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 become an increasing pervasive management concern in protected natural areas and parks where conservation of native plant communities is a primary objective. The magnitude of these effects can vary widely according to variations in local deer numbers and availability of alternate food sources. We used measurements from 11 maple-basswood forest fragments in southcentral Minnesota to examine the predictability of deer grazing intensity on understory forbs based on local winter deer density, composition of the landscape surrounding each forest fragment, and characteristics of forb populations within the forest. In early summer, grazing intensity on 6 palatable forb species at most sites was inversely correlated with the availability of alfalfa within a 1.5-km radius of the stand (r(2) = 0.66); winter deer density and forb flowering rate within the stand were additional important predictors of grazing intensity. Later in the growing: season, most variability in the intensity: of grazing among forest fragments could be explained either by the availability of rom crops, alfalfa, and fields within a 1.5-km radius of the stand (r(2) = 0.75) or by a combination of winter deer density 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-cropping or conversion of land to residential developments) should be an important consideration in the management of deer densities in areas designed to protect native forest communities.
