Incertitudes sur les stocks de carbone dans les forêts françaises
Résumé
At the time of the Kyoto Protocol in 1997, it was decided to establish an inventory of carbon stocks in French forests. The first stage of this involved 2 studies: at the level of the whole of France, soil and humus analyses were carried out in 713 sample plots in diverse climatic regions, in which the most represented forest species were beech [ Fagus sylvatica], pedunculate oak [ Quercus robur], common spruce [ Picea abies], Douglas fir [ Pseudotsuga menziesii], silver fir [ Abies alba] and Scots pine [ Pinus sylvestris]; at the stand level, a biomass study was carried out of 127 ecosystems in the 1566 ha Fougeres National Forest in Brittany, and the carbon stock of the tree (woody) and herbaceous biomass computed from the results. Factors affecting the spatial variability of the carbon stock data from the France-wide soil and humus samples included dry matter content and soil type; factors affecting the spatial variability of the carbon stock data from Fougeres included stand age, species and soil type; illustrative data are tabulated from both these studies. The next stage of the study involved extrapolation of the carbon stock data to include all French forests, based on the analysis of the factors causing variation in carbon stocks in the Fougeres National Forest. This gave a total carbon stock of 442 000-505 000 t, equivalent to 282-322 t C/ha, but the probable error in this estimation is likely to be over 65%. In the Fougeres National Forest itself, half of the carbon stock was found in the soil, 45% in the vegetation and 5% in the humus.