Climate and caribou: effects of summer weather on the Chisana caribou herd

Abstract

In 1989, the Chisana caribou (Rangifer tarandus) herd in the northern Wrangell Mountains, Alaska declined substantially in population size and productivity. Summers were significantly warmer and slightly drier during years the herd was declining (1989-1995) compared with years when the herd was stable or increasing (1981-1988). We increased air temperature and decreased precipitation with a plastic tent, decreased light intensity with a shade cloth, and increased precipitation by adding water to determine climatic effects on nutrient content and biomass of caribou forage during summer in 1994 and 1995 in the subarctic tundra. We determined that short-term variations in climate affected nutrient quality, particularly nitrogen content, in above-ground biomass of caribou forage. The warmer, drier summers (1989-1995) may have affected the Chisana population adversely by increasing insect harassment and decreasing nitrogen content in their forage.