Quelle biodiversité urbaine est observée sur les espaces verts, les friches et les cimetières ? Une illustration à Grenoble

The growth of human population has led to increasing pressures on ecosystems and biodiversity. Urban encroachment on natural habitats threaten biodiversity and urban life contributes to a disconnection with nature. One particular question arises in this context: what is the existing biodiversity in cities? A study was carried out through naturalist monitoring in the city of Grenoble (France) and its conurbation, a densely urbanised valley, strongly contrasting with the neighbouring agricultural or natural spaces. Three types of urban sites (recreational parks, wastelands and cemeteries) were compared on the one hand; on the other hand, impact of park management intensities on biodiversity was assessed. Two taxa were studied: butterflies, an indicator of vegetation diversity, using a citizen science program (PROPAGE, butterflies monitoring by green spaces managers), and spider webs, an indicator of available preys, through a protocol created for the occasion. Butterflies were used to compare types of sites and management intensity; spiders were used for the comparison of site types. Surveys were conducted over two summers (2014 and 2015, three repetitions each year). In Grenoble conurbation, a net decrease in richness and abundance appears between the non-urbanised areas of the Bastille hill and all the other sites. Inside the urban areas, richness and abundance were higher in urban wastelands, then in other types of sites. The alleviation of  management intensity positively impacts the quantity and diversity of butterflies in recreational parks. The study sites seem to constitute, within an unwelcoming matrix, a patchwork of relatively sheltered places for biodiversity. Lighter management practices are positively impacting urban biodiversity.