Canada’s western boreal forest stores vast amounts of carbon. Stretching from Manitoba to the Yukon, the managed portion of this forest region contains the equivalent of about 130 years’ worth of national greenhouse gas emissions and is a globally significant carbon pool. However, increases in aridity in recent decades have caused region-wide losses of forest carbon as moisture stress has both reduced productivity (slowed tree growth) and increased mortality. These changes pose a significant threat as warming temperatures and greater aridity together exacerbate the risk of fire, predispose trees to attack by insect pests, reduce supplies of merchantable timber, and trigger damaging climate change feedbacks when carbon stocks are released to the atmosphere.

To better understand the effects of climate change in this region, we are using a coordinated set of field studies and modelling experiments to:

1. Evaluate how effects of water availability on the growth and mortality of individual trees vary among species, with local competition, and with site conditions;
2. Assess how climatic variation in productivity and biomass turnover within forest stands influence rates of biomass accumulation over time;
3. Project how the current species composition, stem size distribution, and carbon density of forest stands are expected to change under future climate and disturbance scenarios.

This research will provide a clearer understanding of carbon dynamics across a major Canadian forest region for which there is currently little data. Although the conventional thinking is that these forests are a net carbon sink, model projections based on extensive new data could reveal their potential to become a carbon source if moisture stress increases as expected over the coming decades. A better understanding of the sensitivity of the western boreal forest to climate change would resolve important uncertainties concerning its influence on Canada’s national greenhouse gas emissions and the global carbon-climate system.