Restored Vegetation Outcomes in Wetland Mitigation Banks Across Minnesota

Abstract

Wetlands are one of the world’s most important ecosystems, yet they continue to be degraded by urban and rural development. The Minnesota Wetland Banking Program exists as a convenient pathway to replace wetlands that have been destroyed. While the program has been offered since 1994, there has been no assessment of the long-term outcomes of wetland banking projects. Vegetation monitoring occurs for 5 years post-restoration, but even then these sites are ecologically young and conclusions made about the achievement of vegetation restoration goals may be premature. This study aimed to evaluate vegetation outcomes in wetlands restored 8-11 years ago, and to compare these outcomes across four seeding zone types. The results indicate that the emergent zone had the lowest native species richness and highest invasive species cover. In all seeding zones, the number of seeded species present was often quite low even when native richness is high. This study also identified which seeded species and guilds persisted over time and which were consistently absent. This type of data can inform future seed mix adjustments, thereby improving the success and cost-effectiveness of wetland vegetation restoration efforts. Across all study sites, invasive narrow-leaved cattails and reed canary grass were pervasive and seem to be increasing in cover over time. Certain species such as rice cutgrass and tussockforming sedges may compete effectively with invasives. This study highlights the necessity of long-term management to combat the ongoing expansion of invasive species and to promote the persistence of desired native species.