摘要：Potential natural tree-limits for Betula pubescens, Picea abies, Pinus sylvestris and Alnus incana were assessed in the Tärna region of northern Sweden. Analyses of age structure and annual growth increment were used to draw inferences about tree limit dynamism in relation to climatic variability. Tree-limits of different species responded sensitively in the above respects although somewhat individualistically, both to climatic warming and cooling during the present century. Despite a long history of human presence in the area the tree-limits are concluded to be in a dynamic equilibrium with climate on a secular time scale. The study does not support a theory that rising levels of atmospheric carbon dioxide should now be seen as enhanced growth of high-elevation trees in general. A long-term tree-ring chronology of spruce indicates a surge of growth from the late 1820s to the mid-1830s, which reasonably led to lasting effects on plant community structure.
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