Effectiveness of compensatory wetland mitigation in Massachusetts, USA

Published source details Brown S.C. & Veneman P.L.M. (2001) Effectiveness of compensatory wetland mitigation in Massachusetts, USA. Wetlands, 21, 508-518.
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This study is summarised as evidence for the following.

	Action	Category
	Require mitigation of impacts to marshes or swamps Action Link
	Restore/create freshwater marshes or swamps (specific action unclear) Action Link

Require mitigation of impacts to marshes or swamps

A study in 1983–1997 of 114 development projects in Massachusetts, USA (Brown & Veneman 2001) reported that permits requiring compensation for impacts to marshes and swamps did not prevent a loss in their area, and found that compensation was compliant with permit conditions in only 43% of completed projects. The study examined 114 development projects which encroached onto marshes or swamps and for which permits required compensatory mitigation. Compensatory sites required by the permits were 23% larger than impacted sites on average, but they were generally not the same type (e.g. impacted: 71% forested; designated: 61% shrubby). In practice, compensatory sites were 34% smaller than impacted sites. Furthermore, 39% were not even wetlands. In only 47 of 109 completed projects was compensation compliant with the permit (i.e. a wetland was created of similar size to the impacted wetland, with ≥75% cover of emergent vegetation). The study also compared vegetation in compensatory wetlands and remnant natural wetlands – see Action: Restore/create marshes or swamps (specific intervention unclear). Methods: The study examined 114 projects that were granted permits, between 1983 and 1994, to destroy marshes or swamps as long as replacements were created elsewhere. Data were extracted from permit records and collected in vegetation surveys in summer 1997.

(Summarised by: Nigel Taylor)
Restore/create freshwater marshes or swamps (specific action unclear)

A replicated, paired, site comparison study in 1997 of 69 restored/created wetlands in Massachusetts, USA (Brown & Veneman 2001) found that they contained different plant communities to remnant natural wetlands, with fewer plant species and lower cover. After 3–12 years, restored/created sites contained a plant community characteristic of wetland conditions (data reported as a wetland indicator index). However, the overall plant community composition typically differed between restored/created wetlands and remnant natural wetlands (similarity <38% in 66 of 69 cases; statistical significance not assessed). The restored/created wetlands also had fewer plant species (restored/created: 9; natural: 11), fewer wetland plant species (restored/created: 8; natural: 10), and lower vegetation cover (all plants and wetland plants; data not reported). Methods: In summer 1997, vegetation was surveyed in 69 pairs of wetlands. Each pair included one wetland restoration/creation project and one remnant natural wetland. One representative 15 x 30 m plot was surveyed in each wetland. The restoration/creation projects were intended to compensate for damage to wetlands from development projects. The study included both marshes and swamps (number of each not clearly reported).

(Summarised by: Nigel Taylor)