SPATIAL STRUCTURE AFFECTS LANDSCAPE ECOLOGY FUNCTION
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
I would like to dedicate this thesis to my parents, Don and Dianne Whitney, for their
never-ending support and encouragement since I was a child and throughout my
schooling, and for helping to create my love for nature through PBS and Wild Kingdom.
Sincere thanks are due to my advisor and committee chair, Dr. Larry Harris, for
inspiring me as an undergraduate and encouraging me to focus on being a scholar. Dr.
Doria Gordon, guided my research initiatives and provided valuable advice in all phases of
the fire ecology studies. Dr. Phil Hall assisted in my studies and research proposal for the
never-finished research at Camp Blanding Training Site (CBTS) near Keystone Heights,
Others influenced my work, most importantly, Kristina Jackson, a valuable friend
who caused me to meet Dr. Harris and subsequently study wildlife ecology and who also
helped me with the design, fieldwork and statistics of this research. Mr. Tom Hoctor
assisted me with many facets of this research, challenged my thinking of ecological issues
and helped me to improve as a scholar. Kelly McPherson deserves thanks for helping with
statistical aspects of the experimental design and with fieldwork. Thanks go to Dr. Jack
Putz and Dr. Katie Sieving for initial review of this work. Galin Jones of IFAS Statistics
provided invaluable support and advice in my statistical endeavors. Paul Catlett provided
assistance in my research efforts at CBTS. And, I would like to thank the biologists and
technicians from CBTS and (the former) Florida Game and Freshwater Fish Commission
who assisted in the one burn I was able to conduct there.
Last but not least, I would like to thank all the people who helped me in the field
(especially to those who volunteered): Marty Fleming, Larry Harris, Jr., Jerzy Kozlowski,
Mike McBurney, Jim Sadle, Branch Schimmenti, Rob Spitler, and Tom Workman.
TABLE OF CONTENTS
A C K N O W L E D G M E N T S .............................................................................................. iii
RELST OF TABLES ........................................... ..........................16
I NTR O D U C T IO N ................................................................................................. 18.........
Connectivity as a Form of Structure in the Landscape ................................................ 7
Experim mental M model System s ...................................................... 9
L ITER A TU R E C ITED TCH ............................................. ............................................. 35... 27
B IO G R A PH IC A L SK E T C H ......................................................................................... 35
LIST OF TABLES
1. Micro and meso-study bum results, broken down by fire type
(head vs. backing) .. ................................................................. ............. 17
2. Some synoptic factors that may influence the spread of fire through
c o rrid o rs.......................................................................................................... . .. 2 0
3. Examples of fuels (burnable and non-burnable) for each of the
study areas at C am p B landing ................................. ...................... .............. 24
4. Percent burnable cover for each transect in the eight Camp Blanding
stu d y site s ........................................................................................................ . . 2 5
LIST OF FIGURES
1. Controlled bum in a longleaf pine system. Resinous trees often
burn for days and continue to contribute to incipient fire long
after som e im m ediate areas have burned............................................ .............. 6
2. An experimental unit of the micro-scale study, pre-fire..... ............................... 12
3. One of the three meso-scale experimental units. Each meter of
linear distance was demarcated to calculate average rate of fire
spread .......................................................................... . . ..... 13
4. Conceptual design of a meso-scale experimental unit....................................... 14
5. M icro-scale reconnaissance bum study.............................................. .............. 14
6. Meso-scale bum experiment where a) fire is ignited in central patch
and b) spreads along the "spokes"............................. ................... .............. 15
7. Comparison of rates of fire spread for all fire types in the a)micro
and b) m eso-scale experim ents....... ...................... ..................... .............. 17
Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
for the Degree of Master of Science
SPATIAL STRUCTURE AFFECTS LANDSCAPE ECOLOGY FUNCTION
Chairman: Dr. Larry Harris
Major Department: Wildlife Ecology and Conservation
Landscape ecology is distinguished from other subdisciplines because it explicitly
addresses the importance of spatial structure and pattern as well as spatially explicit
environmental forces such as wind, fire and flood that move across the surface of the
earth. These forces lead to 'horizontal' processes that formerly occurred across
interconnected landscape subsystems and may well be essential to the ecological function
and integrity of regional ecological systems. Sheet-flow of water, for example, is
acknowledged as being critical to restoration and maintenance of south Florida's regional
seascape as well as landscape. Fragmentation of ecological systems and their 'horizontal'
functions, habitats, and/or populations of keystone species such as crop pollinators are all
recognized as critical components of the present biodiversity crisis on earth. The degree
to which restoration of formerly existing structural and/or functional connectivity can be
achieved may be critical to regional ecological processes.
