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Research Project: Understanding Ecological, Hydrological, and Erosion Processes in the Semiarid Southwest to Improve Watershed Management

Location: Southwest Watershed Research Center

Title: Runoff and soil erosion on woodland-encroached sagebrush rangeland under simulated rainfall and concentrated flow conditions

Author
item Polyakov, Viktor
item Williams, Christopher
item JOHNSON, JUSTIN - N3b Los Alamos
item PHELPS, ERIN - University Of Arizona
item CHAVEZ, RAVEN - Bureau Of Land Management
item Heilman, Philip
item Rutherford, William
item AL-HAMDAN, OSAMA - Texas A&M University
item Nouwakpo, Sayjro
item HU, JIA - University Of Arizona
item SPAETH, KENNETH - Natural Resources Conservation Service (NRCS, USDA)
item Anderson, Samuel

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/19/2025
Publication Date: 11/25/2025
Citation: Polyakov, V.O., Williams, C.J., Johnson, J., Phelps, E., Chavez, R., Heilman, P., Rutherford, W.A., Al-Hamdan, O., Nouwakpo, S.K., Hu, J., Spaeth, K., Anderson, S.R. 2025. Runoff and soil erosion on woodland-encroached sagebrush rangeland under simulated rainfall and concentrated flow conditions. Catena. 262. Article 109684. https://doi.org/10.1016/j.catena.2025.109684.
DOI: https://doi.org/10.1016/j.catena.2025.109684

Interpretive Summary: The sagebrush steppe of the western US is vulnerable to pinyon and juniper woodland encroachment. These changes alter the plant community structure and hydrological function of the landscape. This study used vegetation measurements and rainfall simulations to evaluate the effect of shrubland-to-woodland transition on runoff and soil erosion. Transition of sagebrush to woodland increased the connectivity of runoff and sediment sources, increased sediment yields 5-fold and promoted rill formation.

Technical Abstract: The encroachment of sagebrush (Artemisia spp.) steppe by pinyon (Pinus spp.) and juniper (Juniperus spp.) (PJ) conifers modifies hydro-ecological functions of hillslopes. This study used rainfall and rill experiments in existing a sagebrush-dominated community (Sagebrush) and an immediately adjacent PJ-dominated community (Woodland) on the same ecological site (R035XY308UT) to evaluate the effects of sagebrush-to-woodland transition at Grand Staircase Escalante National Monument in Kane County, Utah, USA. Fifty-four simula tions were performed on eighteen 12 m2 plots. The goals of the study were to a) quantify soil, hydrological, and vegetation properties on the experimental sites, and b) evaluate how pinyon juniper encroachment into sage brush affects runoff, infiltration, soil erosion, and concentrated flow characteristics. The percentage area of bare soil was similar across the Sagebrush and Woodland sites. However, the Woodland site contained less herbaceous and shrub cover than the Sagebrush site. Biological soil crust cover (37 %) spanned continuous swaths of unvegetated areas in the Woodland site. Tree clusters and intercanopy areas at the Woodland site served different hydrologic functions. The latter was spatially continuous providing efficient overland flow connectivity at the slope scale. The Sagebrush site had a finer vegetation spatial structure with shorter gap distances between plant bases (mean 1.1 m) and greater litter cover (48.1 %), which increased resistance to overland flow and diminished formation of rills. Rill erosion rates measured at 15 L min 1 to 45 L min 1 inflow were ten times greater for the Woodland intercanopy than Sagebrush plots. The total sediment yield from the plots was best correlated with cumulative runoff for all sites (0.77