SCALE OF HETEROGENEITY OF FORAGE PRODUCTION AND WINTER FORAGING BY ELK AND BISON

The relationship between fine-scale spatial patterns of forage abundan ce and the feeding patterns of large ungulates is not well known. We c ompared these patterns for areas grazed in winter by elk and bison in a sagebrush-grassland landscape in northern Yellowstone National Park. At a fine scale, the spatial distribution of mapped feeding stations in 30 m x 30 m sites was found to be random where there were no large patches devoid of vegetation. In areas similar to the mapped sites, th e underlying spatial distribution pattern of biomass was also determin ed to be random. At a broad scale, forage biomass differed among commu nities across the northern range but forage quality did not. These res ults suggest that ungulates are feeding randomly within forage patches (fine scale) but may select feeding sites based upon forage abundance at broader, landscape scales. Contrary to what has been suggested in other systems, ungulates were not 'overmatching' at finer scales.