Controlled burns combined with thinning projects remain the key to slowing down the plague of town destroying fires, according to a growing body of research.

So don’t freak out if you sniff smoke out in the forest — since the Forest Service is taking advantage of the first dash of winter after a hot, dry fall to burn off debris piles in several national forests.

The Coconino and Apache-Sitgreaves Forests this week sent out notices that they’ll be burning piles of debris on hundreds of acres left by thinning and logging projects near Flagstaff and Alpine — with more to come.

But it will take a lot more fires during the cool, wet months to protect forested communities like Payson and Show Low from the catastrophic wildfires that consumed millions of acres and thousands of homes last year. That includes more than 1,000 homes in the suburbs of Denver that burned over the holidays, thanks to continued drought and 100-mile-an-hour winds.

Several recent studies have showed the value of the combination of forest thinning and prescribed burning that lie at the heart of the revamped Four Forest Restoration Initiative.

Recent studies have shown that some of the devastating fires that raged through Oregon, Colorado and California mostly dropped to the ground when they hit portions of the forest that had been thinned — especially if those thinning projects were followed by prescribed fire.

For instance, the devastating Bootleg Fire in Oregon was racing through the treetops of a dense, drought-plagued forest when it entered an experimental forest managed by the Nature Conservancy, according to one recent study. Forest managers had for years been experimenting with different treatments to reduce tree densities — including thinning projects with and without controlled burns. The wind-whipped Bootleg Fire consumed 415,000 acres, 408 buildings and 342 vehicles. It generated columns of superheated smoke and debris that reached 45,000 feet into the atmosphere. At one point, the fire created a “fire tornado.” The flame lengths reached 200 feet. However, when the fire reached the thinned experimental forest — the flame lengths dropped to about four feet, according to a study by researchers from the University of Oregon. Although the fire burned through the experimental forest and killed many trees, the fire intensity changed dramatically — especially where the forest had been thinned in 2016 and then burned three years later.

The same thing happened when the Wallow Fire in the White Mountains hit an area that had been thinned as part of the White Mountains Stewardship Project. In that case, the dramatic reduction in fire intensity in the thinned area likely saved Alpine and Springerville from destruction.

The Forest Service has been trying to foster large-scale thinning operations in northern Arizona for a decade, seeking to protect both forested communities and vital watersheds from destruction.

The 4FRI planners have abandoned the search for a single contractor that can thin 50,000 acres a year, at no cost to taxpayers. Instead, the new plan calls for relying mostly on existing sawmills, loggers, biomass burning power plants and new industry to thin small-diameter sawtimber on the Coconino, Kaibab and Apache-Sitgreaves forests. The Forest Service would in some cases subsidize removal of the commercially worthless biomass — as well as conduct prescribed burns. That’s the approach the White Mountains Stewardship Project took before 4FRI came along — although the Forest Service provided only a fraction of the subsidies needed to maintain a large-scale restoration effort.

On the Tonto National Forest with its oaks, junipers, pinyons and pine thickets, the new 4FRI plan calls for non-commercial thinning projects and controlled burns, perhaps with the help of partners like the Salt River Project, the National Forest Foundation.

The growing body of recent research suggests such an approach can save towns like Payson and Show Low — as well as the watersheds and reservoirs on which the Valley depends. However, it also means those communities will have to live with prescribed burns on a much larger scale. And that, in turn, means those communities will need to adopt Firewise brush-clearing ordinances and fire-hardening wildland-urban interface (WUI) building codes to survive in a forest with both bigger wildfires and more frequent prescribed fires.

The University of Oregon study published in the journal Forest Ecology and Management demonstrated that thinning alone can dramatically reduce fire intensity and rate of spread — at least in the short term, concluded the team of researchers led by OSU researcher James Johnson, according to a summary of that research on the Science Daily website.

The researchers developed computer models based on observing fire behavior in multiple fire parcels in the seasonally dry ponderosa pine forests of northeastern Oregon — which are similar to the pine forests of Rim Country and the White Mountains.

In the thinned areas, loggers had removed most of the trees up to 20 inches in diameter — similar to the 4FRI prescription. The thinning projects actually led to a buildup of fuel for about two years — mostly the slash and debris left by the thinning. However, fuels then declined as the debris decayed and the dramatic reduction in the number of trees reduced the duff and pine needles that accumulated.

“Our work shows that mechanical thinning can moderate fire behavior even in the absence of prescribed fire,” Johnston said. “That’s good news since prescribed fire on national forests has remained flat over the last 20 years because of shortfalls in U.S. Forest Service capacity, a risk-averse agency culture and regulatory constraints on smoke.”

Prescribed fires sometimes escape control. That happened several years ago in New Mexico when the wind came up unexpectedly and a prescribed fire burned 200 homes. The Forest Service responded by curtailing prescribed fires nationally.

Johnson noted that prescribed fires after the thinning projects did remove a lot of excess fuel. More important, periodic controlled burns kept saplings and brush from again resulting in rising fire danger.

He noted only about 20% of the high risk areas in the forest he’d studied had been treated with prescribed fire. “Prescribed fire has been significantly slowed by budget constraints, local opposition to fire use and restrictions imposed by COVID-19 response measures. But our modeling shows thinning can do a lot on its own in terms of rate of fire spread, flame length and crown fire potential.”

Another study underscored the economic challenge of thinning the forest without a significant investment of taxpayer money — and use of relatively low-cost controlled burns wherever possible.

That’s because thinning projects barely make money without a subsidy to get rid of worthless biomass across 80% of the forest, according to another study published in Forest Ecology and Management.

Even when loggers can process the trees up to 20 inches in diameter, they can’t make much money on a thinning project, concluded University of Oregon researcher Chris Dunn and U.S. Forest Service researcher John Hogland in a study of thinning projects in ponderosa pine forests in Oregon.

The study explains the failure of the Forest Service’s decade-long effort to find a contractor who could build small-wood sawmills and find enough of a market for low-value biomass and still turn a profit, even with the guarantee of 50,000 acres a year.

Contact the writer at paleshire@payson.com

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