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The effects of all-terrain vehicle use on the herpetofauna of an east Texas floodplain.

Abstract.--Recreational all-terrain vehicle (ATV) use is known to cause extensive environmental damage in xeric habitats, however their impact has been poorly studied in floodplain ecosystems. Floodplains are complex and important wetland habitats due to their high primary productivity and biodiversity. In this study, amphibians and reptiles are used as indicators of environmental stress from ATV use in a floodplain at the Old Sabine Bottom Wildlife Management Area (OSBWMA), Smith County, Texas. The herpetofauna were surveyed using cover board arrays (wood and tin) placed at nine sites: three within a forest, three along trails open to ATV traffic, and three along trails closed to ATV traffic. No significant differences were observed in abundance, richness, evenness, or diversity of amphibians and reptiles found among these three treatments (P>0.05). The apparent lack of effect could be due to restricted use and the recent opening of the OSBWMA to ATVs, and/or the natural resilience of floodplain ecosystems to disturbance. Additionally, the impact of ATV use may have been masked by the relatively short time period of the study (14 months) and low rainfall during the investigation.


Off-road vehicle use has increased greatly since the 1970s, from approximately 5 to 35 million annual users (Wisdom et al. 2004; USDA 2004). Minimal research has been conducted on the impact of off-road vehicle trails on ecosystems (Phillips & Alldredge 2000; Gaines et al. 2003). Additionally, only xeric regions have been widely examined in studies of the effects of off-road vehicles on ecosystems (Iverson et al. 1981; Adams et al. 1982; Webb & Wilshire 1983).

Recreational all-terrain vehicle (ATV) use can affect wildlife by direct injury or death, by noise pollution, through fragmentation of habitat, and by creating migration barriers (e.g., Webb & Wilshire 1983; Reijnen et al. 1996; Forman & Alexander 1998; Bonnet et al. 1999). Such effects are known to cause changes both in the abundance and diversity of organisms in biological communities (Pearson et al. 1999; Findlay & Bourdages 2000; Trombulak & Frissell 2000). Habitat fragmentation and associated edge effects are considered to have detrimental effects on community composition by specifically impacting interior species (Wilcox & Murphy 1985; Robinson & Quinn 1992; Spellerberg 1998). Even less conspicuous effects of ATV use may harm community structure. Palis & Fischer (1997) found that off-road vehicle use disrupts pond floor microtopography by breaking the hardpan that lies below the pond and causing a shorter hydroperiod, thus decreasing the availability of ephemeral ponds for breeding amphibians. Furthermore, a variety of chemicals derived from gasoline additives can be introduced into a habitat leading to direct toxic effects and indirect disruption of food webs (Trombulak & Frissell 2000; Forman et al. 2003).

Floodplains are a complex and important wetland ecosystem because their high productivity leads to increased biodiversity (Reice 1994; Bayley 1995). The flood-pulse concept, characterized by the predictable advance and retreat of water on a floodplain, is postulated to maintain diversity in a system (Bayley 1995; Ostfeld & Keesing 2000). The primary productivity is augmented by an influx of nutrients that are washed into temporary pools and the forest floor resulting in an increase in plant and animal abundance due to extra energy availability (Bayley 1995; Sparks 1995). Additionally, temporary pools that form during the recession phase (Junk 1973; Sparks et al. 1998) hold fish and function as breeding sites for many amphibians. Both forest floor and temporary pools provide readily available food sources for many carnivores (Molles et al. 1998; Shiel et al. 1998). Despite their biological importance, floodplain ecosystems are among the most threatened natural areas in the eastern United States and, of all wetland types, floodplains have suffered the greatest losses (Bayley 1991; Graham et al. 1997).

