Environmental impact of restoration of riparian ecosystems: Fitting Russian olive (Elaeagnus angustifolia) into the picture.

摘要

Riparian zones in the western United States are threatened by invasive species and increasingly, land management strategies include ecological restoration. Russian olive (Elaeagnus angustifolia) is a riparian invader with a flexible germination scheme and the ability to fix nitrogen through actinorhizal symbiosis. Two literature reviews, one addressing E. angustifolia and another addressing evapotranspiration in western riparian lands provide background on riparian ecology. The foci of this thesis are two field projects to address the effect E. angustifolia and subsequent restoration has on riparian ecology. A multi-site vegetation survey after E. angustifolia removal relates site attributes (predictor variables) to restoration success, which was quantified by vegetation measurements (response variables). Regression tree modeling was used to analyze the data; these models indicate that edaphic and hydrologic variables explain the most variability in restoration success. A biogeochemical study of one of the 22 sites used in the first study quantified monthly soil inorganic nitrogen and moisture measurements in an E. angustifolia stand that subsequently underwent restoration (removal of invasive trees). This study indicates a sharp decrease in inorganic nitrogen concentrations after E. angustifolia removal. These studies are meant to inform land managers dealing with E. angustifolia invasion as well as encourage other researchers to address E. angustifolia in their work.