to my dad in docs/recent research/2015_03_… · to my dad . 4 acknowledgments first, i would like...

FERAL HOG (SUS SCROFA) DISTURBANCE IN SEEPAGE SLOPE WETLANDS

By

MEGAN E. BROWN

A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL

OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

2014

To my Dad

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ACKNOWLEDGMENTS

First, I would like to thank my parents, Larry Brown and Patricia Maddox, who early on

fostered my interest in the natural world and have always encouraged me to pursue my

education. I owe much of my accomplishments to their love and support.

I would like to express my sincere gratitude towards those who helped me throughout my

doctoral experience. Mark Brown gave me the opportunity to be a part of the Adaptive

Management of Water, Wetlands, and Watershed IGERT group. My advisor, Debbie Miller, has

been great mentor and friend over the past six years. My growth as a scientist has benefited from

her experience and guidance. The other members of my committee, Carrie Reinhardt Adams,

Doria Gordon, Kevin Heirs, and Wiley Kitchens have been instrumental in providing wisdom,

inspiration, and encouragement along the way. A big thank you to Tyler Barry, Sean Claypool,

Gina Duke, Hanna Hunsberger, and Allix North for spending many long, hot, humid days in the

field, trudging through snake-infested woods and wetlands, lugging a meter square that never

stayed together, and collecting hundreds of plant specimens....all in the name of data collection. I

also give much thanks to Brett Williams with Jackson Guard at Eglin AFB and John Allen with

the USDA APHIS Wildlife Services for their support of this project. I started this doctoral

journey with seven other amazing women and I am thankful for having had the opportunity to

create such wonderful friendships.

Finally, I am grateful for the tireless support of my husband, Joshua Hornbarger, who

uprooted his life to move with me to Gator Country. I also am eternally grateful for my daughter,

Odelia (3), who provides me with more joy than I ever knew possible. I hope to instill in her an

admiration of the natural world so that she too can know and experience its beauty.

This project was funded in part by a NSF IGERT fellowship, a USDA NIFA pre-doctoral

fellowship, a McKnight Dissertation Fellowship, a Society of Wetland Scientists Student Grant,

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the Doris Lowe and Earl and Verna Lowe Scholarship (UF), and the William C. and Bertha M.

Cornett Fellowship (UF).

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TABLE OF CONTENTS

page

ACKNOWLEDGMENTS ...............................................................................................................4

LIST OF TABLES ...........................................................................................................................8

LIST OF FIGURES .........................................................................................................................9

ABSTRACT ...................................................................................................................................12

CHAPTER

1 INTRODUCTION ..................................................................................................................14

Background .............................................................................................................................14

Research Goals .......................................................................................................................15

2 INDIRECT EFFECTS OF FERAL HOG DISTURBANCE ON FIRE SPREAD .................16

Background .............................................................................................................................16 Methods ..................................................................................................................................18

Study Area .......................................................................................................................18

Data Collection ................................................................................................................20 Data Analyses ..................................................................................................................20

Results.....................................................................................................................................21

Discussion ...............................................................................................................................22

Summary .................................................................................................................................23

3 LONG-TERM MONITORING OF FERAL HOG DISTURBANCE IN SEEPAGE

SLOPES ..................................................................................................................................26

Background .............................................................................................................................26

Methods ..................................................................................................................................27 Study Area .......................................................................................................................27 Data Collection ................................................................................................................29 Data Analyses ..................................................................................................................31

Results.....................................................................................................................................32

Discussion ...............................................................................................................................35

Summary .................................................................................................................................41

4 EFFECTS OF INTENSITY OF FERAL HOG DISUTRBANCE ON VEGETATION

DYNAMICS ...........................................................................................................................49

Background .............................................................................................................................49 Methods ..................................................................................................................................51

Study Area .......................................................................................................................51

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Data Collection ................................................................................................................52

Data Analyses ..................................................................................................................54 Results.....................................................................................................................................55

Foliar Cover .....................................................................................................................55

Richness ...........................................................................................................................57 Camera Detection of Hog Activity ..................................................................................57 Vegetation Composition ..................................................................................................57

Discussion ...............................................................................................................................58 Summary .................................................................................................................................63

5 EFFECTS OF EXPERIMENTAL SOIL DISTURBANCE ON VEGETATION

DYNAMICS ...........................................................................................................................72

Background .............................................................................................................................72

Methods ..................................................................................................................................74 Study Area .......................................................................................................................74 Data Collection ................................................................................................................75

Data Analyses ..................................................................................................................76 Results.....................................................................................................................................77

Foliar Cover .....................................................................................................................77 Camera Detected Hog Frequency ....................................................................................80 Richness ...........................................................................................................................80

Vegetation Composition ..................................................................................................81 Discussion ...............................................................................................................................82

Summary .................................................................................................................................85

6 CONCLUSIONS ....................................................................................................................98

LIST OF REFERENCES ...............................................................................................................99

BIOGRAPHICAL SKETCH .......................................................................................................113

8

LIST OF TABLES

Table page

3-1 Repeated measures ANOVA results for the percentage of hog disturbed plots over

time by zone on Eglin AFB from 2002 to 2012.................................................................43

3-2 Repeated measures ANOVA results for the percentage of hog disturbed plots over

time by hunting access on Eglin AFB from 2002 to 2012. ................................................43

3-3 The number of hogs removed from Eglin AFB from October 1 of the previous year

to September 30 of that calendar year. The percentage of hog disturbed plots and

rainfall totals are also indicated. ........................................................................................43

3-4 Repeated measures ANOVA results for the cover of total vegetation, functional

groups, and A. stricta by zone and access on Eglin AFB in 2002, 2010, and 2012. .........44

4-1 ANOVA results for the foliar cover of total vegetation, functional groups, and A.

stricta and species richness by disturbance intensity and exclosure on Eglin AFB. .........64

5-1 Repeated measures ANOVA results for the foliar cover of total vegetation,

functional groups, A. stricta, Dichanthelium spp., Sarracenia spp., and species

richness by disturbance frequency on Eglin AFB..............................................................86

5-2 Repeated measures ANOVA results for the foliar cover of total vegetation,

functional groups, A. stricta, Dichanthelium spp., and Sarracenia spp., and species

richness by disturbance frequency on Eglin AFB with controls........................................87

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LIST OF FIGURES

Figure page

2-1 The location of seepage slope sites on Eglin AFB. ...........................................................25

2-2 Topographic relationship between seepage slope, upland pine, and baygall

communities including position of zones on seepage slopes. ............................................25




3-3 Percent hog-disturbed plots from 2002 to 2012. Analysis included both UF and Eglin

AFB data. ...........................................................................................................................46

3-4 Total foliar cover by year. ..................................................................................................46

3-5 Foliar cover of functional groups and A. stricta by zone (i.e., position on slope). ............47

3-6 Foliar cover of woody species through time. .....................................................................47

3-7 Foliar cover of Aristida stricta through time. ....................................................................48




4-3 Exclosure and open plot pairs. ...........................................................................................66

4-4 The location of seepage slope sites with motion detecting wildlife cameras. ...................66

4-5 Total foliar cover by intensity by year inside and outside exclosures on Eglin AFB. .......67

4-6 Total foliar cover by exclosure by year on Eglin AFB. .....................................................67

4-7 Foliar cover of woody species by intensity by year inside and outside exclosures on

Eglin AFB. .........................................................................................................................68

4-8 Foliar cover of graminoid species by intensity by year inside and outside exclosures

on Eglin AFB. ....................................................................................................................68

4-9 Foliar cover of graminoid species by exclosure by year on Eglin AFB. ...........................69

4-10 Average number of hog occurrences per month in seepage slopes with cameras on

Eglin AFB from June 2010 through December 2013. .......................................................69

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4-11 Two-dimensional nonmetric multidimensional scaling ordination showing cover by

species in high disturbance intensity and control plots on Eglin AFB. .............................70

4-12 Three-dimensional nonmetric multidimensional ordination showing cover by species

in high disturbance and control plots on Eglin AFB in A) 2010 and B) 2012. .................71




5-3 Total foliar cover by disturbance treatment over time on Eglin AFB. ..............................89

5-4 Foliar cover of forbs by disturbance treatment over time on Eglin AFB. .........................90

5-5 Foliar cover of grasses by disturbance treatment over time on Eglin AFB. ......................91

5-6 Foliar cover of woody species by disturbance treatment over time on Eglin AFB. ..........92

5-7 Foliar cover of A. stricta by disturbance treatment over time on Eglin AFB. ...................93

5-8 Foliar cover of Dichanthelium spp. by disturbance treatment over time on Eglin

AFB. ...................................................................................................................................94

5-9 Foliar cover of Sarracenia spp. by disturbance treatment over time on Eglin AFB. ........95

5-10 Species richness by disturbance treatment over time on Eglin AFB. ................................96

5-11 Three-dimensional nonmetric multidimensional ordination showing cover by species

by disturbance treatment on Eglin AFB in June 2010 and Sept 2013.. .............................97

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LIST OF ABBREVIATIONS

ANOVA

EGLIN AFB

Analysis of Variance

Eglin Air Force Base

MRPP Multi-response permutation procedure

NMS Nonmetric multidimensional scaling

UF University of Florida

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Abstract of Dissertation Presented to the Graduate School

of the University of Florida in Partial Fulfillment of the

Requirements for the Degree of Doctor of Philosophy

FERAL HOG (SUS SCROFA) DISTURBANCE IN SEEPAGE SLOPE WETLANDS

By

Megan E. Brown

May 2014

Chair: Debbie Miller

Major: Interdisciplinary Ecology

Florida is home to one of North America's most unique and diverse natural ecosystems,

the seepage slope wetland. Unusual hydrology and frequent fires have resulted in a habitat that

supports a variety of insectivorous and other endemic, helophytic herbaceous plants. Feral hog

(Sus scrofa) foraging has resulted in widespread soil disturbances in seepage slope wetlands in

the Florida Panhandle. It is proposed that feral hog rooting is a serious threat to this community

because rooting sets back succession, causes changes in species composition and plant

population structure, reduces unique species, and inhibits fire spread. These potential changes in

the seepage slope plant community are particularly important because these wetlands provide

increasingly rare habitat for several threatened and endangered plant species.

We conducted plant surveys to investigate both the long and short-term vegetation

dynamics in response to hog disturbance. We demonstrate that hog disturbance has not declined

since the USDA APHIS Wildlife Services began trapping hogs on Eglin AFB in 2003 and

theorize rainfall and other potential drivers of hog disturbance. The short-term exclosure studies

provide evidence that the intensity and frequency of disturbance alter vegetation composition

even when foliar cover is partially or fully regained. These results also indicate that Aristida

stricta cover is reduced by soil disturbance, while woody cover is maintained. A positive

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feedback is likely to result with reduced grass cover and fire spread, which further contributes to

increased woody cover. In addition, we used GPS collected data to compare areas damaged by

hogs and areas burned during prescribed fires to quantify the indirect effects of hog rooting on

ecosystem function. We found that hog rooting reduced vegetation cover and decreased fire

spread. Through this work, we gain insight to the mechanisms that affect the rate and trajectory

of vegetation development in this plant community, with significance for both theoretical and

management purposes.

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CHAPTER 1

INTRODUCTION

Background

Seepage slope wetlands and bogs of the southeastern United States are of critical

conservation concern due to their high levels of species richness and endemism (Johnson 2001).

Unusual hydrology, oligotrophic conditions, and frequent fires have resulted in a habitat that

supports a variety of carnivorous and other heliophytic, herbaceous plants. The southeastern

coastal plain contains the highest number of carnivorous plant species in North America

(Hermann 1995). Only one percent of seepage slopes that originally existed along the Gulf

Coastal Plain still remain (FNAI 1990). These wetland features have been degraded by

encroachment of woody species in the absence of fire, conversion into ponds, or drainage. As a

result, remnant seepage slopes communities provide increasingly critical but diminishing habitat

for threatened and endangered plant and amphibian species (FNAI 1990; Hermann 1995).

The Spanish explorer, Hernando de Soto, introduced domestic hogs (Sus scrofa) in the

16th Century, (Mayer & Brisbin 1991), and they are now established in 35 states and Canadian

provinces (Giuliano 2009). Feral hogs pose a serious threat to seepage slopes (FNAI 2010)

because they overturn soil when foraging (Howe & Bratton 1976). This behavior creates

hummocks and tussocks that alter edaphic properties (Singer et al. 1984; Jensen 1985) and

hydrology (Arrington et al. 1999), accelerates decomposition, alters soil nutrient concentrations

(Singer et al. 1984; Wirthner et al. 2012; Krull et al. 2013), and facilitates soil erosion (Bratton

1975; Howe & Bratton 1976).

In addition to these changes in edaphic conditions, the mechanical disturbance of hog

foraging deracinates vegetation (Engeman et al. 2007), reduces vegetation cover (Bratton 1974,

1975; Engeman et al. 2007; Siemann et al. 2009; Wirthner et al. 2012), and impacts regeneration

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(Lipscomb 1989; Sweitzer & Van Vuren 2002; Siemann et al. 2009). Hog rooting can result in

reduced species diversity (Bratton 1975; Kotanen 1995; Tierney & Cushman 2006; Siemann et

al. 2009) and altered species composition (Bratton 1974; Aplet et al. 1991; Siemann et al. 2009;

Cuevas et al. 2010). These changes in species composition are due to both direct species

removal, as well as indirect effects on the ecosystem processes including the disruption of the

fine fuel component that facilitates fire spread. Vegetation may (Arrington et al. 1999; Tierney &

Cushman 2006) or may not be able to recover from rooting disturbances (Bratton 1975). Hog

rooting and foraging could lead to the extirpation of species (Bratton 1974; Recher & Clark

1974; Challies 1975; Spatz & Mueller-Dombois 1975). Deleterious impact from extensive,

repetitive rooting of native plants is documented as a critical threat to the conservation of

pitcherplant wetland communities in Florida (Johnson 2001).

Research Goals

It is important to understand how disturbances affect natural communities for both

theoretical and management purposes. This research explored how feral hog disturbance affects

the rate and trajectory of vegetation development in seepage slopes of the Florida Panhandle in

four interrelated studies. Chapter 2 quantifies the effect of this novel disturbance on the historic

fire regime. Chapter 3 investigates vegetation dynamics in seepage slopes over a 10-year period.

Chapter 4 evaluates vegetation development in exclosures erected in areas of varying disturbance

intensity. Chapter 5 assesses the role of frequency of disturbance and time since last disturbance

in determining vegetation composition and species richness. This research will provide better

understanding of: 1) long-term patterns of vegetation dynamics; and 2) mechanisms driving

shifts in plant composition in response to feral hog disturbance. The results of this work can be

used with continued monitoring data to direct management actions to prevent degradation of

seepage slopes on Eglin AFB.

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CHAPTER 2

INDIRECT EFFECTS OF FERAL HOG DISTURBANCE ON FIRE SPREAD

Background

Ecosystems adapted to disturbance by fire are distributed all over the globe (Drewa et al.

2002; Bond & Keeley 2005). These systems include northern latitude boreal forests, lower

latitude shrublands, grasslands, and savannas and eucalyptus woodlands in Australia. Different

fire regimes have selected for and resulted in different plant attributes and adaptations.

Worldwide these fire-maintained systems have different biota, but recent decades of fire

suppression in these systems all demonstrate: 1) risks associated with increasing fuel

accumulation (Bond & Keeley 2005); 2) a loss of fire-dependent species (Frost et al. 1986;

Hermann 1995; Frost 2000; Lett & Knapp 2003; Glitzenstein et al. 2003; Bond & Keeley 2005;

FNAI 2010); and 3) management challenges in establishing habitat needs (e.g., determining fire

return intervals, season of burn, and use of fire surrogates) (Slapcinsky et al. 2010). These threats

and challenges are especially significant in Florida where 70% of the terrestrial ecosystems are

fire-dependent or adapted (FNAI 1990).

