Assisted migration of trees between populations as a climate change mitigation strategy for Canada's boreal forest

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Countries have agreed that deep global net greenhouse gas (GHG) emission reductions are required to hold the increase in global average temperature to less than 2°C above pre-industrial levels. Forest-related mitigation activities have a significant role in such efforts. Notably, human-assisted movements of tree individuals between populations within species ranges (i.e. assisted gene flow) have the potential to increase atmospheric carbon removal by accelerating the rate of tree growth and increasing tree resistance and resilience to environmental and climatic stresses. In recent years, emphasis has strengthened around the utility of such activity as an adaptive measure so to maintain the health of forests in areas negatively impacted by climate change. While assisted gene flow could help to stabilize the health of these forests, it might also contribute to mitigation depending on the implications for forest carbon. Yet, there is uncertainty in this forest-related mitigation potential because a changing climate can pose negative feedback, i.e. assisted gene flow carries the risk if moved provenances remain exposed to climatic stresses to which they were not adapted.     The objectives for this research are to assess the implication of assisted gene flow on the long-term aboveground net primary productivity (NPP) of widespread conifer species in boreal Canada. This will be done by innovative use of dendroecological sampling of a network of common gardens with a process-based modeling framework in which the effects of assisted gene flow on long-term future NPP are tested. Specifically, the work will (1) Develop a retrospective analysis of the evolving NPP and its response to past climate conditions across species, populations, tree lifespan, and common gardens, (2) Find signs of local adaptation present in tree populations and (3) Assess the mitigation potential of assisted gene flow under future exposure to climate change. The hypothesis to be tested is that annual NPP, and its response to climate, exhibits a high degree of variation among populations, suggesting local adaptation and potential for mitigation. We consider forest mitigation potential as an enhancement of NPP that would result from introduction of non-local provenances, relative to a baseline where forests are managed for local provenances.     Canada will need to establish deep targets in keeping with the 2015 Paris Agreement that commits all countries to an aim of achieving a balance between global anthropogenic GHG emissions and removals in the second half of this century. Canada's large forest and its position as a major producer of harvested wood products mean that it is important to explore the potential of forest-related mitigation activities including assisted gene flow. This research will provide science based information that Canadian jurisdictions (e.g. provinces, territories) will be able to use for making informed decisions and policies concerning mitigation.