Invertebrate biodiversity is greater in urban sites with nature-based solutions than control sites: A cross-continental study

Nature-based solutions have gained considerable policy and research attention for enhancing biodiversity and ecosystem services, which face intense pressure from urban development. Assessments of the biodiversity outcomes of nature-based solutions are, however, insufficient. A key unaddressed question is whether such biodiversity effects vary across the urban landscape. We assess whether insect biodiversity (richness, abundance and biomass) effects vary across a gradient of percentage impervious surface in three large cities (Barcelona, São Paulo, Buenos Aires). We focus on Sustainable Urban Drainage Systems (SUDS) which are key in alleviating flood risk and diffuse pollution associated with urban development. We examine habitats that mimic SUDS to investigate well-established habitats, to avoid the risk of underestimating biodiversity benefits arising from lags in the colonisation of recently established nature-based solutions, i.e. taking an observation approach. We do so using random stratification to select survey locations along the urbanisation intensity gradient in each city. Across all cities, NBS sites had greater invertebrate richness, biomass and abundance than control sites. Notably, biodiversity gain is greatest in more urbanised locations where biodiversity is lowest at the control sites. Our work has substantial implications for the cost-effective design and deployment of NBS interventions in urban locations in the Global North and South.