ARCTIC Productivity and Carrying Capacity of a Subarctic

ABSTRACT. Estimates of range composition and net primary productivity for a IO-year period are presented for the semi-arid grasslands of Sheep Mountain, Kluane National Park, Yukon, the winter range of a Dall’s sheep (Ovis dalfi dalli) population. Estimates varied among plots, d e p d i n g on altitude and aspect, as well as among years, according to rainfall during the growing season. Extremes were 29.1 g.m-2 and 120.1 g.m-. Over the IO-year assessment period, the vegetative composition did not change nor was there a grazing-related reduction in productivity. Winter range use by about 200 sheep was within the carrying capacity of the range. A 4 0 % utilization rate of the winter range forage can evidently be sustained and pro-vides a stocking rate of about 1.9 sheep-monthS.ha-I. A significant correlation is demonstrated between forage production of the winter range, lamb survival the following winter, and lamb production the following spring. This correlation indicates that a form of self-regulation of the sheep popula-tion is functioning. Key words: productivity of subarctic, semi-arid grasslands; Dall’s sheep, carrying capacity, Kluane National Park, Yukon &SUM&. L’auteur presente des evaluations de la port&, de la composition et de la productivite primaire nette durant un @riode de IO ans pour la prairie semi-aride de la montagne Sheep, dans le parc national Kluane, au Yukon, le terrain hivernal d’une population de moulfons de Dall (Ovis dalli da l f i). Les evaluations varient selon les terrains, dependent de l’altitude et de l’aspect, et aussi selon les ann&, par rapport B la prkipitation durant la saison de croissance. Les extremes ktaients de 29.1 g.m-2 et 120.1 g.m-2. Au cours de la @riode d’etude de IO ans, la composition vegetative ne changea pas et la phturage n’occasionna aucune rauction en productivite. Le territoire d’hiver occup6 par quelque 200 mouflons pouvait bien sup-porter ces derniers. Un taux d’utilisation de 40 % du fourrage du territoire d’hiver peut evidemment &re soutenu et peut fournir un taux de soutie