Loss of biotic resistance and high propagule pressure promote invasive grass-fire cycles

1. The spread of invasive grasses across Earth are modifying fire cycles resulting in state changes in arid ecosystems. Disturbance, biotic resistance of native biological communities and propagule pressure, are likely important factors influencing the spread of invasive grasses and their influence on changing fire regimes. 2. Over a five-year period (2011-2016), we tested how the potential loss of biotic resistance of native plant and native rodent communities related to fire and rodent exclusion treatments, in concert with increased propagule pressure affected the establishment of Bromus tectorum L. (cheatgrass) and the spread of secondary fires. 3. Our study results suggest that native plant and native rodent communities contribute to biotic resistance against cheatgrass invasion and that fire and high propagule pressure act to diminish biotic resistance by native communities. Five years into the study, cheatgrass establishment was 11-fold greater in burned plots than in unburned p...