17 years later: Changes in Vegetation Structure, Burrow Dispersion and Size-class Distribution at a Gopher Tortoise (Gopherus polyphemus) Site in Alabama

Abstract

There are few studies that reevaluate vegetation structure at a gopher tortoise (Gopherus polyphemus) site after a long period of time in the southern Alabama or Florida panhandle portion of their range. The current study revisits research conducted in 1999 by J.H. Waddle at a study site in Conecuh National Forest in southern Alabama 17 years later. Three types of comparisons of vegetation structure were made: 1999 random points versus 2016 random points, burrows that were active in 1999 and remained active in 2016, and burrows that were active in 1999 but became abandoned in 2016. Compared to 1999 data, in 2016 all plot types had significantly less litter and forbs, and more legumes and shrubs in the understory and more hardwood stems in the midstory. Active burrows that stayed active had no hardwood trees present in either 1999 or 2016. The original study suggested that tortoises were likely selecting the best habitat available for burrow construction in 1999 while this study indicates that habitat may have become more homogenous with few high quality areas to select from. A 3.5-fold increase of the total number of active and inactive burrows was found in the resampled area, indicating either a robust population or one compensating for declining access to forage by increasing number of locations used. The burrow size distribution shifted to bi-modal from uni-modal, indicating a healthy, recovering population. In addition, shifts in spatial relationships among burrows were considered. I used this burrow survey data to estimate tortoise density and evaluate this population according to requirements of a minimum viable population.