Amphibian Use of Man-Made Pools Created by Military Activity on Kisatchie National

Forest, Louisiana

A thesis presented to

the faculty of

the College of Arts and Sciences of Ohio University

In partial fulfillment

of the requirements for the degree

Master of Science

Stephen M. Ecrement

August 2014

© 2014. Stephen M. Ecrement. All Rights Reserved.

2

This thesis titled

Amphibian Use of Man-Made Pools Created by Military Activity on Kisatchie National

Forest, Louisiana

by

STEPHEN M. ECREMENT

has been approved for

the Program of Environmental Studies

and the College of Arts and Sciences by

Kelly Johnson

Associate Professor of Biological Sciences

Robert Frank

Dean, College of Arts and Sciences 3

ABSTRACT

ECREMENT, STEPHEN M., M.S., August 2014, Environmental Studies

Amphibian Use of Man-Made Pools Created by Military Activity on Kisatchie National

Forest, Louisiana (46 pp.)

Director of Thesis: Kelly Johnson

Pools created from military training provide breeding for many amphibian . Six hundred and twenty four surveys were conducted for larval on 48 small man-made pools, created from military maneuver training (tank defilades), on the

Fort Polk Intensive Use Area (IUA) of Kisatchie National Forest, Louisiana. Surveys were conducted monthly from April to early October 2012 and March to September

2013. Anuran species composition varied across tank defilades, with environmental variables explaining the presence and abundance of some species. Bronze

(Lithobates clamitans), Northern Cricket frogs (Acris crepitans), Fowler’s

( fowleri), Eastern Narrow-Mouthed toads (Gastrophryne carolinensis), Gray tree complex (Hyla versicolor/chrysoscelis), and Squirrel tree frogs (Hyla squirellii) were not abundant enough for analysis. Cajun Chorus frogs (Pseudacris fouquettei) and

Southern Leopard frogs (Lithobates sphenocephalus) occurred in 79% of the pools.

Salamanders were not encountered at the study site either year. Of seven variables evaluated using regression models, open canopy, low percent slope, and fish absence were positively related to the abundance of Cajun Chorus frogs (Pseudacris fouquettei).

Percent dissolved oxygen and low canopy closure were positively associated with

Southern Leopard frogs (Lithobates sphenocephalus) abundance. My results show that 4

the two species use these man-made pools differently, highlighting the importance of having pools in varying conditions. In light of documented declines of anuran populations, it has become increasingly important to protect their breeding habitat. It is equally important to gain an understanding of habitat characteristics that attract or deter breeding amphibians from natural or man-made aquatic systems. Although these pools were created unintentionally they now serve as amphibian breeding habitat.

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ACKNOWLEDGEMENTS

I would like to thank my wife, Mariamar Gutierrez Ramirez, for her love and unconditional support during the duration of my master’s thesis. I am eternally grateful because without her I would not have achieved this goal. I also want my family to know how much I appreciate their continuously optimistic attitudes toward my ambition to complete a Master’s degree even when I gave them reason to believe otherwise. I give special recognition and appreciation to Dr. Stephen Richter (Eastern Kentucky

University) for walking me through the research design and statistical analysis via emails and phone conferences. Dr. Richter went above and beyond expectations. A special thanks to my advisor Dr. Kelly Johnson, first for accepting me as a graduate student and second for guiding me through the data analysis and writing process. I thank my committee members – Dr. Natalie Kruse and Dr. Matthew White – for their support and guidance. Special appreciation for the Fort Polk, Conservation Branch and the Center for the Environmental Management of Military Lands (CEMML) supervisors for providing me with the opportunity to finish my graduate course work. My gratitude to the Kisatchie

National Forest for allowing me to conduct my research on their property. I also want to express my sincere gratitude to everyone that assisted me from the day we “discovered” the tank defilades through one year of trial and error and two years of field data collection: Brian Early, Jeff Wilson, Bridgett Goldsmith, Brett Cooper, Jim Johnson,

Christopher Melder, Dean Maas, Willis Sylvest, Ray Geroso, Shane Carnahan, Brittany

Chaumont, Mariamar Gutierrez, Ken Moore, Sheila Guzman, Rocky Numbers, Sarah

Pearce, Jeanne Daigle, Madison Daigle, and Stacy Huskins. 6

TABLE OF CONTENTS

Page

Abstract……………………………………………………………………………………3

Acknowledgements……………………………………………………………….……….5

List of Tables……………………………………………………………………………...7

List of Figures……………………………………………………………………………..8

Introduction………………………………………………………………………………..9

Methods…………………………………………………………………………………..13

Study Site………………………………………………………………………...13

Data Collection…………………………………………………………………..14

Data Analysis…………………………………………………………………….16

Results……………………………………………………………………………………19

Discussion………………………………………………………………………………..34

Literature Cited…………………………………………………………………………..40

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LIST OF TABLES

Page

Table 1: Minimum, maximum and mean of the seven variables used in a Global model for predicting amphibian Catch Per Unit Effort in tank defilade pools in 2012 (A) and 2013 (B), Kisatchie National Forest, Louisiana…………………………………………18