Fire is increasingly recognized as a premier phenomenon that is an integral variable
in the maintenance of ecological integrity of many forested landscapes in the Southeastern
Coastal Plain. Two small-scale experiments assessed the hypothesis that width of fuel
connectors would differentially affect the rate and/or success of fire spreading across rural
north Florida pasturelands. The effects of the two different treatment variables 1) width
(of inter-patch connectors) and 2) orientation (of the connectors relative to ambient wind)
were not sufficient to emerge as important relative to more salient variables including fuel
moisture and humidity, solar position, ambient temperature and wind. Even though
intuitive, head fires were shown to move through the connectors significantly faster than
did backfires. In addition, the variance surrounding the means of the back fire movement
rates was very small. All things considered, the experiments established that structural
connectivity across otherwise open landscapes does have significant effects on the
behavior of prescribed fire, arguably the single most critical variable with respect to
vegetated landscapes in the lower Southeastern Coastal Plain of North America.
Understanding how to restore and maintain spatial ecological processes can be
considered the most important element of landscape ecology (Turner 1989, Harris et al.
1996). Landscape ecology describes the nature of ecological structure and processes as
they occur in two-dimensional space over large spatial scales. In other words, the
fundamental distinguishing factor between landscape ecology and broader ecological
theory is that the latter does not explicate the importance of space. Interactions of
ecological processes and spatial structure are the most important aspect of landscape
ecology (Ims 1999, Pickett and Cadenasso 1995). Understanding fundamental ecological
processes on the landscape may be critical for the maintenance of natural system integrity.
Wind, floodwater and fire that usually moves across the landscape are not only important
in sculpting the pattern of elements on the landscape, they are known to be critical to
long-term system function (Parsons 1981, Harris et al. 1996).
Wind is known to be important over space and time insofar as it spreads fire and
creates dune systems or aeolin landscapes. "Waves" (or gusts) of wind are very important
to the spread of fire in that they can push fires quickly over large areas (Komerek 1967).
The great bluffs along the Missouri River were created or "blown there" by elluviation
from the Rocky Mountains. Dune formations on the southwest coast of France are not
only sculpted by wind but are very actively covering forests on the back slopes (L.D.
Harris, pers. comm.).
Sheet flow used to be a critical landscape process in the structural and functional
aspects driving the Everglades regional system of southern Florida as well as other
hydrologic systems in the SECP, such as flooding of the Suwannee River. Research has
been conducted to demonstrate the influence of sheet flow of water on tree island shape in
the Northern Everglades (Brandt 1997). In the 19th century, Hamilton-Disston contracted
with the State of Florida to expressly prevent sheet flow by digging canals in favor of
rapid water delivery to the sea. As a follow-up to Hamilton-Disston, the U.S. Army
Corps of Engineers dredged a straight canal in the 1950's to subsume the highly
meandered Kissimmee River that connected the Orlando chain of lakes to Lake
Okeechobee. While the drainage facilities increased land available for cattle grazing, they
also terribly degraded water quality in Lake Okeechobee (McCally 1999). Regional scale
restoration projects, such as the restoration of rivers (Kissimmee, Ocklawaha) and water
flow in the Everglades, have proven to be highly debated public policy issues due to the
high monetary costs and intensive restructuring of the systems. Most ecologists, though,
believe that the need to restore and maintain spatial processes is increasingly important to
biodiversity conservation. Another example of the functional influences of floodwater can
be seen in the historical flooding of the SECP riverine systems. Low topographic relief,
causes any water-level rise to expand the water horizontally. This back-and-forth
movement across the floodplain [referred to as a "seasonably migratory ecotone"] is the
critical process responsible for the high productivity in the system (Harris et al. 1996).
Spatial and temporal scales are thus functionally interrelated by these large-scale physical
forces (Harris et al. 1996).
Fire as a Spatial Process
Fire is an important social, biological and political phenomenon in Florida. Fire
shaped the spatial structure of the composition and distribution of forest types in the
Southeastern Coastal Plain (Waldrop et al. 1992). Because fire is such a critical
ecological process in the SECP, it has played a major role in sculpting the distribution of
biota on the landscape. Thus, fire has long been significant to both cultural and natural
history in the Southeast. With respect to fragmentation effects on the once-dominant
longleaf pine system ecology, fire movement is arguably the single most important
Natural fire regimes (with variable timing, stochasticity, fuel loads, and spread)
that are now known to be so critical to the evolution and maintenance of biodiversity in
the Southeastern Coastal Plain (SECP) are consistently altered by anthropogenic
landscape fragmentation by human-built structures such as housing developments, roads
and canals. Therefore, unraveling the variables that influence or control the movement of
fire across landscapes is fundamental to forest management and planning. Physical
environmental factors such as wind, fuel load, fuel moisture and ambient temperature are
without question overriding variables of greatest influence on the nature of fire on the
landscape. But, ensconced within these variables the question of connectivity should also
There is a copious amount of literature published about fire and fire history (see
Frost 1993, Komerek 1963, 1967, Platt and Rathbun 1993), yet, few experiments have
been conducted on spatial aspects of fire movement. This experiment examined the effect
of spatial connectivity of patches as an initial step toward understanding inter-patch
dynamics on/in fragmented landscapes. Manipulations of fuel load and width served as a
proxy for connectivity and connectedness. Through these experimental factors (and
assumptions), an inter-patch process was tested. Given that many physical environmental
factors such as wind may exert greater influence on the rate of spread of fire than does
corridor width, there is a strong need for further research examining the effect of corridor
width on the nature of fire progression across the landscape.
