The extensive root system of natural plant communities adds organic matter to the soil as roots die and are replaced. This organic matter acts as a food source for microbes that reduce nitrogen, break down pesticides, and help build large pores to allow water to percolate into the soil. Woody roots provide strength against streambank collapse. Streambanks are stabilized. Streambanks in healthy riparian zones are stabilized by permanent woody roots and, to a lesser extent, by deep roots of prairie grasses.
All streams tend to move across a floodplain, cutting outside corners of stream bends.
This cutting causes the bank to erode, which is a major source of sediment. Removing permanent vegetation and replacing it with row crop agriculture or intensively grazed cool-season grasses accelerates the streambank cutting and slumping process. Native riparian zone species such as willows, silver maple, cottonwood, and green ash thrive under these conditions, and can reduce streambank erosion. Use of Eastern red cedar, bundles of other cut trees, and willow plantings on the bank itself can rapidly reduce streambank erosion and limit stream meandering. Flood severity is decreased.