Table 2: Species of anurans confirmed using the tank defilades pools for reproduction..19

Table 3: Seven anuran species confirmed using the tank defilade pools for reproduction in 2012…………………………………………………………………………………...20

Table 4: 2012 species abundant enough for analysis of abundance and the output from the Tweedie regression model for statistically significant independent variables……..…….21

Table 5: Five anuran species confirmed using the tank defilade pools for reproduction in 2013….……..…………………………………………………………………………….23

Table 6: 2013 species abundant enough for analysis and the output from the Tweedie regression model for statistically significant independent variables…………………….24

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LIST OF FIGURES

Page

Figure 1: Aerial photo of the 48 tank defilades on the Kisatchie National Forest Intensive Use Area....……………………………..……………………………….…….……...... 14

Figure 2: Total tadpole count for other species encountered at the tank defilade study site in 2012………………....………………………………………………………...………21

Figure 3: Relationship of fish presence (A) (P = 0.010) and canopy closure (B) (P = 0.041) on Pseudacris fouquettei maximum catch per unit effort in 2012. Only two pools with relatively open canopy and no P. fouquettei had established fish populations.…….22

Figure 4: Relationships of percent canopy closure (A) (P = 0.037) and dissolved oxygen (B) (P = 0.081) on Lithobates sphenocephalus maximum Catch Per Unit Effort in 2013………………………………………………………………………………………25

Figure 5: Relationship of fish presence (P = 0.067) to Pseudacris fouquetteii maximum CPUE in 2013…………………………………………………….……………………...26

Figure 6: Relationship of mean % slope (A) (P = 0.015), and % canopy closure (B) (P = 0.026) to Pseudacris fouquetteii maximum CPUE in 2013. Red diamonds indicate pools with relatively open canopy, established fish populations, and no P. fouquetteii larvae..27

Figure 7: Monthly rain data for Fort Polk, Louisiana in 2012 and 2013……….…...... 28

Figure 8: Mean and standard error values for center depth for all 48 tank defilades during each month that the pools were sampled in 2012 (A) and 2013 (B) …………………….29

Figure 9: Mean values and standard error values for wetted surface area for all 48 tank defilades during each month pools were sampled in 2012 (A) and 2013 (B)...………….30

Figure 10: Mean and standard error values for bottom temperature on all 48 tank defilades each month pools were sampled in 2012 (A) and 2013 (B) ……...…………...31

Figure 11: 2012 3D NMDS ordination based on similarity of presence/absence of anuran species and vectors showing the influence of environmental variables (Stress = 0.09, Axis 1R² = 0.62, Axis 2R² = 0.32)…………………………………………………………….33

Figure 12: 2013 3D NMDS ordination based on similarity of presence/absence of anuran species and vectors showing the influence of environmental variables (Stress = 0.07, Axis 1R² = 0.64, Axis 2R² = 0.27)……………………………………………………….....…33 9

INTRODUCTION

Evidence indicates that amphibian populations are suffering from declines, range

restrictions, and species extinctions on a local and potentially global scale (Blaustein et. al. 1994, Alford and Richards 1999, Gardner 2001, Babbitt et. al. 2009), which are often directly or indirectly the result of human activity (Dorcas and Gibbons 2008).

Amphibians require both terrestrial and aquatic , and thus are negatively impacted by clear cuts and habitat fragmentation, poor water quality, development, invasive species, and wetland destruction (Alford and Richards 1999). The conservation of amphibians requiring a habitat mosaic of small, isolated breeding pools in addition to large areas of upland habitat is of global interest (Colburn 2004). Dispersing juveniles and migrating adults of most pool-breeding amphibians are also dependent on terrestrial habitat for foraging and overwintering (Semlitsch 1998; Semlitsch and Bodie 2003).

Conservation planning for pool-breeding amphibians thus must be informed from habitat investigations at multiple scales – pool, local, and landscape scales (Baldwin et al. 2006;

Marsh and Trenham 2001; Semlitsch 2002; Porej et al. 2004)

At the pool-scale, unique environmental features may influence breeding of particular amphibian species. Hydro-period strongly influences growth, survival, and community structure among larval amphibians (Rowe and Dunson 1995; Skelly 1997;

Snodgrass et al. 2000). Other within-pool habitat characteristics that have been shown to affect breeding amphibian species composition include pool size (Burne and Griffin

2005), forest canopy closure over the pool basin (Caldwell 1986, Skelly et al. 1999, 10

Skelly et al. 2002, Werner et al. 2009), and extent of shrubs and persistent non-woody vegetation (Burne and Griffin 2005; Egan and Paton 2004).

