Because invasive species are a major threat to global biodiversity, understanding the factors influencing the invasibility of native communities and documenting effects of invasive species on native communities is important. In this study, we assessed the role of disturbance in mediating the invasion of Asiatic sand sedge, Carex kobomugi Ohwi (Cyperaceae), in New Jersey's coastal dune ecosystems. Stem densities and species richness of native plants were significantly lower within areas invaded by C. kobomugi than in surrounding areas. Species diversity and species richness inside invaded areas at two highly disturbed sites were similar to one another and significantly lower than those in a less-disturbed site (two-way analysis of variance, Wilks' λ F  =  8.4, degrees of freedom [df]  =  78, p < 0.001), suggesting that disturbance enhances the ability of C. kobomugi to outcompete native plant species. A significant correlation between native plant stem densities inside invaded areas and those in surrounding areas suggests that preexisting habitat characteristics also play a role in driving observed differences in native plant densities at each site. However, the lack of a significant relationship between species richness or species diversity inside invaded areas compared with nearby uninvaded areas, suggests that C. kobomugi may be more important than background heterogeneity in influencing both those parameters. No clear differences were found between species richness, diversity, or native plant stem densities based on population size. This may mean that the impact of the sedge does not increase between early and late stages of the invasion. Alternately, it may mean that population size is a poor proxy for invasion maturity.