Regional modelling of forest carbon dynamics for national reporting

Background/Question/Methods

Canada fulfills its international obligation to report forest-related greenhouse gas emissions and removals using the National Forest Carbon Monitoring, Accounting and Reporting System (NFCMARS). The core model of the NFCMARS is the CBM-CFS3 which combines forest inventories, empirical yield tables developed from sample plot data, process-based modelling of dead organic matter and soil C dynamics, statistics on forest management, and remote sensing to estimate area, types and location of natural disturbance and land-use change events. Modelling of forest carbon stocks, stock changes and emissions and removals of CO₂ and non-CO₂ greenhouse gasses for 230 Mha of Canada’s managed forest occurs within a hierarchical spatial framework representing terrestrial ecozones, provincial and territorial boundaries, and forest management units.  Nearly 3 million “stands”, spatially referenced to forest management units, are the fundamental modelling unit of forest C dynamics. Inventory-derived stand-level information on forest characteristics for each of these stands, is used to estimate carbon fluxes (NPP, heterotrophic respiration, disturbance accounting, and forest regrowth). The stand-level results are summed up to regional statistics. 

Results/Conclusions

Here we present and contrast regional differences in C dynamics for the period 1990 to 2010.  We emphasize the importance and magnitude of annual transfers of biomass to dead organic matter pools, from litterfall, stand mortality, and disturbance impacts and the resulting large fluxes from heterotrophic respiration.  We suggest that statistical correlations between biomass and dead organic matter stocks are not adequate to capture the large fluxes associated with large-scale disturbances such as the Mountain Pine Beetle outbreak in Western Canada. The CBM-CFS3 explicitly simulates the transfers of biomass to dead organic matter pools and their subsequent decay to provide a more accurate representation of C dynamics. The Carbon Accounting Team for the Canadian Forest Service is continuously improving the NFCMARS system. The current emphasis is on improving the system by developing methods to overcome some of the limitations of empirical yield tables with their incomplete representation of the impacts of environmental changes.