Passive Ecovoltaics: Solar power plants as semi-natural ecosystems via spontaneous succession in forest landscapes

The rapid expansion of solar photovoltaic (PV) facilities poses challenges for biodiversity conservation. While "Ecovoltaics" aims to reconcile energy production with ecological restoration, current strategies primarily rely on active management, such as targeted seeding, based largely on European agricultural contexts. This study investigated the potential of a "Passive Ecovoltaics" approach in Monsoon Asia, characterized by mosaic landscapes that include forests. Our study site was a PV facility in a Japanese forested landscape, maintained without artificial seeding for five years since becoming operational. We conducted vegetation surveys to compare species diversity and composition across different microhabitats. The results showed that plant communities under solar panels resembled those of forest edges and maintained species diversity comparable to grasslands unaffected by panels. This suggests that shading by panels exerts environmental filtering that facilitates the establishment of forest-dwelling species. Furthermore, despite the large scale of the facility, the vegetation under the panels near the center remained similar to that of the forest edges. This is likely because the intricate shape of the facility enabled sufficient seed dispersal from the adjacent forest throughout the site. We propose a "Passive Ecovoltaics" model, demonstrating that solar PVs can function as regional semi-natural habitats through secondary succession and minimal management (e.g., biannual mowing). However, the success of this model depends on (1) a high potential for seed supply from the surroundings and (2) a facility scale and shape that allow for sufficient seed dispersal. To avoid adverse ecological impacts, careful application in appropriate landscape contexts is required.