The LTAR Common Experiment at Walnut Gulch Experimental Watershed

Authors: Heilman, Philip - Phil; ARCHER, S. - Retired Non ARS Employee; Williams, Christopher - Jason; Scott, Russell - Russ; Goodrich, David - Dave; Holifield Collins, Chandra; NAITO, A.,T. - Northern Michigan University; PONCE-CAMPOS, G. - University Of Arizona

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2024
Publication Date: 10/24/2024
Citation: Heilman, P., Archer, S., Williams, C.J., Scott, R.L., Goodrich, D.C., Holifield Collins, C.D., Naito, A., Ponce-Campos, G. 2024. The LTAR Common Experiment at Walnut Gulch Experimental Watershed. Journal of Environmental Quality. 1-11. https://doi.org/10.1002/jeq2.20643.
DOI: https://doi.org/10.1002/jeq2.20643

Interpretive Summary: Woody shrubs and trees are expanding into grasslands, causing negative impacts such as decreasing forage production, deteriorating wildlife habitat for the species that rely on grass, and increasing runoff and erosion. Brush management practices to reduce woody cover by fire, mechanical, or chemical treatments are possible, but may not work well, or last a long time, or have other negative impacts such as encouraging non-native species, in addition to high cost of treatments relative to the value of increased forage. Land managers need tools to prioritize where treatments should be applied. The Walnut Gulch Experimental Watershed, a site in the Long-Term Agroecosystem Research (LTAR) network, has a project to study brush management on creosote, mesquite, and pinyon juniper plant communities. The results will be improved quantification of the impacts of brush management on hydrologic function and the potential for accelerated erosion that can focus limited resources for treatment to those areas at risk of severe degradation.

Technical Abstract: The Walnut Gulch Experimental Watershed (WGEW) Long-Term Agroecosytem Research (LTAR) network common experiment addresses the aspirational practice of Brush Management (BM) to reverse the prevailing condition of Woody Plant Encroachment (WPE) and increase perennial native grass production in the plant community. Across the western U.S. the decision to implement BM includes consideration of management objectives, cost, and the expected impact on a diverse suite of ecosystem services. This common experiment, focused on hydrologic and erosion impacts of BM, aims to inform land management decisions on three major plant communities in the southwestern USA: creosote bush (Larrea tridentata), mesquite (Prosopis velutina), and pinyon juniper (PJ, Pinus and Juniperus spp). On the WGEW applying tebuthiuron pellets to creosote bush increased grass cover and reduced runoff and erosion. The 2016 BM experiment on the Santa Rita Experimental Range (SRER) applied a commonly used herbicide mixture but achieved only 7% mortality on mesquite, probably because of the timing of the aerial application. Experiments manipulating rainfall amount and intensity on plots receiving fire, chemical or mechanical BM treatments on PJ communities aim to improve process representation in simulation models. The deliverables of these BM experiments will be to (i) improve the performance of runoff and erosion models, (ii) enhance our ability to identify areas most at risk from reduced hydrologic function and soil erosion after shrub proliferation, and (iii) better predict how landscapes will respond to BM interventions.