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The relation between climate and abundance cycles in barren-ground caribou herds of the Northwest Territories, Canada Zalatan, Rebecca

Abstract

The central objective of this research was to determine if there is a relationship between long-term barren-ground caribou (Rangifer tarandus) abundance and climate patterns in the Canadian Arctic. A long-term dataset indexing caribou abundance was obtained from the frequency of trampling scars on tree roots of black spruce (Picea mariana [Mill.] BSP) in the forest-tundra of central Northwest Territories. Samples were collected from roots of live trees along well-used migration trails in the forest tundra. Two groups of sites were sampled that roughly corresponded with the late summer migration routes of the Bathurst and Beverly caribou herds. The scar frequency distributions were dated from A.D. 1760-2000 and both groups of sites showed similar abundance patterns through time. To best determine the relation between long-term climate and the proxy caribou abundance, local climate data were needed. However, the only annually-resolved climate data in the region is the short length of record (63 years) available from Yellowknife (which is up to 300 km away from the furthest sites in this study). Therefore, I developed a series of tree-ring chronologies at seven of the nineteen sites where caribou abundance was reconstructed, in an effort to increase the knowledge of climate variability in this region. Summer temperatures (July-August) were reconstructed using standard dendroclimatological techniques. The final objective of my research was to determine if there was a correlation between patterns in the summer or winter index of the Arctic Oscillation (AO) and long-term caribou abundance. I determined that the AO was most closely correlated to summer temperatures (June-August) at Yellowknife. The summer index of the AO has undergone four major phase changes during the last century. Wavelet coherence demonstrated that the relation between caribou abundance cycles and the AOS changed from inversely related during the first two phases of the AOS, to inphase during the final two phases of the AOS. This study was the first to demonstrate the complexities associated with relating long-term trends in the AO to abundance cycles of barren-ground caribou. Additionally, this study was the first to illustrate the importance of obtaining long-term datasets when relating large-scale climate to caribou abundance cycles.

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