When wetlands are filled, developed, or otherwise destroyed, mitigated wetlands are created to offset the loss of habitat (Clean Water Act, section 404). Although a goal of wetland mitigation is to replace lost wetland functionality, wetlands constructed through mitigation often fail to duplicate natural processes (Lichko and Calhoun 2003, Moreno-

Mateos et al. 2012, Denton and Richter 2013). Artificially made wetlands continue to be measured by area rather than function (Shulse et al. 2010). Many artificially created pools are functionally different than wetlands due to steep slopes that inhibit vegetative growth

(Minkin and Ladd 2003). Although artificial wetlands can provide surrogate habitat for amphibians (Brand and Snodgrass 2010), their suitability for individual species likely depends on incorporating habitat requirements into wetland plans (Pechman et al. 2001,

Shulse et al. 2010).

The military holds over 30 million acres of diverse habitat

(www.army.mil) and Fort Polk, home of the Joint Readiness Training Center (JRTC), make up approximately 100,000 acres of that land. In 1960, the Sikes Act recognized the importance of natural resources on military lands and provided guidelines to protect and enhance these ecosystems while still allowing the military to train its troops. Aquatic and terrestrial habitats required by wildlife species may be influenced by training activity on these lands, and aquatic ecosystems in particular are a vital resource that may be directly or indirectly impacted by military installation development and training. 11

The JRTC at Fort Polk provides realistic, relevant and rigorous training that includes war game scenarios, practicing combat positions and other role play exercises to ready troops for real-life conditions during deployment (http://www.jrtcpolk.army.mil/).

Several locations on Fort Polk and the US Forest Service Vernon unit Intensive Use Area

(IUA) have high concentrations of small artificial vernal pools, called tank defilades, which were created from military maneuver exercises that have not been repaired. During tank exercise maneuvers, the Army creates large pits (tank defilades) using a bulldozer which allow tanks to drive below the surface of the ground. This tactic protects the body of the tank with only the turret above ground and makes it less visible to the enemy along the horizon. Tank defilades that have been abandoned for several years often develop into ideal breeding grounds for amphibians, due to their capacity to hold water temporarily. These man-made temporary pools create a unique opportunity to study pool- scale features of amphibian breeding habitat that may allow us to understand the requirements for particular species. Understanding how vegetation, hydrology, and other local wetland features affect different amphibian species will improve our ability to incorporate these features into future wetland construction (Denton and Richter 2013).

This project focuses on a series of tank defilades, created by military activity, that have developed into pools and function as breeding habitat for several amphibian species.

Although these pools were not constructed for wetland mitigation or amphibian management, I was able to look at the differences in amphibian abundance in comparison to the specific features of each pool. Differences between pools may assist land managers in constructing pools with desirable characteristics for amphibians (Denton and Richter 12

2013). My objectives were to 1) identify herpetofaunal species using this man-made habitat; 2, describe the basic hydrology of this system; and 3, determine whether the abundance of breeding amphibian species across the tank defilade pools can be predicted based on the specific characteristics of each pool. In other words, are there pool-scale characteristics that help predict the abundance of amphibian species?

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METHODS

Study Area

The Vernon unit of Kisatchie National Forest (KNF) is an 85,000 acre tract of land, located in Vernon Parish, Louisiana 10 miles southeast of Leesville, LA. In 2011, approximately sixty tank defilades were identified on KNF; Calcasieu Ranger district,

Vernon unit land adjacent to the Fort Polk US Army installation. This unit of the National

Forest is utilized by the US Army for training and is divided into Intensive Use (IUA) and Limited Use (LUA) Areas. Throughout the 1980’s, Fort Polk hosted the 5th Infantry

Division which used portions of the IUA for heavily mechanized tank training. Army regulation requires that all tank defilades and other fighting positions be filled and repaired, however in the late 1980’s regulations were more relaxed and now these abandoned fighting positions have formed into potential amphibian breeding habitat.

Based on aerial photos provided by the Fort Polk Environmental and Natural Resources

Management Division (ENRMD) - Conservation Branch, the tank defilades on IUA property were created between 1985 and 1991. Prior to conducting amphibian surveys I confirmed that 48 of the 60 tank defilades held water at least seasonally (Figure 1).

My study focused on these 48 tank defilades which are congregated within an 8 hectare area located on State Highway 463, thirteen kilometers north of Pitkin, Louisiana

(31º01’N, 93º13’W). The study site is located in an upland longleaf pine ecosystem with a bluestem-herbaceous (Andropogon sp.) understory. A 300-acre clear-cut military range

(Range 42) is just west/northwest adjacent to the 8-hectares, with two intermittent streams along the northeast and southwest sides of the study site. 14

Figure 1. Aerial photo of 48 tank defilades on the Kisatchie National

Forest Intensive Use Area.

