PARENT SESSION
Symposium #12: Natural Recovery and Restoration of Disturbed Desert Environments in the Mojave Desert .
Organized by: RH Webb and KH Berry
Tuesday, August 6. 8:00 AM to 11:30 AM. Maricopa Meeting Room, TCC.
Fire and exotics in the Mojave Desert: an irreversible change?
Haines, Dustin*,1, Esque, Todd1, Brooks, Matthew1, Schwalbe, Cecil2, Webb, Robert3, 1 USGS, Las Vegas, NV2 USGS, Tucson, AZ3 USGS, Tucson, AZ
ABSTRACT- Several species of invasive exotic plants are ubiquitous in the Mojave Desert and have the potential for increasing fire frequency. Some, such as Bromus madritensis, occur in sufficient densities to provide continuous fine fuel in intershrub spaces, encouraging the spread of fire over large areas. Positive feedbacks between fires and exotics have been observed in some areas; exotics return in higher densities after a fire, increasing susceptibility to future fires. Our goal is to describe state-and-transition models for some Mojave Desert habitats and how they may be affected by fire, exotics, and climate. Climatic fluctuations affect the growth of native and exotic species in both undisturbed and post-burn environments. As an example, changes in annual and perennial species composition have been measured on undisturbed plots at the Nevada Test Site over the past 35+ years. Areas that have burned once usually have a higher biomass of exotic species, different species composition, and less perennial cover than adjacent unburned habitat for burns up to 50 years old. Areas that have burned more than once appear to have been converted from desert scrub to an annual grassland, with exotics dominating the landscape between scattered native perennials. While once-burned areas often show signs of recovery of native species, areas with multiple burns typically show little natural recovery. Annual exotic grasslands may require significant environmental changes for transition reversal to occur, and the transition from desert scrub to annual grassland is irreversible under the current climatic regime.
KEY WORDS: state-and-transition, fire, exotic plants, desert vegetation