Solar Panel Impacts on Environmental Conditions and Annual Plants

The California Solar Initiative has spurred renewable energy development in the Central Valley and Desert regions, with >100,000 hectares of land occupied by energy facilities in planning, permitting, or operational stages. Such facilities increase energy sustainability while reducing greenhouse gas emissions, but are not cost-free in terms of ecological impact. Installations profoundly alter the landscape, with permanent structures changing natural light and water regimes in ways that can strongly affect plant communities. These changes are likely to favor some species over others: invasive plants may increase where infrastructure or related disturbance facilitate seed movement or create altered microsite conditions favoring invader success. Design and siting of facilities to minimize negative impact thus requires understanding how altered light and runoff patterns affect belowground seed reserves as well as aboveground life stages for both native and exotic species.

We installed experimental solar panels at three sites to create microhabitat conditions associated with commercial solar arrays. We used these arrays to ask whether rare, common, and exotic annual species respond differently to these novel microhabitats, and ultimately assess how response indicates potential for long-term population persistence. We also tested for effects of shade on seed viability and germination rates, incorporating these data into models predicting how microhabitat conditions may drive shifts in population performance and community composition.

Some key takeaways from this work include:

• Low rainfall poses an overwhelming constraint on desert annual emergence in some years. In the driest year of our study, no annuals of any kind emerged aboveground on the stressful caliche pan habitat. This is important to keep in mind when vetting potential energy development sites. Searches for rare annuals or perennials that have a belowground, dormant life stage must be conducted in good rainfall years in order to have reasonable assurance that rare populations are not present.

• In years when rainfall was low but sufficient to stimulate annual emergence, rainfall blocking by panels appeared to have a stronger effect on plant performance than panel runoff.

• Panel effects on plants depended on the interaction of rainfall and physical characteristics at the site. On stressful caliche habitat, the rare Barstow woolly sunflower did better under panels in drier years, but worse under panels in a high rainfall year. On gravelly bajada habitat, plants tended to do better in the open than in the shade in drier years.

• Our work suggests that using a common annual species to predict solar panel impacts on a rare relative is a risky approach - particularly when the species pair do not occur on the same habitat type. 

For more details see the Plant Conservation and Saharan Mustard research pages, and see:

Tanner, KE, Moore‐O’Leary, KA., Parker, IM, Pavlik, BM, & Hernandez, RR. 2020. Simulated solar panels create altered microhabitats in desert landforms. Ecosphere, 11(4), e03089.

Hernandez, R.R.; Tanner, KE; Haji, S.; Parker, IM; Pavlik, B.M.; Moore-O’Leary, KA. 2020. Simulated Photovoltaic Solar Panels Alter the Seed Bank Survival of Two Desert Annual Plant Species. Plants, 9, 1125.

Tanner, KE, KA Moore-O’Leary, S Haji, IM Parker, BM Pavlik, RR Hernandez (in press). Microhabitats associated with solar energy development alter demography of two desert annuals. Ecological Applications.