Amphibians and reptiles are often locally abundant, easy to sample, and respond to an assortment of subtle environmental changes, making them good indicators of wetland health (Heyer et al. 1994; Welsh & Ollivier 1998; Christy & Dickman 2002). Alterations of such environmental factors as temperature (Seebacher et al. 2003), precipitation (Heyer et al. 1994), pH (Wyman & Hawksly-Lescault 1987), salinity (Christy & Dickman, 2002), and ultraviolet radiation (Blaustein et al. 1998) have been shown to cause changes in amphibian and reptile abundance and diversity in an area. Because of their importance in ecosystem structure and function, herpetofauna have also been used as indicators of ecosystem integrity (Duellman & Trueb 1994; Petranka 1998; Lips 1999). The amphibian and reptile community in an east Texas floodplain that is partially open to ATV use on floodplain ecosystems.


Study site.--The Old Sabine Bottom Wildlife Management Area (OSBWMA) is located in northern Smith County, Texas and is bordered along its northern edge by the Sabine River. With 2087 ha of hardwood forest, the OSBWMA is one of the largest contiguous bottomland hardwood forests remaining in Texas. The primary vegetation type is a diverse Water Oak-Elm-Sugarberry Forest. Dominant vegetative overstory is comprised of water oak (Quercus nigra), willow oak (Quercus phellos), overcup oak (Quercus lyrata), pecan and hickory (Carya sp.), cedar elm (Ulmus crassifolia), water elm (Planera aquatica), ash (Fraxinus sp.), American hornbeam (Carpinus caroliniana), and black willow (Salix nigra). Periodic flooding occurs at the OSBWMA due to heavy rainfall, opening of the floodgates at the Lake Tawakoni, however, no flooding occurred during this study. Flooding usually occurs in the winter and spring months and results in the filling of both natural ephemeral pools within the forest and the man-made soil compacted ephemeral pools formed from tire ruts in the trails (Hampton & Ford 2007).

Several trails through the OSBWMA were created by the use of motorized vehicles prior to Texas Parks and Wildlife Department (TPWD) ownership of the property. Current trail use includes hiking, horseback riding, and beginning in 2004 the restricted use of all-terrain vehicles for public hunting access on two designated trails from October 1 to May 31 each year. No recreational riding is allowed. The previous use of motorized vehicles and ATVs caused deep tire ruts and compaction of the soil on the trails. Over the course of this study, the trails open to ATV use received an average of one to two users per day during the October to December time period, with less use through the end of May. The on-site staff of the OSBWMA traversed all trails on the area conducting routine trail maintenance and management activities by ATV or medium sized tractor on a year round basis. The personnel at the OSBWMA attempted to restrict their use of the trails to drier periods to reduce impacts (Shaun Crook, pers. comm.).

Methods.--Nine areas were chosen to monitor reptile and amphibian populations: three within the forest (at least 50 m from any edge), three along trails that are open for ATV traffic, and three along trails that are closed to ATV traffic (very limited use since 1996). Each area was divided into five stations, each 50 m apart. Each station consisted of two wooden cover boards (ca. 175 by 80 cm) and two pieces of corrugated tin (ca. 200 by 80 cm). One of each cover type (wood and tin) was placed on each side of the trail at each station. Because there were no trails within the undisturbed forest plots, each station within the forest consisted of one piece of both tin and wood placed approximately two meters from another cover array to emulate the same sampling system as on the trails. The cover items were placed in November 2004 and checked at least once a week from November 2004 to December 2005. In this wetland system cover boards are an effective survey method in a very short time frame (Hampton & Ford 2007). Individual amphibian and reptiles captured under boards were identified, sexed and marked when possible, and subsequently released. Individual identification marking consisted of scale clipping, toe clipping, or PIT tagging depending on the size and species of the captured individual.

Statistical methods and analyses.--Several community indices were computed including Simpson's index of diversity (Krebs 1999), Smith and Wilson's index of evenness (Smith & Wilson 1996; Krebs 1999), and Morisita's index of similarity (Morisita 1959; Krebs 1999). These indices of diversity and evenness as well as abundance and richness of herpetofauna species were compared among sites using an analysis of variance (Systat Software Inc. 2004) to determine if there was a significant difference among treatments.


