Management effects on the annual carbon balance of forests: an analysis of a global database
Résumé
Management of forest targets the production of wood and biomass. It is hypothesized that managed forests show a higher net primary production (NPP) and, among NPP components, wood NPP, than unmanaged forests. In addition, they may have a lower soil carbon content and heterotrophic respiration as a result of (1) site preparation practices such as drainage, fertilisation, ploughing, and (2) exportation of biomass. This presentation provides an analysis about the effects of management on the annual carbon balance of forests at the stand level. It is based upon the database used by the Forest Activity group of the CARBOEUROPE project which is composed of carbon annual flux and stocks covering 124 forest stands classified according to management intensity into four classes: fertilised or irrigated, managed, unmanaged and recently disturbed. Even if the database was not fully representative of management regime at this preliminary stage, we believe such an analysis may take benefit from the large number of sites inventoried to detect some emerging trends of management impacts on forest C balance at the global scale. The management regime explains 48 and 35 % of the net ecosystem production (NEP) and NPP variances respectively. Indeed, the NPP of the wood compartment is highest in fertilised or irrigated stands, intermediate in managed forests and lowest in recently disturbed and unmanaged forests. Management effect on NPP is larger during juvenile stages and weaker beyond the age of 50. Similarly, the management regime affects NEP and to a lesser extent the gross primary production (GPP) with larger effects during younger stages. In summary, the forest management appears to shorten the lifetime of forest stands, to magnify the age effects on the annual carbon balance and to shift the allocation of the allocation of carbon toward the wood compartment.