ABSTRACT: Composition and distribution of vegetation along microtopographically- and climatically- induced permafrost gradients in the Mackenzie Valley, NWT.

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Abstract

Permafrost is an important component of northern landscapes, underlying from 10 to 100 percent of the terrain in Canada’s Northwest Territories. Not only does permafrost directly affect soil processes, but its indirect affect on soil hydrology and active layer depths also has a substantial influence on plant species distribution, and community composition. The relationship betweenvegetation and permafrost is particularly interesting in peatland environments, with plant communities both affected by changes in the permafrost conditions, and yet also able to influence the permafrost environment. The Mackenzie Valley region of Canada presents a unique opportunity to study vegetation along a climatic gradient spanning 10ºC MAT and 227mm PPT, in a region rich in peat deposits, and predicted to be one of most sensitive areas to climate warming in Canada. With permafrost distribution controlled largely by topography and climate, this study endeavours to document current vegetationcomposition along a climatic gradient extending from the sporadic discontinuous permafrost zone in southern NWT to the continuous permafrost environments near the arctic tree line at Inuvik. At each of 25 sites, plots wereestablished in areas of permafrost-affected peatlands (peat plateaux), areas of permafrost thaw (collapse scars), and adjacent forest environments occurring on mineral soils (upland forests). At the northernmost sites, collapse scarfeatures were not present on the landscape, and so were not included in the study, resulting in a total of 69 plots distributed throughout the Mackenzie Valley. Exploratory analysis of the understorey vegetation data was conductedthrough the use of non-metric multidimensional scaling ordinations. Preliminary results indicate that the nonvascular vegetation is primarily structured along a gradient from upland forest to peat plateaux to collapse scars. This gradient reflects variation in local site factors, andis positively correlated with peat depth, and negatively correlated with water table depth. Vascular vegetation is also structured along this site factor gradient and, additionally, varies along a north-south climatic gradient. In the context of future climate change, these results indicate that, while vascular vegetation may be more directly influenced by a changing climate, any climate change which influences the local site factors, such as permafrost collapse,will have a dramatic impact on both the vascular and nonvascular plant communities.

Bibliography of Canadian Geomorphology