Woodland Box Turtle (Terrapene carolina carolina) Abundance Declines with Increasing Urban Land Use in the Piedmont

Abstract

Urbanization increasingly threatens wildlife, as urban extent is expected to triple by 2030. However, the role of urbanization in population declines remains poorly understood for many species. To determine the role of urbanization in the decline of Woodland Box Turtles (Terrapene carolina carolina), we estimated abundances of 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, 1,500 m, and 2,500 m around each sampling area) to capture potential effects at the patch and landscape levels. Female abundance declined most strongly with increasing impervious surface area at a 500 m radius, and to a lesser extent with decreasing forest cover and increasing road density at a 500 m radius, with these variables explaining 42%, 31%, and 29% of the variation in abundance, respectively. Male abundance declined most strongly with decreasing forest cover at the 2,500 m and 500 m radii, but only 18% and 14% of the variation was accounted for by each of these variables, respectively. Observed negative associations between urban landcover and box turtle abundance suggest that urbanization contributes to their decline, especially in females. We advise that preserving or restoring large urban forest patches are important to the long-term persistence of Woodland Box Turtles in ever increasing urban landscapes.