The challenge of Mediterranean sclerophyllous vegetation under climate change: from acclimation to adaptation

Forecasting models for climate change in southern Europe differ from those proposed for central and northern regions mainly with regard to precipitation, which is believed to be reduced strongly. Contrary to what found for boreal and termperate areas, the beneficial effects of rising carbon dioxide on growth and photosynthesis of Mediterranean schlerophyllous vegetation may be partly or fully offset by warming, as Mediterranean vegetation is already living near its average temperature optimum. Increasing drought events have been reported to reduce the productivity of Mediterranean vegetation. In areas where severe and prolonged drought episodes occur, severe photoinhibition and metabolic limitation to photosynthesis may prevent plant to take advantage of higher atmospheric CO2, and may slow down recovery after the end of the dry season. In this context, opportunistic, drought-deciduous species may be favored over evergreen trees. The most sensitive forest types are those made of tree species which are, in the Mediterranean basin, at the southernmost limit of their distribution range. In contrast, thermophilous trees are expected to have a greater diffusion both in southern and central Europe, as winter cold stress will be reduced by warming. Yet due to great variability of ecological features, the alleged substitution of tree species can follow a natural pattern from south to north and from low to high altitudes, without considering obstacles deriving from urbanization. For these reasons, researches on the performance and ecologic plasticity of different genotypes, on species selection, and on planting and management techniques can have strategic importance for adaptive forest management.