Subarctic forest‐tundra vegetation gradients: The sigmoid wave hypothesis

Abstract. Spatial changes in tree and upland tundra cover in response to a complex environmental gradient and to landscape factors were investigated in the high subarctic forest‐tundra of NW Canada. Vegetation and terrain studies provided ground truth for a grid of 1314 air photos which covered 24 % of the Canadian high subarctic and some of the adjacent low subarctic and low arctic. Across the high subarctic, gradual spatial change in % cover of tree and upland tundra vegetation is typical at both high and low cover values, with more rapid change occurring at intermediate cover. Cover gradients of zonal tree and tundra vegetation in the forest‐tundra region in general follow a sigmoid pattern. Tundra and tree patch sizes increase in area and variability with higher tundra and tree cover, respectively.