Nutrient accumu lations in the pine mostly followed the biomass accumulation trends (e.g. N (kg.ha 1 ): 124 in the FW vs. 37 in the C treatment). The long term fertilization and weed control treatments also contributed to shifts in the understory community composition and nutrient accumulation in the actively managed retreated experiment. A shrub community (e.g. Ilex glabra (L.) and Serenoa repens (Bartr.): 61% of total understory biomass and 24% of total N pool in the F treatment) dominated the F and C treatments, and a g rass community (e.g. Andropogon spp. and Dicanthelium spp.: 96% of total understory biomass in the FW treatment) dominated the FW and W treatments. In addition, Ilex glabra was an important accumulator of macro and micro nutrients (e.g. N, 45%; B, 62%; Mn, 82% of total

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139 understory accumulation) in the F treatment and it affected nutrient immobilization and loblolly pine growth. For example, elimination of competing vegetation in the FW treatment resulted in an almost 1.5 fold increase in aboveground pine bio ma ss compared to the F treatment. In the untreated carryover experiment, only the C F treatment was significantly more productive than the other treatments at age 3 yr. Higher growth responses (aboveground biomass: 18 Mg.ha 1 in C F vs. 10 Mg.ha 1 in C C trea tment) and soil P 2 /8 weeks in C F 2 /8 weeks C FW ) in the surface soil horizons of the C F treatment plots suggested that the nutrient pools contained in the forest floor and understory vegetation from the first rotati on (Vogel et al., 2011) served as an important nutrient source, especially for P, upon their decomposition and subsequent mineralization in the second rotation. However, P movement from the E to the Bh and Bt horizons (Mehlich III soil P concentration (mg. kg 1 ): 11.4 in 0 20 cm, 27.5 in 50 100 cm), in the absence of understory vegetation, especially for the combined treatment (C FW ), may have contributed to ea rly P limitations and growth. With time, growth associated with the C FW treatment may increase as th e roots occupy greater soil depths and acce ss greater P supply. These results suggest for flatwoods sites that were previously fertilized with P, the newly regenerated stands could benefit from nutrient management practices like understory mulching and for est floor incorporation, which may alleviate the need for early P applications at establishment. Historical fertilization and weed control treatments in the untreated carryover experiment also caused shifts in the understory community in a manner similar to the actively managed experiment; shrubs dominated the C C and C F treatments and grasses

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140 dominated the C FW and C W treatments. Ilex glabra (L.) was the major accumulator of nutrients in the C F treatment (e.g. N, 43%; Mn, 65% of total understory accumulatio n) and Andropogon spp. was the major nutrient accumulator in the C FW treatment (e.g. N, 80%; Mn, 71% of total understory accumulation). For both experiments, the understory vegetation community reinitiation, diversity, and composition were strongly influen ced by common silvicultural practices (e.g. fertilization and weed control) imposed during the first rotation. Relative to the control treatment, long term fertilizer additions had little influence on the second rotation understory community composition co mpared to the weed control treatment. When both the fertilizer and weed control treatments were combined, however, shifts in understory community composition were evident; shrubby species were suppressed and few herbaceous species like Andropogon spp. were favored (shrub biomass (Mg.ha 1 ): 0.01 in the FW and 0.26 in the C FW treatments; herb biomass (Mg.ha 1 ): 1.1 in the FW and 3.1 in the C FW treatment). Understory species diversity was almost 2.7 fold lower in the FW and C FW treatments compared to the F an d C F treatments. Although silvicultural treatments used in this study were more extreme than operational treatments typically used in southern pine forest management, these results suggest that long term weed control treatments affect ecosystem resilience, at least during the early stages of stand establishment, by reducing the diversity of understory vegetation. However, clear growth gains in loblolly pine were apparent when using fertilizer alone, understory competition control alone, or the combination o f these treatments. In nutrient limited environments, such as this, fertilizer rather than the weed control treatments may be

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141 beneficial for maintaining higher pine productivity without diminishing understory plant diversity. In these young, second rotatio n loblolly pine stands, a long history of fertilizer and weed control treatments influenced soil respiration (SR) rates in both experiments. The effects of fertilizer and weed control on SR were more pronounced in the actively managed retreated experiment than the untreated carryover experiment. Fertilizer additions consistently increased SR compared to the weed control treatments. Strong correlation between aboveground biomass and SR (r = 0.7 in the actively managed and 0.5 in the untreated carryover exper iments) suggested that higher belowground activity and organic matter inputs associated with greater growth of loblolly pine and understory vegetation in the F and C F treatments compared to W and C W treatments likely contributed to such differences in SR. In addition, mass loss of a common organic substrate ( Betula papyrifera (Marsh.) tongue depressors) was slower in the W and FW treatments when compared to the C and F treatments in the actively managed experiment. Similarly, in the untreated carryover expe riment, the C W and C FW treatments had slower decomposition rates of this substrate compared to the C C and C F treatments. The facilitation of greater organic matter decomposition in the C C and C F treatments highlights the potential role that the retention o f understory plants may have on nutrient cycling and mineralization processes on nutrient limited Spodosols. A number of questions regarding long term productivity associated with intensively managed southern pine stands still remain unanswered. In N and P limited soils, it is still important to understand how long historical fertilization treatments continue to support (carryover effects) the growth and nutritional demands of loblolly

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142 pine stands. Continuous monitoring of growth and yield, soil nutrient de mand and supply, along with the competitive role of understory plants for macro and micronutrients, should help frame better nutrient management regimes for loblolly pine plantations growing on Spodosols in the lower Coastal Plain. In addition, belowgroun d influences of fertilization on the understory vegetation community, especially root development, could also help us better understand the competitive influence they exert on southern pine growth, and improve silvicultural practices accordingly. Results f rom this study indicated a negative effect of repeated herbicide application on organic matter decomposition. On nutrient poor sandy soils, where nutrient mineralization following organic matter decomposition plays a pivotal role in maintaining soil nutrie nt availability, mechanistic processes behind such declines need to be explored. Future studies should investigate whether influences of repeated herbicide applications on microbial community composition are direct or indirect, via alteration in litter che mistry. The effect of litter inputs on nutrient mineralization should also be investigated to understand nutrient re cycling in these stands. Studies exploring these processes should widen our understanding of how cultural treatments affect soil nutrient a vailability and sustained productivity in southern pine stands.

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143 APPENDIX A ALLOMETRIC EQUATIONS FOR THE ESTIMATION O F ABOVEGROUND BIOMAS S COMPONENTS OF LOBL OLLY PINE Table A 1 Allometric equations a for estimating foliage, st emwood with bark, branch and aboveground tree biomass in young loblolly pine stands growing on Spodosols of the southeastern United States. Age o p Value 1 p Value R square Standard error Observation Foliage 1 and 2 1.56 <0.01 1.94 <0.01 0.84 0.343 48 Stemwood with bark 1 and 2 2.47 <0.01 2.27 <0.01 0.95 0.203 48 Branch 1 and 2 2.73 <0.01 2.54 <0.01 0.86 0.421 48 Above ground b 1 and 2 1. 03 <0.01 2.18 <0.01 0.90 0.302 48 Above ground b 3 1.2 <0.01 1.81 <0.01 0.91 0.153 56 a Model: Ln(Y) = o + 1 Ln(X) where Y is the biomass component expressed in kilograms dry wt., x is the tree height expressed in meters for age 1 and 2 or DBH expressed in centimeters for age 3. b Adegbidi et al. 2002.

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144 APPENDIX B FOLIAR NUTRIENT CONC ENTRATIONS OF JUVENI LE LOBLOLLY PINE STA NDS Table B 1. Effects of silvicultural treatments on the foliar nutrient concentrations of one year old loblolly pine for the acti vely managed ret reated experiment on Spodosols in north Florida. Note: For a given nutrient, means followed by the same letter are not significantly different among t Standard deviations are provided in parentheses. Treatments --------Macro nutrients ( g.kg 1 ) --------------Micro nutrients ( mg.kg 1 ) ---N P K Ca Mg S B Cu Mn Zn Actively managed retreated Control (C) 14.0 a 1.2 a 5.1 a 1.8 a 1.2 a 0.6 a 13.1 a 2.3 a 212.5 a 28.1 a (3.1) (0.1) (1.2) (0.3) (0.3) (0.02) (3.1) (0.7) (55.3) (3.4) Fertilizer only (F) 15.6 a 1.7 b 6.8 ab 1.8 a 0.9 a 0.7 ab 11.7 a 3.8 a 259.9 a 40.1 ab (1.9) (0.1) (0.2 ) (0.3) (0.2) (0.01) (1.6) (0.9) (113.0) (6.3) Fertilizer+Weed control (FW) 1 9 2 a 1 9 b 8 0 b 1 7 a 0 8 a 0 8 ab 12.6 a 3.4 a 197.8 a 44.6 b ( 3 7) ( 0 2) ( 0 9) ( 0 3) ( 0 1) ( 0 1) (1.3) (0. 2 ) (42. 3 ) (0.9) Weed control on ly (W) 18.7 a 1.6 b 6.9 b 1.8 a 1.0 a 1.0 b 11.8 a 3.2 a 205.9 a 33.5 ab (0.2) (0.1) (0.2) (0.2) (0.1) (0.3) (1.1) (0.8) (72.3) (8.1)

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145 Table B 2. Effects of silvicultural treatments on the foliar nutrient concentrations of one year old loblolly pine for the untreated carryover experiment on Spodosol s in north Florida. t alpha=0.05). Standard deviations are provided in parentheses. Treatments ---------------Macro nutrients ( g.kg 1 ) ------------------Micro nutrients ( mg.kg 1 ) ---N P K Ca Mg S B Cu Mn Zn Untreated carryover Control (C C ) 20.2 a 1 6 a 6 9 a 1 7 a 1 0 ab 1 1 a 1 1.5 a 3.9 a 190.9 a 38.2 ab (1 4) ( 0 1) ( 1 0) ( 0 2) ( 0 1) ( 0 4) (0.4 ) (0. 2 ) (25.9) (2. 4 ) Fertilizer only (C F ) 19.9 a 1 7 a 7 7 ab 1 6 a 0 8 a 0 8 a 11.4 a 3.6 a 227.3 a 45.4 b ( 1 2) ( 0 1) ( 0 5) ( 0 1) ( 0 1) ( 0 1) (0. 9 ) (1.0) (15.1) (2. 9) Fertilizer+Weed control (C FW ) 1 7 0 a 1 5 a 5 9 ab 1 6 a 0 9 ab 0 7 a 10.7 a 3.6 a 207.1 a 36.0 a ( 1 5) ( 0 1) ( 0 4) ( 0 2) ( 0 1) ( 0 1) (0.6) (0.3) (43. 5 ) (2. 9) Weed control only (C W ) 1 9 0 a 1 4 a 0.51 b 2 0 a 1 1 b 0 8 a 11.6 a 3.4 a 201.9 a 30.4 a ( 1 7) ( 0 2) (0.06) ( 0 3) ( 0 1) ( 0 2) (1.1) (0. 4 ) (46.0) (2.3)

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146 Table B 3. Effects of silvicultural treatments on the foliar nutrient concentrations of two year old loblolly pine for the actively managed retreated experiment on Spodosols in north Florida. t alpha=0.05). Standard deviations are provided in parenthese s. Treatments ---------------Macro nutrients ( g.kg 1 ) --------------Micro nutrients ( mg.kg 1 ) -N P K Ca Mg S B Cu Mn Zn Actively managed retreated Control (C) 16.9 a 1.0 a 5.3 a 1.2 a 0.6 a 1.0 a 6.1 a 1.8 a 56.7 a 19.8 a (0.8) ( 0.1) (1.0) (0.1) (0.1) (0.1) (0.7) (0.3) ( 12.9 ) (3.7) Fertilizer only (F) 22.5 a 1.6 a 8 9 a 1 2 a 0 4 a 1 3 ab 5.7 a 2.9 b 80.1 a 26.9 a (2.0) (0.2) ( 0 .6 ) ( 0 2) ( 0 .1 ) ( 0 1) (0.7) (0.1) (32.5) ( 6.8 ) Fertilizer+Weed con trol (FW) 22.6 a 1.5 a 7 3 a 1 2 a 0 4 a 1 4 b 6.2 a 2.3 ab 93.1 a 26.9 a (3.1) (0.3) ( 3 2) ( 0 .1 ) (< 0 .1 ) ( 0 1) (0.9 ) (0.2) (11.4) ( 1.3 ) Weed control only (W) 18.7 a 1.2 a 6 8 a 1 3 a 0 5 a 1 1 ab 6.7 a 1.9 b 74.3 a 20.5 a (2.1) (0 .2) ( 1 8) ( 0 1) ( 0 1) ( 0 .1 ) (0.5) (0.2) ( 16.2 ) (4.0)

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147 Table B 4. Effects of silvicultural treatments on the foliar nutrient concentrations of two year old loblolly pine for the untreated carryover experiment on Spodosols in north Florida. t alpha=0.05). Standard deviations are provided in parentheses. Treatments ---------------Macro nutrients ( g.kg 1 ) ------------Micro nutrients ( mg.kg 1 ) ---N P K Ca Mg S B Cu Mn Zn Untreated carryover Control (C C ) 17.0 a 1.1 a 6.6 a 1.4 a 0.7 a 1.1 a 6.8 a 2.1 a 77.0 a 22.5 a (0.6) (0.1) (1.9) (0.2) (0.1) (0.1) (0.6) (0.4) (18.3) (5.2) Fertilizer only (C F ) 20.2 a 1.1 a 7.4 a 1.2 a 0.5 a 1.1 a 5.7 a 2.2 a 88.8 ab 23.5 a (1.9) (0.1) (1.5) (0.1) (0.1) (< 0.1) (0.4) (< 0.1) (6.2) (2.3) Fertilizer+Weed control (C FW ) 18.6 a 1.1 a 4.2 a 1.6 a 0.6 a 1.3 a 5.7 a 1.8 a 148.3 b 28.7 a (1.7) (< 0.1) (0.2) (0.1) (0.2) (< 0.1) (0.5) (0.4) (42.9) (2.5) Weed control only (C W ) 17.2 a 1.0 a 4.3 a 1.5 a 0.7 a 1.1 a 6.8 a 1.6 a 95.9 ab 22.3 a (2.7) (< 0.1) (1.3) (0.3) (0.1) (0.1) (1.1) (0.3) (15.3 ) (3.8)