Seepage slopes, shrub bogs, and baygalls are wetlands that occur downslope from Pinus

palustris Mill. (Longleaf pine)-upland communities. These communities have a successional

relationship dependent on fire frequency. Frequent fire upslope from shrub bogs and baygalls

maintain the herbaceous component of the seepage slope (Eleuterius & Jones 1969; FNAI 2010).

Fire return intervals are estimated to have been one to three years historically in the surrounding

uplands (Frost 1995; Frost 2000; Frost 2006), while somewhat longer in wet seepage slopes

(FNAI 2010). Further downslope, shrub bogs are estimated to have longer burn return intervals

of 20 to 50 years (Wharton et al. 1976). In the absence of fire, shrub bogs replace the herbaceous

wet prairie species and eventually, these shrub bogs succeed to baygalls dominated by hardwood

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species (Means & Moler 1979). While fire is a disturbance in the classical sense, it is essential to

the stability of the seepage slope community (Frost et al. 1986).

Beginning in the 1920's, suppression of wildfires became public policy in the

southeastern United States. Realizing the importance of fire in the maintenance of natural

communities, land managers now use prescribed fire to mimic natural, lightning-ignited fire.

Most prescribed fire is applied in the dormant season rather than the summer growing season

(Knapp et al. 2009).

Alteration of natural fire regimes can lead to degradation of the remaining seepage slopes

(FNAI 2010). Historically, lightning ignited fires during the spring or the beginning of the

growing season (Olson 1992). This seasonal timing of spring drought and lightning-producing

thunderstorms generated upland fires that would carry down into seepage slopes (Olson & Platt

1995). It is well documented that fire suppression and, in some cases, dormant season prescribed

fires have allowed the encroachment of woody species (Frost et al. 1986; Frost 1995;

Glitzenstein et al. 1995; Olson & Platt 1995; Drewa et al. 2002; Slocum et al. 2003) and loss of

herbaceous species in seepage slopes (Eleuterius & Jones 1969; Folkerts 1982; Frost et al. 1986;

Hermann 1995).

Fire is influenced by multiple factors including fuel conditions, weather and wind

conditions (Cheney et al. 1993; Turner et al. 1994; Brooks et al. 2004), and topography (Weber

1990; Turner et al. 1994; Brooks et al. 2004). This chapter focuses primarily on the relationship

between fuel continuity and fire spread. The horizontal continuity of fuels can determine the

extent of fire spread (Brooks et al. 2004; Nader et al. 2007). For example, wider gap distance

between fuel beds can result in decreased flame contact and thus decreased spread (Weber 1990;

Finney et al. 2010). Modeling has shown that fuel gaps are more likely to inhibit fire spread

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when fuels are heterogeneous (Kerby et al. 2007), like fuels of bunch-grass systems (Finney et

al. 2010) such as the P. palustris (Longleaf pine) / Aristida stricta Michx. (Wiregrass) ecosystem

of the Southeastern United States.

Herbivores can alter a fire regime by ingesting vegetation that is critical for fire spread

(Savage & Swetnam 1990; McNaughton 1992; Knapp et al. 1999; Waldram et al. 2008; Hierro et

al. 2011). Feral hog foraging that results in uprooted vegetation (Bratton 1974; Engeman 2007)

and increased cover of bare ground (Bratton 1975; Kotanen 1995; Engeman 2007; Doupé et al.

2010) effectively reduces the load and continuity of fine fuels. This reduction of fine fuels can

potentially: 1) reduce the extent of fire spread (Harrington & Hodgkinson 1986; McNaughton

1992; Knapp et al. 1999; Kerby et al. 2007; Waldram et al. 2008); and 2) alter the frequency

(Savage & Swetnam 1990; Van Auken 2000; Hierro et al. 2011) and intensity of future fires

(Hobbs et al. 1991; Van Langevelde et al. 2003; Briggs et al. 2005; Kerby et al. 2007; Hierro et

al. 2011). This chapter investigates the indirect effects of hog rooting on ecosystem function. We

sought to determine whether soil disturbances associated with feral hog foraging reduce fire

spread in seepage slopes on Eglin AFB.

Methods

Study Area

Sites for this study were located on Eglin AFB in Walton County in the western Florida

Panhandle (30°29′22″N 086°32′32″W) (Figure 2-1). This area has a mean annual precipitation of

158cm (DoD-Air Force 1995). Precipitation tends to peak in the summer months and is lowest in

May and October. Lightning producing thunderstorms are common in the spring and summer

months (NOAA 2002). Suppression of wildfires and limited use of prescribed fire resulted in

infrequent fire in seepage slopes on Eglin AFB until about 2002. Subsequently, Eglin land

19

managers increased the burning frequency to annual and biennial prescribed fires in both the

growing and dormant seasons (pers. comm. 2014 Eglin AFB land manager).

The soils on the eastern portion of EAFB are loamy sands. Creeks have created rolling

erosional hills with relief of up to about 30 meters (NRCS 1989). The mesic, upland pine

community (FNAI 1990) found on these loamy sands is speckled with wet prairies on hillsides

called seepage slopes (Figure 2-2). These seepage slopes result from groundwater seeping

downslope above an impermeable layer of clay that intersects the hillside. A unique variety of

herbaceous vegetation can be found in seepage slopes including carnivorous plants like

Sarracenia spp. (Pitcherplants), Drosera spp. (Sundews), Pinguicula spp. (Butterworts), and

Utricularia spp. (Bladderworts). Upslope, in the drier portions, characteristic species include

Aristida stricta, Ctenium aromaticum (Walter) A. Wood (Toothachegrass), and Rhexia spp.

(Meadowbeauties), while downslope the longer hydroperiod accommodates Eriocaulon spp.

(Pipeworts), Lophiola aurea Ker Gawl. (Golden Crest), Pleea tenuifolia Michx. (Rush

Featherling), Rhynchospora spp. (Beaksedges), and Xyris spp. (Yelloweyed Grasses). These

wetlands are dependent on ground water and dry out in times of drought. It is during dry spells

that seepage slopes are able to carry fire. Frequent fire is necessary to prevent shrubs, like

Cliftonia monophylla (Lam.) Sarg (Black Titi), from invading from the shrub bogs and baygalls

along the seepage creek and shading out helophytic herbaceous species. Other scattered shrubs

that are common in seepage slopes include Gaylussacia mosieri Small (Woolly huckleberry) and

Hypericum spp. (St. John's-wort) (FNAI 2010).

The baygalls located at the base of the slope are saturated, peat-filled seepage depressions

that support a dense forest of evergreen hardwoods. This forest is dominated by Magnolia

virginiana L. (Sweetbay), Persea palustris (Raf.) Sarg. (Swamp bay), and Gordonia lasianthus

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(L.) J. Ellis (Loblolly bay). Sphagnum spp. (Sphagnum moss) can form mats on the ground

(FNAI 1990). A mature canopy of these fire-intolerant hardwoods indicates the lack of

destructive fire for many years (Clewell 1986). These areas may burn catastrophically in times of

drought (FNAI 2010).

Data Collection

Research questions 1 and 2. Did fire carry through a greater percentage of seepage

slope area with or without hog disturbance? Did hog disturbed areas burn? Prescribed burns were

used to examine the effect of hog disturbance and fuel continuity on the extent of fire spread. We

analyzed fire spread at 21 seepage slopes, some burned more than once (n=37), on Eglin AFB in

2010, 2012, and 2013. Areas where hog foraging resulted in discontinuous fuels were captured

as polygons using a handheld Trimble GPS. These sites, ranging in size from 2,549m2 to

16,316m2, were then burned by fire crews for management purposes, as instructed by Jackson

Guard. After each burn was extinguished, any areas of seepage slope vegetation not consumed in

the fire were captured as polygons using the Trimble GPS.

Research question 3. Was total foliar cover prior to burning greater in plots that carried

fire compared to those that did not? Burn histories for 38 control exclosure plots (no recent hog

disturbance) used in the intensity experiment and 61 experimental disturbance treatment plots

used in the frequency experiment (Chapters 4 & 5) were also examined to determine if prior to

burning unburned plots had less foliar cover than burned plots. Total foliar cover prior to the

burn was recorded at sites burned between 2010 and 2013. Plots were categorized as burned or

unburned after prescribed fires.

Data Analyses


slope area with or without hog disturbance? Did hog disturbed areas burn? ArcGIS 9.2 software

21

(ESRI 2009) was used to determine if there was a difference in: 1) the percentage of hog

disturbed seepage slope that burned and the percentage of undisturbed seepage slope that burned;

and 2) the percentage of hog-disturbed area that burned and did not burn. Areas of hog

disturbance, areas left unburned after the fire, and total seepage slope areas were calculated. The

analysis tool "Union" was used to compute the geometric intersection of the three input layers.

From this output layer, the percentage of the hog disturbed seepage slope that did and did not

burn and the percentage of undisturbed seepage slope that did and did not burn was calculated.

Student’s t-tests (PROC TTEST; SAS 9.3; SAS Institute 2011) was used to reveal any

differences in these percentages.


fire compared to those that did not? Total cover from plots used in the intensity and frequency

experiments at sites that burned was also analyzed using a Student’s t-test (PROC TTEST; SAS

9.3; SAS Institute 2011) to discern any difference in total foliar cover prior to burning in burned

and unburned plots.

Results


slope area with or without hog disturbance? Did hog disturbed areas burn? Soil disturbance

caused by hog rooting is associated with reduced fire spread. Prescribed fires burned

significantly more area in undisturbed portions (75.80%) than hog-disturbed portions (21.04%)

of the slopes (t<0.0001). Also, significantly more hog disturbed area was unburned than burned

after prescribed fire (t<0.0001). This study found that 77.32% of hog disturbed portions of

seepage slopes remained unburned after prescribed burns.


fire compared to those that did not? Pre-burn total foliar cover was significantly lower in plots

22

that did not burn than plots that burned (t<0.0001). Prior to the burn, average total foliar cover of

burned plots was 71.31%, while unburned plots averaged 39.15% cover. This indicates that there

is a threshold between approximately 40% and 70% total foliar cover below which fire spread is

reduced.

Discussion

The literature lacks research concerning indirect effects of introduced herbivores on

ecosystem processes (Stritar et al. 2010), whereas most studies quantify the effects of native

herbivores on fire regime in African ecosystems (Van Langevelde et al. 2003; Waldram et al.

2008; Holdo et al. 2009). As we hypothesized, vegetation in areas of hog disturbance remains

unburned and is associated with reduced fire spread in seepage slopes. Non-indigenous hog

foraging exposes bare ground (Bratton 1975; Kotanen 1995; Engeman 2007; Doupé et al. 2010)

and reduces fine fuel loads, ultimately reducing fire spread. This research indicates that this

novel disturbance affects ecosystem processes in this wet prairie community.

We categorized hog disturbance with less than 40% total foliar cover as high intensity

hog disturbance in Chapter 3. After three years of recovery, areas of high intensity hog

disturbance failed to have average total foliar cover of 70% or greater. This study found that

there is a threshold of between 40% and 70% total cover, below which fire is likely not to spread.

It can be interpreted from these data that areas of high intensity hog disturbance are less likely to

carry fire. Future research may be necessary to investigate the extent of high intensity hog

disturbance in seepage slopes to quantify the degree of this fuel reduction problem.

Reduced fire spread has significant implications for the physiognomy of the seepage

slope. In the absence of fire, the longleaf pine ecosystem experiences increased hardwood

density and decreased herbaceous cover and diversity (Frost et al. 1986; Hermann, 1995; Frost

2000; Lett & Knapp 2003; Glitzenstein et al. 2003; Bond & Keeley 2005; FNAI 2010). As a

23

result, most indicator species groups for bogs and wet savannas (i.e., forbs, sedges, insectivorous

plants) are extremely sensitive to reductions in fire frequency (Glitzenstein et al. 2003). Woody

plants may set up positive feedback that facilitate further woody invasion (Schlesinger et al.

1990; Callaway & Davis 1998), making restoring herbaceous dominance in shrub-encroached

areas unlikely even with the reestablishment of the historic fire regime (Archer 1989; Lett &

Knapp 2003; Briggs et al. 2005).

Losses of this community due to changes in physiognomy in the past have not been well

documented. Like other wet prairies of the southeastern United States that occur on seasonally

saturated soils, seepage slopes can be spatially narrow. Much of the acreage of this wet

community is limited to narrow areas that are less than 50 meters wide between the pyrogenic

upland savanna and deep wetlands. Wet prairies, including seepage slopes, also share a

considerable number of species with the adjacent communities. For these reasons, many authors

have regarded wet prairies as ecotones rather than distinct communities. Thus, losses in this

community due to woody encroachment and other anthropogenic activities have been overlooked

by conservationists (Clewell et al. 2009).

We acknowledge that fire behavior is dynamic by nature, influenced by fuel conditions,

weather or climate, and wind conditions (Cheney et al. 1993; Turner et al. 1994; Brooks et al.

2004) and topography (Weber 1990; Turner et al. 1994; Brooks et al. 2004). While we did not

control for environmental conditions, we found that fuel continuity is a major predictor of fire

spread in seepage slopes.

Summary

Feral hog foraging creates a complex network of novel ecosystem linkages and feedbacks

that have both direct and indirect effects on the biological and physical components of the

ecosystem. Yet, research on indirect effects of this exotic species on community structure and

24

ecosystem function is limited (Barrios & Ballari 2012). Our research indicates that feral hogs

alter fuel continuity in the landscape, indirectly altering the fire regime, and potentially resulting

in changes in community structure. Implications of this finding necessitate management plans to

remove hogs to lower densities or eradicate when possible in an attempt to reduce impacts and

preserve community structure. Further investigations, involving both direct and indirect effects

of feral hog disturbance, should involve a whole-ecosystem approach (Barrios & Ballari 2012).

25

Figure 2-1. The location of seepage slope sites on Eglin AFB.

Figure 2-2. Topographic relationship between seepage slope, upland pine, and baygall

communities including position of zones on seepage slopes.

26

CHAPTER 3

LONG-TERM MONITORING OF FERAL HOG DISTURBANCE IN SEEPAGE SLOPES

Background

Management options to address feral hog damage are limited, with trapping/hunting used

as the primary means to address the threat to natural ecosystems. The effectiveness of hog

removal at reducing hog densities and density-dependent damage is mixed. A study in 2007

assessed the effect of three years of hog trapping on hog disturbance in seepage slopes on Eglin

AFB in northwest Florida. The findings suggest that removal of hogs from the reservation has

dramatically reduced the extent of hog disturbance in seepage slopes (Engeman et al. 2007). In

contrast, recent research shows compensatory reproduction and immigration to increase in

response to hog removal utilizing traps and ground shooting (Hanson et al. 2009; Sparklin et al.

2009). Thus these common management techniques may see limited success in reducing hog

densities due to a density-dependent increase in recruitment (likely immigration) that can exceed

removal rates (Hanson et al. 2009). Hogs also have a high reproductive capacity (Dzieciolowski

et al. 1992; Choquenot et al. 1996; Taylor et al. 1998). Models indicate that pre-removal

densities can be reached in a short period of time if removal techniques do not remove a high

proportion of the population (i.e., greater than 70% instantaneous kill) (Dzieciolowski et al.

1992). Another concern is that trapping success is reduced when hogs become "trap shy" after

previous experience with traps (Saunders et al. 1993; Richardson et al. 1997). Populations of

hogs can rebound after the initial reduction. This failure to reduce hog numbers can then

correspond to failure to reduce hog disturbance (Hone 1995; Sweitzer 1998; Hone 2002;

Sweitzer & Van Vuren 2002).

