Ecosystems on the edge: the ecology of deciduous forest ecosystems near their northern limit in Quebec

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Understanding the factors that control how forest ecosystems function near their northern limits is critical to predicting how forests will respond to climate change. This research aims to increase understanding of the relative role of climate, soil and biotic factors in controlling the distribution of forests dominated by trembling aspen (Populus tremuloides) in the James Bay region of northern Quebec. Our recent work in aspen and black spruce forests in the northern Quebec have shown that establishment and growth of trees depends on the interacting effects of vegetation, soil organic matter decomposition and accumulation, soil nutrition, and site disturbance. We have developed a new approach for multivariate analysis of spatial pattern that improves detection of ecological relationships in the field. The new research will build on these lines of enquiry. The proposed program will study the roles of climate, site, and carbon and nutrient cycling in controlling the distribution of aspen forests across a climatic transect from central Quebec to the northern limit of their range. 'Biocentric' climatic indices will be developed to define the 1300 km transect. Aspen stands will be characterized by tree growth rates, nutrient cycling and soil properties. Patterns of change in these variables with increasing latitude will be compared to patterns of change in climatic indices to test the hypothesis that climate is the dominant control. Since trees respond in an integrated way to multiple stresses, the effect of climate depends on the effects of other factors; favorable conditions in site or soil factors can allow aspen to grow in unfavorable climate. This will be tested in using landscape patterns of aspen forests near their northern limit. We will use C and N isotopic signatures to better gain a better understanding of whether the distribution of aspen forests in changing with changing climate. Overall, the research will increase knowledge of the relative roles of climatic and non-climatic factors in determining the distribution of deciduous forest ecosystems in the north and will provide a better foundation for predicting the effects of climate change.