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148 Table B 5. Analysis of variance for folia r nutrient concentration of loblolly pine stands in the first and second growing season for the actively managed retreated and untreated carryover experiments in north Florida. ---------Actively managed retreated ------------------Untreated carryover --------Nutrients Numerator df Denominator df F value P Value >F Numerator df Denominator df F value P Value >F N 1 14 12.81 0.003 1 4 0.98 0.377 P 1 16 15.06 0.001 1 16 116.89 <0.001 K 1 4 0.27 0.631 1 8 3.81 0.087 Ca 1 8 49.81 <0.001 1 1 6 11.58 0.004 Mg 1 4 62.67 0.001 1 16 51.18 <0.001 S 1 3.36 42.29 0.005 1 3.16 14.73 0.028 B 1 8 129.8 0 <0.001 1 16 278.45 <0.001 Cu 1 16 19.81 <0.001 1 16 78.55 <0.001 Mn 1 2 37.07 0.026 1 7.47 80.66 <0.001 Zn 1 8 89.26 <0.001 1 16 104.5 3 <0.001 values <0.05 denote significant differences between foliar concentrations at age 1 and 2 years.

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149 APPENDIX C UNDERSTORY SPECIES BIOMASS AND NUTRIENT ACCUMULATION

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150 Table C 1. Aboveground biomass accumulation in the understory species for the actively managed retreated and untreated carryover experiments in north Florida. Species ---Actively managed retreated ------Untreated carr yover ----C F FW W CC CF CFW CW Andropogon spp. 173 1565 1056 906 198 669 2997 1164 Carex spp 58 4 10 26 43 3 4 55 Chrysopsis graminifolia 17 Cyperus spp. 78 275 161 2 1 Dicanthelium spp. 81 43 40 422 98 5 45 350 Eleocharis baldwinii < 1 1 7 <1 4 Erectites hierarcifolia <1 5 Eupatorium capillifolium 19 Eupatorium spp. 14 12 56 90 21 <1 Gamochaeta purpurea 5 Gaylussacia dumosa 16 35 4 Gaylussacia frondosa 1 Hypericum spp 21 2 2 133 22 59 <1 Il ex glabra 2457 3758 2383 2222 Juncus spp 1 4 Lachnanthes caroliniana <1 4 55 28 3 Ludwigia decurrens <1 Lyonia ferruginea 1 2 7 1 Lyonia lucida 862 585 175 Panicum hemitomon 25 Myrica cerifera 340 Paspalu m spp 1 1 Persea borbonia 2 4 9 Persea palustris 35 Pteridium aquilinum 2 <1 5 Quercus nigra 19 31 9 10 72 2 Rhexia alifanus 5 Rhexia spp 2 Rhexia virginica <1 Rhus copallina 485 409 36 91 Rubus spp 12 8 79 Scleria spp. 95 <1 59 25 1 1 42 Serenoa repens 1323 641 1239 1212 27 Sorghastrum secundum <1 Smilax rotundifolia 134 97 12 1 56 22 25 7 Solidago fistulosa 1 Sporobolus curtissii <1 30 Vaccinium myrsinites 6 46 11 36 Vitis rotundifolia 186 <1 276 <1 Woodwardia virginica 6 differentiated. The notations C, F, FW, and W represent, respectively, the actively managed retreatment experiment that received control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the untreated carryover experiment that received control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation.

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151 Table C 2 Percentage contribution by species to the total understory aboveground biomass in the actively managed retreated and untreated carryover experiments in north Florida. Species --Actively managed retreated ----Untreated carryover --C F FW W CC CF CFW CW Andropogon spp. 3.06 17.19 65.4 3 47.4 9 4.81 15.67 89.35 68.35 Carex spp 0.97 0.07 1.84 1.91 1.23 0.08 0.1 3 .35 Chrysopsis graminifolia 0.24 Cyperus spp. 1.39 2.62 2.59 0.06 0.08 Dicanthelium spp. 1.27 0.59 30.5 8 34.9 1 2.25 0.1 1.49 18.2 Eleocharis baldwinii 0.01 0.02 0.44 <0.01 0.23 Erectites hierarcifolia <0.01 0.1 E upatorium capillifolium 0.5 Eupatorium spp. 0.2 0.23 2.2 1.79 0.44 0.01 Gamochaeta purpurea 0.7 Gaylussacia dumosa 0.23 0.67 0.13 Gaylussacia frondosa 0.01 Hypericum spp 0.38 0.31 0.1 3.97 0.6 7 1.77 0.02 Ilex glabra 44.06 49.21 49.18 42.1 Juncus spp 0.01 0.17 Lachnanthes caroliniana <0.01 0.05 3.98 0.46 0.14 Ludwigia decurrens 0.01 Lyonia ferruginea 0.02 0.02 0.19 0.02 Lyonia lucida 15.82 5 .91 5.3 Panicum hemitomon 1.38 Myrica cerifera 6.78 Paspalum spp 0.02 <0.01 0.15 Persea borbonia 0.03 0.04 0.51 Persea palustris 0.47 Pteridium aquilinum <0.01 0.06 <0.01 0.16 Quercus nigra 0.29 0.59 1.14 0.19 2.18 0.06 Rhexia alifanus 0.1 Rhexia spp 0.05 Rhexia virginica 0.01 Rhus copallina 8.76 6.73 0.59 2.32 Rubus spp 0.21 0.08 2.38 Scleria spp. 1 .72 <0.01 6.78 0.5 0.03 0.02 2.4 Serenoa repens 19.28 11.87 24.07 23.06 1.56 Sorghastrum secundum 0.01 <0.01 Smilax rotundifolia 2.04 1.73 1.62 0.05 1.14 0.61 0.66 0.44 Solidago fistulosa 0.03 Sporobolus curtissii <0.01 0.77 Vaccinium myrsinites 0.29 1.13 0.29 3.16 Vitis rotundifolia 1.93 <0.01 8.35 0.02 Woodwardia virginica 0.15 Note: Treatments may not sum to 100 because of rounding error. ed to refer to several species of the same genus which were not differentiated. The notations C, F, FW, and W represent, respectively, the actively managed retreatment experiment that received control, fertilizer only, fertilizer + weed control, and weed c ontrol only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the untreated carryover experiment that received control, fertilization only, fertilization + weed control, and weed control only treatments in the previou s rotation.