Monitoring data can be used by managers to determine: 1) if a system is departing from

the desired state; 2) the success of management actions; and 3) the effects of disturbances (Legg

27

& Nagy 2006). At Eglin AFB, seepage slope monitoring was initiated in 2003 to evaluate the

extent of hog disturbance and the success of hog trapping at reducing that extent (Engeman et al.

2007). As with most monitoring programs, there were no true control sites, as half the sites were

trapped and half the sites were sport-hunted. This design can preclude conclusive results. The

observed change in hog disturbance after hog trapping began in seepage slopes on Eglin AFB

was attributed to the trapping (Engeman et al. 2007). Yet change is inherent in all ecosystems, so

the observed change may be unrelated to the management action (Legg & Nagy 2006) (i.e., hog

trapping). Without repeated and contemporaneous sampling before and after the initiation of the

management action at control and treatment sites, causality can only be inferred when a plausible

mechanism is identified and reasonable alternative mechanisms are investigated and rejected

(Schroeter et al. 1993). Also, monitoring data involving hog population dynamics should be

analyzed over a long-term time scale because hog populations can experience great interannual

fluctuation in relation to food availability (Peine & Farmer 1990; Brisbin & Sturek 2009).

The objectives of Chapter 3 are to investigate the long-term fluctuations in extent of hog

disturbance and corresponding floristic changes in seepage slopes on Eglin AFB. We analyze

environmental factors and hog removal data that may affect variability in interannual patterns of

hog disturbance. Finally, we explore the spatial patterns of hog damage within the complex

hydrological gradient within seepage slope wetlands and assess implications of damage across

that gradient.

Methods

Study Area

This research was conducted on Eglin AFB in the western Florida Panhandle

(30°29′22″N 086°32′32″W) where the mean annual temperature is 18.3oC and mean annual

precipitation is 158cm (DoD-Air Force 1995). Precipitation is greatest in the summer months

28

(NOAA 2002). Eglin AFB is a 187,548 ha reservation that represents the largest remnant of

Pinus palustris Mill. (longleaf pine) ecosystems (Compton et al. 2006; Mitchell et al. 2009). A

variety of birds and mammals, including feral hogs, can be hunted for sport on 105,218 ha of

Eglin AFB during hunting season, from mid-October until mid-February (United States Air

Force 2002). Sites were located on the eastern portion of Eglin AFB where soils are of the

Citronelle Formation, the loamy sand remains of a Pliocene-Pleistocene age delta plain. The

gently rolling erosional hills have relief of up to about 30 meters and areas of steeper slope along

creeks (NRCS 1989). The clay component in these sandy soils creates more mesic conditions

than the similar, nearby xeric P. palustris sandhills. These mesic longleaf pine woodlands are

classified as Upland Pine Forest (FNAI 1990).

Embedded in the upland pine community are seepage slopes. Seepage slopes are wet

prairies located on hillsides (Folkerts 1982). Soil saturation is sustained by the downslope

seepage of groundwater above a relatively impermeable layer of clay, organic matter, or rock.

The impermeable layer prohibits groundwater penetration and results in seeps along the hillsides

of dendritic systems of streams. The characteristic dense and diverse herbaceous vegetation

includes Rhynchospora spp. (Beaksedges), Aristida stricta Michx. (Wiregrass), Ctenium

aromaticum (Walter) A.W. Wood (Toothachegrass), Dichanthelium spp. (Witchgrasses), Xyris

spp. (Yelloweyed Grasses), Rhexia spp. (Meadowbeauties), Eriocaulon spp. (Pipeworts), and

Lycopodiella spp. (Club Mosses) (FNAI 2010). Carnivorous plants, including Sarracenia spp.

(Pitcherplants), Drosera spp. (Sundews), Pinguicula spp. (Butterworts), and Utricularia spp.

(Bladderworts), have evolved the ability to trap insects in order to acquire nutrients in these

anaerobic and acidic conditions that limit nutrient availability (Schnell 1976). Frequent fire

within the seepage slope maintains shrubs at a reduced height. In the absence of frequent fire,

29

Cliftonia monophylla (Lam.) Sarg. (Black Titi) and other shrubs invade upslope from the shrub

bogs or baygalls found along the seepage creek (Figure 3-1) and outcompete the heliophytic,

herbaceous vegetation. These wetlands dry out in times of drought due to their dependence on

groundwater (FNAI 2010).

Data Collection

Research questions 1 and 2. Has the extent of hog damage and its effect on foliar cover

changed from 2002-2012? Are hogs preferentially disturbing a particular zone of the slope? In

2002, 222 permanent plots were established at 24 randomly chosen, independent seepage slope

sites on Eglin AFB by UF (Figure 3-2). Half of these 24 sites were located in areas open to sport

hunting and half of the sites were located in areas closed to sport hunting. Each seepage slope

site was stratified by position on slope into three zones (i.e., lower, middle, upper) based on the

approximate distance from the seepage creek. Zonation represented a moisture gradient and was

delineated to account for differences in soil moisture and direct sunlight. Generally the lower

zone near the creek was equivalent to the toe-slope, the mid zone was equivalent to the foot-

slope and the upper zone, furthest upslope, was equivalent to the mid-slope (Figure 3-1). The

lower zone was characterized by saturated, organic mud and seeping water. The middle zone,

although not present at every site due to size and topographic differences, had saturated organic

sands, but was drier than the lower zone. The upper zone consisted of sandy soils with low soil

moisture and organic content. The upper boundary of the slope was delineated by dry, sandy soil

and the dominance of upland species including a canopy of pine trees. Depending on the size of

the slope, up to five 1m2 permanent plots were randomly placed in each zone within each slope.

In the summer of 2002, 2010, and 2012, each permanent plot was characterized as

disturbed or undisturbed, depending on whether hog disturbance was present. A modified

Daubenmire scale was used to estimate cover of total vegetation, forbs, grasses, and woody

30

vegetation. The modified Daubenmire scale (0= 0%, 0.5-5 = 3%, 5-10 = 8%, 10-15 = 13%, 15-

25 = 21%, 25-50 = 38%, 50-75 = 68%, 75-95 = 88%, 95-100 = 98%) reflects the precision of

ocular estimation of foliar cover that can be expected with multiple observers and allows for data

comparison (Daubenmire 1959). Although there can be between-observer error, this study used

pairs of observers and observers trained by the same person in attempt to reduce observational

error to the greatest extent possible (Vittoz & Guisan 2007). Foliar cover of the keystone species

A. stricta was also estimated because it dominates the undisturbed upland pine system and

carries fire through dryer portions of the seepage slope (Noss 1989; Outcalt et al. 1999).

Land managers at Eglin AFB monitored additional seepage slopes, intermingled with

those established by UF. Both groups monitored ten of the same slopes. For the internal Eglin

monitoring project, twenty randomly selected, 1m2 plots were permanently marked with rebar at

each of 28 randomly chosen seepage slope sites on Eglin AFB in 2003. The sites were located

half in areas open to hog hunting and half in areas closed to hog hunting. Cover of hog

disturbance was estimated during surveys in 2003, 2004, 2005, 2007, and 2011. By 2010, seven

sites were excluded because access had become restricted. Data from the remaining 21 sites was

used for this study, bringing the total number of sites for the study to 34. Plots at the 21 Eglin

sites were also surveyed in 2010 by UF researchers.

Research question 3. Does hog removal or do environmental variables account for

changes in hog disturbance? The USDA APHIS Wildlife Services began removing hogs on Eglin

AFB in 2003. Hog removal primarily involved trapping with pen traps for euthanization, with

some control hunting (not sport hunting). Hog removal was conducted in areas closed to sport

hunting from 2003 to 2005 (Engeman et al. 2007). In more recent years, hog removal has been

extended to include areas open to sport hunting. The rainfall on Range C52N, approximately 4

31

kilometers north of the seepage slope sites, and number of hogs removed by trapping each year

were recorded by Eglin AFB The occurrence of prescribed burns in seepage slopes evaluated by

UF and Eglin AFB were also documented by Eglin AFB.

Data Analyses

Research questions 1 and 2. Has the extent of hog damage and its effect on foliar cover

changed from 2002-2012? Are hogs preferentially disturbing a particular zone of the slope? This

study consisted of a completely randomized design with repeated measures. Each seepage slope

site represented a replicate within which there were three fixed zones along a topographic

gradient. Main effects were zone (lower, middle, and upper), year (2002, 2010, and 2012), and

hunting access (open or closed). Significance of main effects and interactions were evaluated

using a repeated measures one-way ANOVA (α = 0.10) in a generalized linear mixed model

(GLIMMIX; SAS 9.3; SAS Institute 2011). Dependent variables were total foliar cover, forb

cover, grass cover, woody vegetation cover, A. stricta cover, and percent hog-disturbed plots.

Seepage slope sites were considered a random effect. Data was square root transformed to meet

assumptions of normality. Analysis of Eglin AFB data from 2003-2005 was previously published

by Engeman et al. (2007). Because the additional plots established by Eglin AFB were not

stratified by zones, analysis of Eglin AFB plots evaluated main effects of year (2007, 2010, and

2011) and hunting access (open or closed) on percent hog disturbed plots. Tukey–Kramer tests

were used for post hoc comparisons (α = 0.05) to analyze differences between means (Zar 2010).

Research question 3. Does hog removal or do environmental variables account for

changes in hog disturbance? Correlations and a multiple regression were used to determine

relationship between precipitation, hog removal, vegetation variables, and percent hog-disturbed

plots. UF and Eglin AFB data were combined for all Pearson correlations. The first correlation

was run (CORR; SAS 9.3; SAS Institute 2011) to detect correlation between percent of hog-

32

disturbed plots and number of hogs removed annually by trapping efforts. In addition, Pearson

correlation analyzed the relationship between total vegetation cover and: 1) rainfall during the

previous 11 months; and 2) time since last burn. Pearson correlation was then used to analyze the

relationship between percent of disturbed plots and total rainfall. The rainfall totals were from

the following time periods: 1) the 11 months prior to vegetation surveys; 2) Jan-May of each

vegetation survey year; 3) March-June of the year prior to vegetation surveys; and 4) August

through November of the year prior to vegetation surveys. Rainfall totals from the previous

spring (March-June) and fall (August-November) were investigated because hog breeding peaks

in the spring and fall in Florida (Giuliano 2009). Pearson correlation was used to evaluate the

relationship between number of hogs removed annually and rainfall totals in the previous spring

and fall. Pearson correlation was also used to identify correlation between time since burn and:

1) percent cover hog damage; 2) woody species cover; and 3) A. stricta cover. A multiple

regression was used to determine the relative importance of independent variables (including

percent hog-disturbed plots, time since burn, and rainfall totals from the previous August-

November) in determining total vegetation cover.

Results

Has the extent of hog damage and its effect on foliar cover changed from 2002-2012?

No clear long-term pattern in the percentage of plots disturbed by hogs was observed (Figure 3-

3). For UF study slopes, there was no difference (p=0.6474) in the percent disturbed between

2002 and 2010 (Table 3-1). However, there was a decline in disturbed plots in 2012. As a result,

there was a significant difference in the percent disturbed from 2002 to 2012 (p=0.0387) and

2010 to 2012 (p=0.0034). There were significantly more hog-disturbed plots in areas open to hog

hunting (p=0.0222) compared to areas closed to hog hunting (Table 3-2). Although not stratified

by slope position, plots established and monitored by Eglin AFB showed an increase in the

33

percent disturbed from 2007 to 2010 (p<0.0001) and from 2007 to 2011 (p<0.0001) (Table 3-1).

Percent disturbed did not differ between 2010 and 2011 (p=0.7938), nor did it differ between

areas open and closed to hog hunting (p=0.6195).

For the most part, total vegetation cover reflected intensity and frequency of feral hog

damage and recovery rate. There was a significant interaction of year with zone (Table 3-4). For

UF slopes, vegetation cover declined from 2002 to 2012, but not in all zones (Figure 3-4). There

was significantly less total cover in the upper zone in 2010 (p=0.0020) and 2012 (p=0.0044)

compared to 2002. There was, however, no difference by year in lower or middle zones. In 2002,

total vegetation cover was significantly less in the lower zone than the upper zone (p=0.0443),

but indistinguishable from the middle zone (p=1.00). The total cover in the three zones did not

differ significantly in 2010 or 2012. There was no difference in total vegetation cover at sites in

areas open and closed to sport hunting (Table 3-2).

The mean cover of functional groups and A. stricta varied depending on zone and was

consistent across years (Figure 3-5; Table 3-4). Forb cover in the upper zone was significantly

less than cover in the lower zone (p=0.0006) and the middle zone (p=0.0002). Grass cover was

significantly less in the lower zone than the middle (p<0.0001) or upper zone (p<0.0001). The

same relationship was observed for A. stricta, with less cover in the lower zone than the middle

(p<0.0001) and upper zones (p<0.0001). In contrast, woody species cover was highest in the

lower zone and differed significantly (p=0.0010) from that of the middle zone. Woody cover in

the upper zone was also greater than the middle zone, although this difference was marginally

insignificant (p=0.0621).

Only cover of woody species and A. stricta differed during the ten years of this study.

Cover of forbs and grasses did not change significantly through time or by sport hunting access

34

(Table 3-4). Woody species cover increased significantly from 2002 to 2012 (p=0.0567) (Figure

3-6). A. stricta cover decreased significantly from 2002 to 2012 (p=0.0310) (Figure 3-7).

Are hogs preferentially disturbing a particular zone of the slope? Feral hog

disturbance was more extensive in the lower, wetter zone of seepage slopes. The percentage

disturbed differed significantly among the three zones (Table 3-1) and consistently across years.

Significantly more plots in the lower zone (50.92%) were disturbed when compared to the

middle (11.02%; p<0.0001) and upper zones (5.07%; p<0.0001). The percentage disturbed in the

middle and upper zones did not differ (p=0.1971).

Does hog removal or do environmental variables account for changes in hog

disturbance? When data from UF and Eglin AFB were combined, there was no correlation

between percentage of plots disturbed by hogs and number of hogs removed annually

(R2=0.0008; p=0.9111) or with the number of hogs removed the previous year (R2=0.0004;

p=0.8149) (Table 3-3). Total vegetation cover at sites, including those monitored by Eglin

managers, was found to have a weak, but significant negative correlation (R2=-0.0558;

p=0.0004) with total rainfall from the previous 11 months. Total vegetation was weakly

correlated (R2=0.0473; p=0.0034) to time since burn. The relationship between the percent of

hog-disturbed plots and total rainfall varied for the four time periods that were investigated.

There was no correlation (R2=0.0061; p=0.2501) between the percent of hog-disturbed plots and

total rainfall from the previous 11 months, from July through May of the sampling year (Table 3-

3). Similarly, there was no relationship (R2=0.0036; p=0.3816) between the percent disturbed

and total rainfall during the five months prior to sampling, January through May. The percentage

of hog-disturbed plots also had no relationship (R2=0.0007; p=0.6951) with total rainfall from

March to June of the previous year, around the time of spring breeding. There was however, a

35

significant relationship (R2=0.0364; p=0.0047) observed with total rainfall from August through

November of the previous year, around the time of fall breeding. The number of hogs removed

was not correlated (R2=0.0335; p=0.9498) with rainfall during this fall time period. The number

of hogs removed from Eglin AFB annually was more strongly correlated (R2=0.7865; p=0.0635)

to rainfall during the previous March through June. Percent cover of hog damage in plots

monitored by Eglin AFB showed no significant relationship with time since burn (R2=0.0043;

p=0.4316). The foliar cover of woody species also had a significant positive relationship

(R2=0.1484; p<0.0001) with time since burn. A. stricta cover was not related (R2=0.0081;

p=0.2530) to time since burn. The multiple regression revealed percent hog-disturbed plots had

the most significant influence (p=0.0003) on total vegetation cover followed by rainfall totals

from the previous fall months (p=0.0054) and time since burn (p=0.0208).

