A functional assessment of restored and reference wetlands along the Cache River, Illinois.

摘要

Functional assessment is an important tool for restoration ecologists to determine restoration success. This study is a functional assessment of wetland soil, vegetation, litterfall, and decomposition in planted, naturally regenerated, and reference wetlands in southern Illinois. Twelve sites along the lower Cache River were classified as reference wetlands (4 sites), or restored sites that were planted (5 sites), or naturally regenerated (3 sites). Reference soils had lower pH and higher soil moisture than either of the restoration treatments, and higher soil organic level than the planted sites. The reference sites provided functional goals for herbaceous and woody wetland vegetation. The naturally regenerated sites shared more vegetation characteristics with the reference wetlands than the planted sites. The difference in vegetation between the naturally regenerated and the planted sites is attributed to incomplete hydrologic restoration, inappropriate match of planted species to hydrology, and a lack of post-restoration control of invasive and exotic species in the planted sites. The amount of litterfall in the naturally regenerated and reference sites was significantly higher than the planted sites. The rates of decomposition for individual species were comparable across the three treatments. Of the variables considered in this study, the most important to functional assessment were soil organic matter and moisture, hydrology, native reference wetland herbaceous and woody vegetation, and the coupled rates of litterfall and decomposition. A comparison of the current vegetation to historical vegetation records suggested that there has been a seven- to ten-fold increase in the presence of Acer and Fraxinus, both light-seeded genera, in the wetlands of southern Illinois. The restoration sites along the Cache River seem to be developing some functional equivalency with the reference sites in respect to the rates of decomposition. Naturally regenerated sites were similar in vegetation, litterfall, and soil characteristics to reference sites. Planted sites were not similar to reference sites due to insufficient hydrological restoration and competition with invasive agricultural weeds. As the planted and volunteer trees continue to mature on the planted sites, managers may want to consider herbaceous vegetation control and reseeding these sites.