The analysis of tree-ring-climate relationships provides models (response functions) of tree-growth calibrated on the inter-annual variability of climate. Output of GCMs can be used as inputs of these models in order to evaluate the change in radial growth induced by climatic change. A spatiotemporal approach applied to a large data set of ring-width chronologies and meteorological data allows the response of trees to be evaluated for different populations of various species in numerous habitats. Such a study was carried out, firstly on ten populations in south-eastern France, then on populations at high-altitude sites. The species involved were Larix decidua, Mill., Pinus sylvestris, L., Abies alba, Mill., and Picea abies Karst. The calibration of tree ring to climate relationships was based on the monthly values of precipitation and temperature provided by meteorological stations more or less distant from the tree sites. Outputs of GCMs were obtained from the ARPEGE model of Météo-France with a simulation on a large grid (2°79 in latitude and 3° in longitude) for the hypothesis of a CO2 doubling.
Results show that climatic change can induce either an increase or a decrease in the mean radial growth. For most of the tree-populations, no significant change was apparent. The results suffer from insufficient data related to the spatial representation of climate (i.e. stations that are too far from the tree populations, only two grid points available from the GCMs, etc.).
In a new research project supported by the European Union, this basic methodology is being proposed, with some improvements in the statistical techniques. The data set is being extended to the whole of south-western Europe, with three target areas centred on the Alps, the Pyrenees, the Mediterranean area, and southern Italy. The spatial coverage of both tree rings and meteorological data will be improved. The spatial variability of climate will be more precisely taken into account through the availability of GCM simulations on finer grids (40–50 km),.