Plant Conservation

Santa Cruz wallflower or Ben Lomond wallflower (Erysimum teretifolium Eastw.; Brassicaceae) is a federally- and state-listed endangered plant that is endemic to the Zayante sandhills, a threatened environment endemic to the Santa Cruz Mountains. The Zayante sandills has a unique diversity of plants and animals that are highly adapted to their edaphic soils, which are composed of an ancient marine layer that was uplifted during the building of the Santa Cruz Mountains. The Santa Cruz wallflower has been dwindling in population numbers across the fragmented Zayante sandhills, and our aim, in collaboration with the U.S. Fish and Wildlife Service and with Justen Whittall at Santa Clara University, was to learn more about the mating system of the endangered plant.

Recent California legislation mandates that 60% of the state’s power come from renewable sources by 2030, spurring large-scale solar projects in the state’s desert region. California's desert flora is incredibly rich, supporting nearly 2,400 vascular plants and ~500 rare plant species. The Barstow woolly sunflower (Eriophyllum mohavense, (I.M. Johnst.) Jeps.; Asteraceae) is a rare annual endemic to the Western Mojave, where it occupies boron-rich soils with a subsurface carbonate hardpan layer (called "caliche"). The Western Mojave has also been disproportionately affected by solar development, and several major solar facilities are within a few miles of core Barstow woolly sunflower populations.

We wanted to learn how solar panels affect demographic performance of this rare species and a common relative found on gravelly desert bajadas, Wallace's woolly daisy (Eriophyllum wallacei, A. Gray (A. Gray). We installed experimental panels on each habitat type and measured the abiotic environment and community diversity underneath panels and in the open. We also collected data on life stage transitions for the rare-common species pair, and used matrix models to explore the effects of microsite and climatic variability on demographic performance. We found that rainfall and the physical conditions at each site interacted to govern panel impacts on plant communities, and that panel effects on demographic performance differed for the closely related species pair: during important high rainfall years, panels had a negative effect on the rare species only. This work suggests that solar development impacts can be context-specific, and that rare species occupying stressful habitat may be more vulnerable to panel-mediated shifts in the local environment.