Evaluating variation in the sensitivity of tree growth, mortality, and biomass allocation to climate-induced moisture stress across the western boreal forest

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Stretching from Manitoba to the Yukon, Canada's western boreal forest region represents 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 climate sensitivity of this forest region, our partnership will establish and repeatedly survey a network of 400 sites across three major boreal ecozones in western Canada. We will use data from ground plots, unmanned aerial vehicle imagery, and terrestrial laser scanning to (1) evaluate how the effects of climatic water availability on the growth and survival of individual trees vary among species, with local competition, and with site hydrology; and (2) examine how climatic water availability and local competition influence partitioning of growth within crowns and in allometric models for aboveground biomass. This research will provide a clearer understanding of forest and carbon dynamics across a major Canadian forest region for which there is currently limited data. To ensure results are widely taken up by key stakeholders, we will develop a freely-available climate risk mapping tool based on our findings. This tool will allow end-users in the forest industry to assess the vulnerability of forest stands and carbon stocks to future drought across a given area of interest. A thorough understanding of how forests vary in their susceptibility to regional climate stress represents a critical step towards the development and deployment of climate adaptation and mitigation strategies across western Canada's forest sector.