Discussion

Has the extent of hog damage and its effect on foliar cover changed from 2002-2012?

This chapter offers insight concerning hog disturbance and vegetation dynamics in seepage

slopes on Eglin AFB. There was fluctuation in the percentage of disturbed plots over this ten-

year period. Engeman et al. (2007) attributed the steady decline in hog disturbance from 2003 to

2005 to hog trapping. However, our data indicates hog disturbance was lower in 2002 and

increased the year hog trapping was initiated. In fact since hog trapping began, there were

periods of increased hog disturbance. Engeman et al. (2007) also indicated that there was more

hog disturbance in areas closed to hog hunting. On the contrary, our results indicate a higher

percentage of hog-disturbed plots in areas open to hunting. This discrepancy may be due to

difference in methods and/or sampling plots between the UF and internal Eglin monitoring

efforts. Our results do however indicate that more extensive monitoring is necessary to draw

conclusions on the effects of hog trapping on hog disturbance.

36

There is potential for hog disturbance to facilitate an increase in woody vegetation cover.

There was an increase in woody cover in the lower and upper zones where shrubs can encroach

from the bordering baygall and uplands respectively in the absence of fire. We found that hog

disturbance that disrupts the continuity of the herbaceous ground cover has the potential to

inhibit fire spread (Chapter 2) because the horizontal continuity of fuels can determine the extent

of fire spread (Brooks et al. 2004; Nader et al. 2007). If hogs migrate following available food,

recently disturbed areas are left to recover in terms of foliar cover. There may be more potential

for hog disturbance to reduce fire spread in places where prescribed fire is infrequent. If

vegetation has time to recover pre-disturbance foliar cover prior to prescribed fire, then it is more

likely that the fire will spread through the slope. While if hog disturbance occurs too frequently

for foliar cover to recover prior to a prescribed burn, then fire spread would be less likely,

providing opportunity for increased woody vegetation cover.

Although there was no change in total foliar cover of grasses, there was a decline in foliar

cover of A. stricta. A. stricta does not recover from intense soil disturbance due to a shallow root

system (Outcalt & Lewis 1990). As a disturbance sensitive species, it may be unable to recover

with continued hog disturbance. Chapter 5 indicates frequent experimental disturbance results in

a decline in A. stricta cover. In seepage slopes on Eglin AFB, more ruderal species, including

Dichanthelium spp., may recolonize disturbed areas more quickly and contribute to the

maintenance of grass cover (Chapter 5). This decline is important because A. stricta acts as a fine

fuel source to carry fire (Noss 1989; Haywood & Harris 1999). Further monitoring is necessary

to determine if this decline is continuing.

There was a significant difference in total forb and grass cover by position on slope. We

found less forb cover in the upper zone than the other two zones, while grass cover in the lower

37

zone was less than the other two zones. This represents the hydrologic gradient (Clewell et al.

2009) inherent to the slopes. The upper zones of seepage slope are generally drier and dominated

by characteristic grass species including A. stricta, C. aromaticum, and Muhlenbergia expansa

(Lam.) Trin (Cutover muhly). The lower zones have longer hydroperiods and are typically

dominated by forb species including Sarracenia spp., Drosera spp., Xyris spp., Eriocaulon spp.,

Pleea tenuifolia Michx. (Rush Featherling), and Lophiola aurea Ker Gawl (Golden Crest).

(FNAI 2010).

Are hogs preferentially disturbing a particular zone of the slope? Hogs commonly

forage in and disturb wet or mesic habitats (Bratton 1975; Wood & Brenneman 1980; Saunders

& Kay, 1991, Mitchell & Mayer 1997; Welander 2001; Chavarria et al. 2007) where it is easier

to root and food is abundant (Mitchell et al. 2007a). Our research indicates that hogs are

preferentially disturbing areas in the lower, wetter portions of the seepage slopes, closer to the

seepage streams. This result suggests that degradation associated with hog disturbance, including

erosion (Bratton 1975; Howe & Bratton 1976), plant mortality (Bratton 1974; Bratton 1975;

Johnson 2001), and increased plant available nitrogen resulting from excrement deposition

(Ruess & McNaughton 1987), is not uniform across the landscape. Preference of hogs to root in

this portion of seepage slopes has serious implications for the persistence of listed plants (e.g.,

Sarracenia spp.) that inhabit the lower zone. Engeman et al. (2007) found hog disturbance to be

negatively correlated with the presence of Sarracenia leucophylla Raf. and Sarracenia flava L.

among other species of interest. This lower zone is also important refugia for rare and endemic

amphibians (e.g., Hyla andersonii (Pine Barrens tree frog), Eumeces anthracinus pluvialis

(Southern Coal Skink), and Rana okaloosae (Florida bog frog)) (Enge 1997). If hog impacts are

38

to be managed in seepage slopes on Eglin AFB, it is important to focus on protecting the lower

zone microhabitat (Mitchell et al. 2007a).

Does hog removal or do environmental variables account for changes in hog

disturbance? Although the number of hogs removed each year from Eglin AFB fluctuated, there

was no correlation with the percent of disturbed plots surveyed that year or the subsequent year.

The number of hogs trapped would not affect the amount of hog disturbance if there were a

density-dependent increase in recruitment (Hanson et al. 2009), but this was not quantified in our

study. It appears that other factors, in addition to hog trapping, may be driving the changes in the

amount of hog disturbance. Extrinsic variations in food availability (i.e., variation in food

availability due to environmental factors not related to the effects of density dependent animal

foraging) have been shown to influence hog population dynamics. Rainfall, an extrinsic factor,

can drive forage biomass and thus hog abundance (Choquenot 1998; Sweitzer et al. 2000). In our

study, rainfall totals from the months of the previous fall were significantly correlated with the

number of hog-disturbed plots. In Florida, feral hogs can breed throughout the year, but breeding

peaks in the spring and fall (Giuliano 2009). Greater precipitation during peak breeding months

may contribute to greater reproductive success and correspond to an increase in hog disturbance

the following year, after sows farrow. The correlation between rainfall during the previous spring

months and the number of hogs removed from Eglin AFB by trapping efforts also supports this

hypothesis. These results are consistent with research that found higher reproductive rates in hog

populations in response to abundant forage (Coblentz & Barber 1987), while drought and limited

forage delayed breeding, reduced reproductive rates (Giles 1980), and increased mortality

(Woodall 1983; Massei et al. 1997). Lower densities of hogs then corresponded to less hog

disturbance (Hone 1995; Sweitzer 1998; Hone 2002; Sweitzer & Van Vuren 2002).

39

Patterns in hog foraging and disturbance can also reflect movement between community

types following mast crop (Howe & Bratton 1976, Bratton et al. 1982). Hogs prefer to feed on

hard mast when it is available (Henry & Conley 1972). Heavy rooting for tubers and roots may

increase during years of poor mast because preferred acorns are not available (Bratton et al.,

1982). After extensive searching, we concluded that information concerning the timing of hard

mast (Quercus spp.) on Eglin AFB has not been recorded. It is known that P. palustris

experienced the first large mast event since 1996 in the winter of 2011 (pers. comm. 2012 Eglin

AFB land manager). Roots of longleaf pine seedlings are a preferred food of hogs (Wood &

Brenneman 1980). This mast event in 2011 increased availability of seedlings in the upland

habitat and may have contributed to the decline in hog disturbance observed in the seepage

slopes in 2012. Bratton et al. (1982) indicate that vegetation may have time to recover from

heavy rooting during good mast years when acorns are plentiful, but will be rooted again when

mast crops fail. Longer trend data, including data on mast crops, is needed in order to identify a

stronger trend in the amount of hog disturbance and its potential drivers.

The percent cover of hog disturbance was unrelated to time since burn, although a variety

of research indicates that herbivores (Vinton et al. 1993; Coppedge & Shaw 1998; Vermeire et

al. 2004) as well as omnivores (e.g., Chen caerulescens (Snow Geese)) (Brennan et al. 2005)

may selectively forage in recently burned vegetation. This could be due to preference for plants

with increased nutritional value (Lemon 1946; Pearson et al. 1972; Shindler et al. 2004) and/or

new growth resulting from the reduction of shade (Copeland et al. 2002). Lack of correlation

between hog rooting and seepage slope burning is potentially a result of one of four scenarios: 1)

hogs show no preference to forage in areas that burned, possibly because the ground is drier and

more difficult for rooting; 2) hogs are foraging for a food source (e.g., invertebrate) that is

40

unaffected by fire; 3) fire spread in seepage slopes is not extensive enough for differences to be

significant; or conversely 4) fire spread in seepage slopes is frequent, uniform, and complete,

leaving no unburned areas from which to differ.

Our results indicated that woody vegetation cover had a significant positive correlation

with time since burn. While fire halts woody recruitment, it is not always effective at reducing

the cover of woody species once they become dominate in seepage slopes. Perennial shrubs

resprout and persist in communities adapted to frequent fire. Mortality from fire only occurs in

the very small shrubs (Olson & Platt 1995). Low mortality and resilient resprouting of

established shrubs after burning may necessitate further management actions to reduce shrub

densities (Olson & Platt 1995; Drewa et al. 2002).

These data also indicate that total vegetation cover is a function of intensity and

frequency of feral hog disturbance and to a lesser extent, rainfall, and time since burn. Over the

past five years, Eglin AFB land managers have focused on increasing fire frequency in seepage

slope areas. Yet even with almost annual prescribed fire (pers. comm. 2013 Eglin AFB land

manager), there was only weak correlation between total vegetation cover and time since burn.

While it is likely that many factors affect total vegetation cover, percent of disturbed plots was

relatively the most important factor in our analysis. Recovery rate of vegetation was not

quantified, but is none-the-less important to total vegetation cover. Recovery via perennial

regrowth, vegetative spread, seedling establishment, and germination requires favorable

environmental conditions, such as adequate soil moisture (Outcalt et al. 1999). Even though there

is less hog disturbance in the drier portion of the slopes, there is lower soil moisture and thus less

recruitment, recovery, and ultimately less cover. This region experienced exceptional drought

conditions (D4) in June of 2011 and was abnormally dry in June of 2012 (D0) (National Drought

41

Mitigation Center 2013). The middle and lower zones of the slope experience longer

hydroperiods and may have had an advantage recovering due to increased soil moisture. No

difference in total cover by year in the lower or middle zones supports this idea.

Significantly less total vegetation cover in the lower zone reflects hog preference for the

wetter portions of the slopes. The total cover in the three zones did not differ significantly some

years. One explanation could be that in years of heavier hog use, disturbance is more uniform

across the slope, while in years of light hog use, there is not enough disturbance for the

difference to be significant. Although hog use as measured by percent plot disturbed was greater

in areas open to hunting, this was not reflected in average total vegetation cover.

Summary

Hog management must involve long-term strategies. As with any ecological data with

inter-annual variation, long-term data are necessary (Krebs 1991; Troeng & Rankin 2005)

because there is the risk of drawing erroneous conclusions from short-term data. Our results

indicate that monitoring seepage slope vegetation and other environmental variables must

continue in order to understand the variability of feral hog disturbance and long-term

consequences. Annual adjustments should be made to management plans depending on

environmental factors, so that hog trapping is increased in years of: 1) mast failure when hogs

are forced to forage for other food sources (Bratton et al., 1982); or 2) high rainfall when hog

densities have the potential to increase (Coblentz & Barber 1987). We recommend that the lower

portions of seepage slopes be protected (e.g., using fence exclosures) because feral hogs target

this area where rare, endemic flora and fauna are found. Due to the increase in woody vegetation

cover we observed, there should also be a concerted effort to ensure fire spreads downslope into

seepage slope areas where fire may not spread unassisted. Larger, more established woody

vegetation may necessitate cutting or clearing by hand. Active management must continue and

42

address multiple facets in order to prevent further degradation of ecosystem structure and

function.

43

Table 3-1. Repeated measures ANOVA results for the percentage of hog disturbed plots over

time by zone on Eglin AFB from 2002 to 2012.

Plots Percentage disturbed (%)

2002 2010 2012 Variable Num df df F P

UF 27.88 30.40 15.98 Year 2 122 5.54 p=0.0050

Zone 2 122 47.63 p<0.0001

Year x Zone 4 122 0.46 p=0.7659

2007 2010 2011 Eglin AFB 31.13 59.60 57.51 Year 2 38 32.76 p<0.0001

Table 3-2. Repeated measures ANOVA results for the percentage of hog disturbed plots over

time by hunting access on Eglin AFB from 2002 to 2012.

Plots Open

Hunting

Closed

Hunting

Variable Num df df F P

UF 38.25 16.67 Access 1 122 5.37 p=0.0222

Year x Access 2 122 1.98 p=0.1430

Eglin AFB 51.77 47.30 Access 1 38 0.45 p=0.5051

Year x Access 2 38 1.00 p=0.3781

Table 3-3. The number of hogs removed from Eglin AFB from October 1 of the previous year to

September 30 of that calendar year. The percentage of hog disturbed plots and rainfall

totals are also indicated.

Year Hogs

Removed

by

Trapping

Percentage

Hog Disturbed

Plots (%)

Rainfall

Previous

July-May

(in)

Rainfall

January-

May (in)

Rainfall

Previous

March-

June (in)

Rainfall

Previous

August-

November

(in)

2002 0 27.88 UF 32.92 16.37 18.86 11.58

2003 0 47.62 Eglin 59.63 26.04 29.22 20.56

2004 439 36.11 Eglin 50.05 13.66 35.13 15.47

2005 189 34.92 Eglin 80.37 45.07 26.34 26.72

2007 68 31.13 Eglin 35.77 10.21 19.95 19.93

2010 261 44.75 Both 76.25 27.74 18.35 29.54

2011 106 57.51 Eglin 38.58 15.38 17.22 18.26

2012 110 15.98 UF 54.88 20.65 10.6 14.15

44

Table 3-4. Repeated measures ANOVA results for the cover of total vegetation, functional

groups, and A. stricta by zone and access on Eglin AFB in 2002, 2010, and 2012.

Percent Mean Cover (%)

2002 2010 2012 Variable Num

df

df F P

Total vegetation 78.75 74.57 77.48 Year 2 122 2.59 p=0.0794

Zone 2 122 5.17 p=0.0070

Year x Zone 4 122 3.76 p=0.0064

Access 1 122 0.04 p=0.8405 Year x Access 2 122 0.08 p=0.9263

Forb 23.69 18.90 22.97 Year 2 122 1.86 p=0.1593

Zone 2 122 11.25 p<0.0001

Year x Zone 4 122 0.69 p=0.6017


Grass 44.09 38.39 39.98 Year 2 122 1.56 p=0.2144

Zone 2 122 21.34 p<0.0001

Year x Zone 4 122 0.50 p=0.7366


Woody 16.53 19.31 21.03 Year 2 122 2.94 p=0.0567

Zone 2 122 6.85 p=0.0015

Year x Zone 4 122 1.09 p=0.3637


Aristida stricta 25.91 16.89 21.63 Year 2 122 3.58 p=0.0310

Zone 2 122 56.34 p<0.0001

Year x Zone 4 122 1.84 p=0.1249


45




46

Figure 3-3. Percent hog-disturbed plots from 2002 to 2012. Analysis included both UF and Eglin

AFB data.

Figure 3-4. Total foliar cover by year. Bars are mean foliar cover ±1 SE, the P-values can be

found in Table 3-4, and different letters above bars indicate significant difference (α =

0.05) in foliar cover following Tukey–Kramer post-hoc tests.

47

Figure 3-5. Foliar cover of functional groups and A. stricta by zone (i.e., position on slope). Bars

are mean foliar cover ±1 SE, the P-values can be found in Table 3-4, and different

letters above bars indicate significant difference (α = 0.05) between zones following

Tukey–Kramer post-hoc tests.

