Carbon in Canada's boreal forest — A synthesis

• Published in: Environmental reviews 2013-12, Vol.21 (4), p.260-292
• Main Authors: Kurz, W.A., Shaw, C.H., Boisvenue, C., Stinson, G., Metsaranta, J., Leckie, D., Dyk, A., Smyth, C., Neilson, E.T.
• Format: Article
• Language: English
• Subjects: Analysis; Boreal forests; Canada; Carbon; Carbon sequestration; Climate change; Control; Deforestation; Disturbance (Ecology); Emissions (Pollution); Environmental aspects; Forest cover; Forest ecosystems; Forest management; Forest soils; Greenhouse gases; Mineral soils; Peat bogs; Permafrost; Productivity; Taiga; Taigas
• ISSN: 1181-8700; 1208-6053
• DOI: 10.1139/er-2013-0041

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 CO2from the atmosphere to replace the 17 Tg of C annually harvested and store an additional 11 Tg of C year−1in 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 atmosphericCO2stabilization targets. The single biggest threat toCstocks is human-caused climate change. LargeCstocks 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.