Flora and factors affecting species diversity in protected ''Natura 2000'' sites of the Ionian area: the Echinades islet group (Greece)

The vascular plant species diversity of the Echinades islet group, quite unexplored so far, is documented by an inventory of flowering plants and ferns, filling a gap in the floristic information available for the National Park to which these islets belong, as well as for the Ionian land-bridge island system, for which detailed studies concerning floristic and phytogeographical relationships were available before. Field investigations on 19 of the 20 Echinades islets generated an inventory of plant species composition for the first time for 18 of them and added 56 taxa as new to the islet of Oxeia as compared to previous literature. The total vascular flora of the Echinades islets comprises 386 plant taxa. Spectra of life-form and chorological categories are presented and discussed. Floristic cross-correlations (beta-diversity) showed that the individual islet floras differ from each other from 25 % to 85 %. Concerning the role of geographical variables as influencing plant species diversity in the area, regression analyses indicated island surface area and elevation as the major predictor variables of species richness, while distance to the mainland plays a subordinate predictive role.