Chloé Tavernier

Post-war agricultural intensification has led to a collapse of farmland biodiversity. In this depleted landscape, solar fields are an increasingly prominent land use. However, given their substantial land requirements, they may pose additional threats to the already declining biodiversity of farmland. Indeed, through their panels, mounting structures, and overall management, solar fields are modifying the microclimate and vegetation composition. These shifts toward more shade-tolerant plant species and sparser and shorter vegetation cover could further degrade habitat quality in agricultural landscapes. Nevertheless, they may also offer alternative habitats within an otherwise homogeneous agricultural matrix. In particular, the absence of agrochemical inputs, the absence of farming practices, and the development of heterogeneous vegetation structure can provide diverse resources for local wildlife. The central question of this thesis was therefore: do solar fields benefit wildlife in the agricultural landscape by increasing habitat heterogeneity, or do they cause harm through habitat degradation? This study aimed to evaluate the use of solar fields by vertebrates, which, given their high dispersal ability, can actively select among habitat patches in the landscape matrix to fulfil their ecological needs. A direct way to evaluate whether solar fields benefit or harm farmland biodiversity is to monitor species diversity and abundance. Indeed, on one hand higher species diversity may reflect a habitat's capacity to provide a broad range of resources, sustaining the needs of different specialist species. Whereas, on another hand, a higher species abundance may reflect an overall high habitat carrying capacity. Chapters 2 and 3 measured bat and terrestrial mammal diversity and occurrence within first generation solar fields build on former intensive agriculture, comparing them against two controls: an intensive grassland, representing a low-quality habitat, and an extensive meadow, representing a high-quality habitat. For both taxonomic groups, solar fields supported lower species diversity than either control. All bat species' activity, examined in Chapter 2, was also lower within solar fields than in both controls. Furthermore, four of the seven mammal species examined in Chapter 3 were equally or less abundant in solar fields than in intensive grasslands. These results suggest an overall degradation of habitat quality associated with solar fields in agricultural landscapes, and indicate that solar fields may fail to provide adequate resources for these species. Nevertheless, solar fields may still benefit certain species. The European hare was one of the few species exhibiting higher abundance in solar fields than in both controls. In Chapter 4, hares were found to preferentially use solar fields during daytime. Since hares are primarily nocturnal foragers and were mostly inactive within solar fields during the day, this pattern does not support the hypothesis that solar fields provide sufficient foraging resources. Instead, solar fields appeared to offer a valuable alternative refuge during daytime, a function normally fulfilled by tall vegetation structures such as hedgerows or vegetation-rich field margins. Given that agricultural intensification has been identified as a key driver of the increasing use of urban habitat by hares, there seems to be a growing demand among farmland species for low-disturbance refuges. Solar fields may therefore still represent a promising alternative habitat, provided that biodiversity-friendly planning, design, and management practices are identified and implemented. Chapter 5 constituted a first step toward this goal. Bird species richness was compared across up to 50 solar fields varying in design and management. While richness in the covered interior of the panels was substantially lower than at field perimeters, perimeter richness was comparable to that of surrounding habitats. Solar field size, panel orientation, and vegetation management were identified as strong predictors of bird richness. Indeed, larger fields, south-facing panels, and mowing vegetation management were associated with higher richness. The relationship with field size may reflect the tendency of larger installations to incorporate a greater proportion of biodiversity-friendly measures, such as ponds, hedgerows, or vegetation-rich strips. For birds, it is therefore possible to design future solar fields with a compact covered area surrounded by a wide, biodiversity-rich perimeter (i.e. the space between the panels and the fences) designed and managed under ecologically informed mowing regimes. This would create a mosaic of low-quality habitat in the covered zone and high-quality habitat at the margins. However, efforts to improve conditions within the covered area should remain a priority for developers, as they constitute the majority of the solar fields area. Overall, the results of this thesis indicate that the design and management of current solar fields are suboptimal for vertebrates. This conclusion aligns with findings on vegetation. Indeed, solar panels have been shown to reduce vegetation cover and biomass beneath them. However, arthropods responses to solar fields have been both positive and negative depending on the species group. Moreover, encouraging result have shown a preferential used of solar fields by some species (European hares, Roe deer, European hedgehog) in comparison with intensive grasslands. Furthermore, the reduced use by others could potentially be reversed or mitigated through appropriate design and management measures. A key remaining question is whether the lower habitat use observed reflects intrinsically poor habitat quality or simply limited availability of solar field habitat in the landscape. This thesis thus provides an initial understanding of the effects of solar fields on vertebrate communities and identifies priority questions for future research on the mechanisms driving wildlife use of solar field habitat