Impact potentiel du changement climatique sur la distribution de l’Épicéa, du Sapin, du Hêtre et du Chêne sessile en France

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There have been many studies all over the world that forecast the impact of global warming on vegetation but there is little information currently available to assess its consequences on French forests. The authors studied the range of four common species — spruce, fir, beech and sessile oak — so as to determine their ecology as accurately as possible and assess their sensitivity to global warming. Their range over the period from 1961-1990 was modelled and mapped for the whole of France using ecological variables that characterize climate, water supply, and soil nutrition. The models constructed predict effects from temperature, the water resource, waterlogging and the trophic level of soils that are consistent with empirical knowledge about these species. Changes in the probabilities of presence during the 21st century investigated by simulating the A2 and B2 scenarios of the HadCM3 climate model. Changes in climate as predicted by this model would lead to a decrease of the probabilities of presence for all four species initially in the first part of the 21st century at the outer limits of their ranges and then a very significant drop in most plains and medium altitude upland areas, even according to the most optimistic forecasts under scenario B2. The reduction in the forest surface areas that are favourable to the species investigated for the period 2070-2100 is estimated, depending on the scenario, to be between 92 % and 99 % for spruce, 80 % and 93 % for beech, 63 % and 83 % for fir and 43 % and 83 % for sessile oak. These forecasted changes are very significant in comparison with the current conditions that are favourable to the presence of these species for which edaphic variables act as a local filter within the overall climate envelope. The authors conclude by underscoring the value of these tools for identifying and mapping the most vulnerable areas so as to be in a position to track the behaviour of these species in these areas and determine the appropriate management measures.