Assessment Of Russian Olive As An Ecogeomorphic Agent On The Powder River
Antonio Reveles-Hernandez1*, Sharon Bywater-Reyes1, and Scott Franklin2
1University of Northern Colorado, Department of Earth and Atmospheric Sciences, Greeley, Colorado, USA
2University of Northern Colorado, School of Biological Sciences, Greeley, Colorado, USA
The invasive species, Russian olive (Elaeagnus angustifolia), may pose a threat to northern U.S. rivers because of its broad and increasing habitat suitability. Russian olive is more shade and drought tolerant compared to the native cottonwood (Populus) and invasive tamarisk (Tamarix). The distribution and spread of Russian olive have been studied extensively in the Southwestern U.S. However, its range and impacts remain unknown in more northern regions. Within this context, the Powder River (Montana U.S.) functions as a model fluvial system for studying the potential impacts Russian olive may have on local species composition and geomorphic processes. Specifically, we measured plant traits (e.g., stem flexural rigidity, stem density, leaf shape, and plant height) known to influence flood hydraulics and associated sediment transport. The best-fit functions for plant bending force (i.e., flexibility) as a function of plant height were exponential and indicated Russian olive is more rigid than both tamarisk and cottonwood, with tamarisk having intermediate values. We additionally measured distribution, percent cover and topographic position of Russian olive, tamarisk and cottonwood within the Powder River riparian corridor. Tamarisk had the widest distribution of elevations relative to the channel, Russian olive had the lowest median elevation. We also used real-time kinematic (RTK) global positioning system (GPS) receivers to survey along 13 transects that had cross-sectional data collected in the past along the Powder River. Preliminary analysis shows apparent channel change in the form of accretion, channel narrowing, and vegetation encroachment. We hypothesize that Russian olive, because of its rigidity, high densities, low channel positions, and widespread existence as a shrubby canopy, likely impacts flow and sediment transport more than both invasive tamarisk and native cottonwood. Additional research will explore relationships between properties of invasive and native woody species and related ecogeomorphic processes, with implications for understanding the associated impacts on river corridors.