Riparian zones possess an unusually diverse array of species and environmental processes. The ecological diversity is related to variable flood regimes, geographically unique channel processes, altitudinal climate shifts, and upland influences on the fluvial corridor. The resulting dynamic environment supports a variety of life-history strategies, biogeochemical cycles and rates, and organisms adapted to disturbance regimes over broad spatial and temporal scales. Innovations in riparian zone management have been effective in ameliorating many ecological issues related to land use and environmental quality. Riparian zones play essential roles in water and landscape planning, in restoration of aquatic systems, and in catalyzing institutional and societal cooperation for these efforts.

Abstract. Riparian corridors possess an unusually diverse array of species and environmental processes. This "ecological" diversity is related to variable flood regimes, geomorphic channel processes, altitudinal climate shifts, and upland influences on the fluvial corridor. This dynamic environment results in a variety of life history strategies, and a diversity of biogeochemical cycles and rates, as organisms adapt to disturbance regimes over broad spatio-temporal scales. These facts suggest that effective riparian management could ameliorate many ecological issues related to land use and environmental quality. We contend that riparian corridors should play an essential role in water and landscape planning, in the restoration of aquatic systems, and in catalyzing institutional and societal cooperation for these efforts.

Invasibility of riparian plant communities was estimated by the percentage of alien species found along the Adour River (Southwest France) and along Lockout Creek, McKenzie River, and Willamette River (Central Cascades, Oregon, U.S.A.). At the patch scale, the invasibilities of riparian plant communities were compared between one exceptionally rich site of the Adour River and patches selected in the Hoh and Dungeness watersheds (Olympic Peninsula, Washington, U.S.A.). Alien species represented 24% of 1396 species for the Adour and 30% of 851 species for the McKenzie. They represented 24% of 148 species for the Hoh drainage and 28% of 200 species for the Dungeness drainage. Similar trends were found along the Adour River and along the McKenzie River for changes in total number of species per site and in percentages of alien species per site. These trends may be related to the intermediate disturbance regimes and to the physical structure of the riparian corridors. Climatic and human factors are also involved in these longitudinal changes. Positive linear relationships were found between the total number of species and the percentage of aliens observed in each site. At the patch scale, most of the sampled communities contained alien species. Although mature vegetative patches appeared to be invasible, young communities contained more alien species than older ones. For entire corridors, a positive linear relationship was found between total species richness and percentage of alien species in each patch type for the richest site of the Adour River. This may be partially explained by landscape features considered in a successional context. We suggest the use of empirical rules, and stress the importance of riparian systems for monitoring the conservation of local and regional species pools are suggested.

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