Thursday, August 9, 2007: 1:30 PM
Blrm Salon VI, San Jose Marriott
Rasoul Sharifi1, Barry A. Prigge1 and Philip W. Rundel2, (1)Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, (2)Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA
The Lane Mountain milkvetch (Astragalus jaegerianus Munz) is an endangered, perennial herb and is endemic to the central Mojave Desert. Its populations are threatened primarily by physical disturbance and habitat fragmentation. Rare recruitment events and the plant’s short life span result in extreme fluctuations in population size from high numbers following a successful recruitment year to very low numbers following several years of average or below average precipitation. Our field studies indicate that in addition to total precipitation, frequency and timing of precipitation are critical for successful recruitment. Our objectives in this study were to determine the effect of different amounts and frequencies of precipitation on seedling survival. Starting with 5 day old seedlings, we grew them for 6 months under nine treatments: 3 amounts (100, 150, and 200mm/wet season) ´ 3 frequencies (1, 2, and 4 times per month) of precipitation, subjected surviving plants to a summer drought, and then watered the dormant plants to determine survival. Our results indicate that 200 mm of precipitation with a frequency of four times per month is required for seedlings to attain a level of development that enables them to endure a summer drought and resprout in the next growing season. We conclude that exceptionally above average and frequent precipitation is required for recruitment to occur. Such conditions are estimated to occur once in about every 10 years in the central Mojave Desert. These specific requirements for seedling germination and establishment represent a model system for understanding the survival of other endangered desert species.