Figure 3-6. Foliar cover of woody species through time. Bars are mean foliar cover ±1 SE and

the P-values can be found in Table 3-4.

48

Figure 3-7. Foliar cover of Aristida stricta through time. Bars are mean foliar cover ±1 SE and

the P-values can be found in Table 3-4.

49

CHAPTER 4

EFFECTS OF INTENSITY OF FERAL HOG DISUTRBANCE ON VEGETATION

DYNAMICS

Background

Herbivores have the potential to greatly modify their habitat (Bratton 1975; Tardiff &

Stanford 1998) in a manner that can be either beneficial or detrimental to ecosystem function and

structure depending on the resident plant species. Herbivory can benefit some plant species when

dominant plants are targeted and the competitive interaction between plants is reduced. Thus,

competitive dominance is prevented and species diversity enhanced (Lubchenco 1978).

Herbivores can also increase spatial and temporal variation in the resources with localized

excrement deposition and soil disturbances resulting from digging (Tardiff & Stanford 1998),

trampling, and wallowing. These activities create competition-reduced gaps that can also have a

positive effect on seedling survival (Silvertown & Bullock 2003). On the contrary, herbivory

targeting competitively inferior species or that is particularly intense can reduce species

diversity. This disturbance may result in the dominance of only a few tolerant species

(Lubchenco 1978). Selective herbivory can also reduce preferred plant species (Bratton 1974;

Recher & Clark 1974; Challies 1975; Howe & Bratton 1976). Depending on the system, species,

and herbivory regime, herbivore effects on plant community composition and diversity can vary

greatly (Maschinski & Whitham 1989).

The modern, Pinus palustris Mill. (longleaf pine) savanna ecosystem of the southeastern

United States came into existence in the early Pleistocene, approximately 2 million YBP. Plant

species evolved under grazing and browsing disturbance from megaherbivore including horses,

tapirs, peccaries, proboscideans, ground sloth, and various ruminants. Modern characteristics of

the P. palustris (i.e., masting, strong taproot and wood) can be interpreted as adaptations to

defend against these megaherbivores (Means 2006). Other modern vegetative characteristics of

50

this system still reflect coevolution with megafauna, such as seeds of herbaceous species being

viable after being digested by livestock (Janzen 1984). However, disturbance resulting from

large herbivores ended after the mass extinction of these animals at the end of the Pleistocene,

approximately 11,000 YBP (Grayson & Meltzer 2002). The Bison bison (American buffalo)

migrated into the Gulf Coastal Plain in the late sixteenth century, but populations were extirpated

in the early nineteenth century (Rostlund 1960). After the Pleistocene extinction of the

megafauna, it is likely that vegetation experienced an ecological release greater than the

influence extant megafauna had on savanna plant characteristics or distributions (Means 2006).

One thing that has not changed through time in this system is the dependence of the P.

palustris-grasslands on fire (Watts 1971; Komarek 1965, 1968, 1974; Myers 1990; Stout &

Marion 1993; Means 2006). Lightning-ignited fire was a major component of the climate,

enough so to frequently burn large expanses and to shape the evolution of pyrophytic vegetation

long before aboriginal peoples (Komarek 1965). Paleoindians were not widespread in the

southeast until 8,500-5,000 BP. It can be inferred that by that time, human-ignited fire

contributed to an increased frequency of fires preventing the pine savanna from succeeding to

broad-leaved forest (Watts 1971). Native Americans burned the forests frequently for cultivation,

hunting, reducing insects, and defense (Williams 1992; Kay 2007). Vegetation has evolved to

recover rapidly after the disturbance of high frequency (1-3 years), low intensity fire. Some

examples of fire-evolved traits include: the early growth of longleaf pine in a grass stage (Keeley

& Zedler 1998); fire induced germination (Wiggers 2011), vigorous resprouting of shrubs

following fire (Olson & Platt 1995); and increased flowering, seed production, and germination

of dominant matrix grasses after growing season fire (Shepherd et al. 2012). It seems that fire has

51

been the principal selective agent in the evolution of longleaf pine savannas of the southeast

(Frost et al. 1986).

Introduced herbivores, including feral hogs, present substantial potential for degradation

to native plant communities resulting from herbivory and altered disturbance regimes (Singer et

al. 1984; Van Vuren & Coblentz 1987; Hobbs & Huenneke 1992; Kotanen 1995). We propose

hogs could either replace the role of now-extirpated megaherbivores or represent a novel

disturbance that results in ecosystem change. In this chapter, we investigate the short-term

floristic response after different intensities of hog disturbance in seepage slopes. We examine the

effect of disturbance intensity on cover, richness, and species composition over a three-year

period. We hypothesize that over the short-term high hog disturbance intensity reduces cover,

species richness, and alters species composition when compared to undisturbed vegetation.

Methods

Study Area

Eglin AFB is located in the western Florida Panhandle, Walton County, USA

(30°29′22″N 086°32′32″W). Seepage slope sites are restricted to the loamy sand soils of the

eastern portion of the AFB. It is here where gently rolling erosional hills have been cut into the

remains of a Pliocene-Pleistocene age delta plane. These dendritic drainage systems have relief

of up to about 30 m and areas of steeper slope along creeks (NRCS 1989). The relatively higher

clay content of these soils, compared to the deep sands of xeric P. palustris sandhills, results in

more mesic conditions. This mesic upland community is classified as Upland Pine Forest (FNAI

1990).

Seepage slopes are grass and sedge dominated wet prairies located on hillsides in the

upland pine community (Figure 4-1) (FNAI 1990). The nutrient poor soils are kept saturated by

the downslope seepage of groundwater above an impermeable layer of clay, organic matter, or

52

rock. Seeps occur along hillsides of these dendritic systems of streams where the impermeable

layer intersects the hillside. During times of drought, seepage slopes may dry out due to this

dependence on groundwater (FNAI 2010).

A diverse suite of herbaceous species inhabit this wet prairie community. Aristida stricta

Michx. (Wiregrass), Ctenium aromaticum (Walter) A. Wood (Toothachegrass), Muhlenbergia

expansa (Lam.) Trin. (Cutover Muhly), and Rhexia spp. (Meadowbeauties) can be found upslope

in the drier soils, while Rhynchospora spp. (Beaksedges), Xyris spp. (Yelloweyed Grasses),

Eriocaulon spp. (Pipeworts), and Lycopodiella spp. (Club Mosses) inhabit the wetter portions of

the slopes (FNAI 2010). Carnivorous plants that acquire nutrients by trapping insects (Schnell

1976) can be abundant, including Sarracenia spp. (Pitcherplants), Drosera spp. (Sundews),

Pinguicula spp. (Butterworts), and Utricularia spp. (Bladderworts). Shrubs are maintained at a

reduced height by frequent fire that burns down slope from the uplands. Cliftonia monophylla

(Lam.) Sarg. (Black Titi) and other shrubs invade from the shrub bogs or baygalls along the

seepage creek, outcompeting the heliophytic, herbaceous vegetation in the absence of frequent

fire (FNAI 2010).

Data Collection

Research questions 1, 2, and 3. Does the difference in foliar cover between disturbance

intensities persist over time? Does species richness differ in areas of varying disturbance

intensity? Does species composition differ in areas of varying disturbance intensity? The

intensity of feral hog foraging and wallowing activity varies within seepage slopes on Eglin

AFB. In 2010, 20 independent, replicate seepage slope sites with the varying levels of hog

disturbance were randomly chosen on Eglin AFB (Figure 4-2). Three hog disturbance intensities

were identified based on percent of uprooted vegetation and total vegetation cover. The

intensities were: 1) undisturbed (control), with less than 3% uprooted and total cover of 75-

53

100%; 2) moderate, with <50% uprooted and total cover of 50-75%; and 3) high, with >50%

uprooted and total cover of 0-50%. Potential plot locations were restricted to flat, open slopes to

minimize the influence of aspect. Plots were placed within the middle zone of the slope to

minimize the effect of the moisture gradient and restricted to the area of the slope with different

intensities of hog damage within close proximity. At each seepage slope site, two locations were

randomly selected for placement of wire fence exclosures (6m in circumference and 1m in

height) within each disturbance intensity (control/undisturbed, moderate, and high). Exclosures

prevented subsequent hog damage. Within each exclosure one 1 m2 permanent plot was

established. Adjacent to each exclosure (approximately .5 m downslope) an open 1 m2plot was

permanently marked (Figure 4-3). This resulted in approximately six open and six exclosure

plots at each site. The two subsamples accounted for within site variability. Two of the 20 sites

only contained two disturbance intensities due to the nature of hog disturbance at the time of plot

initiation. Between 2010 and 2013, eight exclosure plots were compromised by hog disturbance

and removed from the study.

In August of 2010 and 2012, total foliar cover and cover of functional groups was

determined using a modified Daubenmire scale (0= 0%, 0.5-5 = 3%, 5-10 = 8%, 10-15 = 13%,

15-25 = 21%, 25-50 = 38%, 50-75 = 68%, 75-95 = 88%, 95-100 = 98%) within 1 m2 plots inside

and outside exclosures. Total number of species present was recorded. Due to high species

richness, percent cover by species was estimated within ¼ of each 1 m2 plots. Species

nomenclature was based on Wunderlin & Hansen (2008). In August of 2013, total foliar cover

only was estimated in 1 m2 plots inside and outside exclosures.

Wildlife cameras with motion sensors recorded hog activity at 21 seepage slopes (Figure

4-4). Hog observations were tallied independent of size of group or length of time spent foraging

54

at site. Cameras were checked every two to three months to download images and replace

batteries. Over the course of the four-year study, cameras were either stolen (7), burned in

prescribed fire (1), or eventually became inoperable after prolonged exposure to the elements (4).

These losses, in combination with inaccessibility of areas due to military operations and removal

of cameras for prescribed burns, resulted in limited and intermittent data acquisition. This data

represents a conservative estimate of hog activity.

Data Analyses

Research questions 1 and 2. Does the difference in foliar cover between disturbance

intensities persist over time? Does species richness differ in areas of varying disturbance

intensity? The experimental followed a randomized, split plot repeated measure design. Within

each seepage slope site, initial intensity of hog disturbance (control, moderate, and high)

represented whole plots and exposure to subsequent hog disturbance (exclosure vs open) were

split plots. Significance of main effects and interactions (α= 0.10) were evaluated using a

repeated measure one-way ANOVA (PROC GLIMMIX; SAS 9.3; SAS Institute 2011) to

determine significance of recovery with and without potential for further hog disturbance. Means

were arcsine square root transformed when necessary to meet assumptions of ANOVA (Zar

1998). Year, intensity, and exclosure were the main effects. Site was considered a random effect.

Tukey–Kramer tests were used for post hoc comparisons (α= 0.05) to analyze differences

between means. The average number of hog occurrences per month was calculated from the

camera data.

Research question 3. Does species composition differ in areas of varying disturbance

intensity? NMS was used to better understand temporal changes in species of interest with

respect to disturbance intensity and edaphic conditions. We removed all species that occurred in

less than 5% of the plots and grouped all Andropogon spp. (Bluestems), Asteraceae spp. (Asters),

55

Eriocaulon spp., Rhexia spp., Rhynchospora spp., Sarracenia spp., Scleria spp. (Nutrushes), and

Xyris spp. Moderate disturbance intensity plots were removed to reduce overlap with high

intensity and control plots. A Bray-Curtis distance measure was used for the ordination in PC-

ORD. Monte Carlo tests were used to determine if the ordination results were significantly

different from random data. Then we used MRPP to test for differences within and between

disturbance intensity groups (McCune & Grace 2002).

Results

Foliar Cover

Does the difference in foliar cover between disturbance intensities persist over time?

Hog disturbance intensity significantly altered vegetation cover over time (Figure 4-5; Table 4-

1). Foliar cover in high disturbance plots (inside and outside exclosures) increased significantly

(p<0.0001) from 2010 to 2013. There was no significant change in cover in control (p=0.8185)

or moderate (p=0.9994) disturbance plots. Total foliar cover differed among all intensities in

2010 (Year 1): high intensity plots had less cover than control plots (p<0.0001) and moderate

disturbance plots (p<0.0001); while control plots had greater total foliar cover than moderate

(p<0.0001). By 2013, moderate disturbance plots still differed significantly from control

(p=0.0670) and high (p=.0609) disturbance plots. Cover in high disturbance plots also continued

to be less than control (p<0.0001) plots. Initially in 2010, there was no difference (p=0.51) in

foliar cover inside (68.55%) and outside (64.22%) exclosures (Figure 4-6). By 2012, foliar cover

increased both inside (p<0.0001; 83.02%) and outside (p=0.0011; 73.04%) exclosures. However

by 2013, continued, albeit less intense and frequent, hog activity resulted in significantly greater

(p<0.0001) total foliar cover inside (77.19%) compared to outside (68.39%) exclosures.

Cover of woody species increased in plots inside and outside exclosures in all disturbance

intensities from 2010 to 2012 (Figure 4-7; Table 4-1). Initially, high disturbance plots did not

56

differ from moderate disturbance plots (p=0.9952), but had less woody cover than control plots

(p=0.0553). Over time, the only significant change (p<0.0001) took place in high disturbance

plots, where cover of woody species more than doubled. There were no significant differences

between the three disturbance intensities by 2012: high and control (p=0.9995); high and

moderate (p=0.9060); and control and moderate (p=0.9781). There was also no significant

difference between plots inside and outside exclosures.

Intensity of disturbance was a determining factor in foliar cover of forbs (Table 4-1).

Control plots had higher forb cover (34.01%) than high (19.34%; p<0.0001) and moderate

(25.04%; p=0.0207) disturbance plots. There was no difference (p=0.1573) between high and

moderate disturbance plots. Forb cover inside and outside exclosures did not differ significantly.

Foliar cover of grass species changed over time with disturbance intensity (Figure 4-8;

Table 4-1). High disturbance plots (inside and outside exclosures combined) had less grass cover

than control (p<0.0001) and moderate (p=0.0002) disturbance plots in 2010. Control plots did

not differ from moderate (p=0.7272) disturbance plots. By 2012, high disturbance plots still had

significantly less grass cover than control (p=0.0404) and moderate (p=0.0139) disturbance

plots. There was still no difference (p=0.9991) between control and moderate disturbance plots.

Initially in 2010, there was no difference (p=0.4491) in grass cover inside (35.71%) and outside

(32.08%) exclosures (Figure 4-9). By 2012, foliar cover increased both inside (p<0.0001) and

outside (p<0.0001) exclosures. This increase in grass cover resulted in significantly greater

(p=0.0006) grass cover inside (53.27%) compared to outside (43.97%) exclosures.

The cover of A. stricta differed by disturbance intensity with no effect of time (Table 4-

1). High disturbance plots had the lowest cover (7.58%) of A. stricta. The high disturbance plots

had significantly less cover than the control (22.42%; p<0.0001) and moderate (16.51%;

57

p=0.0224) disturbance plots, while control and moderate disturbance plots did not differ

(p=0.1602). Exclosures had greater A. stricta cover (16.27%; Table 3-1) than outside exclosures

(14.74%) throughout the study.

Richness

Does species richness differ in areas of varying disturbance intensity? Species

richness was dependent on time since disturbance, but not disturbance intensity (Table 4-1).

There was no difference in species richness among disturbance intensities at the start of the study

(high and control, p=0.1617; high and moderate, p=0.7780; control and moderate, p=0.8711).

The number of species per plot increased significantly from 2010 to 2012 for all intensities (high,

p<0.0001; moderate, p<0.0001; control, p=0.0017). Still at the end of the study, no significant

difference in richness was detected between the intensities (high and control, p=1.0; high and

moderate, p=0.9975; control and moderate, p=0.9925). There also was no difference between the

species richness inside (15.16) and outside (15.36) exclosures.

