The phytogeography of European and Mediterranean heath species (Ericoideae, Ericaceae): a quantitative analysis

The geographic ranges of heath species in Europe and the Mediterranean and their relationships with environmental (climatic and ecogeographic) variables and biological features are analysed by means of multivariate methods. In particular, TWINSPAN classifications into floristic elements and floristic regions, DCA floristic ordinations, CCA environment-constrained ordinations and CCA biology-constrained ordinations are carried out. Results of the analyses show a correspondence with conventional regionalization analyses based on broader criteria, and less correspondence with numerical analyses of other taxonomic groups at a similar scale. This lack of fit depends on the particular history and ecology of the taxonomic groups under study. A number of climatic (temperature and water stress) and geographic (coast length) variables are associated with different types of heaths according to their geographical ranges (continental, Mediterranean, Atlantic). Biological features of heaths account for a small part of the variation in range, but the association of temperate heaths with a preference for acid soils, of Mediterranean heaths with pubescence, and of Atlantic heaths with plant height is of interest. Heath species richness throughout Europe and the Mediterranean is analysed by multiple regression analyses and, apart from a strong influence of area size, a significant effect of water conditions, temperature and proximity to sea is detected. The area with the highest heath species richness is Western Mediterranean. Additional classification, ordination and multiple regression analyses of heaths in the Iberian Peninsula (Spain and Portugal, the areas with the highest heath diversity) revealed similar patterns to those found in Europe and the Mediterranean. The effect of heterogeneity of the studied units at this latter scale is removed in the Iberian analysis because of the relative homogeneity of the units considered at this scale.