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152 Table C 3 Nitrogen accumulation (kg.ha 1 ) in the understory species for both the actively managed retreated and untreated carryover experiments in north Florida. Species --Actively managed retreated ----Untreated carryover --C F FW W C C CF CFW CW Andropogon spp. 1.1 8.5 8.6 9.9 1.2 3.9 13.3 5.9 Carex spp 0.3 < 0.1 0.1 0.2 0.3 < 0.1 < 0.1 0.3 Chrysopsis graminifolia 0.2 Cyperus spp. 0.6 1.7 1.1 < 0.1 < 0.1 Dicanthelium spp. 0.9 0.4 0.8 4.2 0.8 0.1 0.3 2.6 Eleocharis bald winii 0.1 < 0.1 Erectites hierarcifolia < 0.1 Eupatorium capillifolium 0.2 Eupatorium spp. 0.1 0.1 1.0 0.2 < 0.1 Gamochaeta purpurea 0.1 Gaylussacia dumosa 0.1 0.2 < 0.1 Gaylussacia frondosa < 0.1 Hypericum spp 0.2 < 0.1 < 0.1 1.0 0.3 0.6 Ilex glabra 20.0 22.7 12.7 18.2 Juncus spp Lachnanthes caroliniana 0.1 0.5 0.3 < 0.1 Ludwigia decurrens Lyonia ferruginea < 0.1 < 0.1 0.1 < 0.1 Lyonia lucida 4.2 2.3 1.3 Panicum he mitomon 0.2 Myrica cerifera 5.1 Paspalum spp < 0.1 Persea borbonia < 0.1 < 0.1 0.1 Persea palustris 0.5 Pteridium aquilinum < 0.1 < 0.1 0.1 Quercus nigra 0.2 0.3 0.1 0.1 1.0 < 0.1 Rhexia alifanus 0.1 Rhexia spp < 0.1 Rhexia virginica Rhus copallina 7.0 6.1 1.0 Rubus spp 0.1 0.2 0.6 Scleria spp. 0.5 0.4 0.1 < 0.1 Serenoa repens 9.2 5.1 15.2 12.5 0.3 Sorghastrum secundum Smilax rotundifolia 2.3 0.8 0.2 < 0.1 0.7 0.3 0.2 0.1 Solidago fistulosa < 0.1 Sporobolus curtissii < 0.1 0.2 Vaccinium myrsinites 0.1 0.3 0.1 0.3 Vitis rotundifolia 2.1 < 0.1 3.7 Woodwardia virginica 0.1 Note: Species total within a treatment may not sum to the total N accumulation due to rounding error. differentiated. The notations C, F, FW, and W represent, respectively, the actively managed retreatment exper iment that received control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the untreated carryover experiment that received control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation.

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153 Table C 4. Phosphorus accumulation (kg.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Flori da. Species --Actively managed retreated ----Untreated carryover --C F FW W CC CF CFW CW Andropogon spp. 0.18 1.66 1.26 1.34 0.25 0.94 2.59 1.03 Carex spp 0.02 <0.01 0.01 0.02 0.02 <0.01 0.01 0.05 Chrysopsis graminifolia 0.02 Cyperus spp 0.06 0.53 0.12 <0.01 <0.01 Dicanthelium spp. 0.07 0.04 0.13 0.40 0.08 0.01 0.03 0.22 Eleocharis baldwinii <0.01 <0.01 0.01 <0.01 0.01 Erectites hierarcifolia <0.01 0.01 Eupatorium capillifolium 0.03 Eupatorium spp. 0.01 0.02 0.1 4 0.03 <0.01 Gamochaeta purpurea 0.01 Gaylussacia dumosa 0.01 0.02 <0.01 Gaylussacia frondosa <0.01 Hypericum spp 0.02 <0.01 <0.01 0.15 0.04 0.08 <0.01 Ilex glabra 1.65 3.27 1.54 1.32 Juncus spp <0.01 <0.01 Lachnanth es caroliniana <0.01 0.01 0.05 0.03 <0.01 Ludwigia decurrens <0.01 Lyonia ferruginea <0.01 <0.01 0.01 <0.01 Lyonia lucida 0.44 0.23 0.12 Panicum hemitomon 0.03 Myrica cerifera 0.19 Paspalum spp <0.01 <0.01 Per sea borbonia <0.01 <0.01 <0.01 Persea palustris 0.07 Pteridium aquilinum <0.01 <0.01 0.01 Quercus nigra 0.03 0.04 0.01 0.01 0.10 <0.01 Rhexia alifanus 0.03 Rhexia spp <0.01 Rhexia virginica <0.01 Rhus copalli na 0.61 0.69 0.12 Rubus spp 0.01 0.02 0.06 Scleria spp. 0.05 0.03 0.01 <0.01 <0.01 Serenoa repens 0.55 0.44 0.98 0.96 0.02 Sorghastrum secundum <0.01 Smilax rotundifolia 0.13 0.10 0.01 <0.01 0.04 0.02 0.02 <0.01 Solidago fist ulosa <0.01 Sporobolus curtissii <0.01 0.04 Vaccinium myrsinites 0.01 0.03 0.02 0.03 Vitis rotundifolia 0.30 <0.01 0.32 <0.01 Woodwardia virginica 0.09 Note: Species total within a treatment may not sum to the total P accum ulation due to rounding error. differentiated. The notations C, F, FW, and W represent, respectively, the actively managed retreatment experiment that received c ontrol, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the untreated carryover experiment that received control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation.

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154 Table C 5. Potassium accumulation (kg.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Florida. Species --Active ly managed retreated ----Untreated carryover --C F FW W CC CF CFW CW Andropogon spp. 1.29 7.33 5.93 6.99 1.45 4.02 8.90 3.47 Carex spp 0.20 0.03 0.11 0.16 0.16 0.03 0.02 0.48 Chrysopsis graminifolia 0.21 Cyperus spp. 0.34 2.96 1.16 0.01 0.01 Dicanthelium spp. 0.56 0.17 0.36 3.18 0.67 0.03 0.20 2.06 Eleocharis baldwinii < 0.01 0.01 0.03 < 0.01 0.02 Erectites hierarcifolia < 0.01 0.03 Eupatorium capillifolium 0.17 Eupatorium spp. 0.07 0.15 0.61 0.24 < 0.01 Gamochae ta purpurea 0.03 Gaylussacia dumosa 0.08 0.14 0.01 Gaylussacia frondosa < 0.01 Hypericum spp 0.04 0.01 0.02 0.98 0.22 0.25 < 0.01 Ilex glabra 10.02 14.31 11.48 10.16 Juncus spp 0.01 0.01 Lachnanthes caroliniana < 0.01 0.03 0.86 0.16 0.02 Ludwigia decurrens < 0.01 Lyonia ferruginea < 0.01 0.01 0.05 < 0.01 Lyonia lucida 2.29 0.59 1.19 Panicum hemitomon 0.06 Myrica cerifera 1.47 Paspalum spp 0.01 0.01 Persea borbonia 0.01 0.03 0.03 Persea palustris 0.18 Pteridium aquilinum 0.01 < 0.01 0.02 Quercus nigra 0.07 0.19 0.04 0.02 0.35 0.01 Rhexia alifanus 0.10 Rhexia spp 0.01 Rhexia virginica < 0.01 Rhus copallina 2.90 4.34 0.90 Ru bus spp 0.06 0.13 0.33 Scleria spp. 0.27 0.19 0.05 0.01 < 0.01 Serenoa repens 3.12 2.70 3.57 4.42 0.03 Sorghastrum secundum < 0.01 Smilax rotundifolia 0.96 0.83 0.05 0.01 0.34 0.21 0.15 0.03 Solidago fistulosa 0.01 Sporobol us curtissii < 0.01 0.13 Vaccinium myrsinites 0.02 0.22 0.05 0.13 Vitis rotundifolia 2.05 < 0.01 2.16 < 0.01 Woodwardia virginica 0.06 Note: Species total within a treatment may not sum to the total K accumulation due to rounding e rror. differentiated. The notations C, F, FW, and W represent, respectively, the actively managed retreatment experiment that received control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the untreated carryover experiment that received control, fertilization only, fertilization + weed control, and weed c ontrol only treatments in the previous rotation.

