Gradient Analysis of Relationships Among Fire, Environment, and Vegetation in a Southwestern USA Mountain Range

BARTON, A. M. (Department of Biology, University of Michigan, Ann Arbor, MI 48109). Gradient analysis of relationships among fire, environment, and vegetation in a southwestern USA mountain range. Bull. Torrey Bot. Club 121: 251-265. 1994.-I investigated interrelationships among topography, resources/conditions, fire, and woody vegetation over the lower half of an elevational gradient, from arid lowlands to productive intermediate elevations, in the Chiricahua Mountains in southeastern Arizona. With increasing elevation, soil water potential, litter depth, organic carbon, canopy cover, and fire probability increased, whereas forest-floor light levels, soil temperature, pH, and percentage bare soil decreased. With increasing soil moisture levels, plant cover increased and forest-floor light levels decreased. Fire frequency and soil moisture availability were positively correlated. Comparison of the fire data with published studies suggests that relationships between elevational gradients and fire may change in predictable ways from southern to northern latitudes in western North America. First axes of direct (DCCA) and indirect gradient analysis (DCA) showed a strong relationship between vegetation and variables correlated with elevation, including fire and resource variables such as light and soil moisture. Further variation in plant community composition was explained by a second axis that appeared to relate to variation in soil pH and soil texture, probably resulting from differences in parent material. The major environmental variables explaining axis 1 of the DCCA were the same as those found controlling the elevational distributions of tree species in separate single species studies.