Natural sagebrush areas recover well from wildfire, OSU study says

Areas dominated by native plants in a sagebrush steppe ecosystem are more likely to return to normal after fire than rangelands invaded by exotic, fire-promoting grasses, according to a new study conducted by Oregon State University researchers.

The study shows that the condition of the site before fire dictates the post-fire recovery of the affected plants, said Lisa Ellsworth, a range ecologist in OSU’s College of Agricultural Sciences who led the research.

“Oregon’s big, destructive wildfires within the last few years have created a public perception that any fire is bad news for the sagebrush steppe,” Ellsworth said. “But it is important to recognize that those fires occurred on sites dominated by invasive plants and grasses that promote frequent, continuous fire, and were often degraded by historical livestock overgrazing.

“Our study reinforces the fact that areas with abundant natural vegetation that evolved with periodic fire do just fine post-fire.”

The findings are published in the Journal of Arid Environments.

The researchers conducted the study at Lava Beds National Monument in northern California, about 50 miles southeast of Klamath Falls. Most natural fires occur there from July to September, when lightning strikes dry, dusty land during the hottest months of the year.

They conducted prescribed fires on three sites. One site was dominated by native perennial grasses and plants such as mountain big sagebrush, and where there had been little historic livestock grazing due to a lava flow. The researchers considered this a “pristine” site.

A second site was notable for historical overgrazing and has been overrun by invasive cheatgrass. A third site was characterized by increased western juniper, which has forced out sagebrush over thousands of acres in the Northern Great Basin. Fire had been suppressed there, as well.

At the pristine site, 65 percent of sagebrush survived following fall prescribed fires and 33 percent survived after spring fires. Secondary shrubs also sprouted post-fire.

It was a different story at the cheatgrass-dominated site. Nearly all of the sagebrush and other shrubs didn’t survive. At the western juniper site, less than 50 percent of trees and shrubs survived, with little re-sprouting.

“This invasive annual cheatgrass forms a continuous fuel source,” Ellsworth said. “It spreads fire much more readily than the native vegetation, resulting in larger and more uniform fires.”

Another notable finding in the study was a seasonal effect of the prescribed fires. The spring fires were more destructive to the native shrubs than the fires in the fall. Fall fires, in contrast, created mosaics of burned and unburned patches with low shrub mortality.

“This is important for managers who are still doing prescribed fire in these places,” Ellsworth said. “In the spring, it can be more damaging to the plants if they are burned while they are actively trying to grow. In the fall, they are done growing for the season and there is a lot of dead material that burns away and doesn’t damage the plant’s growth tissues as much.”

The study was co-authored by J. Boone Kauffman, a senior research professor and ecologist at OSU. The Joint Fire Science Program funded the study. The National Park Service provided access to the sites and organized all prescribed fires.