Resilience of western Canadian forests to climatic extremes

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Background Climate warming and extremes are major issues facing forests worldwide. Droughts have caused devastating dieback in mature forests and have compromised reforestation through mortality. At the opposite extreme, severe cold events remain a concern: Early spring warming can stimulate trees to grow too early, making them vulnerable to subsequent frosts when temperatures return to normal. This can cause planted forests to fail and damage older trees, also making them susceptible to other mortality agents. With 350 million ha of forest cover across Canada, and 500 million trees planted every year, consequences can be extensive. What we plant today, and how we manage these stands, will have a large impact for decades - yet we are limited by fundamental knowledge. We urgently need sound predictions as to how drought and frost interact with forest structure, competition and resource availability. Objectives & HQP Long-term, this program will increase understanding on how forest productivity and health are linked to drought and frost tolerance, and their interplay with ecological relationships. This work will result in improved predictions that help reduce impacts of climate change. Within the next five years, 4 graduate and 5 undergraduate HQP will contribute to the following short-term objectives: 1) quantifying inter-tree competition and tree size effects that contribute to drought and frost damage; 2) investigating how nutrient availability interacts with competition to affect response to extremes; and 3) integrating niche partitioning in mixed species stands to predict resilience to climate extremes. This research will benefit from a diverse and inclusive team, and a positive work environment. Individuals will have equitable access to training, resources and opportunities. By working with diversified collaborators, HQP will be exposed to world-class experts in forest sciences, different ways of thinking as well as techniques and technology. Methods This research combines observational tree-ring methodologies with experimental manipulations in long-term field trials. Decades-old trees will be measured in trials controlling nutrients, competition, tree size, and species composition. Tree cores obtained through non-destructive sampling provide archives of responses to past drought or frost events. Functional wood anatomical techniques will link these growth responses to physiological mechanisms. Impact Million-dollar investments in establishing field trials can now be re-purposed as large-scale climate change experiments. Understanding forest responses to extreme climatic events will improve predictions under climate change. This knowledge can guide approaches to mitigating forest mortality, helping sustain communities relying on healthy forests and reducing carbon feedbacks. Collaboration with end-users ensures results uptake and publications in high-ranking journals will lead to broad readership to maximize impact.