The objective of this project is to understand the origin and the reactivity of various carbon pools in acid soils under Beech (Fagus sylvatica L.), according to the stage of the stand and to the corresponding silvicultural operations. A double approach is used to that purpose: (i) assessment of short-term carbon dynamics by means of incubations in controled conditions on bulk and selected soil fractions; (ii) in situ monitoring of the main carbon fluxes at three stages of a high forest in order to quantify input-output budgets by horizon and for the whole rooting zone.