In recent years, the introduction of invasive plants, particularly fire tolerant grasses, into the Great Basin and Mojave Deserts 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 and Mojave Deserts in 2017 and 2018. Over the course of 7 days, the survival of various plant seedlings was tracked in un-burned, burned and re-burned areas. By experimentally excluding small mammal consumers and conducting burn (in fall 2011) and re-burn (in fall 2016) treatments in a full factorial design, replicated five times, it was possible to document the synergistic effects of fire frequency and small mammal exclusion on the establishment of plant communities.
Results/Conclusions
Rodent folivory had more of a detrimental impact on the survival of the seedlings in Mojave Desert than in the Great Basin Desert, however, this rodent effect is not as significant as hypothesised. This suggests that loss of plants at the seedling stage is mostly due to abiotic and other factors unrelated to rodent folivory. Whilst the overall survival of different species varied, grasses, native and invasive, survived better in every case. The hardest hit seedlings were mostly shrubs, Atriplex canescens (fourwing saltbush) and Artemisia tridentata spp. wyomingensis (Wyoming big sagebrush) in the Great Basin Desert, and Ambrosia dumosa (white bursage) and Yucca brevifolia (Joshua tree) in the Mojave Desert. Among the species that survived the best across all treatments were Bromus tectorum (cheatgrass), a highly invasive grass in the Great Basin Desert, and Bromus rubens (red brome), a close relative of Bromus tectorum, in the Mojave Desert. This indicates that at the seedling stage, grass seedlings are significantly better at surviving than forbs and shrubs. Since the most problematic invasive species in these deserts are grasses, it is understandable how they have been able to establish and grow prolifically following burns.