Grass versus trees: Managing riparian areas to benefit streams of central North America

Forestation of riparian areas has long been promoted to restore stream ecos ystems degraded by agriculture in central North America. Although trees and shrubs in the riparian zone can provide many benefits to streams, grassy o r herbaceous riparian vegetation can also provide benefits and may be more appropriate in some situations. Here we review some of the positive and neg ative implications of grassy versus wooded riparian zones and discuss poten tial management outcomes. Compared to wooded areas, grassy riparian areas r esult in stream reaches with different patterns of bank stability, erosion, channel morphology, cover for fish, terrestrial runoff, hydrology, water t emperature, organic matter inputs, primary production, aquatic macroinverte brates, and fish. Of particular relevance in agricultural regions, grassy r iparian areas may be more effective in reducing bank erosion and trapping s uspended sediments than wooded areas. Maintenance of grassy riparian vegeta tion usually requires active management (e.g., mowing, burning; herbicide t reatments, and grazing), as successional processes will tend ultimately to favor woody vegetation. Riparian agricultural practices that promote a dens e, healthy, grassy turf, such as certain types of intensively managed lives tock grazing, have potential to restore degraded stream ecosystems.