Research: thinning, prescribed burning can make a difference
It was several years after the Carlton Complex fire before Susan Prichard felt she could begin asking scientific questions about how the fire behaved.
“I was honestly so devastated for our community I wouldn’t touch it … and I also honestly didn’t want to be perceived as someone taking advantage of such a bad event,” Prichard said in an interview at her home in Winthrop. “So it took me a while to just kind of be like, yeah the science deserves this set of questions.”
Prichard is a wildfire and forestry scientist with the University of Washington who was living in the Methow Valley when the Carlton Complex Fire burned in 2014. After the fire she had a lot of questions. Did thinning and prescribed burning that was done before the fire help reduce the intensity of the burn? How did winds and topography contribute to the fire’s behavior?
To try to answer these questions, she and her co-researchers did a sort of forensic analysis of the hundreds of thousands of burned acres. They created a multi-layered map of the burn area that combined topography with records from the Methow Valley Ranger District of previous thinning and prescribed burning that had been done since 1995.
Then they combined that data with satellite imagery from before and after the fire that showed the varying degrees of severity of the burn across the entire area.
Prichard says the results, which have just been published in the journal Ecological Applications, are both surprising and hopeful.
Happy to be wrong
Even in the face of high wind days, areas that had been previously thinned and burned by forest managers saw lower fire severity than areas that had not. Before gathering all the data, Prichard had a hunch that the Carlton Complex Fire was so intense that no amount of prescribed burns or thinning could have lessened the force of the flames. She’s happy to report that her hypothesis turned out to be wrong.
“I thought we’d go out there and be like, this is the type of fire where fuel treatments are not really effective,” Prichard said. But when she zoomed in on the days during the fire with high winds and looked at how effective prescribed burning and thinning were on those days compared to days with lower winds, she found that either way, active forest management made a difference.
Wind was a critical factor in the rapid spread of the Carlton Complex Fire. More than half the total acreage burned happened on one fateful day: July 17, 2014 — when winds of more than 33 miles per hour swept down the valley.
“I expected that on the wind-driven fire spread days, fuel treatments were not effective and on the benign weather days they’d be effective. But what we found is even in the wind-driven days they [fuel treatments] were still worth it. They still reduced the fire severity significantly,” Prichard said.
The shape of the landscape also provided clues as to how severely the fire burned. After the fire, Prichard spent a lot of time hiking and mountain biking in the burn area, paying close attention to the slopes and inclines of the valley. She was looking for “wind shadows” — places that are shielded from the prevailing winds that blow through the valley. Her multi-layered map revealed that these areas tended to burn less severely.
Prichard said the “wind shadow” phenomenon became vividly clear to her while exploring an area that burned above Pipestone Canyon, a beloved recreational area for Methow Valley residents and visitors alike.
“The fire had raged up a slope with the wind … and then at the ridge line the embers and heat and smoke traveled to the next ridge, and skipped the leeward slope. Some of the leeward slope burned but it was actually from dropping embers,” she said.
Prichard said those small burns that were ignited by the embers were shielded from the wind and didn’t amount to much. The topography of the landscape had provided a haven from the raging winds that moved the fire rapidly down the valley in 2014. Findings like this could be helpful to forest managers in choosing areas to conduct prescribed burns and thinning to complement these natural “wind shadow” fire breaks.
It’s easy to think that in a time of increasing wildfire frequency and severity, alongside the rise of megafires in recent years, that nothing can be done to mitigate wildfire risk to communities living in fire-prone areas. Prichard says her research provides a silver lining to that evolving story: how we manage our forests can make a difference when it comes to reducing wildfire intensity, even in the face of one of the most catastrophic fires the state has ever seen.
“We don’t have to just throw up our hands in the air and say, ‘These forests are going to go away, it’s all dire.’ We can see that if we restore the role of fire in these ecosystems they can absorb future fires. The investments we do put into forest lands to make them more resilient to future wildfire events pay off.”
As the U.S. Forest Service gears up for another season of prescribed burning, this research is timely. Prichard and the co-authors of her research found that thinning, when combined with prescribed burning, was the most effective treatment in lessening the severity of the Carlton Complex burn. Thinning alone was less effective.
Prescribed fires, or controlled burns as they’re sometimes called, are an increasingly relied-upon method for improving wildfire resilience and forest health in the West. In the Methow Valley, the Forest Service aims to burn 3,000 acres of forest each year, but it has a very short window — in the spring and fall — in which it can accomplish those burns safely. A huge amount of planning goes into each prescribed burn, sometimes taking years of modeling, fuel and forest analysis and permitting to make it possible to conduct a burn.
“What our findings can do is help managers make the case that what they’re doing is effective and it does make a difference and could help them make wise choices about how big of a unit to do and where to put it,” said co-author David W. Peterson, with the Pacific Northwest Research Station of the Forest Service in Wenatchee.
“This research could help them prioritize areas to burn and suggest, if you can only do so much, where are the places with the highest leverage that could really make a difference?” Peterson added.
Promising new science
Federal agencies have averaged $3.7 billion in fire suppression spending annually over the past 15 years. Overall, the Forest Service now spends half its annual budget fighting wildfires, which leaves less funding for fire prevention work.
“We know that the risk of fire is high in our dry forests, and — even scarier — that climate change will continue to increase that risk,” said Amy Snover, director of the Climate Impacts Group at the University of Washington, who was not involved with Prichard’s research. “This terrific new science from Susan Prichard and her colleagues shows a way through the thicket. I hope that forest managers realize that their actions can make a difference — and that they use this new science to ensure those actions make the biggest difference possible in building forest resilience to megafires like the Carlton Complex.”
In a fire-weary community like the Methow Valley, the thought of more fires being set intentionally can sometimes ruffle feathers, and raise valid public health concerns.
Children, the elderly and people with respiratory or cardiopulmonary conditions are at highest risk. Public health experts recommend setting air conditioners to re-circulate indoor air, installing HEPA filters and limiting exertion when air quality is bad.
However, according to research from the University of Montana and the Forest Service Fire Science Lab in Missoula, wildfires release 17 times more smoke, on average, than prescribed burns and because they burn more intensely, wildfires also emit more aerosols and fine particulate matter per ton of fuel burned than prescribed fires
Snover’s parents live in the Methow Valley and she and her family have a home in Pine Forest and visit frequently.
“I know just how awful breathing smoke can be for people’s physical and mental health and for the economic and ecological health of the community itself,” Snover said. “But I also want to see forests regrow after fire, because that’s a public health benefit too. So I’m way more willing to accept the tradeoff of more smoke now for more trees later when I know that it’s not just wishful thinking — there’s science behind it.”