A 70-year retrospective analysis of carbon fluxes in the Canadian forest sector

The Carbon Budget Model of the Canadian Forest Sector (CBM-CFS2) is a frame work for the dynamic accounting of carbon pools and fluxes in Canada's fore st ecosystems and the forest product sector. The model structure, assumptio ns, and supporting databases are described. The model has been applied to e stimate net ecosystem carbon fluxes for Canada's 404 Mha forest area for th e period 1920-1989. Changes in disturbance regimes have affected the forest age class structure and increased the average forest age during the period 1920-1979. The resulting changes in dead organic matter and biomass carbon during this period were estimated with the model. In the last decade of th e analysis, large increases in disturbances, primarily fire and insect dama ge, have resulted in a reduction in ecosystem carbon storage. The estimates of biomass pool sizes obtained ore consistent with those of other studies, while dead organic matter carbon pool estimates remain somewhat uncertain. Sensitivity analysis of several sources of uncertainty indicate that the p attern of net changes in ecosystem carbon pools over the 70-yr period was h ardly affected and that the numerical estimates changed by <15%.