Nearly 45% of historic sagebrush ecosystems in the Great Basin – 200,000 square miles of California, Idaho, Nevada, Oregon, Utah and Wyoming – have been lost to invasive plants, grasses and wildfires, according to the federal Bureau of Land Management.
To slow the frequency and severity of such fires, scientists at Oregon State University undertook a 10-year study of the long-term effects of popular fire prevention and mitigation methods to see which ones were successful over many years, and which only had short-term impacts.
In a new report published in the scientific journal Ecosphere, those scientists concluded that thinning vegetation across the sagebrush landscape was the most effective, long-term method for mitigating wildfire spread and severity. Other methods, such as prescribed burns and the use of herbicides to kill non-native grasses and invasive tree and shrub species were only effective in the short term.
The OSU scientists teamed up with specialists from Great Basin states, including Eva Strand, a professor of rangeland ecology and management at the University of Idaho. She said studying this over a decade gave scientists a broader perspective.
“A treatment might be followed for a couple years, but there’s no looking at the long-term response,” she said. “With this, we could see for how long these methods are effective in mitigating wildfire.”
The scientists didn’t ignite fires but used computer models to study how each treatment – thinning, herbicides or prescribed burns – could impact the speed of a fire’s spread and the height of the flames. In their study, the scientists found that herbicides left behind dead vegetation that could create hotter fires with higher flames. They found prescribed burns were effective short term, but long term, invasive grasses quickly returned and re-established themselves, creating a greater fire risk.
Strand said their findings will also impact firefighter safety in a wildfire.
“We were able to model how they actually impact fire behavior,” she said. “We can tell which methods create shorter flame lengths, so firefighters can approach it in a different way.”
Oversight by Bureau of Land Management
The bulk of sagebrush ecosystems in the Great Basin are overseen by the federal Bureau of Land Management, which is currently involved in a project to create fuel breaks along 435 miles of roads throughout sagebrush habitat along the Oregon-Idaho-Nevada border in the Great Basin. These are areas where BLM is reducing vegetation like grasses and trees in order to reduce the probability of a fire spreading and growing in height.
The scientists hope their research can inform the methods the agency adopts to create those fuel breaks.
“We need to be implementing strategies that preserve our good condition sagebrush steppe areas and get ahead of this invasive grass and fire feedback cycle that we’re in,” said Lisa Ellsworth, lead author of the study and a range ecologist at OSU, in a statement.
Ellsworth said that sagebrush ecosystems are among the most fragile ecosystems on the North American continent.
“I feel the pressure of time in these systems,” she wrote.
Sagebrush wildfires historically occurred, on average, every 50 to 100 years, according to the report. During the last few decades, because of climate change and the proliferation of invasive grasses, trees and shrubs, like pinyon juniper, that rate has doubled.
Jeff Fedrizzi, is the Oregon and Washington fire management officer for BLM. He said BLM is creating the fuel breaks in the Great Basin using prescribed burns, herbicides and thinning depending on the specific site.
Because of above average rainfall throughout much of the state, “We are starting to see a grass crop that we haven’t seen for years,” Fedrizzi said. “We manage millions and millions of acres. This is a marathon, not a sprint, to treat all this.”
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