Ecology and benefits of green roofs: a study in Paris region

Since the 90s, the rise of urban nature policies has been accompanied by renewed interest in green roofs. Alongside traditional techniques, which have existed for thousands of years in many parts of the world, more standardized, ready-to-use solutions have rapidly developed. Many ecological benefits are generally associated with roof greening, including biodiversity, water retention and carbon storage, but these are still poorly evaluated in reality. To fill these gaps, and in continuity with previous research work on the subject, the Île-de-France regional biodiversity agency launched the GROOVES study (for green roofs verified ecosystem services) in 2017, with the support of the Muséum national d'histoire naturelle (MNHN), the Conservatoire botanique national du Bassin parisien (CBNPB), the Institut d'écologie et des sciences de l'environnement IEES-Paris and the Institut national de recherche pour l'agriculture, l'alimentation et l'environnement (INRAE-UMR Agroécologie Dijon). Thirty-six roofs of different typologies (extensive, semi-intensive and intensive) were analyzed, via plant and invertebrate inventories (including pollinators) and substrate sampling, to better understand their ecological status and role. After three years of study, the initial results confirm the role played by green roofs in hosting biodiversity and fulfilling ecological functions. They also show that there are limits and variations between different forms of green roofing, which means that some major trends can be identified for designers and managers.