Historically, North American deserts have been relatively resistant to fire. In recent years, however, the introduction of invasive plants, particularly fire tolerant grasses, is increasing the frequency, size, and lasting impacts of desert wildfires. Past studies have discovered that at our study sites in the Great Basin Desert, rodent consumers provide some biotic resistance towards plant invasions, but the influence of this biotic resistance on plants at the seedling stage of development is unclear. Following on from a study by Sharp Bowman et al. (2017), which looked at the effects of fire and rodents on native seedling survival, this study assessed the influence of rodents on the survival of both native and invasive seedlings in the Great Basin Desert over the course of 7 days in unburned, burned and reburned areas. By experimentally excluding small mammal consumers and conducting burn (in fall 2011) and reburn (in fall 2016) treatments in a factorial design replicated five times, it was possible to document the synergistic effects of fire frequency and small mammal exclusion on the establishment of the plant communities.
Results/Conclusions
Small mammal folivory had the most detrimental impact on the survival of the seedlings in unburned areas. Of the nine species used in this study, survival was generally lower in native forbs and highest in both native and invasive grasses. The hardest hit seedlings were Atriplex canescens (fourwing saltbush) and Artemisia tridentata spp. wyomingensis (Wyoming big sagebrush), both native forbs, which had average survivals of less than 45% in the unburned rodent access plots by the end of the week. The species that survived the most across all treatments were Bromus tectorum (cheatgrass), a highly invasive grass, and Poa secunda (sandberg bluegrass), a native grass, which both had average survivals above 70% across all treatments by the end of the study. This indicates that at the seedling stage, rodents prefer forbs seedlings over grass seedlings. According to this data, if invasive grasses can out-compete native grasses, it is understandable how they would be able to establish and grow prolifically following a burn, since once past the seed stage, they are generally left untouched by rodent folivory.