Terrain variables used for predictive mapping of vegetation communities in southern California

Distributions of plant species on the landscape are related to soil-moisture balance in the semiarid Mediterranean-type climate of southern California. Moisture supply, subsurface soil moisture, soil properties related to moisture-holding capacity, and soil-Soisture demand (evapotranspiration) have been shown to be related to topographic variables. Those variables include elevation, aspect, slope, curvature, billslope position and drainage basin position, and more complex topographically derived indices such as potential solar insolation and soil-water balance (Chapters I, 3, and 4 and references therein). In this chapter we discuss the use of terrain variables for predictive vegetation mapping (reviewed by Franklin 1995) of chaparral and riparian vegetation in southern California. Before describing our case studies, we review the following issues related to ecological applications of terrain models: