Plant community recovery after herbicide management to remove Phragmites australis in Great Lakes coastal wetlands

Abstract

Invasive plants, such as Phragmites australis, are a global threat to plant diversity and are commonly controlled using herbicide management. The purpose of this study was to evaluate the plant community response 6–10 years after large‐scale herbicide management to remove Phragmites from Great Lakes coastal wetlands along the shores of western Lake Erie. Vegetation surveys were conducted in nine wetlands undergoing herbicide management and four unmanaged Phragmites‐dominated wetlands. The relative percent cover of Phragmites was dramatically lower in the managed (1.3%) compared to unmanaged wetlands (93.0%; p < 0.001), although relative percent cover of other non‐natives following herbicide management averaged 39.2% (ranging from 6.4 to 67.6%). The cover‐weighted floristic quality index was significantly higher in managed wetlands (p < 0.01), with the highest indices (12.4–17.0) at sites that received prescribed fire after herbicide treatment (p < 0.05). Species richness and diversity were significantly higher in managed wetlands (p < 0.001); however, there was no significant difference between wetlands treated only with herbicide and those treated with herbicide and prescribed fire. Our results indicate that herbicide management is effective in reducing Phragmites and improving floristic quality over timescales of 6–10 years. However, continued spot‐treatment and management of new invasive species may be required, and the return of high‐quality plant communities may be unrealistic in the study region.