Legacy Effects of Russian Olive (Elaeagnus angustifolia L.) in a Riparian Ecosystem Three Years Post-Removal

Exotic invasive plants leave legacy effects when impacts persist following invader removal. Russian olive (Elaeagnus angustifolia L.) is an actinorhizal tree that is widespread along rivers in interior western North America. We monitored soil N and plant community response to E. angustifolia removal in a riparian ecosystem in eastern Colorado, USA. We collected pre-removal data for two years, and tracked post-removal response for three years. Soil N was generally higher in E. angustifolia plots than in reference plots (not under E. angustifolia) within each removal status treatment (No Removal, Removal, Control). Percent cover of native species was higher in reference plots than in E. angustifolia plots, within treatments in all years. Percent cover of exotic species was higher in E. angustifolia plots than in reference plots, except in the Removal and No Removal treatments immediately following tree removal. Underlying this pattern was a shift in exotic species dominance from Nepeta cataria to Bassia scoparia. The removal treatment successfully reduced E. angustifolia populations at the study sites, but three years afterwards riparian soils and plant communities showed little evidence of recovery towards reference conditions. However, E. angustifolia removal did not appear to worsen invasion impacts or produce novel management problems.