Conservation status of Mediterranean coastal dune habitats: anthropogenic disturbance may hamper habitat assignment

Coastal dunes are rich in habitats with a high heterogeneity in species composition. Though widely recognized as very fragile and dynamic ecosystems, they are systematically overexploited. In addition, mismanagement contributes making these habitats highly endangered, especially in the Mediterranean area. In this study, an impoverished dune system was used to investigate whether the lack of indicator species, including characteristic, main diagnostic, alien and non-typical, could mislead habitat assignment. Coastal dune plant communities used in this study are embedded into a high anthropogenic pressure territory, primarily due to the vicinity to a city and by hosting bathing facilities. A cluster analysis based on 49 vegetation plots (releves) was performed in order to assign dune vegetation units to EU habitats (92/43/EEC Habitat Directive) and corresponding phytosociological units. Eight habitat types were classified and two of them were of priority importance. Twelve plant communities belonging to eight different phytosociological classes were recognized. The plant cover value of characteristic, main diagnostic, alien and non-typical plant species, was used to assess the conservation status of each habitat type. Despite the presence of well-preserved plant community, almost all habitats were in unfavourable conservation status. Furthermore, a floristic impoverishment and a zonation interruption on the stabilized dunes were found. This study underlines the difficulty to identify typical coastal dune plant communities and associated habitats when anthropogenic disturbance dramatically changes the environmental conditions. Specific conservation and management actions for the sustainable maintenance of these endangered habitats are suggested.