Woodland box turtle (Terrapene carolina carolina) abundance declines with increasing urban land use in the Piedmont

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Ashley Graham and Kiyoshi Sasaki, Department of Biology, Winthrop University, Rock Hill, SC

Background/Question/Methods
Urbanization is an increasing threat to wildlife populations, as urban extent is expected to triple by 2030. However, the role of urbanization in population declines remains poorly understood for many wildlife species. To determine the role of urbanization in woodland box turtle decline, we estimated abundances of woodland box turtles via timed visual surveys at 11 forest patches along a gradient of urbanization in the rapidly urbanizing Piedmont ecoregion. We related abundance of female and male box turtles to landcover variables indicative of urbanization intensity (forest cover, impervious surface cover, and road density) quantified at three spatial extents (circular areas with a radius of 500 m, 1500 m, and 2500 m around each sampling area) to capture potential effects at the patch and landscape levels.
Results/Conclusions
Abundance of females was best explained by impervious surface at a 500 m radius, and to a lesser extent by forest cover at a 500 m radius, with these variables explaining 42% (D2 = 0.42) and 31% (D2 = 0.31) of the variation in abundance, respectively. Forest cover at the 2500 m and 500 m radii were the best-supported variable for male abundance, but the deviance explained by each of these variables was small (D2 = 0.18 and 0.14, respectively), suggesting that the effects of these variables were weak. Abundance of either sex was not explained by road density at any spatial extent. Observed negative associations between urban landcover and box turtle abundance suggest that urbanization contributes to their decline. The stronger response of females (relative to males) to the extent of impervious surface cover and forest patch size may be explained by their larger home ranges and use of habitat edges and anthropogenic areas during the nesting season. We advise that preserving or restoring large urban forest patches and minimizing urban expansion are important to the long-term persistence of woodland box turtles in ever increasing urban landscapes.