Carbon in Canada’s boreal forest: current status and potential climate change effects

Background/Question/Methods

Forests remove carbon (C) from the atmosphere and store it in the form of biomass, dead organic matter and soil, while also providing other ecosystem services and meeting society’s demands for products such as timber, wood fiber, and energy. Based on data from Canada’s National Forest Carbon Monitoring, Accounting, and Reporting System, the managed boreal forest, which comprises 53% of the 272 Mha of boreal forest in Canada, currently contains a total ecosystem stock of 28 Pg of C. The difference between two large fluxes, C uptake (net primary production) and C release (heterotrophic respiration), largely determines the net annual change in C stock, with significant additional impacts from anthropogenic and natural disturbances. The managed boreal forest in Canada was a sink of 28 Tg C yr⁻¹ between 1990 and 2008, removing CO₂ from the atmosphere to replace the 17 Tg of C annually harvested and to store an additional 11 Tg of C yr⁻¹ in ecosystem C pools. A large portion (~57%) of C harvested since 1990 remains stored in wood products and landfill in Canada and abroad, both replacing C emitted from wood harvested before 1990 and contributing to net increases in forest product pools.

Results/Conclusions

Climate change impacts on forest ecosystem processes in Canada’s boreal forest will become increasingly apparent over the coming decades, and the resulting effects will influence the global C budget and consequently the mitigation effort required to attain atmospheric CO₂ stabilization targets.  Increases in temperatures and disturbance rates could result in a large net C source during the remainder of this century and beyond, which may partially be offset by increases in forest productivity. The magnitude and direction of these responses is uncertain, but the evidence available today suggests that the risk is asymmetric. It is unlikely that increases in productivity will be of sufficient magnitude to offset higher emissions from increased disturbances and heterotrophic respiration. Sustained investment into the quantification of forest C dynamics will be required to reduce uncertainty and to track changes in the C balance of Canada’s boreal forest. The 127 Mha of unmanaged boreal forest, where the C balance is currently not known, will require additional attention, as it contains extensive areas of deep organic soils, peatlands, and permafrost containing large quantities of C that may be particularly vulnerable.