Data Collection

In 2012, access to my study site was difficult due to an active range adjacent to the site, so the order in which data was collected differed from 2013. In 2013, tank defilades were divided into four groups of 12 and each group was sampled in a random order monthly from March through September. In contrast, in 2012 the tank defilades were not grouped and sampled randomly and were rarely sampled within four consecutive days (often several weeks between sampling events). Amphibian surveys and water quality sampling occurred successively between 0600 and 1100. All groups were sampled in four consecutive days when possible, however due to limited access 15

during military training, sampling days were occasionally non-consecutive. At each tank defilade with a pool, two individuals used Cummins deep-style ace mesh nylon nets

(frame size of 16”x9”, handle length of 42”, net depth of 12” and a 1/16” fine mesh) to capture larval stage amphibians. Prior to amphibian sampling, the length and width of each pool within a tank defilade was measured to the decimeter using a reel tape. These measurements allowed me to calculate the surface area of an ellipse (3.14x.5xLx.5xW) in order to determine the number of sweeps needed to meet a one sweep per 2m² protocol. A

“sweep” consisted of extending the dip-net into the water from shore and bouncing the net along the substrate while pulling back toward the surveyor. After sampling the entire edge of the pool, each surveyor would step further into the pool, toward the center, and repeat the dip-netting process. The total number of dip net sweeps was spread out over the entire pool in an attempt to sample the pool as evenly as possible. Sweeps that produced amphibian larvae were dumped into a white bucket to be counted, identified to species, and released on site. I worked under Louisiana State Natural Heritage permit

#LNHP-13-064 and Ohio University protocol IUCUC # 13-L-037.

Habitat characteristics were recorded at each tank defilade pool. I used a YSI 556

MPS unit to determine the total percent of dissolved oxygen, an Eco Testr pH2 for pH and an Accumet AP85 for conductivity and salinity. This equipment was calibrated early in the day prior to sampling the entire series of 48 tank defilades. Water temperature was recorded at the bottom edge and center surface of each tank defilade pool and a turbidity tube was used to determine water clarity. Water quality data was recorded between 0600 and 1100 hours prior to sampling each pool. After sampling for amphibian larvae, water 16

depth was measured at the deepest point and 0.5m from the water’s edge in all four cardinal directions using a meter stick accurate to the centimeter. These measurements were also used to calculate tank defilade slope at the time amphibian larval sampling occurred. Additionally, I noted the presence of fish, macro , adult herpetofauna, egg masses and number of Chinese tallow ( Triadica sebifera) stems within the tank defilade. Fairy Shrimp (Order: Anastraca) and crayfish (Order: Decapoda) were usually in such large numbers that they were recorded as 0, <100, or >100.

Additionally, 0.25m² vegetation plots were sampled at the edge of each pool on all four sides. Vegetation within each plot was visually estimated as percent emergent or open water equaling 100% and averaged across the 4 samples. Using a Model-A spherical densitometer I recorded canopy closure in the center and on all four sides of the pool, facing away from center. These readings were calculated and averaged across the 5 samples for a total percent of closed canopy over that tank defilade. Due to the varying duration that tank defilades held water, hydro-period was divided into four monthly categories of 3, 6, 9 (dried) and 12 (permanent). For data analysis I multiplied the mean length and mean width for each pool to calculate a mean pool size (wetted surface area) within each tank defilade for each year.

Data Analysis

The sampling event with the maximum abundance for each species within each tank defilade was chosen for analysis to avoid counting individual larvae multiple times.

The total number of tadpoles for each species was divided by the total number of dip-net sweeps to calculate a Catch Per Unit Effort (CPUE) and was used as the response 17

variable. Mean, maximum (max) and minimum (min) for each variable was calculated and then Spearman Correlations were run between them (e.g. % Slope mean, max, min) to identify if they were correlated. The max and min of each variable were not correlated to one another; however the mean was consistently correlated to both the max and min.

The mean of each variable was used to run correlation tests across all variables. Predictor variables that were highly correlated (r ≥ 0.7) were excluded from the generalized linear model (Shulse et al. 2010).

Seven predictor variables (Table 1) were chosen as unique features representing each of the forty-eight tank defilade pools for the regression models. A custom Tweedie distribution with a log-link function was used in SPSS version 21 (IBM SPSS, Inc.,

Chicago, IL) with an index parameter that determines the shape of the probability distribution (Shono 2008). A Tweedie distribution can accommodate discrete and continuous data as well as many zeroes and because CPUE standardizes sampling effort allowing count data to become more continuous (Denton and Richter 2013). Parameters p can be > 1 or < 2 when using CPUE data. A p of 1.5 was chosen based on the highest log- likelihood from the goodness -of-fit output as suggested by Shono (2008) and a model using all 7 predictor variables was run. The variable with the highest p-value in the model was manually removed in a backward elimination fashion until all remaining variables had significance P < 0.1.

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Table 1.