An exceptionally high number of lightning strikes (in the region) were most likely
responsible for igniting many fires that could formerly propagate across an interconnected
landscape. Under such conditions even a single lightning strike could change the
ecological function from that of a local disturbance to one at a systems-level (Platt and
Rathbun 1993). As a consequence, biota most likely evolved in response to the frequency
and intensity of recurrent factors such as this (Komarek 1963, Pyne et al. 1996).
Wiregrass (Aristida beyrichiana and A. stricta, see Peet 1993 a,b) is a dominant
understory species that provides fine fuel load that facilitates fire spread throughout
sandhills in the Southeast (Platt et al. 1988, Noss 1989, Whitney unpubl. data). Longleaf
pine (Pinus palustris) also serves two critical functional roles in maintaining the
pine-grassland system on uplands of the lower SECP. Not only do the remarkably long
and resinous leaves complement the wiregrass as a fuel source (Platt and Rathbun 1993),
the longleaf pine actually promotes fire through its highly resinous trees and related bole
and branch structure (Landers 1991). Mature pines seem to serve as lightning receptors
as well as the pyrogenic basis of fire (incendiary litter), which, in turn precludes hardwood
invasion beneath the crowns and into the surrounding matrix (Mutch 1970, Williamson
and Black 1981, Platt et al. 1988, Landers 1991, Platt and Rathbun 1993) (Figure 1).
Landers (1991) suggested that the increased flammability among most species in
the genus Pinus was under selection as a homeorhetic process that strongly favors pines
on harsh sites as well as it is a mechanism for gaining dominance over otherwise
competitive species. Climatic periods with frequent lightning fire under moist conditions
likely selected for these and many other fire-dependent plant species with traits that tend
to increase the probability of fire (Abrahamson and Hartnett 1991, Landers 1991).
One of the first Spanish explorers to chronicle and describe the SECP, Cabeza de
Vaca (1528; cited in Hodge and Lewis 1907), wrote of the frequent "sprays" of lightning
strikes on pines as he traveled through Florida. Bartram (1792) [some 250 years later]
described the structural result; monospecific overstories of longleaf pine comprised of
widely spaced trees over a wide highly-diverse savanna (Landers 1991). Since European
colonization, logging, agriculture, and urbanization have degraded and replaced the pine-
grassland systems of the SECP. Less than 1.0% of the estimated original 92 million acres
now remain in good condition for this community type (Frost 1993). Loss of the area in
longleaf pine landscapes has been so widespread that virtually no old-growth stands
remain today. Those remaining stands are not sufficiently extensive to experience and/or
assimilate "natural" disturbance regimes. Invasion by fungi, rust, and hardwoods are now
common occurrences because there is no longer sufficiently healthy growth of wiregrass
and/or needle fall to facilitate the spread of fire (that controls competitors) and smoke that
both retards disease and facilitates seed germination. In addition, due to fire suppression
there is a build up of "heavy roughs" (accumulation of combustible fuels) that poses a
threat of wildfires (Wade and Lunsford 1989). Because so few experiments have been
conducted on fire movement, further experimentation that focuses on process conveyance
across a multitude of ecosystem/landscape types should follow this research. Thus, in the
eyes of Harris et al. (1996) [and many others] the challenge of conservation in the
Southeast is that of
restoring and maintaining a spatially integrated longleaf pine ecosystem that
can and will maintain the full suite of landscape ecological processes,
including fire (and smoke) that is ignited in one place but allowed to
disperse across the system; a system that .. can remain viable and resilient
because of its extensive nature; .. and a system that is interdigitated with
other community types that provide seasonally important services for the
longleaf pine community and vice versa. (Harris et al. 1996 p.341)
Figure 1: Controlled bum in a longleaf pine system. Resinous trees often bum for days
and continue to contribute to incipient fire long after some immediate areas have burned.
