Expansion and dominance of the highly flammable invasive annual grass, cheatgrass (Bromus tectorum), is transforming native sagebrush ecosystems in the western United States. Invasion is often facilitated by fire, including prescribed fires intended to restore shrub-dominated landscapes. Fire-induced cheatgrass invasion does not occur in all landscapes, however, resulting in a pressing need to understand the ecosystem attributes associated with susceptibility to invasion and to identify appropriate management responses.
In this Demonstration Project, we implemented landscape-scale prescribed burns to examine long-term plant community responses to fire and post-fire seeding treatments in sagebrush ecosystems containing a gradient of pinyon and juniper cover. A Joint Fire Sciences Program Demonstration Area was established in 2001 in Underdown Canyon, a west-to-east draining watershed on the Humboldt-Toiyabe National Forest in the Shoshone Mountains of central Nevada. The study used three pairs of adjacent alluvial fans, distributed along an elevational gradient ranging from 2073 m to 2347 m. One fan in each pair was burned by the USDA Forest Service in 2002 and the other remained unburned (control). Post-fire seeding treatments were located within the burned plots, and included unseeded, seeded with a functionally diverse mix of native perennial species, and seeded with a conventional mix of non-native perennial grass species. We asked (1) how long-term ecosystem resistance to fire-induced cheatgrass invasion varies along major abiotic and biotic gradients, and (2) whether post-fire seeding of perennial species promotes perennial plant establishment and increases resistance to invasion.