Spatial patterns of genus-level phylogenetic endemism in the tree flora of Mediterranean Europe

Aim: The Mediterranean Basin is a major hotspot of plant biodiversity, including forest trees. Over the past centuries, Mediterranean forests have been fragmented and over-exploited, to which the threats of climate change are now added. Our aim is to better understand patterns and processes of tree biodiversity in the Mediterranean and to provide indicators complementing the traditional approaches to biodiversity conservation based on species counts and occurrences, using georeferenced phylogenetic diversity and endemism analyses in a spatial ecological context. Location: Mediterranean Europe. Methods: Using a dated phylogeny of the 64 Euro-Mediterranean tree genera, we calculated phylogenetic diversity for all 50 × 50 km2 grid cells spanning Mediterranean Europe (n = 643) and compared values with those obtained for genus-level taxonomic diversity. Then, we tested the relative influence of geography, past and present climate, and soil on tree diversity (phylogenetic or taxonomic) and its geographical turnover. Geographical patterns of phylogenetic endemism were inferred using the Categorical Analyses of Neo-and Paleo-Endemism (CANAPE) methodology. Results: We showed that phylogenetic and taxonomic diversity within and among cells are correlated and influenced by soil parameters as well as current, Holocene and Late Glacial Maximum climate. Southern Spain, Cyprus and some Aegean islands contained areas of disproportionately high phylogenetic diversity and a concentration of phylogenetic paleo-endemics, while phylogenetic neo-endemism was high in eastern Sicily. Mixed phylogenetic endemism regions were detected in southern Spain and Portugal, in the Balkans and in Crete. Main conclusions: Our phylogenetic approach provides relevant indicators for better protecting forests of the Mediterranean, encompassing past and present evolutionary processes and factors. We consider areas that show a concentration of evolutionary history manifested by high phylogenetic endemism as high priority targets for the conservation of the European tree flora.