Minimum, maximum and mean of the seven variables used in a Global model for predicting Pseudacris fouquettei and Lithobates sphenocephalis Catch Per Unit Effort in tank defilade pools in 2012 (A) and 2013 (B).

Standard A 2012 N Min Max Mean Deviation Pseudacris 40 0 5 0.99 1.48 fouquettei Dependent Variable CPUEmax Canopy Closure 40 22 99 75.25 20.11 Mean Emergent 40 0 85 21.16 21.39 Vegetation Mean Slope 40 0.21 0.77 0.50 0.17 Independent FISH Presence 40 0 1 Variables Mean Wetted 40 10.34 146.66 52.34 30.23 Surface Area Mean pH 40 5.48 6.68 5.79 0.25 Mean DO% 40 3.8 56.48 21.13 12.97

Standard B 2013 N Min Max Mean Deviation Lithobates sphenocephalus 48 0 19 3.2 4.16 Dependent Variables CPUEmax Pseudacris fouquettei 48 0 5 0.63 0.93 CPUEmax Canopy Closure 48 22 99 74.98 19.59 Mean Emergent 48 0 90 17.27 22.43 Vegetation Mean Slope 48 0.19 0.90 0.53 0.18 Independent FISH Presence 48 0 1 Variables Mean Wetted 48 17.90 131.72 54.26 25.98 Surface Area Mean pH 48 5.80 7.1 6.26 0.29 Mean DO% 48 8.63 41.63 21.00 8.58

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RESULTS

Species composition (abundance) varied across the pools with environmental and water quality data explaining the abundance of Lithobates sphenocephalis and Pseudacris fouquetteii. In addition to amphibian larvae, 8 species of adult herpetofauna were observed using the tank defilade pools (Table 2). In 2012, I confirmed tadpoles of seven anuran species in 88% (42 of 48 pools) of the tank defilade pools (Table 3). A total of

4,511 tadpoles were counted as part of 288 pool surveys. Cajun Chorus frogs (2,403 tadpoles) and Southern Leopard frogs (1,985 tadpoles) were the only two species abundant enough for a robust regression analysis. Eastern Narrow-Mouthed toads

(Gastrophryne carolinensis) were the third most abundant species and resulted in only 35 individual tadpoles from four pools. Northern Cricket frogs (32 tadpoles), Squirrel tree frogs (Hyla squirellii) (14 tadpoles), Gray tree frog complex (Hyla versicolor/ chrysoscelis) (20 tadpoles) and Bronze frogs (Lithobates clamitans) (20 tadpoles) were less abundant, and were excluded from further analysis (Figure 2).

Table 2.

Species of anurans confirmed using the tank defilades pools for reproduction Chelydra serpentina Common Snapping Turtle 2012 - 2013 Trachemys scripta Red-Eared Slider 2012 - 2013 Kinosternon subrubrum Mississippi Mud Turtle 2012 - 2013 Nerodia erythrogaster Yellow-Bellied Water 2012 - 2013 Agkistrodon piscivorus Cottonmouth Snake 2012 - 2013 Thamnophis proximus Western Ribbon Snake 2012 - 2013 Alligator mississippiensis American Alligator 2012 Lithobates catasbeanus American Bullfrog 2013

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Table 3.

Seven anuran species confirmed using the tank defilade pools for reproduction in 2012 % of pools Mean 2012 Species No. Individuals ± SE present CPUE Lithobates sphenocephalus 1935 33 1.84 0.44 Pseudacris fouquettei 2403 29 1.08 0.21 Acris crepitans 32 5 0.03 0.02 Hyla chrysoscelis/versicolor 20 2 0.01 0.01 Hyla squirella 14 4 0.02 0.01 Lithobates clamitans 20 2 0.03 0.03 Gastrophryne carolinensis 35 4 0.04 0.03

Cajun Chorus frogs were encountered in 29 pools (60%) while Southern Leopard frogs were encountered in 33 pools (69%). Number of species detected per tank defilade ranged from 0-3 with a mean of 2.

The maximum Cajun CPUE was best explained by two variables within the model; low canopy closure (P = 0.041) and absence of fish (P = 0.010) (Table

4, Figure 3). These two variables were significant for Cajun Chorus frog across both years of the study. Southern Leopard frog data collected in 2012 did not present any significant variables in the model. Green sunfish (Lepomis cyanellus) and mosquito fish

(Gambusia affinis) were the only common fish and were present in 25% (12 of 48) of the pools. Twenty-two of the 48 tank defilade pools did not dry in 2012 (46%).

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Figure 2. Total tadpole count for other species encountered at the tank defilade study site in 2012.

Table 4.

