Patterns of environmental change associated withTypha xglauca invasion in a Great Lakes coastal wetland

Abstract

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 followingTypha invasion. However, relatively little is known about howTypha 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 withTypha 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 ofTypha and confounding variables, particularly water depth. We used space-for-time substitution to investigate whetherTypha-associated changes increased over time, as predicted ifTypha 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 benefitTypha at the expense of native species, potentially generating plant-soil feedbacks that pose special challenges for wetland management and restoration.