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155 Table C 6 Calcium accumulation (kg.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Florida. Species --Actively managed retreated ----Untreated carryover --C F FW W CC CF CFW CW Andropogon spp. 0.16 1.64 1.13 1.04 0.16 0.84 3.37 1.04 Carex spp 0.09 0.01 0.02 0.04 0.06 0.01 0.01 0.07 Chrysopsis graminifolia 0.26 Cyperus spp. 0.22 0.61 0.50 0.01 < 0.01 Dicanthelium spp. 0.10 0.10 0.06 0.60 0.12 0.01 0.07 0.55 Eleocharis baldwinii < 0.01 0.01 < 0.01 < 0.01 Erectites hierarcifolia < 0.01 0.01 Eupatorium capillifolium 0.20 Eupatorium spp. 0.03 0.08 0.42 0.18 0.01 Gamochaeta purpurea 0.06 Gayl ussacia dumosa 0.07 0.43 0.04 Gaylussacia frondosa 0.01 Hypericum spp 0.14 0.02 0.02 0.61 0.12 0.35 < 0.01 Ilex glabra 11.88 16.78 12.82 17.01 Juncus spp < 0.01 0.01 Lachnanthes caroliniana < 0.01 0.06 0.58 0.57 0.04 Ludwi gia decurrens < 0.01 Lyonia ferruginea 0.01 0.02 0.01 < 0.01 Lyonia lucida 4.31 2.40 1.82 Panicum hemitomon 0.02 Myrica cerifera 2.38 Paspalum spp < 0.01 < 0.01 Persea borbonia 0.01 0.02 0.03 Persea palustri s 0.18 Pteridium aquilinum 0.01 < 0.01 0.04 Quercus nigra 0.12 0.14 0.04 0.06 0.41 0.01 Rhexia alifanus 0.06 Rhexia spp 0.01 Rhexia virginica 0.01 Rhus copallina 2.96 1.52 0.68 Rubus spp 0.07 0.05 0.66 Scleria spp. 0.14 0.13 0.05 < 0.01 < 0.01 Serenoa repens 4.82 1.59 1.62 2.87 0.08 Sorghastrum secundum < 0.01 Smilax rotundifolia 0.90 0.45 0.10 0.01 0.61 0.16 0.18 0.07 Solidago fistulosa 0.01 Sporobolus curtissii < 0.01 0. 13 Vaccinium myrsinites 0.04 0.40 0.06 0.15 Vitis rotundifolia 0.75 < 0.01 2.18 < 0.01 Woodwardia virginica 0.04 Note: Species total within a treatment may not sum to the total Ca accumulation due to rounding error. genus is used to refer to several species of the same genus which were not differentiated. The notations C, F, FW, and W represent, respectively, the actively managed retreatment experiment that received control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the untreated carryover experiment that received control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation

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156 Table C 7. Magnesium accumulation (kg.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Florida. Species --Actively managed retreated ----Untreated carryover --C F FW W CC CF CFW CW Andropogon spp. 0.09 0.85 0.77 0.80 0.10 0.25 0.78 0.51 Carex spp 0.05 < 0.01 0.02 0.03 0.03 < 0.01 < 0.01 0.05 Chrysopsis graminifolia 0.17 Cyperus spp. 0.09 0.35 0.21 < 0.01 < 0.01 Dicanthelium spp. 0.09 0.06 0.08 0 .56 0.13 0.01 0.03 0.44 Eleocharis baldwinii < 0.01 < 0.01 0.02 < 0.01 0.01 Erectites hierarcifolia < 0.01 0.01 Eupatorium capillifolium 0.05 Eupatorium spp. 0.02 0.05 0.37 0.06 < 0.01 Gamochaeta purpurea 0.02 Gaylussacia du mosa 0.02 0.08 0.01 Gaylussacia frondosa < 0.01 Hypericum spp 0.06 0.01 0.01 0.29 0.06 0.09 < 0.01 Ilex glabra 3.68 5.06 3.35 4.15 Juncus spp < 0.01 < 0.01 Lachnanthes caroliniana < 0.01 0.02 0.14 0.19 0.02 Ludwigia decurr ens < 0.01 Lyonia ferruginea < 0.01 < 0.01 0.02 < 0.01 Lyonia lucida 1.87 0.59 0.17 Panicum hemitomon 0.03 Myrica cerifera 0.70 Paspalum spp < 0.01 < 0.01 Persea borbonia < 0.01 < 0.01 0.01 Persea palustris 0.05 Pteridium aquilinum 0.01 < 0.01 0.02 Quercus nigra 0.03 0.03 0.01 0.01 0.09 0.01 Rhexia alifanus < 0.01 Rhexia spp < 0.01 Rhexia virginica < 0.01 Rhus copallina 0.93 0.60 0.18 Rubus spp 0.04 0.02 0. 24 Scleria spp. 0.07 0.06 0.02 < 0.01 < 0.01 Serenoa repens 3.45 0.69 2.62 1.72 0.06 Sorghastrum secundum < 0.01 Smilax rotundifolia 0.20 0.16 0.03 < 0.01 0.14 0.04 0.03 0.02 Solidago fistulosa 0.01 Sporobolus curtissii < 0. 01 0.04 Vaccinium myrsinites 0.01 0.07 0.02 0.04 Vitis rotundifolia 0.42 < 0.01 0.66 < 0.01 Woodwardia virginica 0.02 Note: Species total within a treatment may not sum to the total Mg accumulation due to rounding error. ter a genus is used to refer to several species of the same genus which were not differentiated. The notations C, F, FW, and W represent, respectively, the actively managed retreatment experiment that received control, fertilizer only, fertilizer + weed co ntrol, and weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the untreated carryover experiment that received control, fertilization only, fertilization + weed control, and weed control only treatmen ts in the previous rotation

