Investigating the relationship between biological soil crusts and purple amole (Hooveria purpurea var. purpurea), a rare plant on California's Central Coast

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Nora Bales, California Military Department, San Luis Obispo, CA, Nora Bales and Yamina Pressler, Natural Resources Management and Environmental Sciences, California Polytechnic State University, San Luis Obispo, CA

Background/Question/Methods
Purple amole, Hooveria purpurea var. purpurea is a threatened Californian endemic plant known from only four populations. The largest of these four populations occurs at Camp Roberts, a California Army National Guard Training Site. Prior field studies of purple amole have observed greater purple amole plant density in populations associated with biological soil crusts (‘biocrusts’). Although biocrusts are often overlooked, they perform important ecological functions including soil stabilization, water retention, and nitrogen fixation. The objective of this study is to understand the relationship between purple amole abundance and biocrust presence, level of development, and diversity.
Concurrent with annual purple amole population monitoring, we collected the number of purple amole plants and the presence and percent cover of biocrust along 10 permanent monitoring transects; each transect with 20 1 m2 plots (200 total plots). In 2021, we will classify crust community composition and biodiversity in a subset of 80 plots representing the areas with the highest density of purple amole. Crusts will be classified by life form and level of development.
Results/Conclusions
In 2020, we found a positive correlation between purple amole density and biocrust presence. In purple amole’s vegetative stage, biocrust was observed within 36% of sampled plots and had a slight positive correlation to purple amole density (R2=0.17). During the reproductive stage, 57% of observed plants were documented growing with biocrust. Presence of biocrust accounted for 45% of the variation in purple amole density within transects (R2=0.45). Further data on purple amole density and biocrust percent cover collected in spring 2021 will help clarify if this trend persists despite interannual variation in climate and disturbance regime.
Previous management efforts have focused on strategies to increase purple amole reproductive output and recruitment with little to no consideration of biocrust conservation and other habitat parameters. No purple amole habitat restoration projects have ever been undertaken at Camp Roberts. Management strategies have included efforts to introduce a disturbance regime: chiefly prescribed fire and military training in purple amole habitat, however both fire and ground disturbance have been shown to negatively affect biocrusts. Despite two decades of monitoring, the effects of these management activities on purple amole reproductive output and recruitment remain unclear. If purple amole density is correlated with biocrust communities, then any future management, conservation, or restoration efforts for this plant must also consider biocrusts.