Strategies for Restoring River Ecosystems: Sources of Variability and Uncertainty in Natural and Managed Systems

Abstract

<em>Abstract</em>.—Formulating effective restoration goals and strategies for riparian ecosystems requires knowledge of the sources of variability at local and broad landscape scales. We examine sources and influences of natural and human-induced variability in riparian ecosystems and discuss their implications for restoration actions and recovery. We recommend that the development of restoration strategies should apply landscape perspectives that emphasize the connectivity of riparian systems to associated terrestrial and aquatic ecosystems. Particularly important are processes that involve the exchange of surface–subsurface waters, sediments, organic matter, and organisms between riparian and other ecosystems. Furthermore, the development of strategies should be based on understanding how past natural disturbances and human alterations and uses alter the connectivity and processes of riverine habitats throughout a drainage. Historical or retrospective information increases our understanding of how riparian and aquatic ecosystems function and provides insights on how to conserve and restore these resources. Although many restoration initiatives strive to repair ecosystem damage caused by humans, more recent views maintain that restoration efforts should facilitate the self-sustaining occurrence of natural processes and linkages among riparian, terrestrial, and aquatic ecosystems. Three general restoration strategies are presented: conservation, passive restoration (riparian reserves and buffer zones), and active restoration (flow and floodplain manipulations, restoring cottonwood/willow communities, and reducing invasive and exotic plants). Regardless of the strategy employed, restoration objectives should recognize that different portions of a riparian system can exhibit an array of recovery patterns as well as failure scenarios. Thus, objectives and strategies should enable us to evaluate the success of restoration activities as well as possibilities for continued degradation.