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157 Table C 8. Sulfur accumulation (kg.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Florida. Species --Actively managed retreated ----Untreated carryover -C F FW W CC CF CFW CW Andropogon spp. 0.11 1.01 0.55 0.93 0.16 0.65 1.95 0.90 Carex spp 0.04 < 0.01 0.02 0.02 0.03 < 0.01 < 0.01 0.04 Chrysopsis graminifolia 0.05 Cyperus spp. 0.07 0.20 0.13 < 0.01 < 0.01 Dicanthelium spp. 0.16 0.08 0.1 0 0.77 0.19 0.01 0.05 0.53 Eleocharis baldwinii 0.01 0.01 Erectites hierarcifolia < 0.01 Eupatorium capillifolium 0.03 Eupatorium spp. 0.01 0.01 0.13 0.02 < 0.01 Gamochaeta purpurea 0.01 Gaylussacia dumosa 0.01 0.03 < 0.01 Gaylussacia frondosa < 0.01 Hypericum spp 0.02 < 0.01 < 0.01 0.14 0.03 0.08 Ilex glabra 1.09 2.28 0.64 1.45 Juncus spp Lachnanthes caroliniana 0.01 0.04 0.03 < 0.01 Ludwigia decurrens Lyonia ferruginea < 0. 01 < 0.01 0.01 < 0.01 Lyonia lucida 0.48 0.18 0.16 Panicum hemitomon 0.03 Myrica cerifera 0.35 Paspalum spp < 0.01 Persea borbonia < 0.01 < 0.01 0.01 Persea palustris 0.05 Pteridium aquilinum < 0.01 < 0. 01 < 0.01 Quercus nigra 0.01 0.02 < 0.01 < 0.01 0.07 < 0.01 Rhexia alifanus < 0.01 Rhexia spp < 0.01 Rhexia virginica Rhus copallina 0.63 0.37 0.07 Rubus spp 0.01 0.01 0.04 Scleria spp. 0.10 0.06 0.02 < 0.01 Serenoa repens 1.33 0.70 1.56 1.60 0.04 Sorghastrum secundum Smilax rotundifolia 0.16 0.13 0.03 < 0.01 0.08 0.03 0.02 0.01 Solidago fistulosa < 0.01 Sporobolus curtissii < 0.01 0.04 Vaccinium myrsinites 0.01 0.03 0.01 0. 03 Vitis rotundifolia 0.18 < 0.01 0.24 Woodwardia virginica 0.01 Note: Species total within a treatment may not sum to the total S accumulation due to rounding error. genus which were not differentiated. The notations C, F, FW, and W represent, respectively, the actively managed retreatment experiment that received control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. T he notations C C C F C FW and C W respectively, represent the untreated carryover experiment that received control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation

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158 Table C 9. Boron accumulation ( g.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Florida. Species --Actively managed retreated ----Untreated carryover --C F FW W CC CF CFW CW Andropogon spp. 0.7 7.3 4.2 4.7 0.7 2.4 9.4 3.6 Carex spp 0.3 < 0.1 0.1 0.2 0.2 < 0.1 < 0.1 0.3 Chrysopsis graminifolia 0.6 Cyperus spp. 0.5 2.0 1.0 < 0.1 < 0.1 Dicanthelium spp. 0.5 0.5 0.2 2.3 0.5 < 0.1 0.2 2.1 Eleocharis baldwinii < 0.1 < 0.1 0.1 < 0.1 < 0.1 Erectites hierarcifolia < 0.1 0.1 Eupatorium capillifolium 1.1 Eupatorium spp. 0.1 0.5 2.4 0.6 < 0.1 Gamochaeta purpurea 0.3 Gaylussacia dumosa 0.7 2.3 0.2 Gaylussacia frondosa < 0.1 Hypericum spp 0.5 0.1 0.1 2.3 0.6 1.5 < 0.1 Ilex glabra 72.1 77.2 38.1 93.3 Juncus spp < 0.1 < 0.1 Lachnanthes caroliniana < 0.1 0.1 0.5 0.5 < 0.1 Ludwigia decurrens < 0.1 Lyonia ferruginea < 0.1 0.1 0.1 < 0.1 Lyonia lucida 10.6 7.2 2.3 Panicum hemitomon 0.1 Myrica cerifera 7.4 Paspalum spp < 0.1 < 0.1 Persea borbonia < 0.1 0.1 0.1 Persea palustris 0.8 Pteridium aquilinum < 0.1 < 0.1 0.1 Quercus nigra 0.4 0.7 0.1 0.3 1.4 0.1 Rhexia alifanus 0.1 Rhexia spp 0.1 Rhexia virginica < 0.1 Rhus copallina 14.1 10.7 2.9 Rubus spp 0.4 0.3 2.6 Scleria spp. 0.5 0.4 0.2 < 0.1 < 0.1 Serenoa repens 9.0 6.4 9.5 9.8 0.3 Sorghastrum secundum < 0.1 Smilax rotundifolia 2.6 1.6 0.2 < 0.1 1.3 0.5 0.5 0.1 Solidago fistulosa < 0.1 Sporobolus curtissii < 0.1 0.1 Vaccinium myrsinites 0.1 1.2 0.2 0.5 Vitis rotundifolia 3.3 < 0.1 4.6 < 0.1 Woodwardia virginica 0.1 Note: Species total within a treatment may not sum to the total B accumulation due to rounding error. differentiated. The notations C, F, FW, and W represent, respectively, the actively managed retreatmen t experiment that received control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the untreated carryover experiment that received control, fertili zation only, fertilization + weed control, and weed control only treatments in the previous rotation

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159 Table C 10. Copper accumulation ( g.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Flo rida. Species --Actively managed retreated ----Untreated carryover --C F FW W CC CF CFW CW Andropogon spp. 0.6 4.8 4.6 5.4 0.5 1.6 3.8 2.9 Carex spp < 0.1 < 0.1 0.1 0.1 0.1 < 0.1 < 0.1 0.5 Chrysopsis graminifolia 0.3 Cyperus spp. < 0.1 0 .7 0.3 < 0.1 < 0.1 Dicanthelium spp. 0.3 0.1 0.1 0.9 0.2 < 0.1 0.1 0.7 Eleocharis baldwinii < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 Erectites hierarcifolia < 0.1 < 0.1 Eupatorium capillifolium 0.3 Eupatorium spp. 0.1 0.1 0.8 0.2 < 0.1 Gam ochaeta purpurea 0.1 Gaylussacia dumosa 0.1 0.2 < 0.1 Gaylussacia frondosa < 0.1 Hypericum spp 0.1 < 0.1 < 0.1 0.9 0.2 0.4 < 0.1 Ilex glabra 13.2 23.1 11.3 11.7 Juncus spp < 0.1 < 0.1 Lachnanthes caroliniana < 0.1 < 0. 1 0.3 0.2 < 0.1 Ludwigia decurrens < 0.1 Lyonia ferruginea < 0.1 < 0.1 < 0.1 < 0.1 Lyonia lucida 2.2 1.8 0.6 Panicum hemitomon < 0.1 Myrica cerifera 0.8 Paspalum spp < 0.1 < 0.1 Persea borbonia < 0.1 < 0.1 < 0.1 Persea palustris 0.2 Pteridium aquilinum < 0.1 < 0.1 < 0.1 Quercus nigra 0.1 0.3 0.1 < 0.1 0.3 < 0.1 Rhexia alifanus 0.1 Rhexia spp < 0.1 Rhexia virginica < 0.1 Rhus copallina 3.8 2.5 0.6 Rubus spp 0.1 0.1 0.5 Scleria spp. 0.2 0.1 < 0.1 < 0.1 < 0.1 Serenoa repens 3.5 1.4 5.0 3.7 0.1 Sorghastrum secundum < 0.1 Smilax rotundifolia 0.8 0.6 0.1 < 0.1 0.3 0.1 0.1 < 0.1 Solidago fistulosa < 0.1 Sporobolus curtissii < 0.1 0.1 Vaccinium myrsinites < 0.1 0.2 0.1 0.2 Vitis rotundifolia 2.6 < 0.1 1.9 < 0.1 Woodwardia virginica < 0.1 Note: Species total within a treatment may not sum to the total Cu accumulation due to rounding error. nus is used to refer to several species of the same genus which were not differentiated. The notations C, F, FW, and W represent, respectively, the actively managed retreatment experiment that received control, fertilizer only, fertilizer + weed control, a nd weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the untreated carryover experiment that received control, fertilization only, fertilization + weed control, and weed control only treatments in th e previous rotation

