Structural and functional vegetation development in created and restored wetland mitigation banks of different ages

Vegetation surveys of seven Ohio wetland sites were conducted from 2008 to 2010 during peak biomass. These seven sites included five created/restored mitigation bank wetlands, a created riverine research wetland, and a natural reference wetland. All of the created/restored wetlands ranged in age from 3 to 18 years. The objective of this study was to examine the development of vegetation structure and function of mitigation bank wetlands less then 20 years of age and to compare these to reference wetlands. Vegetation structure examined included species richness, floristic quality assessment index (FQAI), Shannon-Wiener diversity index (H), and community diversity index (CDI). Functional attributes included aboveground net primary productivity (ANPP) and functional group composition of dominant species. For both structure and function, the reference wetlands were statistically different from the wetland mitigation bank sites (P < 0.001, MANOVA). Structurally, there were significant differences of FQAI score (P < 0.05) and species richness (P < 0.05) with age in the mitigation sites. Functionally, there was a significant difference between ANPP (P < 0.05) and age in the mitigation sites. Over the different types of wetlands, the reference wetlands had significantly different ANPP, FQAI scores, and species richness than did the mitigation sites (P < 0.001, P < 0.05, and P < 0.001, respectively). CDI and H were not statistically different between mitigation sites and the reference wetlands. ANPP, FQAI, and species richness tended to be higher in the reference sites than in the mitigation sites. Overall, the mitigation bank wetlands were not statistically similar to the reference sites. Within the mitigation banks, the younger sites had higher values for structural attributes than the older mitigation sites.