Plant diversity, composition, and invasion of restored and natural prairie pothole wetlands: Implications for restoration

Hundreds of wetlands comprising thousands of hectares have been restored in the Midwestern United States. In nearly all cases, restoration consisted of simply restoring wetland hydrology. For this reason, the success of these restorations relies on natural colonization. We compared the structure and composition of the vegetation in two types of wetlands: 10 natural wetlands and 17 five-to-seven-year-old restored wetlands. The overall vegetative composition of restored wetlands was different from that of natural wetlands. Restored wetland flora was formed from a subset of species found in natural wetlands. The species restricted to natural wetlands tended to be native perennials and were evenly represented along the elevational gradient. The few species that were restricted to restored wetlands were largely mudflat annuals whose presence is more indicative of the presence of more unvegetated habitat in restored wetlands than of the presence of a distinctive restored wetlands flora. In addition, restored wetlands had lower vegetative cover and species richness than natural wetlands. Both wetland types had similar numbers of exotic species at the whole wetland (4.4 species per wetland) and quadrat scale (1.5 species m(2)), and dominance of exotics increased with elevation. The lower species richness, greater compositional variability, and lack of a distinctive flora support the hypothesis that dispersal limitation is the primary cause of the differences between the vegetation in restored and natural wetlands.