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160 Table C 11. Manganese accumulation ( g.ha 1 ) in the understory species in both the actively managed retreated and untreated carryover experiments in north Florida. Species --Actively managed retreated ----Untreated carryover --C F FW W CC CF CFW CW Andropogon spp. 8.6 94.1 150.9 77.4 6.2 62.9 261.9 37.4 Carex spp 3.6 0.4 5.7 4.7 2.0 1.1 0.4 17.0 Chrysopsis graminifolia 5.7 Cyperus spp. 9.4 41.7 12.5 0.2 0.2 Dicanthelium spp. 9.7 9.7 9.6 61.8 13.4 1.0 19.9 70.9 El eocharis baldwinii < 0.1 0.3 0.6 < 0.1 0.2 Erectites hierarcifolia < 0.1 0.4 Eupatorium capillifolium 4.8 Eupatorium spp. 0.6 3.4 11.9 7.9 0.1 Gamochaeta purpurea 0.5 Gaylussacia dumosa 3.8 17.4 0.5 Gaylussacia frondosa 0.1 Hypericum spp 0.8 0.3 0.5 11.0 4.3 7.9 < 0.1 Ilex glabra 181.3 959.1 126.9 717.4 Juncus spp 0.1 0.9 Lachnanthes caroliniana < 0.1 1.1 11.5 4.8 0.5 Ludwigia decurrens < 0.1 Lyonia ferruginea 0.1 1.3 0.3 0.1 Lyon ia lucida 360.7 428.7 80.1 Panicum hemitomon 1.2 Myrica cerifera 27.3 Paspalum spp 0.1 0.1 Persea borbonia 0.3 1.4 0.8 Persea palustris 4.5 Pteridium aquilinum 0.1 < 0.1 0.6 Quercus nigra 0.8 4.4 0.3 1.9 1 5.6 1.6 Rhexia alifanus 1.8 Rhexia spp 0.2 Rhexia virginica < 0.1 Rhus copallina 37.8 19.6 24.2 Rubus spp 1.6 4.2 23.1 Scleria spp. 15.6 3.8 1.7 0.3 0.1 Serenoa repens 224.5 36.1 33.4 54.1 1.7 Sorghastrum sec undum 0.1 Smilax rotundifolia 52.3 12.7 3.5 0.3 10.5 3.9 14.6 0.7 Solidago fistulosa 0.1 Sporobolus curtissii < 0.1 8.3 Vaccinium myrsinites 0.8 5.2 2.1 1.2 Vitis rotundifolia 43.2 < 0.1 146.5 < 0.1 Woodwardia virginica 0.8 Note: Species total within a treatment may not sum to the total Mn accumulation due to rounding error. differentiated. The notations C, F, FW, and W r epresent, respectively, the actively managed retreatment experiment that received control, fertilizer only, fertilizer + weed control, and weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the untrea ted carryover experiment that received control, fertilization only, fertilization + weed control, and weed control only treatments in the previous rotation

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161 Table C 1 2 Zinc accumulation ( g.ha 1 ) in the understory species in both the actively managed retr eated and untreated carryover experiments in north Florida. Species --Actively managed retreated ----Untreated carryover --C F FW W CC CF CFW CW Andropogon spp. 2.9 31.7 35.2 26.0 2.1 16.4 47.7 23.2 Carex spp 0.3 0.1 1.1 1.5 0.3 0.3 0.1 3.2 Chry sopsis graminifolia 2.7 Cyperus spp. 0.6 4.9 2.0 < 0.1 < 0.1 Dicanthelium spp. 5.8 5.6 3.3 15.7 6.2 0.3 7.1 14.7 Eleocharis baldwinii < 0.1 0.1 0.1 < 0.1 < 0.1 Erectites hierarcifolia < 0.1 0.2 Eupatorium capillifolium 2.3 E upatorium spp. 0.4 1.4 5.1 4.6 < 0.1 Gamochaeta purpurea 0.1 Gaylussacia dumosa 0.4 2.8 0.1 Gaylussacia frondosa < 0.1 Hypericum spp 0.8 0.3 0.2 5.0 2.0 2.4 < 0.1 Ilex glabra 152.7 884.5 114.2 529.6 Juncus spp < 0.1 0.1 Lachnanthes caroliniana < 0.1 0.3 3.2 2.1 0.3 Ludwigia decurrens < 0.1 Lyonia ferruginea < 0.1 0.1 0.2 < 0.1 Lyonia lucida 46.7 103.4 11.3 Panicum hemitomon 0.7 Myrica cerifera 7.7 Paspalum spp < 0.1 0.1 Persea borbonia 0.1 0.4 0.4 Persea palustris 2.2 Pteridium aquilinum < 0.1 < 0.1 0.2 Quercus nigra 0.6 1.5 0.3 0.4 2.5 0.9 Rhexia alifanus 1.9 Rhexia spp 0.3 Rhexia virginica < 0.1 Rhus copallina 13.1 11.8 5.1 Rubus spp 0.5 0.5 3.1 Scleria spp. 4.3 1.4 0.4 0.1 < 0.1 Serenoa repens 31.9 5.3 14.1 11.8 0.2 Sorghastrum secundum < 0.1 Smilax rotundifolia 6.5 3.5 0.4 < 0.1 1.5 0.9 1.1 0.1 Solidago fistulosa 0.1 Sporobolus curt issii < 0.1 8.5 Vaccinium myrsinites 0.3 1.6 1.2 1.3 Vitis rotundifolia 11.1 < 0.1 5.4 < 0.1 Woodwardia virginica 0.3 Note: Species total within a treatment may not sum to the total Zn accumulation due to rounding error. differentiated. The notations C, F, FW, and W represent, respectively, the actively managed retreatment experiment that received control, fertilizer only, fertilizer + wee d control, and weed control only treatments in both rotations. The notations C C C F C FW and C W respectively, represent the untreated carryover experiment that received control, fertilization only, fertilization + weed control, and weed control only trea tments in the previous rotation

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162 Table C 1 3 Macro and micro nutrient accumulation in the belowground biomass of Andropog on spp. for the untreated carryover experiment in north Florida. Treatments Root (kg.ha 1 ) b/a ratio (s.d.) -----------Macro nutri ents (kg.ha 1 ) ---------------Micro nutrients (g.ha 1 ) ---N P K Ca Mg S B Cu Mn Zn Fertilizer+weed control (C FW ) 864 0.28 (0.09) 4.4 0.3 1.5 0.3 0.2 0.4 2.9 1.8 8.7 14.4 Weed control only (C W ) 285 0.24 (0.03) 1.7 0.1 0.4 0.1 0.1 0.1 0.8 0.4 2.1 4.8 represents standard deviation.

