Common stream restoration practices inherently cause massive soil disturbance to the stream banks and floodplains. Soils affect plant community functions, and soil disturbance has been linked to exotic plant invasion. I designed this study to characterize the soils, determine the extent of invasion, and assess the presence of native woody plant species at stream restoration sites. I studied 11 restored streams in the NC Piedmont, as well as 6 reference streams. Reference streams are unrestored and generally undisturbed streams that are used as models during restoration design.
Restored streams, with 34% exotic cover, were more invaded than the references, with 10% exotic cover. The restored streams also had more exotic species present per square meter, greater frequency of exotic species, and greater exotic stem density. The native woody vegetation growing at the restorations and references differed in terms of the species present and their abundances. Fourteen of the 20 physical and chemical soil properties differed by site type, as did many morphological soil characteristics. Soil properties explained 20% of the variation in exotic species cover and 34% of the variation in native woody species cover.
The differences in vegetation and soil indicate the lasting impact of restoration practices. The restored stream communities do not have the same structure as the references, and are unlikely to have the same function. It would be very feasible for restorationists to address the differences we found. Efforts to chemically control exotic plants could be increased, and restorationists could limit the species they plant to those that are found in the project’s associated reference community. Soils could be adjusted by testing and amending as necessary. Efforts such as these, in addition to further research into restoration practices and design, will be necessary to improve restoration success.