Camera Detection of Hog Activity

Hog detection by the cameras fluctuated a great deal, but there was a decreasing trend

from 2010 until the end of 2011 (Figure 4-10). The average number of hog occurrences detected

by cameras was lower in the summer months. Overall, hog occurrences increased from 2012 to

the highest numbers in the fall of 2013.

Vegetation Composition

Does species composition differ in areas of varying disturbance intensity? MRPP

indicated that there were significant differences in vegetation composition depending on soil type

when all seepage slope sites were included in the analysis (T=-8.1775; A=0.0349; p<0.0001).

The subsequent multivariate analyses focused on 10 sites located on the Leefield-Stilson Loamy

58

Sands soil type. This soil type was selected in an attempt to reduce variability and retain the

largest sample size possible.

NMS ordination and MRPP revealed differences in species composition. Vegetation

composition at sites located on the Leefield-Stilson Loamy Sands soil type differed between high

disturbance and control plots when years were combined (T=-56.9861; A=0.3296; p<0.0001;

Figure 4-11). A two-dimensional ordination was optimal (stress = 6.1094) with axis 1 explaining

82.7% and axis 2 explaining 15.9% of the variation. Monte Carlo test determined that the

ordination differed from random data (p=0.0164). Comparable results were observed when years

were analyzed individually. Both of these analyses had three-dimensional solutions. When 2010

data was analyzed separately (stress=17.8216), axis 1 explained 11.9%, axis 2 explained 24.4%,

and axis 3 explained 37.6% of the variation observed. When 2012 data was analyzed separately

(stress=19.0722), axis 1 explained 20.0%, axis 2 explained 20.6%, and axis 3 explained 31.5% of

the variation observed. This analysis revealed that the difference between disturbance intensities

and separation between groups decreased over time as the high intensity disturbance recovered

(2010: T=-16.6659, A=0.0616, p<0.0001; 2012: T=-8.8013, A=0.0284, p<0.0001, Figure 4-12a

and 4-12b).

Discussion

Does the difference in foliar cover between disturbance intensities persist over time?

Three years of field observations suggest that heavily hog-disturbed areas differ from

undisturbed areas in both cover and composition. The most obvious change resulting from hog

disturbance is loss of total foliar cover (Bratton 1974, 1975; Challies 1975; Cuevas et al. 2010).

Even after three years of recovery inside exclosures, high intensity disturbance plots still have

significantly less cover than moderately disturbed and control plots. Although theoretically

successional communities maintained by frequent disturbance should recover more quickly than

59

"climax equivalents" (Baron 1982), these results indicate that more time is necessary before

heavily disturbed seepage slopes areas are indistinguishable in terms of total cover.

Total cover increased over time both inside and outside exclosures due to reduced hog

foraging. This region experienced moderate to exceptional drought conditions (D1-D4) from

October 2010 to June 2012 (National Drought Mitigation Center 2013). We discussed previously

in Chapter 3 that rainfall drives forage biomass and can influence hog abundance (Choquenot

1998; Sweitzer et al. 2000). Drought and limited forage delays breeding, reduces reproductive

rates (Giles 1980), and increases mortality (Woodall 1983; Massei et al. 1997). A drought and

subsequent decline in hog numbers corresponds to less hog disturbance outside exclosures and

likely explains the observed increase in cover outside exclosures. Our camera data also

substantiates this idea with fewer hog occurrences (i.e., images) from 2011 through 2012.

However with an increase in hog activity and disturbance in 2013, our exclosure study showed

that continued hog disturbance outside exclosures was enough to result in significantly lower

total foliar cover compared to inside exlosures.

Hog foraging has the potential to have different effects on woody cover at different

scales. Uprooting vegetation, including woody species, reduces cover at the small scale. In the

absence of intense and/or frequent hog disturbance during our study, the cover of woody species

increased significantly over time in heavily disturbed plots as vegetation recovered. At the large

scale, hog rooting reduces herbaceous cover that acts as fuel to carry fire (Chapter 2). Woody

species then have an opportunity to become established with reduced fire spread from the

uplands, increasing woody cover at the large scale. This idea is discussed in further detail in

Chapter 2. The effect of exclosures on woody cover would likely have been significant given

60

more time or if hog disturbance had been heavier in seepage slopes in 2012 (Mitchell et al.

2007b; Taylor et al. 2011).

Although hogs are omnivorous (Taylor & Hellgren 1997), previous studies have found

herbaceous vegetation can account for the greatest proportion of the diet of feral hogs (Challies

1975; Everitt & Alaniz 1980; Coblentz & Baber 1987; Cuevas et al. 2010). While little is known

about the diet of feral hogs in this system, our findings indicate that either direct consumption or

indirect soil disturbance associated with rooting results in greater forb and grass cover in

undisturbed areas. The observed increase in graminoid cover was greater inside the protection of

exclosures where ruderal species (e.g., Dichanthelium spp.) quickly recolonize disturbed soil

(Rodgers & Provencher 1999). In the absence of hog foraging, other studies have observed

similar increases in herbaceous cover (Siemann et al. 2009; Cole et al. 2012).

Aristida stricta is a dominant perennial bunchgrass in the longleaf pine system and

considered a keystone species (Noss 1989). This native understory species is critical for carrying

frequent, low-intensity fire (Clewell 1989; Haywood & Harris 1999). Hog rooting has been

found to have little impact on native perennial bunchgrasses in coastal meadows of California

because these species are deep rooted and difficult to uproot (Kotenan 1995; Cushman et al.

2004). However, A. stricta has a shallow root system and is notorious for not recolonizing after

intense soil perturbations (Outcalt & Lewis 1990; Huffman & Judd 1998). It was no surprise that

A. stricta cover was significantly lower in high intensity than control plots. Although it may

seem concerning that A. stricta cover was reduced in plots outside exclosures, the difference

between inside and outside exclosures was within one cover class and present from the beginning

of the study. Again with 2012 being a particularly dry year, hog disturbance was negligible

compared to years with greater rainfall (Chapter 2). Future periods of heavy rainfall, like that of

61

2013, could potentially be conducive to hog rooting with greater effect on A. stricta cover and

thus fire spread.

Does species richness differ in areas of varying disturbance intensity? The effects of

hog rooting on diversity varies depending on plant community type. Hog disturbance results in

increased plant species richness in coastal grasslands in California (Kotanen 1995, 1997;

Cushman et al. 2004), while it can reduce plant species richness in Grey Beach Forests of the

Great Smoky Mountains National Park (Bratton 1974, 1975; Howe & Bratton 1976; Bratton et

al. 1982), floodplain marshes of Central Florida (Arrington et al. 1999), and mixed pine-

hardwood forests in Texas (Siemann et al. 2009). The vegetative response depends on whether

the community is adapted to that particular disturbance regime (Hobbs & Huenneke 1992;

Doupé et al, 2010). Similar to studies in other systems (Doupé et al. 2010; Taylor et al. 2011;

Cole et al. 2012), our study did not find that intensity of hog rooting affected plant species

richness. It is hypothesized that because seepage slope vegetation is subject to stress from

periods of prolonged soil saturation, there is less potential for competitive exclusion; thus soil

disturbance has a less pronounced effect on diversity (Huston 1979). Another possibility could

be that this study was too short-term to detect this community level change (Taylor et al. 2011).

The change we observed in richness was an increase over time with recovery and increase in

cover. More time may be necessary to detect an exclosure effect.

Does species composition differ in areas of varying disturbance intensity? Our results

from the NMS ordination analyses indicate significant differences between: 1) plant assemblages

on differing soil types within the same community; and 2) undisturbed (controls) assemblages

and those that are recovering from high intensity hog disturbance. Although the difference

between disturbance intensities and similarity within groups decreased over time as vegetation

62

recovered in high hog disturbance, the composition of these groups remained significantly

different even when only one soil type was included. It may take more than three years without

disturbance by hogs for heavily hog disturbed areas to succeed from an early successional state

(Kirkman et al. 2004).

It could be contested whether or not it is beyond the scope of this study to conclusively

state that the difference in plant composition (and abiotic components) of disturbed and

undisturbed areas is a direct result of hog disturbance. Siemann et al. (2009) suggest that hog

disturbance is not random, but targets a particular biotic or abiotic component. Thus

observational studies cannot quantify effects of hogs on vegetation because the area was likely

inherently different from undisturbed areas. On the contrary, Arrington et al. (1999) indicate that

years of observational data of vegetation composition showed areas of hog rooting were similar

to undisturbed areas before rooting occurred. We followed similar protocol to Cuevas et al.

(2010) and set up rooted plots in close proximity to undisturbed plots in an attempt to reduce

abiotic and biotic variability. Field observations over the course of this study validate the

observations of Arrington et al. (1999) as undisturbed areas were converted to heavily rooted

areas overnight, indicating little difference between the pre-disturbance states of undisturbed and

heavily disturbed plots.

Although domestic hogs (Sus scrofa) were first introduced over 400 years ago, no record

of large numbers of hogs on Eglin AFB exists prior to domestic herds that were free-range until

1960 (Mayer & Brisbin 1991). Considering that hogs have been in this area for a substantial

amount of time, there is no definitive way to determine if undisturbed areas were different from

disturbed areas prior to the presence of hogs. Hogs could be acting as ecological engineers, as

rooting is known to exacerbate abiotic differences (e.g., increase depth of depression and water

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retention), perpetuating biotic differences (Cuevas et al. 2010). However this study did not

discover that hog rooting created unique plant associations (e.g., Lachnanthes caroliana (Lam.)

prairies) as other research in peninsular Florida has indicated (Huffman & Judd 1998).

Summary

The resilience of a system describes the amount of disturbance that system can withstand

and still remain in the same state (Holling 1973). There is not enough data to indicate that hog

disturbance has pushed seepage slopes on Eglin AFB past a threshold to an alternative stable

state. Feral hogs could be ecologically equivalent to extinct megaherbivores in regards to soil

disturbance just as it is hypothesized that an intermediate level of feral hog disturbance replaces

activities of the extirpated Ursus arctos L. (grizzly bear) in California (Work 1993) Still, it is

dangerous to interpret these results as if feral hog disturbance is ecologically benign. State

changes in ecosystems occur when there are changes in the key variables that affect the stability

of the system. The popular heuristic of a ball in a cup can be used to illustrate this change, where

changes in the shape of the cup correspond to alteration of both stability (return time) and

resilience (width of stability domain) (Gunderson 2000). Hog disturbance has likely reduced the

resilience of the seepage slope community on Eglin AFB and thus it may be approaching a

threshold even though a threshold has not yet been crossed.

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Table 4-1. ANOVA results for the foliar cover of total vegetation, functional groups, and A.

stricta and species richness by disturbance intensity and exclosure on Eglin AFB.

Variable Num df df F P Total Vegetation Year 2 287.7 17.34 <0.0001

Intensity 2 55.54 75.12 <0.0001

Year x Intensity 4 304.5 14.60 <0.0001

Exclosure 1 80.51 27.02 <0.0001

Year x Exclosure 2 287.4 2.61 0.0800

Inten. x Exclos. 2 64.35 0.89 0.4143

Yr. x Inten. x Exclos. 4 201.8 0.75 0.5592

Woody Year 1 157.5 20.76 <0.0001

Intensity 2 54.30 1.75 0.1836

Year x Intensity 2 157.5 6.65 0.0017

Exclosure 1 152.7 1.47 0.2276

Year x Exclosure 1 152.7 1.26 0.2625

Inten. x Exclos. 2 152.7 1.39 0.2519


Forb Year 1 156.9 0.68 0.4101

Intensity 2 53.88 10.61 0.0001

Year x Intensity 2 156.9 1.05 0.3522

Exclosure 1 152.2 0.0 0.9919

Year x Exclosure 1 152.2 1.04 0.3097

Inten. x Exclos. 2 152.2 0.21 0.8118


Grass Year 1 159.8 72.53 <0.0001

Intensity 2 55.22 15.43 <0.0001

Year x Intensity 2 159.8 4.70 0.0103

Exclosure 1 153.9 14.5 0.0002

Year x Exclosure 1 153.9 2.73 0.1006

Inten. x Exclos. 2 153.9 0.42 0.6583

Yr. x Intens. x Exclos. 2 153.9 0.26 0.7735

Aristida stricta Year 1 153.0 0.22 0.6408

Intensity 2 53.06 10.44 0.0002

Year x Intensity 2 153.0 2.11 0.1250

Exclosure 1 151.0 4.54 0.0347

Year x Exclosure 1 151.0 0.24 0.6262

Inten. x Exclos. 2 151 1.4 0.2506

Yr. x Intens. x Exclos. 2 151 0.72 0.4891

Richness Year 1 158.0 89.34 <0.0001

Intensity 2 54.19 1.08 0.3471

Year x Intensity 2 158.0 3.47 0.0336

Exclosure 1 152.7 0.55 0.4582

Year x Exclosure 1 152.7 1.05 0.3063

Inten. x Exclos. 2 152.7 0.58 0.5590

Yr. x Intens. x Exclos. 2 152.7 2.16 0.1193

65




66

Figure 4-3. Exclosure and open plot pairs were located in the middle zone of the slope.

Figure 4-4. The location of seepage slope sites with motion detecting wildlife cameras.

67

Figure 4-5. Total foliar cover by intensity by year inside and outside exclosures on Eglin AFB.

Bars are mean foliar cover ±1 SE and different letters above bars indicate significant

difference (α = 0.05) in foliar cover following Tukey–Kramer post-hoc tests.

Figure 4-6. Total foliar cover by exclosure by year on Eglin AFB. Bars are mean foliar cover ±1

SE and different letters above bars indicate significant difference (α = 0.05) in foliar

cover following Tukey–Kramer post-hoc tests.

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Figure 4-7. Foliar cover of woody species by intensity by year inside and outside exclosures on

Eglin AFB. Bars are mean foliar cover ±1 SE and different letters above bars indicate

significant difference (α = 0.05) in foliar cover following Tukey–Kramer post-hoc

tests.

Figure 4-8. Foliar cover of graminoid species by intensity by year inside and outside exclosures

on Eglin AFB. Bars are mean foliar cover ±1 SE and different letters above bars

indicate significant difference (α = 0.05) in foliar cover following Tukey–Kramer

post-hoc tests.

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Figure 4-9. Foliar cover of graminoid species by exclosure by year on Eglin AFB. Bars are mean

foliar cover ±1 SE and different letters above bars indicate significant difference (α =

0.05) in foliar cover following Tukey–Kramer post-hoc tests.

Figure 4-10. Average number of hog occurrences per month in seepage slopes with cameras on

Eglin AFB from June 2010 through December 2013.

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Figure 4-11. Two-dimensional nonmetric multidimensional scaling ordination showing cover by

species in high disturbance intensity and control plots on Eglin AFB. Samples from

2010 and 2012 are combined. Each point represents a plot and the distance between

points is proportional to the difference in species composition.

Control

High

71

A. B.

Figure 4-12. Three-dimensional nonmetric multidimensional ordination showing cover by

species in high disturbance and control plots on Eglin AFB in A) 2010 and B) 2012.

Each point represents a plot and the distance between points is proportional to the

difference in species composition. By 2012, high disturbance intensity plots are

recovering and separation between groups has decreased.

Control

High

Control

High

72

CHAPTER 5

EFFECTS OF EXPERIMENTAL SOIL DISTURBANCE ON VEGETATION DYNAMICS

Background

Disturbances are environmental fluctuations or destructive events that cause abrupt

changes in the community or population structure of natural communities. They can be biological

or physical in nature and differ in magnitude and distribution over time. The irregular nature of

these events can produce heterogeneous or patchy effects (Sousa 1984; Pickett & White 1985;

Moloney & Levin 1996). It is generally accepted that disturbances keep natural communities in a

state of nonequilibrium, maintaining diversity by preventing competitive equilibrium. A dynamic

balance is reached between the frequency of disturbance and rate of competitive displacement

when competitive equilibrium is prevented and thus a stable level of diversity is maintained

(Connell 1978; Huston 1979). The intermediate disturbance hypothesis (IDH) proposes that high

diversity results from an intermediate disturbance regime. Longer-lived species are lost when

disturbance is too great or too often, while ruderal species are lost when disturbance is

insignificant or too infrequent (Connell 1978; Petraitis et al. 1989; Reynolds 1993; Shea et al.

