Species-area relationships in isolated coastal sandy patches: implications for the conservation of beach-dune flora in a rocky coastal region of western Japan.
Questions: In many places worldwide, dune vegetation has rapidly declined owing to the expansion of various land uses, which pose a serious threat to many native dune plant species. A better understanding of species-area relationships in coastal sandy patches (i.e., beaches and dunes) is valuable for designing effective management strategies for the conservation of beach-dune flora in coastal regions. We investigated how the area and other attributes of sandy patches affect the number of species (dune, inland, and alien species) and whether the occurrence of all dune species is area-dependent. Location: Sandy coast of San'in Kaigan National Park, western Japan. Methods: All vascular plants at 43 sites (sandy patches) were recorded. Using generalized linear models, we analyzed the relationships of the area and other attributes of sandy patches with the number of species and the relationship between the area of sandy patches and the occurrence (presence/absence) of each dune species. Results: Larger sandy patches maintained a greater number of dune species and harbored some nationally threatened ones. The number of inland and alien species also increased with an increasing area of sandy patches, although the effects of other size and site attributes varied; shoreline length, beach-dune height, and high openness of the beach were selected as important positive factors for the number of dune species. Furthermore, most dune species in herb and dwarf shrub zones were area-dependent and tended to occur in larger sandy patches, whereas some species of the tidal drift zone, including locally threatened dune species, were area-independent. Conclusions: Effective conservation of beach-dune flora demands not only the protection of larger sandy patches but also the selective preservation of sandy patches with better developed dunes. Moreover, the maintenance of unstable habitats for area-independent dune species is important.