Short-Term Response of Vegetation and the Riparian Bird Community to Dam Removal on the Rogue River, Oregon

摘要

Both establishment and subsequent removal of dams inevitably alter river systems and may impact aquatic and terrestrial organisms. Despite both stated and implicit restoration goals of dam removal, relatively few studies have examined ecological response. Using a before-after-control-impact framework one year before and two years after, I evaluated the short-term effect of a dam removal on the Rogue River in southwestern Oregon on vegetation, bird community composition, and abundance of eight riparian-associated bird species. No differences were detected for tree and shrub strata cover after dam removal for either treatments or controls. Within the three treatment habitat types (mainstem, slough, wetland), shrub and ground cover declined only in wetland areas, likely as a result of post dam removal vegetation management. Significant changes in relative abundance were found for only one of eight focal bird species. Chamaea fasciata (Wrentit) abundance declined on treatment points following dam removal, possibly a response to the decrease in cover of the shrub and ground vegetative strata in the wetland. Bird community composition did not differ between controls and treatments either before or after dam removal. In combination, the similarities in bird community composition and lack of detectable change in abundance for seven riparian associated species are consistent with the results for vegetative cover, suggesting shrub and tree components of riparian habitat did not change substantially in the two years following dam removal. Results from this study have important management implications for maintaining or restoring riparian vegetation in conjunction with future dam removals.