Using areal composition of riparian vegetation communities to identify thresholds in prairie streams

Authors: MEEHAN, MIRANDA - North Dakota State University; O'Brien, Peter

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2019
Publication Date: 11/6/2019
Citation: Meehan, M.A., O'Brien, P.L. 2019. Using areal composition of riparian vegetation communities to identify thresholds in prairie streams. Rangeland Ecology and Management. 73(1):162-170. https://doi.org/10.1016/j.rama.2019.09.004.
DOI: https://doi.org/10.1016/j.rama.2019.09.004

Interpretive Summary: Rangeland managers often use vegetation communities to gauge the ability of the land to provide ecosystem services, as well as to identify potential risks associated with land degradation. However, assessing vegetation communities in riparian areas can be difficult because multiple communities are present that often shift with annual precipitation trends. Land managers need a consistent, broadly applicable framework to guide them in determining if changing vegetation patterns are the result of seasonal variation or land degradation. We mapped different plant communities along rangeland streams in North Dakota, USA and assessed the size of each plant community in relation to a variety of stream characteristics. We found that larger areas of riparian vegetation were present along stable streams than along unstable streams, with much of the increased area consisting of an additional transitional plant community not present along unstable streams. These trends in plant communities were related to stream characteristics that dictate how much and how frequently the streams flood. These findings will provide a foundation upon which to construct Riparian Complex Ecological Site Descriptions and identify thresholds of change in riparian systems. Land managers can use this information to make management decisions that allow for continuing multifunctional rangeland use, including beef production operations and long-term environmental stewardship.

Technical Abstract: Vegetation communities are often used to assess land ecological status in upland systems but applying that principle to riparian systems may not be appropriate. Riparian areas often have multiple plant communities that may change rapidly due to seasonal hydrological shifts. However, the variation of those plant communities may not necessarily indicate transitioning ecological status. Geomorphic parameters may be better indicators of a transition in ecological status, but they cannot be understood separately from plant community dynamics. This research includes stream geomorphology and riparian plant communities in a discussion of stream stability and ecological status. The area of three plant community components (PCC) associated within riparian complexes were mapped along 34 reaches of 8 streams in North Dakota, USA. Stream cross-section and longitudinal profile data was collected to classify Rosgen stream channels into stable (E and C channels), at-risk, (B channels), and unstable (F, and G channels) states. The area of PCC1, the community nearest the stream bank consisting of wetland obligate species, was similar among stable and unstable streams, but PCC2 and PCC3, transitional plant communities, had greater area along stable reaches than along unstable reaches. Thus, the proportion of PCC1 in stable reaches was much lower (˜20%) than in unstable reaches (˜75%). Entrenchment ratio was the only stream parameter that was a good predictor of PCC areas, likely due to its relationship with floodplain connectivity. These findings may be valuable in developing riparian complex ecological site descriptions, specifically identifying potential thresholds between the unstable and stable states.