Lichen Availability on the Range of an Expanding Caribou (Rangifer tarandus) Population in Alaska

Abstract

Terrestrial lichen abundance, lichen availability as affected by snow, and winter fecal composition were investigated for the Delta Caribou Herd (DCH), which recently quadrupled in size and expanded its early winter range. Mean lichen abundance was relatively low (10-85 g/m2). However, even on heavily-used range, caribou ate only 7% of lichen standing crop annually. Snow affected lichen availability only slightly on peripheral tundra ranges, since lichens predominated on xeric sites with little snow. On traditional ranges, lichens were shorter and rarely found in high-density patches; disproportionate grazing and trampling of exposed lichens had caused reduced lichen availability. This was reflected in lower fecal lichen for caribou on traditional ranges, however DCH population growth or seasonal movements probably were not substantially affected. A model of caribou cratering energetics indicated that loss of potential foraging time may influence energy balance more than does cratering energy expenditure.