Thesis (Ph. D.)--Oregon State University, 1992. / Includes mounted photographs. Typescript (photocopy). Includes bibliographical references (leaves 173-186). Also available online.

Thesis ( Ph.D. ) -- University of Texas at Arlington, 2008.

Prior to 1963 no previous vegetation studies had been undertaken in this region of the Low Arctic Subalpine/Foothill Zone of the Canadian Western Arctic, although several studies had been completed in similar regions in Arctic Alaska. This study was initiated in 1965 to obtain quantitative and qualitative data on vegetation and environmental relationships, including soil data for characterization of Low Arctic Subalpine/Foothill Zone soils. With these basic data it was considered possible to analyze, integrate and interpret community and soil relationships and to propose a usable classification system for the recognizable ecosystematic units in this portion of the zone. Initial criteria for selecting communities were based on uniformity and discreteness. Vegetation in each community was studied by the single plot method employing phytosociological techniques of the Zurich - Montpellier School as modified by Krajina (1933). Data on environmental conditions collected for each of 166 communities included degree of slope, profile, pattern of topography, exposure, altitude and wind influence. Coefficients of similarity between communities were computed using the formula 2W/A+B X 100, where A is the sum of all measures (abundance and presence) for one community, B is the sum of all measures for another community, and W is the sum of the lower values for each species which the two communities have in common. To determine the degree of affinity and relative hiatus points between groups of communities cluster analysis using the weighted pair - group method was employed. A two-dimensional dendrogram illustrated the individual plots and succeeding clusters. One soil pit was dug in every analyzed plot to either permafrost, water table, coarse ice shattered parent material or bedrock. A total of 498 soil samples for laboratory analysis were collected from all recognizable horizons. Chemical analyses were undertaken to determine organic matter content, total nitrogen, carbon/nitrogen ratio, absorbed phosphorus, exchangeable calcium, magnesium, potassium and sodium, cation exchange capacity pH. Because soil profiles showed considerable variation the results of the chemical analyses were averaged for the organic, organic - mineral and mineral horizons. On the basis of similarity of species composition six orders, eight alliances, fourteen associations, ten subassociations and thirteen variations were distinguished. The order Betuletalia glandulosae dominated the two study areas, occurring on moderately to well drained mesic to xeric slopes. Community development within this order appeared stable under the present topographic and climatic conditions. The Vaccinio - Betuletum glandulosae closely approximated the climatic climax in mesic habitats. Successional concepts on upper slopes appeared of limited value because communities tended to be discrete. Communities dominant on the lower slopes and in the wetlands were characterized by a narrow active, poor to impeded drainage conditions and more intensive frost action. Classification was more difficult in such areas because communities appeared to be less stable. Successional development in such areas with permanent seepage was toward the Betulo - Eriphoretum vaginati. Snow bed habitats were characterized by the order Petasitetalia frigidii , which was distinguished for the first time in North America, and included the previously undescribed Salicetum chamissonis. Sharp environmental gradients between chionophilous and chionophobous communities suggested that the climate had undergone no significant change in the recent past. Similarities between the Low Arctic Subalpine/Foothill Zone communities and those in other arctic regions, especially Scandinavia, were shown to occur. Twelve soil types were distinguished. In all but two cases each soil type was associated with a particular plant association. A form of podzolization previously described in Arctic Alaska was recognized in the Arctic Brown soils. Gleization, however, appeared to be the major soil forming process in this region of the zone. It was associated with both chionophobous and chionophilous vegetation. In the former, it was favoured by poor drainage, a shallow active layer and intensive frost action; in the latter, it appeared related to materials deposited on the snow that were later incorporated into the soil following snow melt. The high organic content and cation exchange capacity and the low acidity and base saturation were concluded to be important chemical characteristics of these soils. Final results using classification methods showed that the present position of the communities in this region of the Low Arctic Subalpine/Foothill Zone were related to elevation, exposure, soil moisture, thickness of the active layer, duration of snow cover, congeliturbation and topography. / Science, Faculty of / Botany, Department of / Graduate

Ecotones are gradients of change between expanses of similar species composition. These regions often mark co-occurring range limits for several species, and thus are ideal for elucidating ecological and biogeographical phenomena. The forest to tundra transition (FTT) is one of the world's most prominent ecotones, but remains poorly studied especially with regard to vertebrate species occurrence. Vertebrate diversity, ecological structure and resource selection were characterized across the Yukon FTT using diversity metrics, ordination, hierarchical clustering, and resource modeling. The FTT represents an abrupt drop in vertebrate species richness within the more gradual, continental scale diversity gradient. Despite the patchiness and complexity in vegetative structure over this ecotone, the terrestrial vertebrate community is divisible into boreal, taiga, and tundra compartments. Most species conform to resource associations reported closer to the core of their range, generating remarkably consistent habitat and species associations despite a complex patchwork of contrasting habitat types.

No description available.