Developing a Topographic Model to Predict the Northern Hardwood Forest Type within Carolina Northern Flying Squirrel (Glaucomys sabrinus coloratus) Recovery Areas of the Southern Appalachians
The northern hardwood forest type is an important habitat component for the endangered Carolina northern flying squirrel (CNFS; Glaucomys sabrinus coloratus) for den sites and corridor habitats between boreo-montane conifer patches foraging areas. Our study related terrain data to presence of northern hardwood forest type in the recovery areas of CNFS in the southern Appalachian Mountains of western North Carolina, eastern Tennessee, and southwestern Virginia. We recorded overstory species composition and terrain variables at 338 points, to construct a robust, spatially predictive model. Terrain variables analyzed included elevation, aspect, slope gradient, site curvature, and topographic exposure. We used an information-theoretic approach to assess seven models based on associations noted in existing literature as well as an inclusive global model. Our results indicate that, on a regional scale, elevation, aspect, and topographic exposure index (TEI) are significant predictors of the presence of the northern hardwood forest type in the southern Appalachians. Our elevation + TEI model was the best approximating model (the lowest AICc score) for predicting northern hardwood forest type correctly classifying approximately 78% of our sample points. We then used these data to create region-wide predictive maps of the distribution of the northern hardwood forest type within CNFS recovery areas. 1. Introduction 1.1. Environmental Setting The Blue Ridge portion of the southern Appalachians, extending from northern Georgia to central Virginia [1], has been labeled a “biodiversity hotspot” due to its assemblage of unique ecosystems and number of imperiled species that occur therein [2, 3]. Natural and anthropogenic disturbance history has significantly altered the landscape and continues to impact the habitat of endemic species such as the endangered Carolina Northern flying squirrel (CNFS, Glaucomys sabrinus coloratus), a Pleistocene relict that uses the montane northern hardwood and red spruce (Picea rubens)-Fraser fir (Abies fraseri) forests for denning sites and foraging areas [4–6]. In the southern Appalachians, high elevation forest communities above 1200？m have been subjected to varying degrees of disturbance over the last 200 years. Disturbance to these areas began with Native Americans and early European pioneers clearing land for high-elevation pasture and then large-scale timber harvesting to exploit vast forest resources during the industrial logging period around the turn of the 20th century [5, 7]. The extent and type of harvests during this time
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