2012 species abundant enough for analysis of abundance and the output from the Tweedie regression model for statistically significant independent variables Species 95% C.I. 95% C.I. Wald Sig. 2012 Variable B S.E. Lower Upper Chi Sq df (P) Pseudacris Intercept 1.70 0.73 0.26 3.14 5.37 1 0.02 fouquettei (Cajun Canopy Chorus -0.02 0.01 -0.04 -0.00 4.16 1 0.04 Closure Frog) Fish -1.72 0.67 -3.03 -0.42 6.71 1 0.01 Presence

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A

B

Figure 3. Relationship of fish presence (A) (P = 0.010) and canopy closure

(B) (P = 0.041) on Pseudacris fouquettei maximum catch per unit effort in

2012. Only two pools with relatively open canopy and no P. fouquettei had established fish = 23

In 2013, I confirmed tadpoles of five anuran species in 88% (42 of 48) of the tank defilade pools (Table 5). A total of 8,882 tadpoles were counted as part of 336 pool surveys. Cajun Chorus frogs (6,784 tadpoles), Bronze frogs (998 tadpoles), and Southern

Leopard frogs (990 tadpoles) were the most abundant species. Northern Cricket frogs (54 tadpoles) and Fowler’s toads (56 tadpoles) were less abundant, excluding them from statistical analysis of abundance. Southern Leopard frogs and Cajun Chorus frogs occurred in 71% (34 of 48) and 79% (38 of 48) of the tank defilade pools, respectively.

Though Bronze frogs were slightly more abundant than Southern Leopard frogs they were only encountered in 16% of the pools (7 of 48) which was not enough for a robust regression model. Number of species detected per tank defilade ranged from 0-4 with a mean of 2.

Table 5.

Five anuran species confirmed using the tank defilade pools for reproduction in 2013

Mean 2013 Species No. Individuals % of pools present ± SE CPUE Lithobates sphenocephalus 990 34 0.63 5.42 Pseudacris fouquettei 6784 38 3.2 33.78 Acris crepitans 54 3 0.02 0.88 Lithobates clamitans 998 8 1.04 11.11 Anaxyrus fowleri 56 1 0.02 1.17

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In 2013, only 27% of the tank defilades held water throughout this season of the study (13 of 48). Green sunfish and mosquito fish were the only common fish and were present in 25% of the pools (12 of 48). Cajun Chorus frogs were only dip-netted from one tank defilade pool that had a permanent hydro-period and fish presence. The maximum

Southern Leopard frog CPUE was best explained by two variables within the Tweedie regression model; low canopy closure (P = 0.037) and mid levels of mean % dissolved oxygen (P = 0.081) (Table 6, Figure 4). The maximum Cajun Chorus frog CPUE was best explained by three variables within the model; absence of fish (P = 0.067) (Figure 5), low canopy closure (P = 0.026), and mean slope (P = 0.009), a measure of the depth of the pool (Table 6, Figure 6).

Table 6.

2013 species abundant enough for analysis and the output from the Tweedie regression model for statistically significant independent variables 95% C.I. 95% C.I. Wald Sig. Species 2013 Variable B S.E. Low Upper Chi Sq. df (P) Pseudacris Intercept 3.80 0.64 2.55 5.05 35.41 1 0.00 fouquettei (Cajun Chorus Canopy -0.02 0.01 -0.03 -0.00 4.94 1 0.03 Frog) Closure Fish -0.84 0.46 -1.74 0.06 3.37 1 0.07 Presence Mean -2.88 1.10 -5.03 -0.72 6.86 1 0.01 Slope Lithobates Intercept 2.00 1.09 -0.13 4.13 3.37 1 0.07 sphenocephalus (Southern Canopy -0.02 0.01 -0.04 -0.00 4.35 1 0.04 Leopard Frog) Closure Mean -0.05 0.03 -0.11 0.01 3.04 1 0.08 DO% 25

A

B

Figure 4. Relationships of percent canopy closure (A) (P = 0.037) and dissolved oxygen (B) (P = 0.081) on Lithobates sphenocephalus maximum

Catch Per Unit Effort in 2013. 26

Figure 5. Relationship of fish presence (P = 0.067) to Pseudacris fouquetteii maximum CPUE in 2013.

27

A

B

Figure 6. Relationship of mean % slope (A) (P = 0.015), and % canopy closure (B) (P = 0.026) to Pseudacris fouquetteii maximum CPUE in 2013.

Red diamonds indicate pools with relatively open canopy, established fish populations, and no P. fouquetteii larvae. 28

In 2012, fourteen of the 48 tank defilade pools had a second hydro-period due to a heavy rain event from July 6th through July 17th that produced nearly 20cm of rain

(Figure 7). Four of those 14 had a third hydro-period from approximately 6cm of rain that occurred August 24th through September 1st. Hydrological patterns in the form of center depth (Figure 8), wetted surface area (Figure 9), and bottom temperature taken 1 meter from shoreline (Figure 10) were highly variable over the duration of this study. A total of

10 Squirrel tree frogs were dip netted out of two tank defilades with a third hydro-period.

Cajun Chorus frogs did not occur in any pools after the first hydro-period and Southern

Leopard frogs only occurred in one pool after the first hydro-period with a total of 10 larvae netted. Tank defilades that dried during the 2013 season did not have a second hydro-period within the time-frame of my study. Only two tank defilade pools did not produce any amphibian larvae throughout both years.

