Flood depth, duration, and frequency are important components of wetland hydrology and influence the characteristics of wetlands. While seasonal, low magnitude flood regimes may support stable and diverse wetland plant communities, prolonged or frequent, extreme flooding may create conditions that lead to less diverse wetland plant communities. In this study, we analyzed flood regime and plant communities at 20 floodplain wetland restoration sites in Illinois, USA, with contributing watershed areas ranging from 4 to ~1.8 million km2, to provide a watershed-scale evaluation of the influence of flood exposure on wetland plant community characteristics. We used a flood exposure index (FEI) calculated from continuous hydrologic data to characterize the flood regime at each site. Plant communities in the restored wetlands were evaluated using 11 indices including species richness, floristic quality index (FQI), and mean wetland indicator status (WIS). We used linear regressions to relate characteristics of the vegetation to FEI. Results show moderately strong, inverse correlations of species richness, FQI, and percent of perennial species with maximum annual FEI, suggesting that higher magnitude flood exposure causes reduced species richness and altered plant community composition when viewed from a watershed scale. Contrary to the expectation of a strong positive correlation of percent hydrophytes and WIS with FEI, the analysis showed a marginally significant, weak relationship with average percent of hydrophytes, and no correlation with WIS. This lack of correlation may be due to several factors that influence plant communities at the local scale such as topographic heterogeneity, site drainage after floods, and adjacent land use. The results of the analysis suggest that consideration for flood exposure should be given when evaluating the progress of wetland restoration, particularly when species richness or metrics that include species richness (e.g., FQI) are used to evaluate attainment of performance standards.
|Original language||English (US)|
|Title of host publication||Wetlands in a Complex World|
|State||Published - 2012|