PS 38-49 - Potential for ecological site recovery following large scale disturbance across the Mojave Desert of California

Abstract: Across much of the Mojave Desert of southern California, biological soil crusts (biocrusts) and vegetation face an uncertain future due to human land-use pressures and climate change. Understanding the role of human disturbance, either via direct (e.g. trampling, infrastructure development) or indirect (e.g. invasive species spread) actions will impact species distribution, recovery, and future trajectories. Therefore, investigating how biological soil crusts are responding to previous land disturbances across a range of sites with different topography and elevation, soil types, and disturbance histories is vital for anticipating the future direction and potential for recovery of many sensitive Mojave ecosystems.

To investigate the rate of biocrust and vegetation recovery following known disturbances, we surveyed sites in 2005-06 and 2022 that previously experienced large-scale disturbance due to the underground installation of a natural gas pipelines (Mojave National Pipeline: MOPI) in the early 1990s and the removal of coaxial cable communication lines (COAX) in the late 1990s. For each disturbance site, biological soil crusts and vegetation cover were measured along a 100 m transect over the known disturbed area, as well as a reference 100 m transect located ~70 m parallel to the known line of disturbance. Along the transect line, at every one meter we recorded vegetation and ground cover, while at every 5 m we recorded maximum plant height and conducted a 20-point frame analysis of biological soil crusts.

Initial results suggest that late successional biocrust cover is highest along reference transects, yet previously disturbed sites are showing some signs of biocrust recovery. However, biocrust cover was strongly related to each site, indicating that microclimate and soil type likely play an important role in biocrust distribution and recovery. The invasive annual grasses of Schismus spp. (S. arabicus and S. barbatus) were found along both the disturbed transects and the reference transects, with marginally higher rates of establishment in the disturbed sites. Schismus spp. may be present across the greater landscape due to large-scale road development that occurred with infrastructure projects, which has been suggested to be a strong environmental correlate with the spread of invasive annual plants. Future analysis will focus on the dynamics of native vegetation cover and soil stability to further explore the resiliency of Mojave ecosystems following disturbance.