Figure 7. Monthly rain data for Fort Polk, Louisiana in 2012 and 2013. 29

A

B

Figure 8. Mean and standard error values for center depth for all 48 tank defilades during each month that the pools were sampled in 2012 (A) and

2013 (B).

30

A

B

Figure 9. Mean values and standard error values for wetted surface area for all 48 tank defilades during each month pools were sampled in 2012 (A) and

2013 (B).

31

A

B

Figure 10. Mean and standard error values for bottom temperature on all 48 tank defilades each month pools were sampled in 2012 (A) and 2013 (B). 32

In addition to regression analysis, a 3D non-metric multidimensional scaling

(NMDS) ordination of the 48 tank defilade pools was completed for each year based on

Bray-Curtis similarity. Ordinations were based on presence/absence similarity of anuran species with the influence of environmental variables shown as vectors. In 2012 (Figure

11) the 48 tank defilades are not separating out into different groups but are falling into one round cluster not revealing any strong gradient (Stress = 0.09, Axis 1R² = 0.62, Axis

2R² = 0.32). In 2013 (Figure 12) it is also more of a shotgun pattern not really showing any significant use of the tank defilade pools (Stress = 0.07, Axis 1R² = 0.64, Axis 2R² =

0.27). Stress levels from both years indicate that the configuration is not just random yet there is no discernable pattern based on presence/absence data.

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Figure 11. 2012 3D NMDS ordination based on similarity of presence/absence of anuran species and vectors showing the influence of environmental variables (Stress = 0.09, Axis

1R² = 0.62, Axis 2R² = 0.32).

Figure 12. 2013 3D NMDS ordination based on similarity of presence/absence of anuran species and vectors showing the influence of environmental variables (Stress = 0.07, Axis

1R² = 0.64, Axis 2R² = 0.27).

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DISCUSSION

This study suggests that pool-level characteristics such as canopy closure, shallow-slope, and fish presence play a role in determining amphibian larval abundance.

These features are important for determining what may provide quality habitat for breeding amphibians. The abundance of Southern Leopard frogs, which are considered habitat generalists (Shulse et al. 2010), were associated with two habitat features. This finding supports the claim that habitat generalists are actually rare among breeding anurans (Skelly et al. 1999).

Cajun Chorus frog abundance was negatively associated with canopy closure during both years of this study and Southern Leopard frog abundance was negatively associated with canopy closure in 2013. These results are consistent with prior studies that have shown that forest canopy affected species presence and population sizes.

Caldwell (1986) found that during cold weather periods in South Carolina, Southern

Leopard frogs laid eggs in shallow, sunny locations. Werner et al. (2009) determined that closed canopy were sink habitats for Western Chorus frogs (Pseudacris triseriata) in Michigan, and populations in open-canopy ponds exhibited growth and maximum and minimum densities that were much higher than in closed-canopy ponds. Burne and

Griffin (2005) and Skelly et al. (2005) also found that tree canopy cover was negatively associated with overall amphibian richness in and Connecticut, respectively; however their studies did not analyze the effects on abundance. Brown and

Richter (2012) recognized that canopy closure can affect water chemistry (i.e., pH, 35

dissolved oxygen), temperature, and primary productivity (plant abundance), which have been documented to affect species composition.

The preference for pools with relatively open canopy by Cajun Chorus and

Southern Leopard frogs at this site could be explained by their earlier breeding season

(beginning as early as October) when temperatures are lower. Cajun Chorus frog breeding activity occurs from about 4°-21°C (Lemmon et al. 2007) and Leopard frogs will breed throughout the year but mainly from fall to spring (Dorcas and Gibbons 2008) after a rain event. Although I did not measure temperature during the winter months, pools with more exposure to sunlight likely warm faster early in the breeding season.

During the winter months, eggs and embryos are exposed to low temperatures. During colder weather, egg masses are usually laid in shallow sunny locations (Caldwell 1986).

Burne and Griffin (2005) suggested that creating conservation priorities for pool-breeding amphibians with open canopies should be considered. An assessment of herpetological communities in longleaf pine habitats of south Mississippi by Baxley and Qualls (2009) also suggested that open canopies are an important contributing factor to faunal diversity.

Emergent vegetation from open canopies may also be a factor, although it did not prove to be significant at this study site (p = 0.331). Cajun Chorus frogs lay 500 – 1,500 eggs in small clusters attached to vegetation (Dundee and Rossman 1989), and Leopard frogs lay 1,000 – 1,500 eggs in clusters attached to vegetation (Dorcas and Gibbons

2008). Breeding sites for Upland (now Cajun) Chorus frogs are invariably shallow pools where emergent vegetation is abundant (Dundee and Rossman 1989). In Missouri, Shulse et al. (2010) found that Boreal Chorus frogs (Pseudacris maculata) were most abundant 36

in heavily vegetated wetlands, and Burne and Griffin (2005) associated richness of amphibian species to percent of emergent vegetation.

