Winter Ecology of Moose on the Northern Yellowstone Winter Range
Project Status: Completed
Winter Ecology of Moose on the Northern Yellowstone Winter Range
by Daniel Bruce Tyers
ABSTRACT
Shiras moose (Alces alces shirasi) invaded the Northern Yellowstone Winter Range (NYWR) in the1800s. Management of this species has been handicapped by limited population data and reliance on habitat use paradigms from other areas in North America. For example, although moose in most regions forage in recently disturbed forests with abundant deciduous shrubs, I did not find this to be true on the NYWR. I used multiple methods to determine population status, including aerial surveys, horseback surveys, road surveys, and ground counts in willow habitats. Moose were most easily seen when they foraged in willow (Salix spp.) stands in November–December and May–June. Attempts to count moose at other times resulted in marked under-sampling. Fires in 1988 removed mature forests at a landscape level resulting in a loss of preferred winter habitat and a sustained population reduction. I also investigated moose winter foraging activities among burned (1988), logged, forested, and forest edge environments. Logged areas and recent burns were rarely used, but forest interiors were important habitat. The edge effect did not benefit moose in winter. NYWR moose coped with winter by seeking concentrations of food to maximize feeding and minimize movement. They optimized foraging by using 2 taxa that grow in patches, willow and subalpine fir (Abies lasiocarpa). Moose fed in willow until snow forced them to nearby forested hillsides where they browsed subalpine fir <5 m in height. Subalpine fir, a shade tolerant tree, grows more rapidly under a forest canopy. It can reproduce through layering, creating an expanding patch of small trees around the parent. Patches are largest and most numerous in the oldest lodgepole pine (Pinus contorta) forests. Moose used other characteristics of lodgepole forests to reduce energy output by finding routes with less than average snow depth to reach subalpine fir patches. Moose also browsed gooseberry (Ribes spp.) and buffaloberry (Shepherdia canadensis), nutrient rich shrubs that are scattered and energetically expensive to obtain. Exclosure studies showed willow was suppressed before 1988, and fires and drought increased negative effects. Higher willow utilization rates in 1989 probably reflected a response by moose to a loss of winter habitat due to the 1988 fires, a foraging strategy that may have contributed to observed willow mortality. From 1989 to 1997, some willow showed signs of recovery. Replacement of older forests where moose foraged before 1988 could take several hundred years. Maintaining remaining populations should concentrate on minimizing loss of mature forests and adjacent willow and careful hunting management.