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163 APPENDIX D SOIL NUTRIENT SUPPLY Table D 1 Soil nutrient supply rates (micrograms/10cm 2 /8weeks; 0 15 cm) for the actively managed retreatment experiment in north Florida. The actively managed retreatment experiment received control, fertilizer only, fertilizer + weed control, and weed control only treatments in the current and previous rotation. Soil nutrient supply rate 2 /8 weeks) Treatments N P K Ca Mg S B Cu Mn Zn Fe Control (C) 8.4 10.2 65.3 269.2 162.1 26.7 0.2 0.1 3.1 1.0 2.3 (10.7) (6.2) (22.6) (126.8) ( 81.9) (18.9) (<0.1) (<0.1) (2.4) (0.4) (0.8) b ab a b a b a b b b a Fertilizer only (F) 62.1 36.2 103.9 531.4 264.9 31.1 0.2 0.9 9.1 4.4 5.3 (41.6) (3.3) (56.0) (102.2) (28.7) (13.9) (0.1) (0.3) (3.9) (1.3) (3.6) ab a a ab a ab a a ab a a Fertilize r+Weed control (FW) 222.2 29.0 78.3 740.1 299.8 88.3 0.2 0.7 9.4 5.4 5.8 (167.6) (21.9) (22.8) (286.1) (121.6) (53.7) (0.1) (0.3) (3.0) (1.7) (2.4) a a a a a a a a a a a Weed control only (W) 9.6 4.1 74.3 270.4 173.9 25.0 0.1 0.1 3.2 1.1 3.2 (3.6) ( 1.4) (38.6) (84.1) (38.3) (8.5) (<0.1) (<0.1) (1.7) (0.5) (1.1) b b a b a b a b b b a Note: Supply rates are for eight weeks beginning in August 2011. Standard deviations are provided in parentheses. Within each nutrient, treatments followed by the same letter were not significantly different at alpha=0.1.

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164 Table D 2 Soil nutrient supply rates (micrograms/10cm 2 /8weeks; 15 cm) for the untreated carryover experiment in north Florida. The untreated carryover experiment received control, fertilizer only, fertilizer + weed control, and weed control only treatments in the previous rotation. Soil nutrient supply rate 2 /8 weeks) Treatments N P K Ca Mg S B Cu Mn Zn Fe Control (C C ) 6.2 8.9 67.5 351.8 180.0 22.0 0.2 0.1 3.1 1.0 3.2 (1.3) (5.1) (32 .7) (210.8) (104.3) (15.8) (<0.1) (<0.1) (1.9) (0.2) (2.5) a a a a a a a a a a a Fertilizer only (C F ) 3.3 20.8 75.1 440.7 218.6 23.4 0.2 0.4 11.3 3.8 2.2 (1.5) (4.9) (23.7) (64.9) (35.5) (6.4) (0.1) (0.3) (4.0) (0.6) (0.9) a b a a a a a a b b a Fer tilizer+Weed control (C FW ) 4.5 8.2 58.2 353.1 163.0 12.5 0.2 0.2 4.3 3.6 2.4 (1.9) (7.1) (34.5) (35.9) (2.9) (3.2) (0.1) (<0.1) (2.1) (1.3) (0.7) a a a a a a a a a b a Weed control only (C W ) 5.4 3.7 46.7 282.5 170.5 23.0 0.2 0.1 2.4 1.4 2.7 (4.7) (1 .2) (56.2) (239.9) (133.9) (12.1) (<0.1) (<0.1) (0.6) (0.4) (1.2) a a a a a a a a a a a Note: Supply rates are for eight weeks beginning in August 2011. Within each nutrient, treatments followed by the same letter t were not significantly different at a lpha=0.1. Standard deviations are provided in parentheses.

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165 LIST OF REFERENCES Adegbidi, H.G., Comerford, N.B., Jokela, E.J., Barros, N.F., 2004. Root development of young loblolly pine in spodosols in southeast Georgia. Soil Science Society of America Journal 68, 596 604. Adegbidi, H.G., Jokela, E.J., Comerford, N.B., 2005. Factors influencing production efficiency of intensively managed loblolly pine plantations in a 1 to 4 year old chronosequence. Forest Ecology and Management 218, 245 258. Adegbidi H.G., Jokela E.J., Comerford N.B., Barros N.F., 2002. Biomass development for intensively managed loblolly pine plantations growing on spodosols in the southeastern USA. Forest Ecology and Management 167, 91 102. Albaugh, T., Allen, H.L., Fox, T. R., C arlson, C.A., Rubilar, R.A., 2009. Opportunities for fertilization of loblolly Pine in the sandhills of the southeastern United States. Southern Journal of Applied Forestry 33, 129 136. Albaugh, T.J., Allen, H.L., Fox, T. R., 2007. Historical patterns of f orest fertilization in the southeastern United States from 1969 to 2004. Southern Journal of Applied Forestry 31, 129 137. Allen, H.L., 1987. Forest fertilizers: nutrient amendment, stand productivity, and environmental impact. Journal of Forestry 85, 37 4 6. Allen, H.L., Dougherty, P.M., Campbell, R.G., 1990. Manipulation of water and nutrients practice and opportunity in southern U.S. pine forests. Forest Ecology and Management 30, 437 453. Allen, H.L., Fox, T. R., Campbell, R.G., 2005. What is ahead for intensive pine plantation silviculture in the South? Southern Journal of Applied Forestry 29, 62 69. Ballard, R., 1978. Effect of first rotation phosphorus applications on fertilizer requirements of second rotation radiata pine. New Zealand Journal of For estry Science 8, 135 145. Baskerville, G.L., 1972. Use of logarithmic regression in the estimation of plant biomass. Canadian Journal of Forest Research 2, 49 53. Bengtson, G.W., 1979. Forest fertilization in the United States: progress and outlook. Journa l of Forestry 77, 222 229. Benoit, R., Starkey, R., 1968. Inhibition of decomposition of cellulose and some other carbohydrates by tannin. Soil Science 105, 291 296.

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185 BIOGRAPHICAL SKETCH Pr aveen Subedi was born in Pokhara, Nepal in 1986. After gra duating from high school he j oined the Institute of Forestry for his undergraduate degree in 2004 In 2009, he received a Bachelor of Science in forestry degree from the Institute of Forestry, Trib huvan University, Nepal. In 2010, he joined the School of Forest Resources and Conservation at the University of Florida to pursue his graduate study.