Recovery of Boreal Forest Carbon Pools Following Stem-Only Harvesting in Quebec, Canada.

Climate change and global demand for wood products continue to raise concerns over the resilience of boreal forest ecosystems to natural disturbances and harvesting events. Forêt Montmorency (FM), Quebec, provides an opportunity to use a chronosequence experimental design to evaluate the effects of harvesting and natural disturbances on carbon recovery trajectories at the stand level over a period of 77 years in balsam fir-white birch stands. By comparing these empirical estimates of forest carbon pools with those simulated in the Carbon Budget Model (CBM-CFS3), it is possible to test and refine, as appropriate, the model assumptions for predicting carbon dynamics in this eastern boreal forest.

Carbon (Mg C ha^-1) has been quantified in FM for 19 forest carbon pools, which were compared with those predicted by CBM-CFS3. The model was initialized using forest inventory data, spatially explicit environmental conditions, and disturbance matrices designed to represent historical spruce budworm epidemics in FM. Over the course of the chronosequence, the total ecosystem carbon pool increased significantly (p = 0.05) following harvest, reaching 279 ± 8 Mg C ha^-1 in year 67 (mean ± SE: total tree biomass, deadwood, and soil pools accounting for 95 ± 3, 19 ± 2, and 163 ± 9 Mg C ha^-1, respectively). The increase in total ecosystem carbon suggests that FM carbon pools are recovering after seven decades to pre-harvest levels.

Although CBM-CFS3 was able to predict total ecosystem carbon stocks within 7% of the empirical mean at stand maturity, many of the predicted carbon pools deviated from field observations in both C amounts and trends over time. The greatest differences in C stock trends were associated with deadwood and soil carbon pools, indicating that the model initialization of dead organic matter pools did not adequately simulate the 1000 year history of C transfers and stand dynamics leading up to the harvest of FM in 1933. These results suggest future modifications to CBM-CFS3 initialization assumptions will be required to more accurately simulate the long-term effects of natural disturbances on carbon pools for this forest region.