We conducted a landscape-level survey of Microstegium vimineum (Trin.) A. Camus (Japanese grass, Nepal grass) at the Oak Ridge National Environmental Research Park to: (1) document the distribution of this species, (2) measure several important characteristics of the populations and invaded habitats, (3) identify biotic and abiotic environmental factors that may limit its distribution, and (4) quantify its response to environmental gradients. We found that M. vimineum exhibits the broad environmental tolerance of many “weedy” species, and it appears that no single variable explains presence or performance. Presence of M. vimineum was correlated only with soil pH, whereas M. vimineum performance was positively correlated with canopy openness and biomass of other species. Explanatory variables differed among sites, which suggests that other factors (such as disturbance or dispersal) may be locally important, or that different factors may interact to control the distribution and performance of this species at any given site. The nearly ubiquitous presence of M. vimineum along roads and trails in the study area, and the frequent incursion of roadside populations into adjacent forested habitat, highlights the importance of early control of source populations at forest edges.