The originality of Mediterranean-climate ecosystems can be explained by complex interaction between historical biogeography patterns and unique ecological processes.
Insights of paleoecology and phylogeography indicate the importance of paleogeographical and paleoclimatic events in shaping this massive and unique Mediterranean biodiversity and ecosystem types. Recent phylogenetic methods of comparative biology have demonstrated that the evolution of evergreen sclerophylls, formerly designated as 'typically Mediterranean', may have occurred long before the origin of Mediterranean climates. The predominance of sclerophylly and related conserved life-history traits in numerous keystone ligneous plants of Mediterranean ecosystems reflect mainly the ecological success of these taxa under climatic stress and fires, following by some evolutionary refinements in physiology, rather than a real origin of these traits under Mediterranean climates. But if these species and ecosystems were able, to a great extent, to surmount past environmental changes, their immediate future seems now quite worrying.
At present, these Mediterranean ecosystems are faced with rapid and previously unknown global environmental changes with important repercussions in structure and function. Several models predict that the greatest changes on a world scale are expected in Mediterranean regions, with the highest vulnerability in mountain areas. Climate projections for Mediterranean-type ecosystems suggest drier and warmer conditions, which have probably already triggered species distribution shifts, ecophysiol-ogy, phenology, and species interactions. The elevation of atmospheric CO2 linked to anthropogenic causes could induce an increase of the productivity of many Mediterranean trees, as has already been measured for Quercus ilex and Quercus pubescens in the northern Mediterranean. On the other side, experimental studies have demonstrated that a decrease in water availability and an increase in temperature might affect the growth pattern and annual productivity of dominant shrubs, with alteration of competitive abilities. These modifications could change, in turn, species composition and structure of several Mediterranean habitats. Furthermore, the generalized and deep magnitude of human impact in the Mediterranean regions accentuates the effects of climatic change, and could obliterate the efficient capacity of ecological resilience of Mediterranean-type ecosystems, even if they have been submitted in the past to other drastic and rapid changes.
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