In 2013, shallow slopes were positively associated with Cajun Chorus frog abundance (p=0.009), supporting results from Shulse et al. (2010) in northern Missouri that included a negative correlation between increasing within-wetland slope and Boreal

Chorus frog (Pseudacris maculata) abundance. Shulse et al. (2010) also found high numbers of chorus frog species and leopard frogs in shallow-sloped sites. No one has explicitly tested a series of slopes to determine the best for breeding amphibians, however

Porej and Hetherington (2005) and Shulse et al. (2012) tested steep (4:1 or 25%) versus shallow (15:1 or < 7%) slope design in Ohio and Missouri, respectively.

Shulse et al. (2012) found that Boreal Chorus frogs were negatively associated with steep slopes. Also, with the exception of one individual all Leopard frog metamorphs from their study were only found exiting shallow slope wetlands. Porej and

Hetherington (2005) found a positive association between shallow littoral zones and several species including Western Chorus frogs (Pseudacris triseriata), Northern

Leopard frogs (Lithobates pipiens), and Gray tree frogs (Hyla versicolor). Shallows provide habitat for calling, thermoregulation, foraging, and refuge from predators

(Semlitsch 2002), as well as the ability to leave the aquatic system after metamorphosis.

The lowest mean % slope in the series of tank defilade pools was greater than 15% with an average slope of 49%. All of the pools at my study site would be considered steep and far exceed the shallow slopes tested in the aforementioned studies. However, Cajun

Chorus frog abundance was best explained by the shallow slopes available at this site. 37

These results further support the need of gradual slopes for suitable amphibian breeding habitat. Testing this in more depth is warranted.

Pools that supported fish populations were not suitable for Cajun Chorus frogs at this study site. In Missouri, Shulse et al. (2010) found that Boreal Chorus frogs

(Pseudacris maculata) and Spring Peepers (Pseudacris crucifer) were most abundant in fish-free wetlands. Hecnar and M’Closkey (1996) found that Western Chorus frogs in

Ontario, Canada were less likely to be located in ponds with predatory fish. Also, Porej and Hetherington (2005) found that Western Chorus frogs (Pseudacris triseriata) were only breeding in pools with no fish and shallow littoral zones. Cajun Chorus frogs are small with an adult measuring approximately 2.54 cm (1inch) and a full size tadpole is less than 3.2 cm (1.25 inches) in length (Dorcas and Gibbons 2008). Tadpoles are prey to a large array of potential predators from fishing spiders (Pisauridae) to Western Ribbon (Thamnophis proximus), so increasing the chance of offspring survival by breeding in pools without predatory fish is logical.

The use of these tank defilades as an aquatic resource for an assortment of indicate that some historic military maneuver activity could have a positive effect on wildlife, particularly amphibians. Indeed, other studies have shown the beneficial impacts that moderate military disturbances can have on plant (Leis et al. 2005) and butterfly species (Ferster and Vulinec 2010). Though created for very different reasons, these pools now serve as amphibian breeding habitat and results indicate that having pools with heterogeneous conditions (open canopies, shallow slopes) would benefit several species. Sampling earlier in the year and collecting data on other wetland features 38

(i.e. soils, nutrient levels) may provide additional information on how these amphibians are selecting habitat for breeding. Small pools similar to these are necessary for amphibian reproduction and Army training has increased this ecologically valuable habitat. Temporary pools should be protected when possible and productive seasonal pools with features similar to these tank defilade pools should be increased throughout

Fort Polk and Forest Service property.

Current policy requires that all “damage” from training, historic or current, be repaired or filled in after training is completed. However, this study demonstrates that these tank defilades created by military training have a positive effect on amphibian breeding habitat. I suggest that some disturbances from military training, particularly historical, may prove beneficial and should remain as wildlife habitat and encourage the development of additional aquatic resources on US Army and Forest Service land.

Additionally, this site allows us to study amphibian breeding habitat that developed without conservation, mitigation, or even wildlife in mind. This unique group of small pools within man-made tank defilades also holds value as a potential long term study site for herpetologists and ecologists. The presence of exotic Chinese tallow trees (Triadica sebifera) could prove valuable as a field lab scenario for future research looking at the effects this invasive species has on larval amphibians. Cotten et al. (2012) found that

Cajun Chorus frogs and Southern Leopard frogs had lower survival rates in T. sebifera treatments. Characteristics of these unintentionally developed pools may also provide further insight into what makes functionally suitable high quality wetlands. As Semlitsch 39

(2008) suggested, wetlands constructed for mitigation or otherwise should be built with consideration for function and quality, not quantity exclusively.

40

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