Spatial Arrangement

Community Prediction Map

The spatial arrangement of community types on mountain landscapes is strongly affected by terrain, which influences local climatological conditions, soil moisture and fertility. Site factors such as geology, hydrology, and soil are also important, but environmental gradients of these and other factors are generally correlated with the lay of the land. A number of ecologists have correlated community occurrence with elevation and landform. Geographic information systems (GIS) can be used to model the locations of these communities in mountain landscapes.

The map to the right shows the predicted spatial distribution of seven community types for a portion of the Craggy Mountains in western North Carolina. The locations of these communities were predicted using a GIS model based on Whittakers (1956) research on communities in the Great Smoky Mountains. The GIS model uses a elevation map, a map of landform, and a set of programmed instructions to predict community types.

Legend to Prediction Map

The reliability of the predicted locations is affected by the spatial accuracy of the input maps, an accurate understanding of the environmental gradients associated with these data, and the strengths of the responses of communites to these gradients. Among the community types depicted, heath balds are the most difficult to predict. While heath balds tend to occur at high elevation sites with exposed landforms, such as sharp, rocky ridges, other factors such as disturbance history and local geology seem tostrongly influenceoccurrence. Since these factors were notentered inthe GIS model the locations should be considered unreliable. In nature, many sitesthat havethe suite of environmental characteristics associated with heath balds are covered by forest instead.