A total of 403 amphibians and reptiles representing 16 species were recorded under cover boards. Totals included two salamander, one anuran, three lizard, and 10 snake species. Of the total animals captured, 31 (7%) were salamanders, 23 (6%) were anurans, 236 (59%) were lizards, and 113 (28%) were snakes (Table 1). Ten species were captured in all of the treatments. Forty-five marked individuals were recaptured during the sampling period. Thirty-one recaptures were lizards.
Table 1. Numbers of amphibian and reptile species captured on ATV
trails, Non-ATV trails, and within forest control plots at the Old
Sabine Bottom Wildlife Management Area, Smith County, Texas.

Taxon ATV Non-ATV Control Total
Class Amphibia
 Order Caudata
 Ambystoma opacum 1 0 0 1
 Ambystoma texanum 10 13 7 30
 Order Anura
 Rana utricularia 10 5 8 23

Class Reptilia
 Order Squamata
 Eumeces fasciatus 26 31 37 94
 Eumeces laticeps 10 4 12 26
 Scincella lateralis 42 32 42 116
 Agkistrodon piscivorus 5 5 3 13
 Agkistrodon contortrix 3 3 0 6
 Pantherophis obsoleta 0 1 0 1
 Farancia abacura 1 0 0 1
 Lampropeltis getula 1 0 1 2
 Nerodia erythrogaster 11 12 10 33
 Nerodia fasciata 2 0 2 4
 Nerodia rhombifer 0 2 0 2
 Storeria dekayi 5 2 3 10
 Thamnophis proximus 11 14 16 41

Total Individuals 138 124 141 403
Total Species 14 12 11 16

The ATV trails had the highest species richness. The highest abundance was observed in the forested control areas. However, abundance, richness, evenness, and diversity of amphibians and reptiles were not significantly different among ATV, non-ATV active trails, or control treatments (f=0.04, 1.05, 0.26, 1.61, P>0.05 respectively; Table 2). Based on Morisita's index of similarity, community structures were extremely similar ([C.sub.[lambda]]=1.00 for all comparisons).
Table 2. Abundance, richness, diversity, and evenness for
amphibians and reptiles captured on ATV trails, non-ATV
trails, and forest control plots at the Old Sabine Bottom
Wildlife Management Area, Smith County, Texas.

 ATV Non ATV Control F P

Abundance 138 124 141 0.04 0.962
Richness 14 12 11 1.05 0.406
Diversity 0.846 0.839 0.816 0.26 0.780
Evenness 0.409 0.460 0.427 1.61 0.855


Habitats in the three areas where cover boards were placed were visibly different. Damage in the area where ATVs were in current use included destruction of vegetation within and next to trails, packing of soil in some parts of the trail, and loosening of mud in deeper, wet areas creating suspended silt. The ATV restricted trails showed some packing and older ruts from previous vehicle use, but much less vegetation damage. The forested area had natural depressions and damage from tree falls but little or no human impact. The methods used to place boards in each area resulted in some stations being near pools or rutted areas and some stations being near dry parts of the trail. A total of 54 captures of only three species of amphibians were recorded. This reflects a much lower abundance than in previous work at the OSBWMA (Hampton 2004; Hampton & Ford 2007). These studies utilized boards in close proximity to ephemeral pools or deep ruts on trails. The lower number of amphibians obtained during the current study may relate to the random placement of cover objects in relationship to pools of water. Additionally, an unusually low amount of precipitation occurred in the second half of 2005. The average rainfall in nearby Dallas, Texas during November and December is 6.12 cm. In 2004 the average precipitation for November and December was 8.50 cm but for 2005 was only 0.60 cm (NOAA 2006) reflecting the very dry second half of the study period. During this study 349 reptiles belonging to 13 species were recorded. These numbers are more typical for the site and reflect that lizard and snake numbers were less influenced by low rainfall.

Species richness, abundance, diversity, and evenness of herpetofauna did not vary among trails open to ATV use, trails closed to ATVs, and the internal forest areas at the OSBWMA (Table 1). This suggests that the changes to the trails by the ATV use did not affect the biodiversity of amphibians and reptiles in this floodplain ecosystem during the study period. This lack of effect contrasts with previous studies of off-road disturbance (e.g., Iverson et al. 1981; Adams et al. 1982; Webb & Wilshire 1983; Luckenbach & Bury 1983; Palis & Fischer 1997; Wisdom et al. 2004). Several hypotheses are proposed concerning the lack of significant impact of ATV use at OSBWMA.

