Tree and Tundra Cover Anomalies in the Subarctic Forest-Tundra of Northwestern Canada

Factors that may account for subarctic vegetation patterns that are not reconcilable with synoptic climate were sought by reference to data on local climate, soils, parent materials, vegetation, and topography. Where the forest-tundra lies climatically northward, the vegetation transition zone is relatively narrow, and the soils are nutrient-rich, fine-textured loamy Cryosols derived from sedimentary rocks. Where the forest-tundra lies south of its climatic potential, the zone is wide, and the soils are relatively dry, nutrient-poor loamy sand and sandy loam Brunisols derived from crystalline rocks. Seven regional anomalies in landscape cover of tree and upland tundra vegetation are discussed with reference to topoclimate, edaphic controls, and bioclimatic feedback. Prominent anomalies include the Thelon River tree oasis, the great breadth of the southeastern foresttundra, and the southward plunge of the forest-tundra north of Great Slave Lake. Elevation differences as small as 50 m are shown to affect tree cover.