2004). Therefore the diversity pattern observed in disturbed environments is unimodal (Shea et

al. 2004). An alternative hypothesis to the IDH is that diversity and richness are independent of

disturbance (Mackey & Currie 2001).

Glitzenstein et al. (2003) hypothesized that in the longleaf pine ecosystem the open,

herbaceous ground cover is maintained with maximum species diversity when burning occurs as

frequently as fuels allow. The authors referred to this as the "Most Frequent Fire Hypothesis"

(MFFH). This idea is supported by other studies that found frequent fire (i.e. one to two years

interval) necessary to achieve reduced woody cover and dominance of diverse herbaceous

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vegetation (Walker & Peet 1983; Waldrop et al. 1992; Brockway & Lewis 1997; Haywood &

Grelen 2000; Glitzenstein et al. 2003; Glitzenstein et al. 2012).

Multiple types of disturbances with different characteristics often interact to make up the

disturbance regime of a community (Collins 1987) and may result in complex patterns not

described by the IDH (Collins & Barber 1985) or other hypotheses. Alternatively, it may be the

type and characteristics of the combined disturbances that determine effect on post-disturbance

community trajectory (Collins 1987; Paine et al. 1998; Platt et al. 2002). Grassland disturbance

regimes may include combinations of fire, grazing, and soil disturbance by animals where the

effect of each disturbance is variable depending on scale, frequency, and intensity (Collins

1987). For example, one disturbance could reduce competitive superiority (e.g., grazing), while

another could increase habitat heterogeneity (e.g., soil disturbance). Still, community response is

dependent upon the historical disturbance regime (Collins & Barber 1985). It is ultimately

divergence from the historical disturbance regime that can leave native species ill adapted for

successful recovery (Denslow 1980; Hobbs & Huenneke 1992) and may result in extirpation or

even extinction (Connell 1978).

All over the world, disturbance regimes are changing due to climate change,

anthropogenic modifications, and biological invasions (Shea et al. 2004). Introduced species of

both plants and animals have the potential to alter disturbance regimes. These species can

increase or reduce the frequency and/or intensity of disturbances, like fire or erosion, which can

quickly result in mortality of a significant portion of the community. Introduced feral hogs

demonstrate that the invader can also be the actual agent of disturbance (Mack & D'Antonio

1998). Regardless of mechanism, these alterations to the disturbance regime can cause dramatic

changes in composition and successional trajectory of the invaded community (Bratton 1975;

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Mack & D'Antonio 1998). The purpose of Chapter 5 is to assess the short-term effect of four

experimental soil disturbance regimes, meant to simulate hog disturbance, on community

structure and composition in the seepage slope community. We examine the effect of disturbance

frequency and time since last disturbance on foliar cover, richness, and species composition over

a four-year period.

Methods

Study Area

This study was conducted on Eglin AFB located in Walton County, Florida, USA

(30°29′22″N 086°32′32″W). On the eastern portion of Eglin AFB, dendritic drainage systems

have cut into the remains of a Pliocene-Pleistocene age delta plane, leaving erosional hills with

relief of up to about 30 meters (NRCS 1989). Here the loamy sand soils allow for the formation

of seepage slopes. Along hillsides, the Pinus palustris Mill. canopy opens up into grass and

sedge dominated wet prairies (Figure 5-1). Nutrient poor soils are saturated by groundwater that

seeps downslope above an impermeable layer of clay, organic matter, or rock. Depending on the

size of the watershed, these wetlands may dry out during times of drought, as soil saturation is

dependent on groundwater (FNAI 2010).

The hydrologic gradient inherent to the slopes is reflected in the diverse herbaceous

vegetation. Upslope tends to be drier and dominated by Aristida stricta Michx. (Wiregrass),

Ctenium aromaticum (Walter) A. Wood (Toothachegrass), Muhlenbergia expansa (Lam.) Trin.

(Cutover Muhly), and Rhexia spp. (Meadowbeauties). The lower slope generally has a longer

hydroperiod and is dominated by Eriocaulon spp. (Pipeworts), Lycopodiella spp. (Club Mosses),

Rhynchospora spp. (Beaksedges), Xyris spp. (Yelloweyed Grasses), and a diverse suite of

carnivorous plants (FNAI 2010). Sarracenia spp. (Pitcherplants), Drosera spp. (Sundews),

Pinguicula spp. (Butterworts), and Utricularia spp. (Bladderworts) acquire nutrients by trapping

75

insects (Schnell 1976). The heliophytic, herbaceous vegetation of this community is dependent

upon frequent fire because without it, Cliftonia monophylla (Lam.) Sarg (Black Titi) and other

shrubs will move in from the shrub bogs or baygalls and dominate (FNAI 2010).

Data Collection

How does frequency and time since last disturbance effect foliar cover, richness and

species composition? In June 2010, two 1m2 plots were randomly selected and surveyed at 20

independent seepage slope sites on the eastern portion of Eglin AFB, Walton County, Florida,

USA (Figure 5-2). Plot locations were chosen in undisturbed vegetation on flat, open slopes in an

attempt to reduce the influence of aspect and reduce the variability of the hydrologic gradient.

Experimental disturbance treatments were applied using a shovel to turn the soil in each plot to a

depth of ~7-15 cm (Kotanen 1997). Wire fence exclosures (6m in circumference and 1m in

height) were erected to protect plots from future hog disturbance. Two disturbance treatments

were applied at 10 sites while another two disturbance treatments were applied at the remaining

10 sites (e.g., F1 and I1 at 10 sites; F4 and I4 at 10 sites). The disturbance treatments applied

were categorized as one of the following four classes.

1. F1- One plot at 10 of 20 sites was disturbed frequently (quarterly) for one year (2010).

2. F4- One plot at 10 of 20 sites was disturbed frequently (quarterly) for four years.

3. I1- One plot at 10 of 20 sites was disturbed infrequently (once), for one year (2010).

4. I4- One plot at 10 of 20 sites was disturbed infrequently (once annually) for four years

(June, 2010; September 2011; December 2012; and June 2013).

Prior to application of the four disturbance treatments, foliar cover was estimated in June

2010, September 2010, December 2010, and March 2011 before subsequent disturbances. A

modified Daubenmire scale (0= 0%, 0.5-5 = 3%, 5-10 = 8%, 10-15 = 13%, 15-25 = 21%, 25-50

= 38%, 50-75 = 68%, 75-95 = 88%, 95-100 = 98%) was used to estimate foliar cover of total

vegetation, forbs, grasses, woody vegetation, Aristida stricta, and Dichanthelium spp.

(Witchgrasses) in the 1m2 plot. A. stricta was chosen because it is considered a keystone species

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(Noss 1989) due to its importance in fire spread (Clewell 1989; Haywood & Harris 1999).

Dichanthelium spp. were chosen because they may be less sensitive to disturbance. Foliar cover

for individual species was estimated for one quarter of each plot. Species nomenclature was

based on Wunderlin & Hansen (2008). Richness was also estimated. Plots were also surveyed in

June 2011, September 2011, March 2012, June 2012, September 2012, March 2013, June 2013

and September 2013 preceding disturbances. Undisturbed, control plots inside exclosures were

established in 2010 and surveyed in June 2010, June 2011 (total cover only), June 2012, and

September 2013.

Data Analyses

How does frequency and time since last disturbance effect foliar cover and species

richness? This experiment followed a balanced incomplete blocking design. Each seepage slope

site was considered a block with a subset (two of four) of all disturbance treatments present in

each block. Each disturbance treatment had equal replication within blocks. Repeated measure

one-way ANOVA (PROC GLIMMIX; SAS 9.3; SAS Institute 2011) was used to evaluate

significance of main effects and interactions (α= 0.10). Means were arcsine square root

transformed when necessary to meet assumptions of ANOVA (Zar 1998). Survey date and

disturbance treatment (frequency and time since last disturbance) were the main effects. Site was

considered a random effect. Tukey–Kramer tests were used for post hoc comparisons (α= 0.05)

to analyze differences between means. Additional ANOVAs were run to analyze data from

controls because the control plots were surveyed fewer times (once a year) than the experimental

plots. The data from wildlife cameras with motion sensors used in Chapter 4 was also used to

analyze annual frequency of hog occurrences at seepage slopes. The number of hog occurrences

per site per year was calculated from the camera data and averaged across cameras for each year.

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How does frequency and time since last disturbance effect species composition?

NMS ordination was used to depict temporal changes in species in terms of disturbance regime,

burn events, and soil type. Species that occurred in less than 5% of the plots were excluded.

Andropogon spp. (Bluestems), Asteraceae spp. (Asters), Eriocaulon spp., Rhexia spp.,

Rhynchospora spp., Sarracenia spp., Scleria spp. (Nutrushes), and Xyris spp. were grouped. In

PC-ORD, a Sorenson (Bray-Curtis) distance measure was used in addition to shortest path for

data with high beta-diversity and partially disjunct outliers. Monte Carlo tests determined if the

ordination results were significantly different from random data. MRPP was additionally used to

test for differences within and between disturbance treatment groups (McCune & Grace 2002).

This method is effective for testing differences when sample sizes are small or distributions of

the data are unknown.

Results

Foliar Cover

How does frequency and time since last disturbance effect foliar cover? Disturbance

frequency and time since last disturbance affected total foliar cover across dates (Figure 5-3;

Table 5-1; Table 5-2). Pre-treatment total foliar cover among plots was indistinguishable (p=1.0).

There was a significant decline in total foliar cover after the initial disturbance treatments

(p<0.0001). Frequently disturbed plots (F1 and F4) continued to decline the first year of the

study (p<0.0001). Total foliar cover was significantly less in all treatment plots (F1, I1, F4, and

I4) than controls (p<0.0001) in June 2011. Although infrequently disturbed plots (I1 and I4)

began to recover, total foliar cover remained significantly lower after one year than pre-

treatment (p<0.0001). Plots that were not disturbed after the first year of the study (F1 and I1)

continued to increase in total foliar cover over the next three years. Only I1 plots recovered to

pre-disturbance cover (p=0.9991) and were indistinguishable from controls (p=0.9632). After

78

three years of recovery, cover for F1 plots remained significantly lower than cover pre-

disturbance (p=0.0012) and the controls (p<0.0001). F1 plots were indistinguishable from I1

plots (p=0.8116) by September 2013. Total cover continued to decline after subsequent

disturbances when disturbed once a year (I4) for the next three years. After four years of annual

disturbance (I4), cover was 16.6%, significantly lower than pre-disturbance (p<0.0001) and the

controls (p<0.0001), but not different from F4 plots (p=1.0). Plots disturbed quarterly for four

years (F4) declined steadily to 8.60% and had the lowest cover out of all treatments except I4, at

the end of the study. Frequency of disturbance affected total cover, however these effects are

confounded by time since last disturbance.

Cover of functional groups also changed by disturbance treatment over time (Table 5-1;

Table 5-2). As expected, there was a decline in forb (Figure 5-4), grass (Figure 5-5), and woody

species (Figure 5-6) cover after the initial disturbances (p<0.0001). I1 plots recovered to pre-

disturbance cover for forbs (p=1.0), grass (p=1.0); and woody (p=0.9994) by the end of the study

and did not differ from controls (forbs, p=0.9947; grass, p=1.0; woody, p=1.0). F1 plots had less

forb cover than pre-disturbance plots (p<0.0001), but did not differ from controls (p=0.2099).

Grass and woody cover in F1 plots recovered to levels indistinguishable from the pre-disturbance

levels (p=1.0) and controls (grass, p=0.9901; woody, p=1.0). Plots disturbed over the entire four

years (F4 and I4) experienced the greatest decline in cover by functional group. Forb and grass

cover was significantly less than pre-disturbance cover (p<0.0001) and controls (p<0.0001) by

2013 for F4 plots, while woody vegetation cover recovered to levels comparable to pre-

disturbance levels (p=0.6209) and controls (p=0.2428). The same pattern was observed for I4

plots. Forb and grass cover did not recover to pre-disturbance levels (p<0.0001) or to that of

controls (p<0.0001). Woody cover in I4 plots remained lower than controls (p=0.0463), but did

79

not differ from pre-disturbance levels (p=0.9996). By 2013, cover of forbs did not differ between

F4 and I4 plots (p=1.0), but both treatments were significantly lower than I1 (p<0.0001). F1 plots

had forb cover that was indistinguishable from I1 plots (p=1.0), but significantly greater than I4

and F4 plots (p=0.0766; p=0.0030 respectively). By 2013, cover of grasses did not differ

between F4 and I4 plots (p=1.0), but both treatments were significantly lower than I1

(p<0.0001). F1 plots had grass cover that was indistinguishable from I1 (p=1.0), but significantly

greater than I4 plots and F4 plots (p=0.0002; p=0<0.0001 respectively). By 2013, cover of

woody vegetation was significantly greater in F1 and I1 plots than I4 (p=0.0917; p=0.0964

respectively). The cover of woody species did not differ between the remaining disturbance

treatments by the end of study (F1&F4, p=0.4372; F1&I1, p=1.0; I1&F4, p=0.4500; and I4&F4,

p=1.0).

Aristida stricta (Figure 5-7) and Dichanthelium spp. (Figure 5-8) varied in their

responses to the experimental disturbance treatments (Table 5-1; Table 5-2). Aristida stricta and

Dichanthelium spp. experienced a significant decline (p<0.0001; p=0.0310 respectively) in cover

after the first disturbance event. A. stricta cover continued to decline and was significantly

reduced by Sept. 2013 in all disturbance treatments (F1, p=0.0033; F4, p<0.0001; I4, p<0.0001)

except I1 plots (p=0.3859) and controls (p=0.9999). At the end of the study, A. stricta cover was

indistinguishable between controls and I1 plots (p=0.4033), but A. stricta cover was significantly

reduced in F1 plots (p=0.0044), I4 plots (p=0.0011), and F4 plots (p=0.0008) compared to

controls. All treatments were indistinguishable in terms of A. stricta cover by 2013 (F1& I1,

p=0.9811; F1&I4, p=1.0; I4&F4, p=1.0; F1&F4, p=1.0; F4&I1, p=0.9073; I1&I4, p=0.9278). It

should be noted that while I1 did not significantly differ from the other treatments, A. stricta

cover was double that observed in the other treatments. Also, A. stricta cover observed in

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controls was double that of I1 plots. Dichanthelium spp. were able to recover to pre-disturbance

values in all disturbance treatments (I1, p=1.0; F1, p=0.9996; F4, p=0.7268; I4, p=0.9253) and

was not significantly different from controls (I1, p=0.6118; F1, p=0.9359; F4, p=0.7855; I4,

p=0.9979) by the end of the study. F4 plots had significantly less Dichanthelium spp. cover than

I1 plots (p=0.0263), but no other treatments differed by 2013 (F1& I1, p=1.0; F1&I4, p=0.4896;

I4&F4, p=1.0; F1&F4, p=0.1128; I1&I4, p=0.1856).

Cover of Sarracenia spp. declined significantly over the four-year study in treatment

plots (Figure 5-9; Table 5-1; Table 5-2). The effect of disturbance regime was significant. These

results indicate that soil disturbance has a negative effect on Sarracenia spp.

Camera Detected Hog Frequency

Our estimate for the number of hog occurrences at each camera site each year is

conservative considering the number of months that cameras were stolen, broken, or non-

functional. Still, on average there were more than two hog occurrences at each site every year of

the study. Cameras were first set up in June 2010 and averaged 3.79 hog occurrences in 2010. In

2011, the average hog occurrences at camera sites were 2.29. Hog occurrences increased to 5.75

in 2012 and 5.13 in 2013.

