COS 295-2 - Revisiting successful wetland mitigation projects in New Jersey - is five years of monitoring sufficient?

Abstract: The New Jersey Department of Environmental Protection - Division of Land Resource Protection's Wetland Mitigation Unit requires approved wetland mitigation sites in New Jersey to satisfy specific criterion by the end of a five year monitoring period to be deemed successful. These requirements include the establishment of 85% areal cover comprised of desirable native hydrophytic vegetation; planted trees are healthy and a minimum of five feet tall; less than 10% of vegetative cover is comprised of undesirable invasive vegetation; and the mitigation site has established the targeted hydrological regime necessary to support a wetland plant community. To achieve these targets adaptive management plans are an integral component of a wetland mitigation site's development and, ultimately, their success. However, what happens to mitigation sites once they have satisfied all the conditions and monitoring and associated adaptive management plan implementation activities cease? Do these mitigation sites remain on positive development trajectory's? Do they revert to their pre-mitigation site plant community over time? Two case studies, one in a tidal wetland setting, and one in a freshwater wetland setting, are revisited ten years, and fourteen years later, respectively, to analyze the development of each mitigation site without ongoing monitoring or implementation of any adaptive management measures to assess, empirically, the effectiveness of a five-year monitoring program. The results indicate that the establishment of a suitable hydrologic regime and associated suitable substrate for plant media do support a hydrophytic plant community, however, the herbaceous stratum of the plant community within the freshwater wetland setting has reverted to a largely monotypic stand of reed canary grass (Phalaris arundinaceae) while the shrub and forest strata continue to develop on a positive developmental trajectory. The tidal wetland has continued to support a healthy and thriving estuarine marsh with desirable native low and high marsh species with little encroachment of undesirable invasive species. In conclusion, the five years of monitoring for these two mitigation sites was sufficient with regard to the establishment of a suitable hydrologic regime; and suitable substrate that supports hydrophytic plant species, however, the composition of the plant community within the freshwater wetland mitigation site, specifically the herbaceous stratum, does not support a diverse suite of native plant species while the tidal wetland mitigation site continues to support a desirable estuarine plant community.