Community Dynamics and Soil Seed Bank Ecology of Lane Mountain Milkvetch (Astragalus jaegerianus Munz)
Final rept. Oct 2008-Oct 2012
CALIFORNIA UNIV LOS ANGELES DEPT OF ECOLOGY AND EVOLUTIONARY BIOLOOGY
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The Lane Mountain milkvetch, Astragalus jaegerianus, is an endangered species that exists in fragmented populations in the Mojave Desert. UCLA monitored populations have declined by 76 since 1999 due to drought. Reintroduction experiments support this idea supplemental water increased seedling survivorship. Phenological studies suggest that between-year differences in A. jaegerianus phenology are pronounced, and controlled by annual differences in precipitation. Seed production per plant is highly variable. Study plants had significant reproductive potential that was unrealized in 2011 and 2012. High precipitation in 2011 is a likely explanation for increases in seed production in some plants, but the strong negative effect of herbivory on other plants appears to have overwhelmed the positive effect of precipitation on seed production. The soil seed bank may be categorized as low, persistent, and largely restricted to the area beneath host shrubs with active A. jaegerianus. Seed dispersal is low. The post-dispersal seed bank, significantly declined in 2011 despite increases in precipitation. Decreases in soil seed density are attributable to two factors 1 a decrease in seed production due to increases in herbivory, and 2 an increase in seed predation due to high seed predator populations and an extended fruit dehiscing period.