Connectivity as a Form of Structure in the Landscape
Connectivity is a fundamental feature of most natural landscapes (Merriam 1984,
Noss and Harris 1986, Forman and Godron 1986, Noss and Harris 1989). The role of
connectivity in reserve design resulting in creation of ecological networks is to help
restore naturally connected landscapes and assist in the maintenance of indigenous
ecological processes under which these landscapes evolved. Linkages that allow for
spatial and temporal interactions to occur at the level of the regional landscape may well
constitute a critical system attribute. The theoretical works of Preston (1962), MacArthur
and Wilson (1963, 1967) and Diamond (1975), coupled with considerable empirical
evidence (see Beier 1993, 1995, and Beier and Noss 1998) suggest that physically
connected patches of habitat on the landscape are one means to support and maintain a
greater richness of indigenous species and system integrity (Harris and Scheck 1991).
Many have articulated ideas leading to this hypothesis on how dispersal and source-sink
dynamics are recurrent processes in the landscape (Levin 1974, Roff 1974a, b, Roff 1975,
Levin 1976, Henderson et al. 1985, Pulliam 1988, Harris and Gallagher 1989).
To maintain biodiversity over long periods of time, natural landscape patterns of
heterogeneity and other emergent ecological processes must be recognized and addressed
at the level of regional ecological planning (Harris and Kangas 1979, Harris 1984, Noss
and Harris 1986, Noss 1987, Hansson and Angelstam 1991, Harris and Atkins 1991,
Harris and Scheck 1991). Essential to this type of planning is the recognition of
functionality of landscapes. This can be most easily maintained or restored by attaining
critical minimum levels of connectivity that facilitate horizontal ecological processes.
Functional landscape systems will, in turn, allow energy flow and other ecological
processes to propagate across multiple spatial scales and create critical levels of structural
heterogeneity such as edges and patches.
Both the benefits (Forman and Godron 1986, Noss 1987, Henein and Merriam
1990, Hobbs 1992) and costs (Simberloff and Cox 1987, Simberloff et al. 1992) of
corridors have been discussed in the scientific literature. Still, the consensus among
leading ecologists is that an overarching paradigm of spatial connectivity is a prominent
aspect of landscape structure and function.
Although the value of connectivity of the landscape seems to be recognized in both
the scientific and management communities, empirical data on the roles of corridors and/or
connectedness are limited (Baudry and Merriam 1988). Moreover, questions regarding
the spatial distribution, configuration, and physical aspects of corridor must be better
defined. Baudry and Merriam (1988) noted how connectivity is a parameter receiving
value from processes moving across landscape elements while connectedness is
demonstrated through structural landscape features. McDonnell and Stiles (1983) also
showed how the importance of processes may be revealed through structural elements
(i.e., its connectedness). For instance, several questions were posed regarding the
structural aspects of corridors as well as the length and shape of corridors (spatial
configuration) (McDonnell and Pickett 1988, Adams and Dove 1989, Nicholls and
Margules 1991, Noss 1993). Given the entire debate, the most pervasive and recurring
question pertains to corridor width: "How wide should a corridor be?" Some authors
have addressed this issue (Harris and Atkins 1991, Harris and Scheck 1991, Baur and
Baur 1992, Polla and Barrett 1993) and have therefore suggested that it depends on what
function it must serve (e.g., habitat, dispersal conduit for plants and/or animals, etc.; see
Noss (1993). The role of environmental corridors in facilitating seed dispersal and the
movement of animals and other phenomena such as disease has been reviewed in depth
(Beier and Noss 1998, Simberloff et al. 1992, Saunders and Hobbs 1991, Harris and
Gallagher 1989, Noss 1987, Forman and Godron 1986). But the role that corridors might
play in the movement of an ecological process such as fire has not been experimentally
addressed. A logical extension of this idea is that these processes are affected by the
nature, shape, and connectedness of the habitats in which they are conveyed.
Experimental Model Systems
Wiens et al. (1985) noted how "so few proper experimental designs have been
applied to probe the effects of patch boundary variables on ... the flow of matter between
landscape elements, especially in view of the perceived importance of such processes in
landscape ecology" (Ims 1999, p.46). On the other hand, it is indeed possible to construct
such experiments where aspects of a landscape-level process can be tested in experimental
landscapes designed at a fine (or "micro") scale (Ims 1999). In these experimental model
systems, demonstrated through the work of Ims and Stenseth (1989), Wiens et al. (1993),
and Bowers et al. (1996), landscape heterogeneity and landscape-level population
dynamics can be replicated and tested using experimental treatments at a small scale (Ims
Because of the difficulty of conducting larger-scale experiments, experimental
model systems (EMS) may be used to evaluate ecological responses to spatial
heterogeneity (Ims 1999, With 1997, Wiens 1989). These EMS consist of
"microlandscapes" where researchers can mimic spatial aspects at "micro" scales in the
hope of understanding broader-scale processes (With 1997). Scientists can then
extrapolate results from small-scale experiments to larger scale landscapes; especially with
the aid of spatially explicit modelling (O'Neill, 1979). For example, Wiens and Milne
(1989) conducted an experiment that used beetles to evaluate models based on percolation
theory to assess responses to various landscape configurations. These studies are most
relevant because they came close to isolating a single or a few ecological processes from
an otherwise "tangled bank" of confounding variables (With 1997). No ecologist doubts
the need to understand horizontal or spatial processes across both real and/or
"experimental" landscapes (With 1997, Rastetler et al. 1992, With and Crist 1996). Many
consider the functional role spatial processes have in the landscape to be the central issue
in ecology (Levin 1992, Harris et al. 1996). It is subsequently believed that conservation
of ecosystems and communities are destined to fail if component systems are isolated from
the processes that drive their function.
