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

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 pre‐fire to modify post‐fire 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 (glyphosate followed by 2 years of imazapic) on post‐fire 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. 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 for reducing cheatgrass abundance can persist post‐fire. Grazing, however, might not produce consistent results, and season of grazing can affect outcomes. Employing pre‐fire management strategies to interrupt the cheatgrass‐fire cycle may have utility. Some of our treatments were able to reduce cheatgrass abundance after fire, but despite our intensive interventions, we did not find a strategy that led to full restoration of native perennial species.

Ecological benefits of strategically applied livestock grazing in sagebrush communities

“…Similarly, when compared with short‐term (5 years) grazing exclusion, moderate off‐season grazing before fire also reduced postfire invasive annual grass biomass and density and maintained plant community diversity (Davies, Bates, Boyd, et al, 2021). In northern Nevada, targeted applications of spring grazing for two years prefire also led to reductions in invasive annual grass biomass and densities measured two years postfire (Gornish et al, 2023). As mentioned in prior sections, the accumulation of dry fuels near the meristematic tissue in ungrazed communities likely increases the probability of fire‐induced mortality of bunchgrasses (Davies et al, 2009, 2018).…”