EDAPHIC FACTORS AND COMPETITION AFFECT PATTERN FORMATION AND INVASION IN A CALIFORNIA GRASSLAND

Abstract

We used soil analyses, a greenhouse experiment, and a field experiment to examine the roles of competition and abiotic soil factors in plant community pattern formation in a California grassland. We collected soils from five microhabitats: one dominated by the native perennial grass Sporobolus airoides Torrey (alkali sacaton), two dominated by the nonnative annual grass species Hordeum marinum (Hudson) ssp. gussoneanum (Parl.) Thell (foxtail) and Bromus diandrus Roth (ripgut grass), and bare soil created either by gopher mounds or by high salt concentrations (sodic soils). We used principal components analysis (PCA) to determine whether soils from these five microhabitats differed in any discernible pattern. In the greenhouse we examined the emergence, growth, and survival of the native perennial in soil from the five habitat types. In the field we then examined a combined survival and reproduction measure to assess how competition with the two nonnative annual grasses affected the fitness of S. airoides....