The Sagebrush Cooperative

Management Issues: Fire

Fire is a natural feature of sagebrush vegetative communities. Unfortunately, a change in the natural fire regime is decreasing the extent of sagebrush ecosystems, and wildlife populations that depend on sagebrush are undergoing steep declines because of habitat loss (USGS 2002). Fire suppression, prescribed fire to remove sagebrush, and the invasion of exotic annual grasses, such as Bromus tectorum (cheatgrass), are currently modifying fire regimes in much of the sagebrush steppe biome.

Fire return interval in pre-settlement Wyoming big sagebrush habitat is estimated to have been about 50-100 years (Wright and Bailey 1982). Fire is now more common on this landscape. Post-settlement invasion by annual grasses has provided a dense and continuous source of fuel that extends the season for fires and increases the frequency of fires in the region (USGS 2002). Wyoming big sagebrush recovers slowly from disturbance and frequent fires may eventually eliminate the native sagebrush and facilitate secondary invasion by additional noxious weeds (Cooper 2007). Annual grasses like cheatgrass also change soil nutrients, especially carbon and nitrogen, such that invasive annual grasses are favored over the native vegetation (USGS 2002). Alternatively, in mountain big sagebrush habitat, pre-settlement fire return interval is estimated to have been between 10 and 40 years; much shorter than that of the Wyoming sub-species (Miller 2001, Winward 2004). This mountain sub-species grows at higher elevation, receives more precipitation, exhibits greater vegetation productivity, accumulates more fine fuels and experiences more lightening caused fires. Currently, fire suppression has decreased the fire return interval in mountain big sagebrush habitat, resulting in widespread undesirable changes on the landscape (ODFW 2006). Most mountain big sagebrush-dominated areas were once a mosaic of successional stages, from recently burned areas dominated by grasses and forbes to old sagebrush dominated stands (ODFW 2006). Fire suppression has reduced this diversity and resulted in large areas dominated by older big sagebrush with an understory of invasive annual plants. As a result of this fire suppression and other degrading factors, western juniper encroaches into and further degrades sagebrush communities (Miller et al. 2005, ODFW 2006).

Prescribed fire is often used to control juniper encroachment. However, due to the aforementioned issues regarding the relationship between fire and invasive annual grasses, use of prescribed fire in sagebrush restoration can be complicated (USGS 2002). Prescribed fires tend to raise levels of nitrogen for two to three months following a fire. Prescribed fires are also typically conducted in fall; timing which tends to increase the seed production of annual grasses such as cheatgrass (USGS 2002). Additionally, some sagebrush habitats, such as low sagebrush communities, are extremely slow to recover from fire disturbance (ODFW 2006).

When reintroducing fire into fire-suppressed sagebrush, sites should be carefully evaluated to determine if prescribed fire is appropriate and caution should be used in low productivity low sagebrush sites where recovery times are prolonged (Miller et al. 2005, ODFW 2006). If fire is determined to be ecologically beneficial, reintroduced natural fire regimes should utilize site-appropriate prescriptions which account for the historic fire regime, as well as area size and vegetation characteristics that affect resiliency and resistance to disturbance (ODFW 2006).