Mechanisms and reversibility of the effects of hybrid cattail on a Great Lakes marsh

• We studied mechanisms of effect of hybrid cattail on a Great Lakes marsh.
• Cattail litter has greater effects than live cattail on marsh plants and ecosystem.
• Removal of litter is necessary to restore light conditions and plant diversity.
• The restored community was dominated by terrestrial grasses and forbs.
• Recruitment success of native sedges and rushes was poor.

Invasive plants compete with natives, and their litter can suppress natives and alter ecosystem function. Understanding the mechanisms of effect of invasive plants and testing whether invader removal reverses these effects is important to guide restoration and management. We addressed these questions in a Great Lakes marsh invaded by Typha x glauca (hybrid cattail), which produces monodominant stands with considerable litter accumulation. We teased apart effects of live T. x glauca versus its litter on the marsh ecosystem with a live/litter transplant experiment, and tested whether effects were reversible by a live/litter removal experiment in a Typha stand. Over two to four years, in both native marsh and Typha stand, the presence of litter decreased light and increased inorganic nitrogen. Live T. x glauca addition to the native marsh increased inorganic nitrogen and soil organic matter, but removal did not reverse these effects. Litter addition decreased native richness and abundance, and litter removal reversed these effects; however, characteristic native marsh sedges and rushes were not restored, but rather terrestrial grasses and forbs recruited. This suggests that litter removal is essential in cattail restoration projects to increase diversity, but that further active management will likely be necessary to restore marsh communities per se. Because many wetland invaders share similar traits with T. x glauca, including litter accumulation, conclusions are broadly applicable to a variety of wetland invasions.