Comparison of Russian Olive, Tamarisk, and Cottonwood Plant Traits with Implications for River Morphodynamic Trajectories
Sharon Bywater-Reyes1, Antonio Reveles- Hernandez, Scott Franklin
1University of Northern Colorado
The strength of interactions between plants and river processes is dependent on plant traits such as stem density, plant frontal area, and stem bending properties. The U.S. Southwest has long been a natural laboratory for studying how plant invasion dynamics, combined with plant traits, can dramatically alter river processes. For example, the well-studied displacement of native cottonwood (Populus ssp.) by Tamarisk (Tamarix ssp.) was accompanied by aggradation and channel narrowing in many instances. These changes in sediment transport are due in large part because of plant-traits differentially affecting hydraulics and sediment transport. Tamarix has higher rigidity, inducing more drag compared to Populus of the same size, resulting in a greater influence on near-bed flow velocities, and subsequently sediment transport. Recently, Russian olive (Elaeagnus angustifolia) has competed with Tamarix in U.S. Southwest rivers as the dominant invasive and may pose a threat to rivers beyond the U.S. Southwest because of its broad and increasing habitat suitability. Within this context, we studied the distribution, percent cover, topographic position, and rigidity of Russian olive, Tamarix and Populus species within a northern river. Cluster analysis found woody communities from river’s edge to floodplain interior of (1) Russian olive with an herbaceous understory, (2) Populus as a canopy with a Russian olive midcanopy, and (3) Populus with an herbaceous understoryThe best-fit functions for plant bending force (i.e., rigidity) as a function of plant size were exponential and indicated Russian olive is more rigid than both Tamarix and Populus, with Tamarix having intermediate values. 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 Tamarix and native Populus. 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.