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 isstill 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 firstgrowing seasons in elevated CO2. In Mediterranean landscapes importantsoil fertility gradients can be found. Such differences, mainly in soilnitrogen, may interact with elevated CO2, as shown by the enhancement ofthe response to high CO2 by abundant N in Fraxinus angustifolia (adeciduous, riparian tree) and Quercus suber (an evergreen oak). Giventhe characteristics of the regional climate, special attention inresearch was given to the interaction between elevated CO2 and thesummer stress, i.e., heat and high irradiance stresses superimposed onwater deficits. We discuss the possibility that elevated CO2 mayalleviate some of the negative effects of that summer stresses, as wasfound in Quercus suber seedlings under controlled conditions or inQuercus ilex with a life-time exposure to elevated CO2.