The role of tree diversity in the responses of Mediterranean forests to climate change.

Increasing temperatures and drought through climate change are expected to have detrimental effects on the Mediterranean ecosystems and forests. Current modeled simulation suggests future expansion of forests at the highest latitudes and altitudes, alongside with a reduction of forest surface in the hottest and driest Mediterranean regions of South Europe. Extinction of populations with low ecological plasticity may occur especially at the Southern edges of the largely distributed tree species or in the case of isolated (relict) populations. The natural substitution of tree species can be hampered by co-factors of climate change, such as forest fragmentation, increased frequency and intensity of forest fires, extreme weather events and the migration of invasive alien species of pests and fungi. On the other hands, Mediterranean forests may represent a reservoir of germoplasm useful to cope with climatic changes in Central European regions. In fact in Italy there are the Southernmost provenances of tree species widely distributed in Europe. Moreover there are evidences about the suitability of the possible use of evergreen oak species in the future climatic conditions in Central Europe. The persistence of the current forest types can be assured thanks to the genetic variability and the phenotypic plasticity of the populations. At stand level the functional interactions between different tree species may play a relevant role in assuring the ecological stability of the forests, for ex. by optimizing the use of the water resources with different ecological niche strategies. Moreover a large scale assessment of the role of forest diversity in driving the responses to climate change is now possible by using monitoring data such as the National Forest Inventories and the Level I ICP-Forests network. This presentation shows some evidences, from literature and observational/ experimental activities, about the role of forest diversity in persistence and adaptation of Mediterranean forests.