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regime, but differ quite substantially in biological, climatic, and geomorphic
aspects (Brown 1968; Bender 1982; MacMahon 1985; Osmond et al. 1990).
Plant growth and activity are, of course, constrained by limited soil moisture
availability in each of these deserts. In the northerly and higher elevation
Colorado Plateau and Great Basin Deserts, cold winter temperatures further
restrict activity to the spring and early summer months (Caldwell 1985;
Comstock and Ehleringer 1992). Seasonal precipitation patterns further
differentiate these deserts, with the Mojave Desert being primarily a winterprecipitation desert and the Chihuahuan Desert a summer-precipitation
desert. The Sonoran Desert, geographically at the center of the deserts,
rocky slopes
bajadas
playas
virginensis
Ambrosio dumosa
bojodos
and rocky slopes
playas
Viguiera multif lora
8ebbia juncea
Encelia frutescens
washes
playas
Fig. IS.1. Top Cross section of elevational transect in the Sonoran Desert showing the
three dominant macrohabitats - rocky slopes, bajadas (coarse alluvium), and playas (fine
alluvium). With the bajadas and rocky slopes are washes of varying size and dimension.
Middle Distribution of common drought-deciduous shrubs along elevational transect on
bajadas and rocky slopes near Needles, California. Bottom Distribution of common
drought-deciduous shrubs along elevational transect in washes near Needles, California