SUB-ARCTIC FOREST-TUNDRA VEGETATION GRADIENTS - THE SIGMOID WAVE HYPOTHESIS

Spatial changes in tree and upland tundra cover in response to a compl ex environmental gradient and to landscape factors were investigated i n the high subarctic forest-tundra of NW Canada. Vegetation and terrai n studies provided ground truth for a grid of 1314 air photos which co vered 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 b oth high and low cover values, with more rapid change occurring at int ermediate cover. Cover gradients of zonal tree and tundra vegetation i n the forest-tundra region in general follow a sigmoid pattern. Tundra and tree patch sizes increase in area and variability with higher tun dra and tree cover, respectively.