| Summary: | An investigation was carried out on a population of Dall sheep and their range in southwestern Yukon from 1969 to 1973. The results are presented in two separate, distinct portions. Part I deals with the geography, geology, glaciology, soils and climate of the study area. It describes in detail the vegetation of the three biogeoclimatic zones and breaks it down into 32 plant associations, grouped into 23 alliances and 17 orders, following the Braun-Blanquet methods of phytosociology. Part II covers the sheep population, which has during the study period remained fairly constant at a level of about 200 adults. Detailed population statistics are presented on such parameters as: natality and mortality rates, productivity, sex ratios, densities and historical information about this herd is reviewed. The range use pattern and the forages selected by this population are discussed on a monthly basis. The response of sheep to some environmental variables as temperature, wind, snow depths is analysed. Based on a life table and classified counts a model of the population structure is presented which is useful for management questions such as calculating "allowable" harvests. Science, Faculty of Zoology, Department of Graduate
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