Dendroecology, which is based on annual growth variable measurements, is in possession of data particularly well adapted to analyse the impact of global change on vegetation production. But the classical statistical methods of quantification of tree ring-climate relationship cannot take into account the effect of CO2 increase. Therefore, a biogeochemistry model (BIOME3) has been adapted to these data and then validated on Pinus cembra. The results indicate that the production is reduced by 14% if only the climatic changes are taken into account. If both climatic changes and CO2 increase are taken into account the production is increased by 62%. The direct fertilisation effect of CO2 increase will have more influence on the productivity than the indirect climatic effect.