American chestnut (Castanea dentata) habitat modeling: identifying suitable sites for restoration in Shenandoah National Park, Virginia

Abstract

Since 2008, The American Chestnut Foundation’s (TACF) Appalachian Trail MEGA-Transect Project has engaged citizen scientists to collect American chestnut occurrence data over the length of the Appalachian Trail. This data helps TACF to locate surviving trees for use in their breeding program and expand their knowledge of chestnuts across the East Coast. However, this dataset is limiting in that it considers only the ridge-top habitat of the trail. To remedy this, we conducted an extensive sampling of side-trails in Shenandoah National Park in order to study more diverse elevation and habitat gradients. Expanding the dataset allows us to draw more informed conclusions about habitat for surviving American chestnuts. To achieve this, I developed a series of species distribution models, including GLM, CART, and Maxent models, based on field observations and spatial data of environmental variables. These predictive distribution models were then combined to generate a comprehensive map of the most likely surviving American chestnut occurrence locations across Shenandoah National Park. Additionally, projections based on future climate were made for the Maxent model to 2050 and 2070 in order to see if habitat for surviving trees might shift in the face of climate warming. Overall, the three species distribution modeling techniques tended to agree on location, but not quantity, of suitable habitat for surviving chestnuts. All models found elevation, sand, and slope to be the most significant habitat predictors in Shenandoah. Climate change models produced only subtle range shifts; as a generalist species, American chestnuts may not face adverse effects of future climate warming. Mapping these results provides valuable information to both Shenandoah National Park and TACF as they continue to search for, study, and restore American chestnuts in the Appalachian forest.