A complex interplay shapes plant diversity patterns in Mediterranean coastal dunes.

A long history of human colonisation has profoundly altered coastal plant communities of Mediterranean coastal dunes, as well as their capacity of providing ecosystem services. Analysing the drivers of plant diversity loss is thus crucial for preserving Mediterranean coastal ecosystems. Using 20 cm resolution orthophotos, we mapped a wide Mediterranean coastal landscape and obtained a set of variables describing the distribution, abundance and size of natural (coastal dune habitats) and anthropogenic (urban areas and tourism facilities) patches. The study found no negative impact of anthropogenic activities on coastal vegetation plant species richness. However, disturbances favour ruderal plant species, while typical foredune species decrease. This indicates that (i) focusing on species richness may underestimate the impact of anthropogenic activities on coastal dune vegetation; (ii) human-related activities change the composition of dune vegetation, eventually promoting the establishment of ruderal species, which cannot support the functioning of coastal ecosystems and the provisioning of the related ecosystem services. Finally, structural equation models results highlighted that coastal erosion is an indirect driver of plant diversity loss, through its influence on the coastal landscape configuration.