Impacts of Plant Roots on Debris-Flow Bed Erosion in Laboratory Experiments

Debris flow—plant interactions are ubiquitous, yet we have limited understanding of how plants affect debris-flow erosion. Ignoring the effects of plants in debris-flow studies potentially leads to mistakes in hazard assessments. While debris-flow erosion has been the focus of recent studies, the influence of plant roots on this process has not yet been explored. Therefore, we unravel plant rooting effects on debris-flow bed erosion, using scaled experiments. We show how fast-growing Sorghum bicolor (Sudan grass) seedlings enable scale experiments with plant-debris flow interactions. Our experiments reveal a strong, non-linear correlation between root length density and debris-flow bed erosion. Increasing root length density amplifies root-soil contact, enhancing soil stability and reducing erosion. In turn, the reduced erosion could prevent potentially hazardous debris-flow volume growth. Our results yield insights into the potential effects of changes in vegetation characteristics on debris-flow erosion and open up possibilities for biogeomorphic scale experiments for slope processes.