Vegetation, Microtopography, and Depth of Active Layer on Different Exposures in Subarctic Alpine Tundra.

Four slopes with different exposures (southeast-, southwest-, east-, and north-facing), but with similar gradients, elevations, and rock type, were studies in the Ruby Mountains of southwest Yukon Territory, Canada, Vegetation was best developed on the southeast facing slope, was successively less on east- and southwest-facing slopes, and least on the northfacing slope. Solifluction lobes were present in varying degrees, and their development largely followed that of vegetation in that they were best developed on the southeast-facing slope and least well developed on the north- and southwest-facing slopes. The vegetation occurred in sharply delineated communities across the lobes on the southeast-facing slope, and the communities repeated themselves in predictable patterns. The same communities were present on the east-facing slope, but were not as distinct. Plant cover was relatively impoverished on southwest- and north-facing slopes, where there fewer microhabitats and where soil, moisture, and temperature conditions were not found in favorable combinations. Depth of the active layer largely corresponded to the presence of vegetation and microtopography. The active layer was shallowest and most variable on the southeast-facing slope. Plant cover, in general, was more important than exposure in determining the depth of thaw.