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

Abstract

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.

Four Decades of Plant Community Change in the Alpine Tundra of Southwest Yukon, Canada

“…A component of this research involved the detailed description of vegetation on each of the four slopes as related to solifluction lobe development (Price 1971). A single transect was established along each of the four slopes in order to include representative areas of the major tundra plant communities.…”

“…We established two new transects on each slope to account for uncertainty in the exact location of the original transects . c Slope profiles along the length of each of the four transects illustrating the approximate boundaries of the different community types as originally defined by Price (1971) and to test for within-slope variability (Rogers et al 2008). …”

“…In addition to the repeat photography and plant community data collection, we collected cross sections from the stems of 10 Salix pulchra shrub patches found growing near the transects on the southeast-facing slope. Price (1970Price ( , 1971 does not mention shrubs of any species when describing the vegetation so we wanted to identify the age of these individuals. Most shrubs were found growing on solifluction lobes in close proximity to the fronts.…”

“…These were later identified with the assistance of B. Bennett, Territorial botanist with the Yukon Government. Price reported the relative importance values derived for each species in each of the original quadrats (Price 1970(Price , 1971, but the raw data recorded from each quadrat (abundance and cover) was discarded in the years following the original research. Frequency is a transect-level derivative, and the raw frequency data were calculable from the published data by knowing the number of quadrats each species was present in.…”

“…Fortunately, research conducted in 1967 and 1968 by Price (1970Price ( , 1971) provides a wealth of systematic work on alpine plant community composition in the Ruby Range, southwest Yukon, Canada. Although there are a few other contemporary observations from this region (for example, Douglas (1974) also conducted several surveys in alpine areas of the Kluane National Park and Reserve), the exact locations were not well documented and observations were often only descriptive.…”