Burrow Abandonment by Gopher Tortoises in Slash Pine Plantations of the Conecuh National Forest

Abstract

We investigated burrow dynamics and factors associated with abandonment of burrows hy gopher tortoises (Copherus polyphemus) in mature slash pine (Pinus elliottii) plantations of the Conecuh National Forest (CNF) in southcentral Alabama. Our objectives were to determine how frequently gopher tortoises abandoned burrows in pine plantations, if burrow abandonment was associated with changes in vegetation conditions, and how rapidly these changes occurred. Burrow survey data collected over 5 years indicated gopher tortoises abandoned burrows at an average rate of 22%/year. We believe burrow abandonment occurred frequently in pine plantations, primarily in association with a change in overstory structure that shaded active burrows. Abandoned gopher tortoise burrows had greater total basal area (P = 0.012), hardwood basal area (P = 0.016), and tree density (P = 0.003) than did active burrows. There was a significant positive correlation between age of active gopher tortoise burrows and canopy closure (total basal area: r 2 = 0.19, P = 0.007; pine basal area: r 2 = 0.20, P = 0.004; tree density: r 2 = 0.14, P = 0.018). We estimated that overstory conditions at newly active burrows changed to those observed at abandoned burrows in only 5-7 years. Increases in total basal area to 70 m 2 /ha and tree density to 1,400 trees/ha were associated with burrow abandonment. Active burrows had greater total plant cover (P = 0.009) and grass cover (P = 0.016) than did abandoned burrows. However, we found no correlation between age of active burrows and structure and composition of ground cover vegetation (r 2 values ranged from 0.00 to 0.07; P-values ranged from 0.096 to 0.987). Stand thinning to a basal area of 30 m 2 /ha and prescribed growing-season burns should improve habitat quality, thereby increasing burrow fidelity of gopher tortoises.