Heteropogon contortus recently and rapidly increased in dominance in grasslands where it once had been aminor component. Ecological effects of this increase are unknown, but landmanagers are concerned about the potential negative economic and ecological impacts. We examined compositional and structural characteristics of the vegetation community along a gradient of dominance of H. contortus to quantify changes, compare the effects to invasions by nonnative grasses, and provide insights about management. As H. contortus increased, grass richness decreased across the gradient by 6 species·m^-2 (95% CI: 2–10) in summer and 10 species·m^-2 (6–15) in winter. Cover of other native grasses decreased 8–10% in both seasons for every 10% increase in H. contortus. Presence of seven individual plant species and cover of five species decreased, but presence of five species and cover of one species increased with H. contortus. Canopy cover increased and soil nutrients were higher in dense H. contortus, potentially facilitating further ecological changes. We suggest that managing H. contortus and other species that become invasive within the ecosystem where they were once native likely requires reducing rather than wholly eliminating the species, which may differ from management strategies for nonnative species.