We needed data on temporal changes in caribou forages after fire and relative use of age-classes of forests by caribou to help devise a fire suppression priority strategy for caribou winter range in north-central Canada. Consequently, from 1983 through 1986, we estimated the abundance of vegetation and relative use by caribou at 197 sites in western and eastern study areas on the winter range of the Beverly herd of caribou {Rangifer tarandus). Species of lichens attained peak biomass at different periods after fire - as early as 40-60 years for Cladonia spp. to > 150 years for Cladina rangiferina and Cetraria nivalis. Biomass of the primary "caribou lichen", Cladina mitis, increased rapidly from 21-30 years after fire to 41-50 years and attained maximum biomass at 81-90 yeats in the west and 41-60 years in the east. However, total lichen biomass increased with age of forest to 100-150 years because biomass of Stereocaulon spp. did not peak until after 100 years. The biomass of "caribou lichens" {Cladina spp. and Cetraria nivalis) stabilized after 61-80 years in the west and 41-60 years in the east. The biomass of terrestrial lichen species can be predicted from their cover. Caribou lichen abundance apparently was only one of several factors that caused caribou to use stands 151-250 years after fire more than othet age classes

The islands of the Canadian Arctic Archipelago lie immediately north of mainland North America in the Arctic Ocean. They are surrounded by ice for most of each year. Caribou (Rangifer tarandus) cross the sea ice in seasonal migrations among the islands and between the mainland and Arctic Islands. We compiled observations of 1272 discrete caribou crossings on the sea ice of northeastern Franklin Strait, Bellot Strait, Peel Sound and Baring Channel in the south-central Canadian Arctic Archipelago during four May—June search periods from 1977 to 1980. We clustered the 850 caribou trails found on the sea ice of northeastern Franklin Strait and on outer Peel Sound as 73 sea-ice crossing sites. We investigated whether caribou at the origin of a sea-ice crossing site could see land on the opposite side at the potential terminus. We measured the straight-line distance from where the caribou first came onto the ice (origin) to the first possible landfall (potential terminus). Potential termini were geodetically visible to caribou from elevated terrain near 96% of the origins of the 73 sea-ice crossing sites and still visible at sea-level at the origins on 68%. Caribou are able to take advantage of seasonal use of all of the islands and the peninsula by making sea-ice crossings, thereby helping to increase the magnitudes and durations of population highs and reduce their lows. Knowledge of these alternative pat¬terns of use made possible by sea-ice crossings is necessary to fully understand the population dynamics of these caribou and the importance of possible future changes in ice cover

The number of Peary caribou (Rangifer tarandus pearyi) on the Queen Elizabeth Islands, Canadian High arctic, is at an all-time known low. yet some populations are still hunted, and there is no adequate monitoring program in place to determine the consequences. We evaluate information from the Peary caribou population on the south-central Queen Elizabeth Islands as a standard for an accurate and realistic assessment of what controls Peary caribou population dynamics. Between 1973 and 1997, major population crashes related to severe winter or spring weather are known to have occurred on the south-central Queen Elizabeth Islands in four caribou-years (i.e., 1 July-30 June). Population losses were 67% in 1973-74, 33% in 1994-95, 78% in 1995-96, and 83% in 1996-97. There is no evidence for direct density-dependent responses during either the favorable weather years of population growth or during any one of the years with a disastrous die-off. It appears that Peary caribou on the Queen Elizabeth Islands are living in a non-equilibrium grazing system driven mainly by abiotic factors (emergent properties), particularly by exceptionally unfavorable snow or ice conditions. Changing levels of predation by the High arctic gray wolf (Canis lupus arctos) compound the uncertainty. In this High arctic ecosystem, non-equilibriumgoverned population dynamics plus wolf predation represents an appropriate conceptual model for Peary caribou populations on the Canadian High Arctic islands. The application of our findings to decision making, together with an adequate monitoring program by the responsible agencies, would promote the biological management and ecological conservation of Peary caribou on the Queen Elizabeth Islands. key words: arctic Canada, population dynamics, Rangifer tarandus pearyi, weather-related density-independent population crashes rÉSUMÉ. Le nombre de caribous de Peary (Rangifer tarandus pearyi) répertoriés dans les îles de la reine-Élisabeth, Extrême-arctique canadien, se trouve au niveau le plus bas à n'avoir jamais été enregistré. Pourtant, certaines populations font toujours l'objet de la chasse et il n'existe aucun programme de surveillance adéquat pour en déterminer les conséquences. Nous évaluons ici des données relatives à la population de caribous de Peary des îles centre-sud de la Reine-Élisabeth afin d'aboutir à une norme d'évaluation précise et réaliste pour déterminer ce qui influence la dynamique de population des caribous de Peary. Entre 1973 et 1997, d'importants déclins de population attribuables aux hivers ou aux printemps rigoureux ont été enregistrés dans le centre-sud des îles de la reine-Élisabeth sur une période de quatre années-caribous (c'est-à-dire du

