Plant phenology drives seasonal changes in shear stress partitioning in a semi-arid rangeland

Authors: ZIEGLER, NANCY - Environmental Laboratory, Us Army Engineer Research And Development Center, Waterways Experiment St; WEBB, NICHOLAS - New Mexico State University; GILLIES, JOHN - Desert Research Institute; EDWARDS, BRANDON - New Mexico State University; NIKOLICH, GEORGE - Desert Research Institute; Van Zee, Justin; COOPER, BRAD - New Mexico State University; Browning, Dawn; Courtright, Ericha; LEGRAND, SANDRA - Environmental Laboratory, Us Army Engineer Research And Development Center, Waterways Experiment St

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2022
Publication Date: 1/5/2023
Citation: Ziegler, N., Webb, N., Gillies, J., Edwards, B., Nikolich, G., Van Zee, J.W., Cooper, B., Browning, D.M., Courtright, E.M., Legrand, S. 2023. Plant phenology drives seasonal changes in shear stress partitioning in a semi-arid rangeland. Agricultural and Forest Meteorology. 330. Article 109295. https://doi.org/10.1016/j.agrformet.2022.109295.
DOI: https://doi.org/10.1016/j.agrformet.2022.109295

Interpretive Summary: The amount of surface roughness (e.g., vegetation, rocks and other non-erodible objects) in a landscape is a key control on wind erosion. This is because roughness elements cover a portion of the soil surface and create drag, which reduces wind erosivity downwind. The effect of roughness in reducing the wind erosivity is described in terms of the ratio of wind shear stress over the roughness to that at the soil surface - called the drag partition. Wind tunnel and field studies have examined roughness effects on drag partitioning. However, the spatial and temporal variability of wind erosivity and shear stress ratio remain poorly described. Here, we examine the spatiotemporal variability of the shear stress ratio before, during, and after vegetation green-up at a honey mesquite (Prosopis glandulosa Torr.) shrub-invaded grassland in the Chihuahuan Desert, New Mexico, USA. Our data show that vegetation green-up, the emergence of leaves, led to increased drag and surface sheltering and a reduction in wind erosivity at the soil surface. We found that the wind shear velocity, an indicator of erosive force, decreased from 20% to 5% of the total wind shear velocity above the vegetation canopy. The variability of the shear stress ratio in space and time was found to be linked directly to plant phenological phases. Our results suggest that wind erosion models need to represent seasonal vegetation change to more accurately predict the timing and amount of wind erosion. The drag partition response to mesquite phenological phases also provided insight to potential mesquite herbicide treatment effects which, if successful, could increase wind erosivity and the onsite and downwind impacts of wind erosion unless protection by herbaceous plants is maintained.

Technical Abstract: Accurate representation of surface roughness in predictive models of aeolian sediment transport and dust emission is required for model accuracy and for models to inform wind erosion management. While past wind tunnel and field studies have examined roughness effects on drag partitioning, the spatial and temporal variability of surface shear velocity and shear stress ratio remain poorly described. Here, we use a four-month dataset of total shear velocity (u*) and soil surface shear velocity (us*) measurements to examine the spatiotemporal variability of the shear stress ratio (R) before, during, and after vegetation green-up at a honey mesquite (Prosopis glandulosa Torr.) shrub-invaded grassland in the Chihuahuan Desert, New Mexico, USA. Results show that vegetation green-up, the emergence of leaves, led to increased drag and surface aerodynamic sheltering and a reduction in us* and R magnitude and variability. We found that us* decreased from 20% to 5% of u* as the vegetation form drag and its sheltering effect increased. Similarly, the spatiotemporal variability of R was found to be linked directly to plant phenological phases. We conclude that drag partition schemes should incorporate seasonal vegetation change, via dynamic drag coefficients and/or R, to accurately predict the timing and magnitude of seasonal aeolian sediment fluxes. The drag partition response to mesquite phenological phases also provided insight to potential mesquite herbicide treatment effects which, if successful, could increase wind erosivity and the onsite and downwind impacts of wind erosion unless protection by herbaceous plants is maintained.