Pre-fire grazing and herbicide treatments can affect post-fire vegetation in a Great Basin rangeland

Authors: GORNISH, ELISE - University Of Arizona; GUO, JESSICA - University Of Arizona; Porensky, Lauren; PERRYMAN, BARRY - University Of Nevada; LEGER, ELIZABETH - University Of Nevada

Submitted to: Ecological Solutions and Evidence
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2023
Publication Date: 3/7/2023
Citation: Gornish, E.S., Guo, J.S., Porensky, L.M., Perryman, B.L., Leger, E.A. 2023. Pre-fire grazing and herbicide treatments can affect post-fire vegetation in a Great Basin rangeland. Ecological Solutions and Evidence. 4. Article e12215. https://doi.org/10.1002/2688-8319.12215.
DOI: https://doi.org/10.1002/2688-8319.12215

Interpretive Summary: Cheatgrass (Bromus tectorum) invasion is a critical challenge for managers in the western U.S. We asked whether pre-fire targeted grazing (spring and fall), native plant seeding (seeding rate, seed coating and spatial seeding arrangement), or herbicide could help reduce cheatgrass after wildfire. To address this question, we used a long-term, large-scale experiment in a highly invaded system in the Great Basin, U.S. We found that spring grazing reduced postfire cheatgrass more effectively than fall grazing. Grazing also increased forb biomass. Herbicide overall and in conjunction with grazing reduced cheatgrass and fuel loads. Among seeding treatments, seed mixtures reduced cheatgrass count and cover more effectively than seeding monocultures. However, many seeding approaches resulted in higher cheatgrass dominance and thus higher fuel loads. This work suggests that herbicide and spring grazing treatments applied pre-fire can work to reduce cheatgrass abundance for several years post-fire. However, coupling these typical management approaches with seeding of native grasses does not provide much additional benefit. More research is needed to identify socially and ecologically acceptable prefire management strategies for cheatgrass dominated systems.

Technical Abstract: Management of wildfire associated with spread of the highly invasive annual grass Bromus tectorum (cheatgrass) is a critical need in the western U.S. We investigated the utility of coupling common rangeland management strategies prefire to modify postfire plant community outcomes. We used a long-term, large-scale experiment to test the separate and combined effects of pre-fire targeted grazing (spring and fall), native plant seeding (seeding rate, seed coating and spatial seeding arrangement), and herbicide on postfire plant community outcomes in a highly invaded system in the Great Basin, U.S. We found grazing and herbicide effects were consistent across cheatgrass biomass, count, and cover. Spring grazing reduced cheatgrass more effectively than fall grazing; however, this effect was detected primarily outside of the seeding treatments. Grazing also increased forb biomass. Herbicide overall and in conjunction with grazing reduced cheatgrass and fuel loads. Among seeding treatments, seed mixtures proved more effective than monocultures for reducing both cheatgrass count and cover, particularly when combined with low seed rate. However, many seeding approaches resulted in higher cheatgrass dominance and thus higher fuel loads. This work suggests that effects of pre-fire herbicide and spring grazing treatments in reducing cheatgrass abundance can persist for several years post-fire. However, coupling these typical management approaches with seeding of native grasses does not provide much additional benefit in terms of reducing cheatgrass dominance post-fire. Clearly, more research must be conducted to identify effective socially and ecologically acceptable prefire management strategies of cheatgrass dominated systems.