The LTAR Grazing Land Common Experiment at Walnut Gulch Experimental Watershed

• Published in: Journal of environmental quality 2024-11, Vol.53 (6), p.1037-1047
• Main Authors: Heilman, Philip, Archer, Steven R., Williams, C. Jason, Scott, Russell L., Goodrich, David C., Collins, Chandra Holifield, Naito, Adam T., Ponce‐Campos, Guillermo E.
• Format: Article
• Language: English
• Subjects: Agriculture - methods; Conservation of Natural Resources - methods; Ecosystem; Environmental Monitoring
• ISSN: 0047-2425; 1537-2537; 1537-2537
• DOI: 10.1002/jeq2.20643

The Walnut Gulch Experimental Watershed (WGEW) Long‐Term Agroecosystem 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. Across the western United States, the decision to implement BM includes consideration of management objectives, cost, and the expected impact on a diverse suite of ecosystem services. Maintaining or restoring grass cover will help meet the LTAR sustainable production, economic, and social goals, and averting degradation will meet environmental goals. 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 United States: 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 applied a commonly used liquid herbicide cocktail 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. Ranchers, land management agencies, and watershed conservation organizations will benefit from training and availability of improved tools to focus treatments on areas where greatest net benefits might be realized. Plain Language Summary A common problem in the Southwest is the expansion of shrubs and trees into grasslands. Known as Woody Plant Encroachment, this process can reduce grass for livestock forage, damage habitat of the wildlife species that need grass, and the site may degrade without the protective cover of grass to intercept rain and slow overland flow. We are investigating brush management practices on three vegetation types (creosote, mesquite, and pinyon–juniper [PJ]) to better understand trea