Reorganization of biotic interactions and distributions of tree species under a warming climate: A biogeochemical perspective

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Climate change is threatening the capacity of forests to provide its various services by causing unprecedented ice-storms, drier summers, changes in fire regimes, modifications in the phenology of key pests, etc. Canada is committed to maintaining forests that are resilient to current and imminent global change. Hence, the development of more robust simulation models of forest response to climate change is crucial as they are key to identifying the best possible adaptation strategies. To forecast forest mortality events and tree species shifts under climate change, scientists have recently recognized the need to develop models not just based on regional climates, but also based on the reorganization of interactions between tree species and possible feedbacks. This research program deals with adaptation and shifts in the distribution of sugar maple under climate change. Will maple migrate North to find its environmental (climatic) niche in the boreal forest? Will it adapt locally? Will it expand? Or will it suffer from range contraction? Specifically, we will study the ecological/biogeochemical interactions between maple and other eastern Canadian tree species. Our objective is to assess whether maple has a competitive disadvantage for soil nutrients and water uptake over other species as this could decrease its capacity to adapt to climate change. We are developing a conceptual model using maple as the response species because it is an emblematic and commercially important species for Canada that is jeopardized by many threats. This model will be instrumental to determine if the distribution of other species will shift, expand or undergo contraction. We have set up a field study consisting of three sites forming the largest possible latitudinal gradient in Quebec for maple. At these sites, maple is found with an increasing abundance of: (1) the conifer species confronting maple at the southern edge of the boreal forest, and (2) American beech which is gradually replacing maple in deciduous forests of eastern North America. The research consists in a series of field and laboratory studies to test the impacts of various tree species composition (canopy types) on soil nutrient availability, maple seedling establishment and survival, and seedling/sapling foliar nutrition, water use and growth. We will also study maple litter decomposition and myccorhizal fungi associations with roots under the various canopy types as a means to understand the processes affecting maple nutrition and growth. This research will lead to improved adaptation strategies by augmenting knowledge on the functioning of complex forests and developing new tools to better predict the impacts of human activities on forests.