The purpose of this research was to investigate the role of inter-patch connectivity
and configuration on the movement of fire. It was hypothesized that configuration of
experimental "corridors" would affect inter-patch process conveyance. Specifically, I
tested this hypothesis by manipulating fuel load and configuration and examining the
resulting connectivity of fire between patches. In the larger view, fuel quality and
connectedness constitute an important control in the movement of fire across a landscape.
Each experiment consisted of a central patch where the fuel was ignited so that the
fire had equal opportunity to spread outward in a 360 pattern across the landscape. The
treatment variable consisted of replicated radiating "corridors" of two different widths.
Orientation of the different-width corridors helped to allay the effects of stochastic
variables such as wind direction and speed. The three treatments of varying width were
applied to the replicated units so that each experimental corridor would have an equal
chance of propagating fire outward to another patch.
The micro-scale experiment consisted of four experimental units, each unit
resembling a cross that consisted of a central pyre (radius = 5 m) and four radiating
"spoke-corridors" (length = 10 m). The corridor width treatment was 1 meter versus 2
meters. Within each replicate unit, the coupled linear treatments of width were randomly
oriented in either a north-south or east-west direction (Figure 2). These micro-scale units
were created on a mowed bahiagrass pasture converted from a sandhill community. Fuel
enhancement consisted of evenly distributed pine straw loaded at lkg/m2 (dry weight)
within the radiating corridors. The micro-scale prescribed fire was performed on
November 23, 1996 starting at 11:15 a.m. The day was clear and sunny, with maximum
air temperature of 23, and relative humidity of 28%. Winds were variable from the south,
ranging from 0-10 k.p.h.
Figure 2: An experimental unit of the micro-scale study, pre-fire.
The meso-scale experiment consisted of three experimental units of the same
configuration as the micro-scale experiment. The four 15 meter perpendicular spokes that
radiated out from a central pyre (radius = 10m). The corridor width treatments were 2
meters and 5 meters. Again, each replicate was located in north-south and east-west
directions and each width treatment was randomly oriented to each of the cardinal
directions within each unit (Figures 3 and 4). These units were established on a different
converted sandhill pasture in western Alachua Co., Florida. The experimental site
consisted of bare, previously burnt pasture and fuel load manipulation consisted of evenly
distributed pine straw at 1.5 kg/m2, similar to that used in rate of spread studies such as
McAlpine and Wakimoto (1991). The meso-scale study prescribed fire was performed on
March 12, 1997, starting at 12:30 p.m. The day was party cloudy and sunny, with
maximum air temperature of 27, and relative humidity was 36%. Winds were variable
from the northwest, ranging from 0-10 k.p.h.
In both the micro-scale and the meso-scale prescribed fire experiments, fire was
ignited in the center of the central pyre. Fire spread and radiated out to each of the
treatment spokes. Time for the fire to reach each of meter intervals was recorded so the
rate of fire spread and means could be calculated (Figure 5, Figure 6). To avoid aspects
of autocorrelation because cumulative time was recorded per meter for the meso study,
slopes and intercepts from the linear regressions were used to test for effects. In the linear
regression, time and distance were analyzed. Both the intercepts and slopes of these lines
were regarded as the response variables in the appropriate ANOVA model with individual
tests for plot, plot width, and interaction between orientation and width within a plot. The
analysis was performed as a randomized block design, with replicates as the block effect
(includes variation in land condition, terrain, weather, time, etc.) and path width as the
principal treatment. A probability of 0.05 was used for all ANOVA analyses to demarcate
statistical significance in the results.
Figure 3: One of the three meso-scale experimental units. Each meter of linear distance
was demarcated to calculate average rate of fire spread.
Patch of fire
cn gnat c~
Figure 4: Conceptual design of a meso-scale experimental unit.
Figure 5: Micro-scale reconnaissance bum study.
Figure 6: Meso-scale bum experiment where a) fire is ignited in central patch and b)
spreads along the "spokes".
