| Summary: | The Lower Anderson River Valley was chosen as a study area to investigate the effects of slope, aspect, and insolation on plant community composition and distribution through the treeline ecotone. Seventy-one plant communities were surveyed; abiotic measurements included soil temperature and depth to frozen soil. Soil samples were taken and later analyzed for pH, conductivity, and particle size distribution. TWINSPAN, a divisive clustering algorithm, defined 4 basic community-types for study area: Tundra, Forest, Steppe, and Sparse. Except for Sparse these community-types have quite discrete distributions along a potential insolation gradient. Sparse communitytypes are associated with acidic, high conductivity soils near smoking bituminous shale deposits. Equivalent latitude, a variable expressing potential insolation relative to flat surfaces at given latitudes, explained about 7 times more of the variance in Detrended Correspondence Analysis axis 1 scores than latitude alone. N Canonical Correlation Analysis was employed to further investigate the relationship of plant community composition to the measured environmental variables. The most important trend underlying plant community composition was found to be a potential insolation-soil temperature gradient. Anderson River Steppe is the eastern-most example described to date of so-called 'arctic steppe', which is thought to have been much more extensive in Beringia during the Wisconsin glacial maximum. Steppe communities occurred primarily on southfacing slopes and occupied at least 560 hectares/kilometer along the Lower Anderson River. Three major northward range extensions were associated with species found in south-facing Steppe. Science, Faculty of Botany, Department of Graduate
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