Empirical and Predicted Boreal Forest Carbon Pools Following Stem-Only Harvesting in Quebec, Canada

Climate change and global wood products demand raise concerns about boreal forest ecosystem resilience to natural disturbances and harvesting. A chronosequence experiment located in Foret Montmorency, Quebec was used to evaluate the effects of harvesting on carbon (C) recovery trajectories at the stand level over a period of 77 years in balsam fir-white birch stands. Empirical estimates of 19 Foret Montmorency forest carbon pools were compared with those simulated by the Carbon Budget Model (CBM-CFS3) to test model assumptions for predicting carbon dynamics in this forest. The model was initialized using forest inventory data, spatially explicit environmental conditions, and disturbance matrices designed to represent historical spruce budworm epidemics in Foret Montmorency. Over the chronosequence, total ecosystem C increased significantly (p = 0.05) following harvest from 211 Mg in year-zero to 279 +/- 8 Mg C ha(-1) in year 67 (mean +/- SE), suggesting that FM carbon pools were recovering to pre-harvest levels after seven decades. The CBM-CFS3 model predicted total ecosystem C stocks within 10% of the empirical mean at stand maturity; however, several predicted C pools deviated from field observations in both C amounts and trends over time. The greatest differences were in deadwood and soil C pools, suggesting that model initialization of dead organic matter pools did not adequately simulate the 1000-yr history of C-pool transfers and stand dynamics leading up to the harvest. Modifications to CBM-CFS3 initialization assumptions and default decay parameters may more accurately simulate long-term effects of natural disturbances on C pools for this forest region.