Effects of wind (orientation) were evident in the outcomes of both "micro" and
"meso" experiments. Most apparent in the study were significant effects of orientation of
the "corridors"; not surprising since wind direction (and/or speed) helps or hinders the
spread of fire along a given path. Wind can hinder the spread of fire when airflow
direction is opposite to the direction of fire spread. There was high correlation between
time and distance for each "spoke/corridor" within experimental units. Significant
differences emerged from the ANOVA for the slopes of the regression lines (P = 0.04, F =
5.15, df= 1); but not the intercepts for orientation of treatments (P = 0.94, F = 0.0, df= 1,
respectively) in the micro-scale study. No significant difference was found for width (P =
0.77, F = 0.08, df = 1 and P = 0.21, F = 1.74, df = 1, respectively) nor was there any
significant interaction effect between orientation and width (P = 0.85, F = 0.04, df = 1, P =
0.51, F = 0.45, df= 1, respectively).
Significant differences were evident between the regression slopes for orientation
for orientation of treatments (P = 0.003, F = 17.58, df = 1); but not the intercepts (P =
0.61, F = 0.28, df= 1) in the meso-scale experiment. The analysis of the width treatments
did not show significant differences for the slopes or intercepts (P = 0.12, F = 2.88, df= 1,
and P = 0.74, F = 0.12, df= 1, respectively). Nor, was there a statistically significant
interaction between orientation of the treatments and treatment width (P = 0.26, F = 1.44,
df = 1, and P = 0.82, F = 0.05, df= 1, respectively).
Differences in the width treatments were most evident through the
comparison of rates. For both micro and meso studies, there was a trend towards
greater rate of spread in the wider width treatments, independent of orientation on
the treatments, although these results did not show a strong enough effect to be
statistically significant (Table 1, Figure 7).
Table 1: Micro and meso-study burn results, broken down by fire type (head vs.
Average rate (m/s) for orientation (head vs. back) head fires back fires
Micro-scale 0.09 0.05
Meso-scale 0.20 0.08
F f ,re types In te, a-mire
a) -e experiments.
I -iT.OhN batk -re
Figure 7. Comparison of rates of fire spread for all fire types in the a)micro and b) meso-
Corridor width, or the physical configuration of the patch-to-patch connectors, did
not significantly influence fire spread in these experiments at the scale conducted. The
only variable that played a significant role in the spread of fire was fire type as influenced
by orientation of the "corridors." This result was predicted because it seems to be
intuitive that wind would be sufficiently strong as to favor or hinder the spread of fire
along a given path. Wind has been previously demonstrated to be an influential factor in
many studies (Smith and Gilbert 1974, Rothermel 1983, McAlpine and Wakimoto 1991).
Wind speed and direction are strong forces that influence the intensity and rate of spread
of fire, and are some of the most important factors to consider when prescribing a fire or
preparing to contain or suppress a wildfire (Rothermel 1983).
Rates of spread and measures of intensity are often used to quantify behavior of
wildland fires (Pyne et al. 1996, Johnson and Miyanishi 1995). This information allows
managers to predict potential fire behavior and design methods and/or guidelines in which
to suppress wildfires. It is not uncommon that fire spreads most rapidly in the direction of
local wind. Head fires such as these are predicted to achieve an elongated shape as they
move faster (Pyne et al. 1996). Although the fires exhibited through this experiment were
not large enough to be typical of an average fire with respect to behavior, the trend
towards a width effect in my experiments were opposite to general trends where greater
width means a lower rate of spread (Rothermel 1972, Rothermel 1983, Johnson 1992).
Granted, under natural conditions (i.e., experiments conducted within existing forest and
having a scale of larger magnitude) the behavior of fire within a forest would surely exhibit
this response. However, for smaller fire through delineated areas or open spaces, it is not
clear what type of response would most commonly be evident.
There are various synoptic factors that would influence fire movement through a
corridor (Table 2) and would need to be assessed for determining potential spread. These
factors are important both in prescribed fire and in fire suppression efforts.
Based upon the meso-scale experiment head fires, there appears to be some type of
wind effect evident. Although there were no statistically significant differences between
the corridor width treatments, there were practical differences evident in the comparison
of the mean rates of spread. Differences in mean rates of spread (most evident in the
meso-study head fires), showed a trend towards a width effect. This was similar to what
was expected from this experiment. The wider "corridors" did have a showed a trend
towards a greater rate of spread from patch to patch, although it was not significant at the
p = 0.05 level. However, in the presence of gusty winds (when wind speed shifted from 3
to 10 k.p.h) blowing flames over the fuel, it seems that virtually no width variance at the
small scale used would matter, and the much wider corridor widths would be necessary to
demonstrate this effect. Almost unexpectedly, but certainly logically, the width effect
revealed itself in almost every single fire that was aided by wind (head fires) along each
Table 2: Some synoptic factors that may influence the spread of fire through corridors.
Factors Relevance to Fire Spread
Time Effects from ambient temperatures and humidity (hours) to
physical/chemical aspects of fuel load (decades) to slope or
topographic features (centuries) (Johnson 1992).
