The role of large predators in maintaining riparian plant communities and river morphology

Beschta, Robert; Ripple, William

Studies assessing the potential for largepredators to affect, via trophic cascades, the dynamics ofriparianplantcommunities and the morphology of river channels have been largely absent in the scientific literature. Herein, we consider the results of recent studies involving three national parks in the western United States: Yellowstone, Olympic, and Zion. Within each park, key largepredators were extirpated or displaced in the early 1900s and subsequent browsing pressure by native ungulates initiated long-term declines in recruitment (i.e., growth of seedlings/sprouts into tall saplings and trees) of palatable woody species and impairment of other resources. Channel responses to browsing-suppressed riparian vegetation included increased widths of active channels via accelerated bank erosion, erosion of floodplains and erraces, increased area of unvegetated alluvium, channel incision, and increased braiding. A reduced frequency of overbank flows indicated these rivers have become increasingly disconnected from historical floodplains because of channel widening/incision. Results from Zion National Park also identified major biodiversity affects (e.g., reduced abundance ofplant and animal species). Although these studies were conducted in national parks, results may have implications concerning riparianplantcommunities, biodiversity, and channel morphology for streams and rivers draining other public lands in the western US. It is on these lands that native and introduced ungulates have often heavily utilized riparian areas, largely in the absence of key predators, with significant consequences to plantcommunities and channels.

The role of large predators in maintaining riparian plant communities and river morphology

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