Russian olive (Elaeagnus angustifolia) impacts on soil N, light, and plant community structure in eastern Colorado

Background/Question/Methods

Russian olive (Elaeagnus angustifolia) was introduced to the US from western Asia and southern Europe in the early 1900’s. It has since become the third most common riparian tree in the western US. While it has great potential to impact ecosystems through its abundance, ability to fix atmospheric nitrogen (N) and deep shade under its canopy, the ecological impacts of Russian olive have not been fully evaluated. This information would provide land managers and policy makers with a better understanding of the strength, duration and environmental context of Russian olive impacts and inform management decisions. Removal and restoration efforts are currently underway along the South Fork Republican River and throughout eastern Colorado. In summer 2010, we initiated a study to quantify the extent and duration of the impacts of Russian olive, and to evaluate the effects of removal efforts on plant communities at sites scheduled for tree eradication. Using a paired plot design, we collected percent cover by species, soil N and available light data from 200 plots underneath Russian olive canopy (Russian olive plots) and 200 plots at least three meters away from its canopy (reference plots) in 2010 and 2011.

Results/Conclusions

Russian olive plots differed greatly from reference plots for available N, light attenuation and plant community structure. Mean plant available N (estimated using ion-exchange resin bags) was 73.8% higher (33.97 vs. 19.54 mg\L) under Russian olive compared to adjacent reference plots and light levels were significantly lower for both early season (April, before trees had leafed out) and mid-season (June, full canopy). Exotics had significantly higher percent cover and natives had significantly lower percent cover in Russian olive plots than reference plots for both years. Additionally, plant functional groups greatly differed between Russian olive and reference plots, with significantly greater cover of annual and perennial forbs and significantly lower cover of perennial C4 grasses under Russian olive compared to reference plots. This pattern was driven by a few species being more common in one plot type, particularly the exotic perennial forb N. cataria under Russian olive and the native perennial C4 grass P. virgatum in reference plots. These results indicate that Russian olive changes soils and understory environments and alters understory plant community composition, including promoting invasion by other exotics.