Vegetation Patterns as Affected by Aspect and Elevation in Small Desert Mountains

Abstract

Studies of vegetation patterns on small desert mountains have rarely been conduct- ed. The purpose of this study was to evaluate the influence of aspect and elevation on vegetation of Mt. Summerford, a small desert mountain characteristic of the Basin and Range Province of southwestern United States and northern Mexico. Vegetation was randomly sampled on 4 aspects and 3 elevations (0-80 m, 80-160 m, and 160-240 m) of the mountain. South (S) and west (W) aspects had lower grass cover and higher shrub density than east (E) and north (N) aspects. Grass cover decreased as elevation increased on E and N exposures. In contrast, grass cover increased as elevation increased on S and W exposures. A high density of succulent species was found on lower elevations of the S and W aspects. The most frequent species on the mountain were Bouteloua curtipendula, Bouteloua eriopoda, Muhlenbergia porteri, Aristida ternipes, Aloysia wrightii, Ericameria lari- cifolia, Gutierrezia sarothrae, Fouquieria splendens, Dasylirion wheeleri, and Opuntia. Composition of these species, as a mosaic unit, was significantly different among the aspect-elevation units. Species richness was higher in S and W than in E and N aspects. Differences in vegetation patterns were attributed to differential water and nutrient availability on aspects and elevations. This study sug- gests that topographical change is responsible for vegetation patterns in mountains less than 500 m high.