More than weeds: Spontaneous vegetation in streets as a neglected element of urban biodiversity

Compared to green spaces, the ecological value of built elements has been largely ignored despite representing the main land cover in cities. In streets, pavements are linear built elements which are omnipresent in all neighborhood types and which extend over large cumulative areas in cities. We assessed the capacity of pavements to promote spontaneous flora and investigated the drivers of pavement plant assemblages. Based on a plant survey along 48 km of pavements in a French city which no longer uses pesticides, we examined the relative importance of multi-scale factors (i.e. landscape context, pavement characteristics and frequency of manual weeding) on different aspects of pavement plant communities including total plant cover, species richness and beta-diversity. More than 300 species were recorded. Plant assemblages were mainly determined by the pavement type, plant cover and species richness being much higher on sandy than on asphalt pavements. There were marked differences in species composition between pavement types with many more species associated with sandy than with asphalt pavements. We found a higher species richness and plant cover on pavements located in commercial and industrial areas than in residential neighborhoods. The effects of weeding frequency and the presence of green space around pavements were marginally important. We demonstrate that pavements with a high level of permeability play a major role in promoting urban biodiversity which should be taken into account by urban planners. We recommend that ecologists work with civil engineers and landscape architects to develop new urban ecological designs.