Richness

How does frequency and time since last disturbance effect species richness? Richness

was also affected by the experimental disturbance treatments (Figure 5-10). Overall, a seasonal

pattern in richness was detected, with lower richness in March and higher richness in June. The

initial disturbance resulted in a significant decline (p<0.0001) in richness. Richness in I1 plots

increased until September 2011 when there was no significant difference (p=0.9903) compared

to pre-disturbance levels. Richness in F1 plots were indistinguishable from pre-disturbance

values (p=1.0) by June 2012, with values not significantly different from controls and I1

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(p=0.9999). Until the end of the study, richness continued to increase and did not significantly

differ from pre-disturbance (I1 and F1, p=1.0) and controls (I1, p=0.9912; F1, p=1.0). Plots

disturbed for the duration of the study (F4 and I4) exhibited further declines in richness. I4 plots

regained pre-disturbance richness (p=0.1611) with values that continued to differ from the

controls (p=0.0005) by the end of the study. F4 plots never regained pre-disturbance richness

(p<0.0001) and richness was significantly lower than the control (p<0.0001), I1 (p<0.0001), and

F1 (p<0.0001), yet indistinguishable from I4 (p=1.0).

Vegetation Composition


NMS ordination and MRPP revealed increasing compositional change with increased

disturbance frequency and decreased time since last disturbance (T=-14.1016; A=0.0875;

p<0.0001; Figure 5-11). Vegetation composition in control plots and I1 plots clustered together

and changed relatively little over the four years. F1 and I4 treatments changed vegetation

composition, but the most extreme change in vegetation composition was observed in the F4

treatment. A three-dimensional ordination was optimal (stress = 18.8439) with axis 1 explaining

9.6%, axis 2 explaining 36.4%, and axis 3 explaining 25.4% of the variation. Monte Carlo test

determined that the ordination differed from random data (p=0.0164). When data were grouped

by time since disturbance (i.e., I1 & F1 compared to I4 & F4), MRPP showed that time since

disturbance is important in the clustering of groups in the NMS ordination (T=-12.2302;

A=0.03451; p<0.0001). MRPP also illustrated that soil does influence community composition

(T=-7.4020; A=0.0385; p<0.0001), although disturbance regime was most reflected in the NMS

ordination clusters.

82

Discussion

The results from these analyses demonstrate that the effect of disturbance on seepage

slope vegetation cover, richness, and composition was a function of frequency of occurrence.

Recovery of vegetation was, in turn, a function of time since disturbance. Frequent disturbance

for four years (F4) resulted in the lowest cover and richness and most altered composition, while

frequent disturbance for one year (F1) with three years of recovery resulted in cover, richness,

and composition that was similar to controls and plots only disturbed once (I1).

How does frequency and time since last disturbance effect foliar cover? Dominant

flora such as A. stricta, was negatively affected by soil disturbance treatments. This shallow

rooted (Outcalt & Lewis 1990) keystone species (Noss 1989) is important to carry fire (Clewell

1989; Haywood & Harris 1999). Hog foraging results in soil disturbance that is novel in type,

intensity, and frequency. Aristida stricta experienced significant declines in all treatments except

plots disturbed once (I1) and failed to reestablish in plots that were disturbed more than once.

The decline in A. stricta cover that occurred in 2013 in all treatments and controls could not be

explained by removing from the analysis plots that burned in prescribed fires during the spring of

2013. It is likely that some other unquantified variable affected cover. Still, these observations

substantiate those in Chapter 3 where A. stricta cover was significantly lower in high intensity

than controls. The loss of this keystone species is significant, especially considering that woody

species were less negatively impacted by disturbance regime. It seems that a positive feedback is

established through soil disturbance where A. stricta cover is lost and woody cover maintains,

both of which reduce fire spread (Chapter 2), ultimately leading to increased woody cover.

Unlike A. stricta, some Dichanthelium species are commonly found in early, secondary

successional communities. These grasses require bare soil to recolonize and capitalize on post-

disturbance conditions with decreased competition and increased colonization opportunities,

83

increasing dramatically in terms of cover (Estes 2006). In plots that were disturbed during the

first year of the study (F1, I1), Dichanthelium species actually increased in cover from pre-

disturbance cover, although this increase was not significant. Cover of Dichanthelium species

kept grass cover high even while other grasses, such as A. stricta, declined.

Sarracenia species are sensitive to hog disturbance (Johnson 2001). Trampling and

rooting, both the physical action and associated changes in soil moisture, negatively impact

survival of juvenile Sarracenia (Hermann 1995). Research has also shown that abundance of

white-top pitcherplants and yellow trumpets are both negatively correlated with areas of hog

disturbance (Engeman et al. 2007). Our results also indicate that Sarracenia species are sensitive

to soil disturbance as cover declined in all treatments, although cover did not decline in controls.

Our experimental soil disturbance results indicate that soil disturbance more than once a

year will reduce species important to the function and unique composition of the seepage slope

community. Motion sensor wildlife cameras detected a true frequency of hog foraging around

two to five hog occurrences at each site every year of the study. This conservative estimate of

true hog disturbance frequency in specific portions of particular slopes is greater than our

experimental frequency that resulted in degradation of the community in terms of cover of

important/keystone species. As a result, hogs appear to return to disturb seepage slopes

frequently enough to negatively impact the community composition, structure, and function.

How does frequency and time since last disturbance effect species richness? This

analysis did not find richness to vary unimodally across a gradient of disturbance frequencies,

but rather found that highest species richness resulted from the lowest experimental soil

disturbance frequency and longest time since soil disturbance. This richness was equivalent to

the observed pre-disturbance richness levels. In the P. palustris-A. stricta ecosystem, fire is a

84

large-scale disturbance that reduces aboveground competition, but does not reduce richness

(Kirkman et al. 2001). High diversity is achieved in P. palustris communities when frequent fire

limits hardwood species dominance (and competitive exclusion) and perennial life histories

allow species to persist once established (Brockway & Lewis 1997; Kirkman et al. 2001).

Seepage slope vegetation is also subject to prolonged soil saturation and thus this stress (Huston

1979). This stress combined with frequent disturbance from fire limits the potential for

competitive exclusion enhancing diversity (Kirkman et al. 2001). Also, oligotrophic conditions

slow the rate of recovery from disturbance due to the lack of available nutrients (Walker & Peet

1983), which explains why recurrent soil disturbance at any frequency reduces seepage slope

plant diversity temporarily. Species richness then has the opportunity to recover with increasing

time after the disturbance. This recovery of richness should not be the only metric used to

interpret recovery as differences in species composition is not taken into account (McLachlan &

Bazely 2001).


Deterministic factors of life history characteristics (Kirkman et al. 2004) and competitive

relationships of resident plant species influence the vegetation dynamics and recovery trajectory

after disturbance events. Many resident species in seepage slopes, like other successional

communities maintained by frequent disturbance, have life history traits that allow for

resprouting and vegetative expansion after fire. This response facilitates (when given three years

to recover) the community returns to the pre-disturbance composition (Halpern 1988). The NMS

and MRPP analyses revealed that continued disturbance (F4, I4), even at a low frequency of

once a year, alters species composition. Once extirpated from a site, species with limited

dispersal take longer to reestablish in disturbed sites then seeds of plants that are wind or animal

85

dispersed (Kirkman et al. 2004). Further research is necessary to determine if seepage slopes

with prolonged disturbance will recover in terms of species composition given more time

considering other studies in P. palustris savannas have found that some species are particularly

vulnerable to disturbance and do not reestablish even after extended periods of time (i.e. 65

years) (Kirkman et al. 2004).

Summary

A fundamental question in ecology is whether or not communities have an inherent

resilience to recover pre-disturbance structure and function, or if historical events create legacies

that allow for more than one alternative state. The successional trajectory and development of a

community after a disturbance event is dependent upon remaining vegetation and recruitment,

which in turn depends on dispersal limitations and differences in mechanisms of establishment

(Young et al. 2001). This experiment demonstrated: 1) development of a legacy effect in plots

that had continued disturbance for four years; and 2) differences among the ability of species to

recover and recruit after varying levels of disturbance. Frequent disturbance for four years (F4)

created a legacy that impaired foliar cover, richness, and altered species composition. Longer-

term continuation of this study would be necessary to determine if a threshold has been crossed

to an alternative stable state.

86

Table 5-1. Repeated measures ANOVA results for the foliar cover of total vegetation, functional

groups, A. stricta, Dichanthelium spp., Sarracenia spp., and species richness by

disturbance frequency on Eglin AFB.


Total Vegetation Time 11 375.5 90.95 <0.0001

Treatment 3 35.99 40.22 <0.0001

Time x Treatment 33 375.5 17.71 <0.0001

Forb Time 11 374.9 27.46 <0.0001

Treatment 3 35.18 15.81 <0.0001

Time x Treatment 33 374.8 5.62 <0.0001

Grass Time 11 376 33.4 <0.0001

Treatment 3 36.09 23.46 <0.0001

Time x Treatment 33 375.9 9.82 <0.0001

Woody Time 11 375.5 14.07 <0.0001

Treatment 3 36.12 6.1 0.0022

Time x Treatment 33 375.5 2.83 <0.0001

Aristida stricta Time 11 376 17.19 <0.0001

Treatment 3 36.33 11.3 <0.0001

Time x Treatment 33 375.9 4.01 <0.0001

Dichanthelium spp. Time 11 375.4 17.46 <0.0001

Treatment 3 35.96 7.16 0.0008

Time x Treatment 33 375.4 3.5 <0.0001

Sarracenia spp. Time 11 377.9 3.17 <0.0001

Treatment 3 36.44 2.75 0.0743

Time x Treatment 33 377.9 0.99 0.5497

Richness Time 11 375.9 68.68 <0.0001

Treatment 3 36.34 16.49 <0.0001

Time x Treatment 33 375.9 6 <0.0001

87

Table 5-2. Repeated measures ANOVA results for the foliar cover of total vegetation, functional

groups, A. stricta, Dichanthelium spp., and Sarracenia spp., and species richness by

disturbance frequency on Eglin AFB with controls in 2010, 2012 and 2013. Total

vegetation cover was also surveyed in 2011.


Total Vegetation Time 3 161.5 325.6 <.0001

Treatment 4 55.21 142.6 <.0001

Time x Treatment 12 161.4 54.86 <.0001

Forb Time 2 105.3 37.75 <.0001

Treatment 4 52.96 16.97 <.0001

Time x Treatment 8 105.3 6.98 <.0001

Grass Time 2 106.7 25.57 <.0001

Treatment 4 54.12 11.84 <.0001

Time x Treatment 8 106.7 12.95 <.0001

Woody Time 2 106.1 7.24 0.0011

Treatment 4 54.73 5.67 0.0006

Time x Treatment 8 106.1 1.4 0.2200

Aristida stricta Time 2 105.8 48.68 <.0001

Treatment 4 54.63 7.44 <.0001

Time x Treatment 8 105.7 5.7 <.0001

Dichanthelium spp. Time 2 106.9 0.68 0.6041

Treatment 4 55.52 2.54 0.0441

Time x Treatment 8 106.9 2.9 0.0111

Sarracenia spp. Time 2 106.3 2.78 0.4446

Treatment 4 55.35 1.92 0.3745

Time x Treatment 8 106.3 1.29 0.5518

Richness Time 2 107.7 5.48 0.0159

Treatment 4 55.87 12.05 <.0001

Time x Treatment 8 107.7 6.98 <.0001

88




89

Figure 5-3. Total foliar cover by disturbance treatment over time on Eglin AFB. Different letters

above points indicate significant difference (α = 0.05) within each survey date

following Tukey–Kramer post-hoc tests. Dotted lines indicate annual disturbance

treatment.

90

Figure 5-4. Foliar cover of forbs by disturbance treatment over time on Eglin AFB. Different

letters above points indicate significant difference (α = 0.05) within each survey date


treatment.

91

Figure 5-5. Foliar cover of grasses by disturbance treatment over time on Eglin AFB. Different



treatment.

92

Figure 5-6. Foliar cover of woody species by disturbance treatment over time on Eglin AFB.

Different letters above points indicate significant difference (α = 0.05) within each

survey date following Tukey–Kramer post-hoc tests. Dotted lines indicate annual

disturbance treatment.

93

Figure 5-7. Foliar cover of A. stricta by disturbance treatment over time on Eglin AFB. Different



treatment.

94

Figure 5-8. Foliar cover of Dichanthelium spp. by disturbance treatment over time on Eglin

AFB. Different letters above points indicate significant difference (α = 0.05) within

each survey date following Tukey–Kramer post-hoc tests. Dotted lines indicate

annual disturbance treatment.

95

Figure 5-9. Foliar cover of Sarracenia spp. by disturbance treatment over time on Eglin AFB.

Dotted lines indicate annual disturbance treatment.

96

Figure 5-10. Species richness by disturbance treatment over time on Eglin AFB. Different letters

above points indicate significant difference (α = 0.05) within each survey date


treatment.

97

Figure 5-11. Three-dimensional nonmetric multidimensional ordination showing cover by

species by disturbance treatment on Eglin AFB in June 2010 and Sept 2013. Each

point represents a plot and the distance between points is proportional to the

difference in species composition.

98

CHAPTER 6

CONCLUSIONS

The seepage slope community is, for the most part, poorly understood despite its intrinsic

beauty and scientific value (Hermann 1995). This research addresses a data gap by quantifying

hog disturbance and its impact on this unique wetland habitat. Our results strongly suggest that

hog management should be viewed as a long-term management strategy that may need to be

adjusted on an annual basis depending on environmental factors (Bieber & Ruf 2005). Managers

should protect the lower portions of seepage slopes (e.g., using fence exclosures) where feral

hogs prefer to forage and where rare, endemic flora and fauna are found. Additionally, it is

evident that this novel soil disturbance reduces cover of A. stricta and alters vegetation

composition, likely indicating that ruderal species recolonize hog-created gaps where

competition is decreased (Cushman et al. 2004). This research indicates that the exclusion of

feral hogs from seepage slopes is the first step towards the conservation and/or restoration of this

endangered plant community. In some cases and where practical, it may be necessary to actively

restore portions of a slope with appropriate combinations of soil stabilization, direct seeding,

and/or outplanting of seedlings of native species. Considering that so little of the original extent

of this community is still intact (FNAI 1990), encroachment of woody species into remaining

seepage slopes is a serious threat. It may be necessary for prescribed fire crews to push fire

downslope into areas where fire may not spread unassisted or cut and clear these areas by hand.

Continued active management, including hog control and monitoring, is essential to mitigating

hog damage and preserving the ecological integrity of this rare resource.

99

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113

BIOGRAPHICAL SKETCH

Megan was born and raised in a small town south of Richmond, Virginia. She graduated

from the University of Virginia in 2002 with a Bachelor of Arts degree in biology. Megan went

on to earn a Master of Science degree in geological sciences from Virginia Polytechnic Institute

and State University in 2004. An internship working with the Bureau of Land Management and

Chicago Botanic Garden took her to the tiny town of Vale in eastern Oregon. This experience

fostered her interest in wetlands and restoration. After leaving Oregon, Megan went back east to

teach biology laboratories at Virginia State University in 2005. Restless for a job with more time

outside, she saw an opportunity to go back to school and conduct wetland research at the

University of Florida. In 2008, she became a fellow in the Adaptive Management of Water,

Wetlands, and Watershed Integrative Graduate Education and Research Traineeship (IGERT)

program that was funded by the National Science Foundation. Megan earned her Ph.D. in

interdisciplinary ecology from the University of Florida in May of 2014.

to my dad in docs/recent research/2015_03_… · to my dad . 4 acknowledgments first, i would like...

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