The benefits of thinning crowded forests and igniting prescribed fires to get rid of the combustible debris that’s left hardly qualify as newly discovered truths.

But recent research led by scientists from the College of Forestry at Oregon State University, besides adding to the evidence that such work helps protect forests from catastrophic wildfires by reducing the fuel load, also shows that in some cases thinning alone can yield tangible advantages even before the managed flames are kindled.

James Johnston, a research associate at OSU, and his colleagues published their findings in Forest Ecology and Management. The study, which looked at years of data from areas in ponderosa pine forests in Northeastern Oregon, “shows that mechanical thinning can moderate fire behavior even in the absence of prescribed fire,” Johnston said.

Johnston and the other researchers, including Julia Olszewski, Becky Miller and Micah Schmidt from the College of Forestry, Lisa Ellsworth from OSU’s College of Agricultural Sciences, and Michael Vernon of Blue Mountains Forest Partners, used computer modeling to predict how fire would behave in areas that were thinned, as well as forest parcels that weren’t.

Their research showed that although fuel on the ground increases for a year or two after thinning, the amount declines thereafter, as does the amount of litter and duff on the forest floor.

The researchers’ findings are important not because they diminish the importance of prescribed fire.

Indeed, Johnston notes prescribed burning “is still a key tool for meeting fuel reduction and fire management objectives in the ponderosa pine forests of the southern Blue Mountains and elsewhere.”

But Johnston also points out that prescribed burning, for a variety of reasons, can take longer to be approved compared with thinning.

“Less than one-fifth of the area treated with mechanical thinning in the southern Blues has also been treated with prescribed fire,” he said. “Prescribed fire has been significantly slowed by budget constraints, local opposition to fire use, and restrictions imposed by COVID-19 response measures.”

Weather can be an impediment, too. Prescribed burning usually is done during spring and fall, but in some seasons it’s either too wet for effective fires, or too dry to light them without the risk of flames getting out of control.

Congress has over the past decade or so allocated more money for projects, including thinning and prescribed burning, in Eastern Oregon and elsewhere. An example is the East Face project, which includes about 48,000 acres of public land from the Anthony Lakes Highway north to the Ladd Canyon area. The East Face project includes thinning — some of which involves trees large enough to be sold to mills — and prescribed burning. Much of the work is along roads and ridgelines and is designed to create fuelbreaks, places where firefighters would have a better chance of stopping a wildfire. In all, Congress has spent more than $17 million between 2012 and 2020 to thin about 215,000 acres in the southern Blues.

The research from Johnston and his colleagues shows this public money is being well-spent, and lawmakers should seek to accelerate the effort.

With climate change leading to longer and often more severe fire seasons, thinning and prescribed burning are more vital than ever.

It’s gratifying to see scientific proof that thinning by itself helps protect forests.

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