Channel Morphologic Response to Invasive Vegetation Removal Across the Southwestern U.S.

Invasive plants such as tamarisk, Russian olive, and giant cane are prolific within riparian corridors throughout the Southwestern US (SW). Introduced in the early 19th century for cultivation and riverbank stabilization, invasive riparian vegetation (IRV) has spread extensively, salinized soils, modified wildlife habitats, increased fire risks, and contributed to altered stream channel morphologies. River regulation and drought over the past several decades has amplified the expansion of IRV and associated channel narrowing and simplification. River restoration to control or remove IRV is widespread and prompts the question of whether removal leads to reversal of channel narrowing or facilitates channel complexity. Isolated studies on rivers in the SW show that removal may increase channel width and mobility in some cases, but there is a lack of regional investigations of the post-vegetation removal response or the factors promoting or resisting it. We compiled available high spatial-resolution aerial imagery at 15 sites to delineate the active channel boundary and quantify channel change before and after removal. Each IRV removal site was paired with a control site where IRV was not removed to quantify channel response (defined as changes in channel width and migration rate) attributable to IRV removal. Preliminary results indicate channel width and centerline migration changes are linked to IRV removal method, flood occurrence, and stream power. Initial results show greater channel widening in more than half of the treatment reaches compared to control reaches following removal, but channel narrowing, or minimal channel response occurred in some rivers due to the lack of erosive floods. Preliminary channel migration analyses suggest mechanical removal methods and greater magnitude and frequency of floods following removal leads to increased channel response. Our results highlight the need to understand channel morphologic response following IRV removal and inform land managers and restoration practitioners of possible erosion issues that may arise from channel widening. This data set continues to grow. Please let us know if you are aware of riparian invasive species removal efforts that might be added to this study.