Great Lakes coastal wetland plant biodiversity increases following the manual removal of invasive Phragmites australis

Invasive Phragmites australis australis is invading and homogenizing Great Lakes coastal wetlands at an alarming rate. Phragmites australis is thought to reduce wetland biodiversity both directly and indirectly through the acquisition of resources and alteration of habitat. Restoration efforts to manually remove approximately 10,000 m² of P. australis from Point Pelee National Park began in 2020 and here, we assess the effect of manual cut and burn P. australis removal on emergent aquatic vegetation communities. By using systematic transects stratified across water depth and wetland composition we compared emergent vegetation communities among a P. australis-invaded wetland, a P. australis-treated wetland, and a non-invaded wetland. We found that 2 years post-restoration, vegetation species richness and the prevalence of non-P. australis vegetation were greater in the treated and non-invaded wetlands than the invaded wetland. More specifically, we found almost twofold more plant species in the treated and non-invaded wetland compared to the invaded wetland, with only seven plant species found within the invaded wetland. Analysis of similarity and non-metrical multi-dimensional scaling analysis revealed that the vegetation community of the treated wetland resembled the vegetation community of the non-invaded wetland, and the vegetation community of the invaded wetland was very different from both the treated and non-invaded wetlands. Manual removal of P. australis is time-consuming and labour-intensive, however; these findings confirm that small-scale manual removal of P. australis can result in the return to native plant assemblages in coastal wetlands two years after treatment.