Limiting invasive plant-fire feedback in creosote bush scrub

The presence of alien grasses like Bromus and Schismus spp. greatly increase the extent and severity of fires in creosote bush scrub.  These species can also become dominant following fire, thus promoting the invasive plant – fire feedback cycle.  Fire is especially problematic in creosote bush scrub since most components are poorly adapted to this type of disturbance.  Methods to control alien grasses are needed to help prevent fires in unburned conditions and to also promote native succession following fire.  We tested the effectiveness of several alien grass control treatments in burned and unburned creosote bush scrub stands during 2004-05 and 2005-06.  Treatments included grass-specific herbicide, grass-specific herbicide plus hand-removal of alien forbs, two levels of carbon addition, and soil raking.  All treatments significantly reduced alien grass cover and biomass, and soil raking also significantly decreased alien grass density.  Treatments utilizing grass-specific herbicide were most effective at promoting native annual cover and richness in understory habitat, while only grass-specific herbicide plus hand-removal of alien forbs significantly increased native annual cover in the interspace.  In general, the competitive release of native annuals was greatest when coupled alien grass and forb removal was applied.  However, the control of alien grasses alone may be sufficient to dramatically limit invasive plant – fire feedback in this system since the alien forbs (primarily Erodium cicutarium) present in this study contributed low amounts of non-persistent fuel.