Quantifying ecosystem geomorphology of the southern Appalachian mountains

Geomorphology is a dominant factor influencing vegetation distribution in the southern Appalachians, and quantifying landform characteristics is increasingly important for forest ecosystem classification. This study used slope gradient and two previously published geomorphic indices, terrain shape index and landform index that quantify landform shape and protection, to develop a field-based landform quantification system at four study areas in the southern Appalachians. Six major landform types (ridge-tops, nose slopes, linear hillslopes, coves, stream ravines, and stream bottoms) exhibited quantitatively different characteristics, and these differences among landforms were not evident when using only categorical landform descriptions (e.g., convex, concave) that have been most common in southern Appalachian ecological research. Discriminant function resubstitution based on quantitative geomorphic variables distinguished 78% or more of categorical landform types, and misclassifications partly resulted from inadequacies of categorical data for capturing the continuum of landform characteristics. I applied the geomorphic quantification system by developing a classification tree model to predict the presence or absence of eastern hemlock (Tsuga canadensis) ecosystems in northwestern South Carolina. The quantitative model correctly identified 86% of sites actually supporting a hemlock ecosystem, substantially higher than a model using categorical landform data that correctly identified only 57% of hemlock sites.