Plant and insect diversity in solar facilities: the role of site-level and landscape-scale factors

Net-zero carbon emission climate plans are increasing the establishment of large-scale ground-mounted photovoltaic solar facilities around the world. Will solar facilities create positive or negative impacts for wildlife? Prior research has shown that one way facility managers can mitigate negative impacts on pollinators is by using a native seed mix to establish floral resources. This practice benefits wildlife and may reduce the establishment and dominance of non-native vegetation that favors the new or frequently disturbed habitats. Over the course of two years, we conducted systematic quadrat and transect surveys at 10 solar facilities that encompass a broad gradient of surrounding forest cover and that employed different management practices (e.g. whether or not the site was seeded with a native wildflower mix). During each survey we documented the unique floral and insect taxa present and the number of their interactions. In our investigation we explored the questions:1) what floral and insect communities are present at the sites, 2) what is the relationship between native floral composition and insect abundance and richness, 3) what is the relationship between habitat management (i.e. use of a wildflower seed mix) and landscape context (i.e. proportion forest in the surrounding landscape) on floral and insect diversity (i.e. abundance and richness), and lastly, 4) what are the direct and indirect effects of the landscape on insect communities mediated through changes in the floral community. We found high diversity of both plants and insect floral visitors at solar facilities. The most common insect taxa were hover flies (Diptera; Syrphidae), the European honey bee (Hymenoptera; Apis mellifera), and bumble bees (Hymenoptera; Bombus spp.) while the plant community was dominated by non-native species, including multiple species of clover (Fabaceae; Trifolium spp.). Most insect visits were to non-native plants, though the native Partridge Pea (Fabaceae; Chamaecrista fasciculata) was also very frequently visited. We found that floral richness was positively linked to insect abundance and richness, and similarly a higher proportion of native plant taxa was also linked to higher insect abundance. We found an interactive relationship between seeding with a wildflower mix and forest cover in the landscape where sites that seeded with a native wildflower mix had a high proportion of native plant taxa, regardless of landscape context, while sites that did not use a seed mix had lower proportion of native plant taxa in more heavily forested landscapes. Our results highlight that solar facilities can and do provide habitat for pollinators, while also providing ample opportunity for non-native flower species to expand. Our results suggest that targeted management, such as seeding with native plant taxa, is key for solar facilities to mitigate the expansion of non-native plant taxa and increase benefits to biodiversity across a range of landscape contexts.