Effects of Russian Olive on Stream Organisms and Ecosystem Processes
Kaleb Heinrich1*, Colden Baxter2, and Madeleine Mineau3
1University of Alabama, Tuscaloosa, Alabama, USA; kheinrich@ua.edu
2Idaho State University, Pocatello, Idaho, USA; baxtcold@isu.edu
3New Hampshire Sustainable Energy Association, Concord, New Hampshire, USA; madeleine@nhsea.org
Russian olive (Elaeagnus angustifolia) is a non-native riparian tree that has become common and continues to spread throughout the western US. Due to its dinitrogen-fixing ability, Russian olive has the potential to subsidize streams with nitrogen, which may alter nutrient dynamics in riparian systems. Furthermore, it has the potential to alter primary production, due to shading, and stream organic matter budgets by adding litter/olives. Inputs from Russian olive may alter the composition of food resources for stream animals, native and non-native, which could influence their abundance and productivity. Here we summarize a combination of recent and ongoing studies aimed at investigating the ecological effects Russian olive may elicit in streams. A comparative study of stream reaches in Idaho and Wyoming invaded by Russian olive had higher organic nitrogen concentrations and exhibited reduced nitrogen limitation of aquatic primary producers compared to reference reaches. Using a before-after invasion comparison at Deep Creek, Idaho, we found that Russian olive invasion was associated with a significant increase in litter input to the stream and that this litter was recalcitrant compared to that of native willow. In this stream, Russian olive invasion was associated with an increase in organic matter stored in the streambed, but not significant changes in gross primary production or community respiration, translating into a decrease in ecosystem efficiency. We found no significant change in total secondary production of invertebrates, though there were changes in some individual taxa. Diet and stable isotope evidence indicate that Russian olive litter is selected against by the dominant, native macroinvertebrates because it is used in lower proportion relative to its availability. Most recently, studies in Deep Creek suggest that invasive carp (Cyprinus carpio) are being subsidized by Russian olive. This scenario is characteristic of an ‘invasional meltdown,’ with attendant changes in food webs and ecosystem processes.