Typha x glauca (hybrid cattail) is an aggressive invader of wetlands in the upper Midwest, USA. There is widespread concern about declines in plant diversity following Typha invasion. However, relatively little is known about how Typha alters habitat characteristics, i.e., its potential to act as an “ecosystem engineer”. Over five years, we measured physical, chemical, and plant community changes associated with Typha invasion in a Lake Huron wetland in northern lower Michigan. We compared uninvaded areas with patches varying in invasion intensity. Our study was observational, but we used statistical inference to try to separate effects of Typha and confounding variables, particularly water depth. We used space–for–time substitution to investigate whether Typha–associated changes increased over time, as predicted if Typha invasion was in part a cause (not only a consequence) of abiotic changes. Relative to uninvaded areas, Typha–invaded areas differed in plant–community composition and had lower species richness, higher litter mass, and higher soil organic matter and nutrient concentrations (all P < 0.001). Overall, Typha invasion appeared to displace native species and enrich wetland soils. These changes could benefit Typha at the expense of native species, potentially generating plant–soil feedbacks that pose special challenges for wetland management and restoration.