First, the current study was limited to a 14-month duration. This time period included the first year the OSBWMA was open to ATV traffic since establishment of the wildlife management area in 1996. Although physical and vegetation damage from ATVs was evident, the number of vehicles on each trail was very low (an average of 1--2 users per day; Shaun Crook pers. comm.). Direct mortality from ATVs would have been unlikely and impacts like siltation in ruts where amphibian eggs or larva occurred also may have been limited. Previous researchers have also suggested that time lags of greater than a year can exist between disturbance and ecological responses (Magnuson 1990), and most studies in upland or desert areas have been at least two years in length (Luckenbach & Bury 1983). Additionally, these aforementioned areas were usually open to and extensively used by off-road vehicles for many years prior to data collection, (Luckenbach & Bury 1983; Wisdom et al. 2004). The abundances and diversity of amphibians and reptiles at the OSBWMA may still be affected over time by ATV use.

A second possibility is that floodplain communities are resilient to disturbances that include ATV activity. Previous studies of off-road vehicle disturbance have been conducted in upland forest (Palis & Fischer 1997; Wisdom et al. 2004) or xeric desert habitats (Iverson et al. 1981; Adams et al. 1982; Webb & Wilshire 1983; Luckenbach & Bury 1983). One of the main effects of ATV disturbance is habitat fragmentation, which causes migration barriers and leads to decreased mobility and limited prey access (Nour et al. 1998; Cushman 2006). This affect may be less apparent in floodplain ecosystems because the major source of nutrient influx is from flooding. The temporary pools formed by the recession of floods become stocked with fish and create amphibian breeding grounds. As the pools dry the fish and larva are available food sources for many carnivores. Ruts created by ATVs simulate these pools and may also contain fish and amphibian larva. The survival of organisms in those ruts, as opposed to natural pools, is not known, but some species associated with floodplains may be adapted to deal with perturbations. However, observations made during this study revealed that siltation in deep ruts appeared to kill some anuran eggs. A secondary aspect of floods would be that they allow for animal dispersal. Though the impact of the trails during flooding is not known, the trails may acts as corridors as the water often is channeled through them.

Frequent disturbances are known to cause complex effects on ecosystems that can either amplify or mask anthropogenic affects (Swetnam & Betancourt 1998; Hobbs & Morton 1999; Sherman 2001). It is possible that the lack of effect from ATV disturbance was confounded by the low amount of rainfall activity during the study, whereas this habitat is normally subjected to multiple flood events each winter. It seems intuitive that ATVs driving through pools of amphibian egg masses or larva would have a negative impact on those species. Indeed, it is almost certain that the drought lowered amphibian activity during this study. Although these conclusions are that the limited ATV use in this floodplain appeared to have no significant effect on the herpetofauna, the authors caution that further study is needed. It is suggested that these data represent a good baseline for additional studies, particularly with the amphibians of the OSBWMA.


We thank Larry LeBeau and Shaun Crook of Texas Parks and Wildlife for access to the study site and information regarding ATV use at the OSBWMA. We thank Dr. Ron Gutberlet, Dr. Darrell Pogue, and Andree Clark for comments on earlier versions of this manuscript. We thank Stephan Lorenz, Jessica Coleman, Paul Hampton, Casey Wieczorek, Robert Hunkapiller, Jr., and Rachel Buerger for field assistance.


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TRH at:

Timothy R. Hunkapiller, Neil B. Ford and Kevin Herriman

Department of Ecology and Evolutionary Biology

University of Tennessee, Knoxville, Tennessee 37996

Department of Biology, University of Texas at Tyler,

Tyler, Texas 75799 and Texas Parks and Wildlife Department Lindale, Texas 75771
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Author:Hunkapiller, Timothy R.; Ford, Neil B.; Herriman, Kevin
Publication:The Texas Journal of Science
Article Type:Report
Geographic Code:1USA
Date:Feb 1, 2009
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