Plant Community Influences on Intermittent Stream Stability in the Great Plains

The composition of the greenline plant community is linked to the stability of riparian ecosystems. Cool season exotic grasses are invading native plant communities across the northern Great Plains, potentially compromising streambank stability and increasing the risk of erosion within riparian ecosystems. To determine how the species composition of the greenline community impacts stream type and the risk of streambank erosion, thirty five reaches across five watersheds were sampled to determine the dominant greenline vegetation. At each reach, a cross-section was sampled to determine stream type, greenline vegetation, and risk of streambank erosion. Channel types were delineated using Rosgen's classification of natural rivers. Canopy cover and composition was assessed using the line point intercept method along a 30.5 m transect in the greenline community. Plants recorded were grouped by their wetland indicator status for the central Great Plains. The Bank Erosion Hazard Index (BEHI) was used to assess the streams risk of erosion by calculating the difference between the bank height and bank full height, average plant rooting depth and density, bank angle degree, and the dominant texture of the bank material. Bank height ratio (BHR) was assessed as a measure of streambank stability and floodplain connectivity. A Nonmetric Multidimensional Scaling ordination was performed to analyze plant community influences. Analysis of the data determined that the most stable stream types (E and C channels), lower BEHI scores, and stable bank height ratios were associated with high amounts of litter and facultative wet species. In comparison, unstable F channels were associated with early successional species and bare ground. Sites with the higher BEHI scores were associated with greenlines comprised of upland and facultative upland and saline tolerant species. Late successional facultative wetland species were found to provide the most protection to intermittent streambanks.