To compensate for losses in overwintering habitat, elk are fed hay in winter at approximately 37 locations throughout the western United States. These winter feeding programs concentrate elk activity, and there is concern that such concentrations could degrade plant communities. Except for one study focused exclusively on aspen (Populus tremuloides), ours is the first to quantify vegetation responses to supplemental winter feeding of elk. The western Wyoming feedground we studied was established in winter 1981–1982, and supplemental feeding occurred every winter through 2006. Transects were arranged in a before-after control-impact (BACI) design, and vegetation data were gathered in the midsummers of 1981 and 2006. Over the study period, the feedground became invaded by smooth brome (Bromus inermis), a nonnative grass constituent of hay fed to the elk. The smooth brome invasion was attended by declines in native forb cover and the apparent extirpation of shrubs from the feedground. The smooth brome invasion did not extend beyond the feedground, but an area 125 m from the feedground showed decreases in shrubs. At areas ≥750 m from the feedground, forbs and shrubs did not decrease demonstrably, and in some cases they showed evidence of increasing over the study period. Supplemental winter feeding at a feedground in western Wyoming degraded the plant community, but, with the possible exception of aspen, the degradation did not appear to extend great distances beyond the small area where the animals were fed.