Monday, 17 November 2003
Fire temperatures and effects on alien and native annual plants in the Mojave Desert
Very little is known about the ecological effects of fire in the Mojave Desert because it was historically infreqeunt. As fire frequency has increased since the 1970ís in this region, there has emerged the need to understand its ecological effects. In this poster we describe patterns of peak fire temperature and their effects on alien and native annual plants in two microhabitats typical of creosote bush scrub vegetation of the Mojave Desert. Microhabitats ranged from high amounts of fuel beneath creosote bush (Larrea tridentata) canopies, to intermediate amounts at the canopy dripline, to low amounts in the interspaces between them. We also compared temperature patterns with postfire changes in soil properties and annual plant biomass and species richness to infer potential mechanisms by which fires affect annual plants. Beneath creosote bushes, lethal fire temperatures for annual plant seeds occurred above and below-ground, resulting in 4 postfire years of reduced annual plant biomass and species richness due most likely to seed mortality, especially of the alien grass Bromus rubens and native forbs. At the canopy dripline, lethal fire temperatures occurred only above-ground, reducing annual plant biomass for 1 year and species richness for 2 years, and increasing biomass of the alien grass Schismus sp., the alien forb Erodium cicutarium, and native annuals after 3 years. Negligible changes were caused by fire in interspaces and between spring and summer. Fire effects models for creosote bush scrub vegetation must account for patterns of peak fire temperature along the shrub-intershrub gradient. The responses of annual plants to this gradient vaires depending on the species composition of the seedling cohort, their microhabitat affinities, and their respective phenologic stages at the time of burning.