Identifying drought resilient populations and genotypes of forest trees to address climate change

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The capacity of trees to withstand drought conditions is key to forest health and productivity under observed and projected climate change in western Canada. This research program has the following strategic objectives: (1) research drought resilience mechanisms of tree species in selected forest ecosystems where water deficits are high; (2) discover genotypes and locally adapted populations with a useful genetic portfolio of drought tolerance traits; and (3) reveal tradeoffs, where structural or physiological adaptations to better cope with drought episodes might impact growth potential when growing conditions are favorable, and identify genotypes where these tradeoffs are minimized. The research program builds on two general approaches. First, we will use tree ring analysis in mature trees to retrospectively assess response to drought episodes (resilience, resistance, and recovery of annual growth rates). A novel aspect of this research program is that these methods will be applied to long-term genetic test plantations of important Canadian forest tree species that have experienced drought episodes over the last 30 years. In search for additional genotypes that may not have been captured in current seed collections and test plantations, we will also sample natural stands exposed to high water deficits and frequent drought conditions. Second, we aim to discover the underlying traits that are responsible for drought response observed in long-term genetic field tests. For this purpose, we will carry out seedling experiments in controlled growth chamber environments using the same seed lots used to establish the genetic field trials decades ago, and which have been archived in provincial and federal seed banks. This allows us to carry out detailed measurements of physiological, hydraulic and structural drought tolerance traits and investigate their heritabilities and genetic correlations. The detailed trait data on drought tolerance mechanisms and tradeoffs discovered in seedlings can subsequently be validated against field data of tree growth and health of the same populations and genotypes grown for decades under field conditions. While this research program has primarily fundamental research goals in discovering drought tolerance mechanisms, the information will be essential to screen for drought tolerant planting stock in reforestation and tree improvement programs in western Canada. Approximately 200 million seedlings per year are planted in western Canada, and the proposed project could yield profound benefits by leveraging this reforestation activity to improve the genetic resilience and productivity of planted forests under climate change.