Impacts of climate change and elevated CO2 on trees in regions with a Mediterranean type of climate

Research on the effects of global changes on Mediterranean trees is still limited. In terms of growth response to elevated CO2, Mediterranean trees were not different from temperate-zone trees, i.e., growth enhancement seems to be short-lived, declining after the first growing seasons in elevated CO2. In Mediterranean landscapes important soil fertility gradients can be found. Such differences, mainly in soil nitrogen, may interact with elevated CO2, as shown by the enhancement of the response to high CO2 by abundant N in Fraxinus angustifolia (a deciduous, riparian tree) and Quercus suber (an evergreen oak). Given the characteristics of the regional climate, special attention in research was given to the interaction between elevated CO2 and the summer stress, i.e., heat and high irradiance stresses superimposed on water deficits. We discuss the possibility that elevated CO2 may alleviate some of the negative effects of that summer stresses, as was found in Quercus suber seedlings under controlled conditions or in Quercus ilex with a life-time exposure to elevated CO2.