Canadian Forest Service Publications
Carbon in Canada’s boreal forest — A synthesis. 2013. Kurz, W.A.; Shaw, C.H.; Boisvenue, C.; Stinson, G.; Metsaranta, J.; Leckie, D.; Dyk, A.; Smyth, C.; Neilson, E.T. Environmental Reviews 21(4):260-292.
Issued by: Pacific Forestry Centre
Catalog ID: 35301
Availability: PDF (download)
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Canada’s managed boreal forest, 54% of the nation’s total boreal forest area, stores 28 Pg carbon (C) in biomass, dead organic matter, and soil pools. The net C balance is dominated by the difference of two large continuous fluxes: C uptake (net primary production) and release during decomposition (heterotrophic respiration). Additional releases of C can be high in years, or in areas, that experience large anthropogenic or natural disturbances. From 1990 to 2008, Canada’s managed boreal forest has acted as C sink of 28 Tg C year−1, removing CO2 from the atmosphere to replace the 17 Tg of C annually harvested and store an additional 11 Tg of C year CO2 in ecosystem C pools. A large fraction (57%) of the C harvested since 1990 remains stored in wood products and solid waste disposal sites in Canada and abroad, replacing C emitted from the decay or burning of wood harvested prior to 1990 and contributing to net increases in product and landfill C pools. Wood product use has reduced emissions in other sectors by substituting for emission-intensive products (concrete, steel). The C balance of the unmanaged boreal forest is currently unknown. The future C balance of the Canadian boreal forest will affect the global atmospheric C budget and influence the mitigation efforts required to attain atmospheric CO2 stabilization targets. The single biggest threat to C stocks is human-caused climate change. Large C stocks have accumulated in the boreal because decomposition is limited by cold temperatures and often anoxic environments. Increases in temperatures and disturbance rates could result in a large net C source during the remainder of this century and beyond. Uncertainties about the impacts of global change remain high, but we emphasize the asymmetry of risk: sustained large-scale increases in productivity are unlikely to be of sufficient magnitude to offset higher emissions from increased disturbances and heterotrophic respiration. Reducing the uncertainties of the current and future C balance of Canada’s 270 Mha of boreal forest requires addressing gaps in monitoring, observation, and quantification of forest C dynamics, with particular attention to 125 Mha of unmanaged boreal forest with extensive areas of deep organic soils, peatlands, and permafrost containing large quantities of C that are vulnerable to global warming.
Plain Language Summary
This summary of the scientific literature outlines the current understanding about the role of Canada’s managed boreal forests in exchanging carbon with the atmosphere. In years with low disturbances by fires and insects these forests remove more carbon from the atmosphere than they release, but in years with many disturbances they release more carbon. The single biggest threat to carbon stored in these forests is human-caused climate change. Large amounts of carbon have accumulated in the litter and soil of the boreal because decomposition is limited by cold temperatures. Increases in temperatures and disturbances that kill trees could result in large carbon releases during the remainder of this century and beyond. In some regions this process has already started. Uncertainties about the impacts of global change remain high with some processes increasing the carbon removal and others the carbon release. Because the net balance of these changes in processes strongly affects Canada’s balance of greenhouse gas emissions, ongoing monitoring and research on the forests’ response to the impacts of climate change is important.