Global Changes and European Terrestrial Ecosystems

Abstract: Global environmental changes are topics of important societal concern and current scientific interest. These changes are driven by many different forcing and feedbacks occurring at various time and geographic scales and are largely influencing the various Earth systems. Despite the fact that the natural component of these changes has always occurred, today it's the anthropogenic component and its magnitude which is worrying. At the European scale, such changes are likely to profoundly affect terrestrial ecosystems in term of physiology, phenology, distribution and evolution. In order to improve our understanding of the effect of global changes on ecosystems, this thesis describes a range of diverse analyses into the different forcing factors for different periods of time. In the first study, palaeorecords show that climatic conditions similar to the ones predicted to occur during the coming century already occurred. European terrestrial ecosystems however were different in structure and composition. Future predictions of climatic conditions associated to plant species specific tolerances ranges have been used in the second and third studies to quantify geographically the risk for such species in being able to find suitable climate space by the end of the century. In general, northern species will face a drastic reduction of their suitable climatic space as southern species are likely to face an expansion in climate space. However, to reach a suitable climate species may have to travel great distances and overcome natural and human barriers. Finally, the last two studies explored with the help of the state of the art dynamic vegetation model LPJ-GUESS, the different interactions between climatic changes, disturbances rates and exotic plant invasion and Mediterranean European ecosystems compositions and functions. Disturbance has been shown to be the main driving factor of these ecosystems characteristics, and influenced largely the likely success of invasions in some ecosystems. However, at the local scale, climatic conditions and the degree of invasion, were likely to influence ecosystems composition, distribution and functions but in a less radical ways. Such approaches, allowed us to explore the relevance of the different forcing factors on ecosystems changes. Future development of these analytic methods by adopting more integrating methods should aim to support societal decisions and actions.