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

了解控制北部边界附近森林生态系统功能的因素对于预测森林如何应对气候变化至关重要。本研究旨在了解气候、土壤和生物因子在控制魁北克北部詹姆斯湾地区颤杨（Populus tremuloides）林分布中的相对作用。我们最近在魁北克北部的白杨林和黑云杉林中的工作表明，树木的建立和生长取决于植被、土壤有机质分解和积累、土壤营养和场地干扰的相互作用。我们开发了一种新的空间格局多元分析方法，提高了对野外生态关系的检测。新的研究将建立在这些研究的基础上。拟议的项目将研究气候、地点、碳和营养循环在控制从魁北克中部到其范围北部的气候样带白杨林分布中的作用。将开发“生物中心”气候指数来定义1300公里的样带。杨树林分将以树木生长速率、养分循环和土壤性质为特征。这些变量随纬度增加的变化模式将与气候指数的变化模式进行比较，以检验气候是主要控制因素的假设。由于树木以综合的方式对多种压力作出反应，因此气候的影响取决于其他因素的影响；有利的场地条件或土壤因素可以使杨树在不利的气候条件下生长。这将在其北部边界附近使用白杨林的景观模式进行测试。我们将利用碳和氮同位素特征来更好地了解白杨林的分布是否随着气候的变化而变化。总的来说，该研究将增加对气候和非气候因素在确定北方落叶林生态系统分布中的相对作用的认识，并将为预测气候变化的影响提供更好的基础。

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.