Wind speed and direction Local temperature differences and/or differences in terrain
can have a great influence in wind from gentle breezes to
persistent winds (Pyne et al. 1996).
Frequency of Bum Relates to fire intensity and duff (partially decomposed
organic horizon beneath litter) consumption; composition of
vegetation, etc. (Johnson and Miyanishi 1995).
Fuel type Forest type (coniferous, closed/open canopy, deciduous, open
grasses, etc. (Taylor et al. 1997) influences fire intensity.
Fuel moisture Dead fuels versus live fuels exhibit major differences in
combustion and spread and intensity and rate of spread
Landscape character Influences the severity of fire, exhibited by ground versus
Source patch sizes and crown type fires, erosional losses, and effects on ecosystem
ecological edge function (Agee 1998).
Recent literature has discussed width factors in corridors for a multitude of
functions (Price and Gilpin 1996, Wiens 1996, Farina 1998). Dramstad et al. (1996) have
noted that "width and connectivity are the primary controls on the five major functions of
corridors (i.e., habitat, conduit, filter, source, sink)." Specific parameters of corridor
width have mostly addressed riparian or riverine corridors (Dramstad et al. 1996),
although some specifications of width have been suggested for mammalian underpasses in
southern Florida (Smith 1993). Although the overall purpose of these corridors is to
retain or maintain ecological function, the specifications are mostly qualitative (such as
number order in streams or variable widths of buffer zones). Because functional
connectivity is a vital element of landscape studies (Taylor et al. 1993, Clergeau and Burel
1997), is it of utmost importance to continue research efforts on quantifying physical,
structural and ecological aspects of interpatch connections in landscapes.
In spite of the fact that the experiment was designed to mitigate stochastic forces
at different scales, a larger scale study would have likely revealed significant width effects
(see Appendix). The scale of the two studies reviewed in this paper was small enough for
environmental variables to have a strong influence on fire behavior. Fire behavior
literature most often documents interior forest and/or wild fires, therefore stochastic
forces affecting forest fires are somewhat buffered in comparison. These forces and
variables, such as wind direction and speed, sun position and relative humidity, had a
moderate to strong effect on the consumption of the fuel and respective rates of fire
spread along a given path in this research. This was most evident in the comparison of
mean time to reach the end patches and mean rates of spread for the 2 meter "corridors" in
the micro-scale and meso-scale experiments. In the micro-study, which was conducted in
November, the mean time to reach the end point of 10 meters was nearly twice the time to
reach 15 meters in the meso-scale study (which was conducted in March). Although
initial conditions of the experimental units were identical (with slight changes in terms of
dry weight of the fuel), these differences demonstrate the importance of relative fuel
moisture and ambient conditions.
Recent discussions regarding fire regimes that have been altered due to
fragmentation and how landscape function may or may not have been altered imply that
fragmentation is important, or at least it is a testable hypothesis. Environmental corridors
are one means of maintaining and/or restoring physical connectivity in an otherwise
fragmented landscape. Surely, if fragmentation and/or inter-patch connectivity were truly
important to landscape-level ecological function, wouldn't their effects be manifested on
arguably the most significant ecological factor of the SECP? It is also quite possible that
physical connectivity on the landscape does not necessarily mean ecological connectedness
or vice-versa. The results certainly confirm that two concepts, physical connectivity and
ecological connectedness, are causally related to mechanisms such as structure (e.g.,
corridor width) and ecological function (e.g., wind driven vs. wind-suppressed fires). To
help test these hypotheses, landscape ecologists need to consider experimentation as a
necessary approach (Ims 1999). This research constituted an initial attempt to gain
empirical evidence regarding corridors as a conduit of energy. Though the results did not
directly demonstrate implications for corridor design or fire management strategies, one
can develop further hypotheses based on this research.
MACRO-SCALE BURN EXPERIMENT
The entire experimental aspect of this thesis research was predicated upon three
spatial scales of field studies, micro-, meso- and macro-. During the summer of 1997,
eight experimental plots were constructed at Camp Blanding Training Site, near Keystone
Heights, Florida. The plots were located in two types of longleaf pine forest patches,
sandhill habitat (four plots) and flatwoods habitat (four plots). Both of these system types
evolved with frequent fire regimes (see Introduction) and contained wiregrass. The basis
of this large (or macro-) scale experiment was that there might be "real-world"
implications based on plot size. In other words, it may be more realistic or understandable
for land managers to extrapolate data from fire behavior evident at a macro-scale designed
The design of this macro-study was similar to the first two experiments discussed
in the thesis, only larger. In the plot's center was a large 250 m2 area that would have
been the "central pyre". And, similar to the other bum studies, the plot was designed like
a cross with north-south and east-west aspects. These crossing aspects (previously
described as "corridors" or "connectors") were either 10 meters wide or 50 meters wide
and were 100 meters in length.
