Precipitation and the relative abundances of desert winter annuals: a 6-year study in the northern Mohave Desert

Abstract

The relationship between winter annual plants and the amount and timing of precipitation was studied for 6 years in Rock Valley, Nevada, U.S.A. Sixty-two annual species, whose year-to-year densities commonly varied 100-fold, were encountered in sampling quadrats. While dominance–diversity curves varied markedly between years, the similarity in relative abundances of annuals between years was correlated with differences in September–October precipitation of the previous fall; thus, in a comparison of years, the more similar the amount of precipitation in the early fall months, the more similar the relative abundances of annuals. Between-year differences in the total amount of fall and spring precipitation, or in precipitation in November-December or January-February, were not related to compositional similarity. Annual composition was not related to that of the previous year. The proportional abundance of species varied less than did their absolute abundances. These results suggest that compositional dynamics of annual plants in the Mohave Desert are keyed to processes that affect germination.