PLANT-SPECIES RICHNESS AND EXTINCTION ON ISOLATED DUNES ALONG THE ROCKY COAST OF NORTHWESTERN SPAIN

Data on distribution and abundance of rare plant species on isolated coastal dunes along the rocky coast of northwestern Spain were compared with the local floristic literature in order to reconstruct past distribution and local extinction of species. Species extinction was not confined to species with a narrow distribution but also included widely distributed ones. Moreover, there was no evidence of colonization. Species number was related to beach and dune area, but species differed in the minimum area required for occurrence. The largest dune reserve possible would probably be insufficient to avoid further extinctions, so also small areas containing particular species should be preserved. There was no significant relationship between abundance of species in the local dune communities and their total distribution, and there were few satellite species. The former might be attributed to low fertility and habitat diversity.