ABSTRACT. The number of caribou (Rangifer tarandus) on Prince of Wales, Somerset, and Russell islands in the south-central Canadian Arctic declined by 98% in 15 years, from an estimated 6048 (16% calves) in 1980 to an estimated 100 (0% calves) in 1995. Those estimates were obtained by systematic aerial surveys that used the same design and methods and comparable survey coverage. We do not have the data needed to determine the rate of decrease between 1980 and 1995 or its possible causes. There is no evidence for large-scale winter mortality in any one year or few consecutive years. A probable explanation for the decline is consequential reductions in long-term survival rates, both of breeding females and of calves in their first year of life, associated with continued caribou harvesting and markedly increased wolf (Canis lupus) predation on the dwindling number of caribou through the 1980s and early 1990s. The delay in detecting the decline and the lack of understanding of its causes will handicap the development of an ecologically sound recovery plan. As previous caribou declines have been followed by recovery, some comfort may be drawn from the likelihood of unaided recovery. However, the number of caribou has declined to the point where recovery will be tenuous and lengthy, at best. Unaided recovery could easily fail to occur, so we should not be complacent, especially as extirpation of these few remaining caribou would remove a distinct genetic group and reduce the biodiversity of caribou on Canada's Arctic Islands.Key words: biodiversity, Canada, conservation, decline, endangered, population size, Rangifer tarandus, recovery actions RÉSUMÉ. Le nombre de caribous (Rangifer tarandus) se trouvant sur les îles Prince of Wales, Somerset et Russell, dans le centresud de l'Arctique canadien, a chuté de 98 % en 15 ans, passant d'un nombre estimé à 6 048 (dont 16 % étaient des veaux) en 1980 à un nombre estimé à 100 (dont aucun veau) en 1995. Ces estimations ont été obtenues au moyen de relevés aériens systématiques recourant aux mêmes définitions, aux mêmes méthodes et à des aires de relevés comparables. On ne possède pas les données nécessaires pour déterminer le taux de diminution entre 1980 et 1995 ou les causes possibles de cette diminution. Par ailleurs, rien n'indique qu'un taux de mortalité hivernal élevé a été enregistré pendant une année quelconque ou pendant quelques années de suite. Il se peut que le déclin du nombre de caribous enregistré dans les années 1980 et au début des années 1990 soit attribuable aux réductions correspondantes des taux de survie à long terme chez les femelles de reproduction et les veaux pendant leur première année de vie, le tout jumelé au prélèvement continuel des caribous ainsi qu'à la prédation grandement accrue des caribous par les loups (Canis lupus). Le retard à détecter ce déclin et le manque de compréhension de ses causes pourront nuire à l'élaboration d'un plan de récupération solide du point de vue écologique. Puisque les déclins précédents de caribous ont été suivis d...

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