PREDICTORS OF WHITE-TAILED DEER GRAZING INTENSITY IN FRAGMENTED DECIDUOUS FORESTS

White-tailed deer (Odocoileus virginianus) can cause major changes in the composition and structure of forest communities by browsing shrubs and tree seedlings and grazing understory forbs. Such effects have be come an increasing pervasive management concern in protected natural a reas and parks where conservation of native plant communities is a pri mary objective. The magnitude of these effects can vary widely accordi ng to variations in local deer numbers and availability of alternate f ood sources. We used measurements from 11 maple-basswood forest fragme nts in southcentral Minnesota to examine the predictability of deer gr azing intensity on understory forbs based on local winter deer density , composition of the landscape surrounding each forest fragment, and c haracteristics of forb populations within the forest. In early summer, grazing intensity on 6 palatable forb species at most sites was inver sely correlated with the availability of alfalfa within a 1.5-km radiu s of the stand (r(2) = 0.66); winter deer density and forb flowering r ate within the stand were additional important predictors of grazing i ntensity. Later in the growing: season, most variability in the intens ity: of grazing among forest fragments could be explained either by th e availability of rom crops, alfalfa, and fields within a 1.5-km radiu s of the stand (r(2) = 0.75) or by a combination of winter deer densit y and forb abundance within the stand (r(2) = 0.75). Results show that parks and preserves with low densities of palatable plant species in the forest understory may be especially susceptible to effects of deer grazing. Changes in landscape composition (e.g., increased. row-cropp ing or conversion of land to residential developments) should be an im portant consideration in the management of deer densities in areas des igned to protect native forest communities.