Invasive grass influences on the fire cycle and treatment effectiveness to control their abundance in the Intermountain West

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Many non-native invasive grass species increase wildfire activity and regenerate more quickly than native species. This invasive grass–fire cycle has severe negative consequences for ecosystems, creating a need to understand how different invasive grass species alter fuel characteristics and fire behavior, as well as effective treatments to control their abundance. To address these needs and increase fire and natural resource management preparedness, we performed a review and meta-analysis of recent (1985 to 2023) scientific literature. We focused on the Intermountain West, USA, where six dominant invasive grass species have already transformed ecosystems, including winter annuals—cheatgrass, medusahead, red brome, and Mediterranean grass; and summer perennials—buffelgrass and Lehmann’s lovegrass. Within the 204 selected articles, cheatgrass was the most well-studied species, treatment effectiveness was the most common study type, and more studies addressed fuel accumulation than fire characteristics. While initial reductions in cheatgrass following wildfire were followed by large increases, buffelgrass initially increased and then steadily declined, and other invasive grass species had no significant post-fire changes over time. Chemical treatments were more effective than other treatments for cheatgrass, buffelgrass, and Mediterranean grasses, although medusahead had a greater reduction with chemical treatments compared with the other species. In many cases, treatment effectiveness was enhanced when treatment types were combined or repeat treatments were conducted. Both cheatgrass and medusahead increased to pretreatment conditions within 3 and 5 yr, respectively, although there were no detectable trends for other species. Our results provide comprehensive comparisons of the effect of invasive grass species on fuel and fire characteristics and much needed insight on effective strategies for reducing invasive grass impacts to ecosystems.