Simulated solar panels create altered microhabitats in desert landforms

Abstract

Solar energy development is a significant driver of land-use change worldwide, and desert ecosystems are particularly well suited to energy production because of their high insolation rates. Deserts are also characterized by uncertain rainfall, high species endemism, and distinct landforms that vary in geophysical properties. Weather and physical features that differ across landforms interact with shade and water runoff regimes imposed by solar panels, creating novel microhabitats that influence biotic communities. Endemic species may be particularly affected because they often have limited distributions, narrow climatic envelopes, or specialized life histories. We used experimental panels to simulate the effects of solar development on microhabitats and annual plant communities present on gravelly bajada and caliche pan habitat, two common habitat types in California's Mojave Desert. We evaluated soils and microclimatic conditions and measured community response under panels and in the open for seven years (2012-2018). We found that differences in site characteristics and weather affected the ecological impact of panels on the annual plant community. Panel shade tended to increase species richness on the more stressful caliche pan habitat, and this effect was strongest in dry years. Shade effects on diversity and abundance also tended to be positive or neutral on caliche pan habitat. On gravelly bajada habitat, panel shade did not significantly affect richness or diversity and tended to decrease plant abundance. Panel runoff rarely affected richness or diversity on either habitat type, but effects on abundance tended to be negative-suggesting that panel rain shadows were more important than runoff from low-volume rain events. These results demonstrate that the ecological consequences of solar development can vary over space and time, and suggest that a nuanced approach will be needed to predict impacts across desert landforms differing in physical characteristics.

Simulated Photovoltaic Solar Panels Alter the Seed Bank Survival of Two Desert Annual Plant Species

“…In general, we found that seed bank survival was significantly greater in shade microhabitats compared to runoff microhabitats and control microhabitats. Shade microhabitats within PV systems are notable for receiving less PAR and having lower soil moisture and temperatures, and we found this to be true for our experiment [ 47 ]. For example, soil moisture was consistently lowest in the shaded microhabitat after storms, and significantly so at the Caliche Pan site [ 47 ].…”

“…Global installed PV solar energy exceeded 500 GW of capacity at the end of 2018 and is projected to provide a majority of global energy reaching 30 to 70 terawatts by 2050, underscoring the importance of understanding its impact on terrestrial ecosystems [ 46 ]. The tilt of a panel effectively intercepts and diverts precipitation to its lower edge, creating an area of runoff which can be significantly greater in soil moisture than areas under the panel [ 47 ]. In shaded areas directly under a panel, Tanner et al [ 47 ] found soil temperatures were significantly cooler and photosynthetically active radiation (PAR) lower.…”

“…The tilt of a panel effectively intercepts and diverts precipitation to its lower edge, creating an area of runoff which can be significantly greater in soil moisture than areas under the panel [ 47 ]. In shaded areas directly under a panel, Tanner et al [ 47 ] found soil temperatures were significantly cooler and photosynthetically active radiation (PAR) lower. Such changes may elicit dramatic responses in seeds.…”

“…For example, desert seeds in microhabitats with higher soil moisture may be more likely to germinate and/or be infected by fungal pathogens facilitated by such anomalously wet conditions [ 30 ]. Tanner et al [ 47 ] and Grodsky and Hernandez [ 45 ] found significant alterations in aboveground plant community composition and structure owing to ground-mounted panel infrastructure but did not evaluate effects on seed banks [ 2 ]. As both theoretical and empirical studies have identified seed bank survival as a driver of annual plant demography in variable environments, it is important to understand how seed banks may respond to changes in the environment owing to the siting of solar energy infrastructure in places where desert annuals exist [ 13 , 48 , 49 , 50 , 51 , 52 ].…”

“…We use this framework to compare seed bank survival between the common and rare annual desert plant species [ 8 , 38 ] and to evaluate seed bank survival across microhabitats (shade, runoff) and control microhabitats that vary in soil moisture and light and emulate effects of PV solar energy infrastructure ( Figure 3 ). We interpret our findings both in the context of theory on rare and common species, including responses to changes in environmental conditions, and as they inform the study of annual plant responses to microhabitat variation needed to guide land-use planning and management decisions [ 47 ]. Overall, our aim is to contribute conceptual and observational insight into desert annual seed banks, including their responses to changes in microhabitats imposed by anthropogenic disturbances [ 5 ].…”