For each of the plots, the vegetative cover was sampled to give a relative estimate
of the percent burnable cover or connectivity of fuel for a low-intensity fire. A linear
transect was located through the center of each plot at ten meter increments. For each
ten-meter length, the percent burnable vegetation was recorded. Fuel types were classified
as either burnable (i.e., wiregrass, longleaf pine litter, 1/10/100 hour fuels (pine
cones/twigs/down logs), turkey oak leaves, etc.) to non-burnable (i.e., herbs, turkey oaks,
saw palmetto, sand, lichen, etc.) (Table 3). Percent burnable cover ranged from 30 to
100% demonstrating instances where the fuels were discontinuous (Table 4). In general,
the fuels were mosaic or patchy in nature having mostly continuous fuels but including
small areas where fuel connectivity was low. Averages of the fuel continuity for all
transects ranged from 85% to 96%. Although the fuels were highly connected, this
macro-study would have examined whether inter-patch fires would have burned to their
respective completion points (although it was quite likely that they would).
Table 3. Examples of fuels (burnable and non-burnable) for each of the study areas
at Camp Blanding.
Woodbury Wolf Branch Magnolia Lake
Longleaf pine litter wiregrass wiregrass
Turkey oak leaves Longleaf pine litter Turkey oak leaves
saw palmetto herbaceous (Vaccinium herbaceous (Asimina
sp., Asimina sp.) sp., Pterocaulon sp.)
1/10/100 hour fuels saw palmetto lichen (Cladonia spp.)
(cones, twigs, logs)
wiregrass 1/10/100 hour fuels Longleaf pine litter
(cones, twigs, logs)
lichen (mostly Cladonia spp.) gopher apple sand
sand oak saplings
herbaceous (Vacinium sp., gopher apple
Ilex sp., Pterocaulon sp.)
Longleaf pine seedlings 1/10/100 hour
fuels(cones, twigs, logs)
Table 4. Percent burnable cover for each transect in the six Camp Blanding study
There were physical and chemical methods to delineate the experimental plots
from the forest matrix. The physical method of separation involved raking no less than
two feet away from the "corridor" edge and clearing the vegetation (i.e., removing down
trees or cutting parts of saw palmetto) that crossed the line. The chemical method
involved the application of the fire repellent gel called Barricade (Fire Protection, Inc.
Woodbury Wolf Branch Magnolia Lake
100 90 100 85 95 100 70 85
80 100 95 70 100 75 100 30
75 95 100 90 90 80 80 75
95 80 95 100 100 95 90 90
95 85 100 100 90 90 100 95
85 100 100 90 100 95 95 85
90 75 100 65 100 90 95 90
95 95 95 70 100 95 90 95
100 100 80 85 100 100 80 100
95 95 95 95 100 60 95 85
90 95 95 80 100 100 95 90
70 80 95 100 60 70 100 100
One of the eight experimental bums was nearly completed at Camp Blanding in
March 1998. It was necessary to terminate the burn due to time limitations (the bum was
not finished by nightfall). The average cumulative times to reach 75 meters were 4.23
hours (head fires) and 7.76 hours (back fires). Again, one can note that the back fires
took nearly double the time to complete the same distance. In addition, the average rates
of head versus back fires were 0.005 and 0.003 meters/second, respectively. There was
not enough data collected to make any statistical inferences regarding width or orientation
of the corridors. And, if I had an inkling of the upcoming multiple-year fire bans, I would
have used the two smaller scale studies as base input data for a fire model that replicated
the macro-scale study.
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Karen Angela Whitney was born in Miami, Florida. She arrived in Gainesville in
the summer of 1988 when she began her undergraduate career. After starting her
undergraduate education in psychology, she met Dr. Larry Harris, who would become her
graduate chair. Since that time, Karen has pursued her scholastic endeavors in wildlife,
landscape ecology and conservation biology. Karen was involved in many aspects of the
wildlife department, from being an undergraduate representative of the Wildlife
Department and member of student council to being president of the student chapter of
The Wildlife Society.
After graduating, Karen moved to the state of Washington for a year to pursue
higher education, but due to funding limitations, she was unable to start her graduate
career there. Thanks to the Florida Greenways Program and Professor Peggy Carr, Karen
was able to return to the University of Florida to more deeply examine landscape
ecological theory and experimentation. This allowed her to experience more of Dr.
Harris' tutelage, learn the "ins and outs" of ecological modeling using geographic
information systems (GIS), and play with fire! Although experiencing many hardships
throughout her graduate career, from the death of her father to the multiple years of fire
bans, Karen was finally able to analyze and bring her data together in a cohesive state.
She now endeavors to combine work in ecological modeling and landscape analysis with
natural resource management.