Open Access Senior Thesis
Bachelor of Arts
2023 Riley S Scaff
Wildfires are a novel disturbance type in the Mojave Desert, but have been increasing in size and frequency since the 1970s due to the proliferation of invasive grasses. Burned areas are more susceptible to invasion, which can lead to the establishment of a grass-fire cycle. For this reason, restoration is often necessary to facilitate natural plant community recovery, but the extreme desert climate makes returning native vegetation to burn areas challenging. Planting in nutrient-rich soil microhabitats could be a helpful tool to improve revegetation success, but has yet to be tested. This study surveyed natural postfire recruitment across two seasons and re-established a host of native perennial plant species, including the threatened joshua tree (Yucca jaegeriana), using two common restoration methods—broadcast seeding and outplanting. I also evaluated whether geochemical and microbial differences between soils under burned yucca shrubs and surrounding soils impacted outplant survival. The spring community was dominated by the invasive annual grass Bromus rubens along with a host of native annuals, while the fall community was dominated by two native bunchgrasses (Bouteloua spp.). The prevalence of both native and invasive grasses across both seasons suggests type conversion from scrubland to grassland is likely. Seeding was ineffective at restoring native plants, but outplanted Hilaria rigida and Sphaeralcea ambigua performed well when caged. While shrub microhabitats did not affect outplant survival, soils beneath burned Yucca baccata canopies were characterized by elevated carbon, nitrogen and nutrients, but harbored lower bacterial and fungal biomass than interspaces, suggesting complex, microhabitat-specific soil resource dynamics that impact soil microbial communities. Based on these results, restoration practitioners should focus on outplanting strong performers such as Hilaria rigida and Sphaeralcea ambigua. Restoration efforts should also invest in cages to deter herbivory, as this was essential to short-term outplant survival.
Scaff, Riley, "Restoring an Iconic Joshua Tree Forest: Natural Recovery, Restoration Success, and Soil Microhabitats on a Desert Burn Area" (2023). Pitzer Senior Theses. 173.
Available for download on Thursday, May 01, 2025