How thinning could help prevent wildfires

The rundown on what scientists find actually works to protect forests and homes.
Reducing 'fuel' in forests may protect them from destruction — but may not help local towns. DepositPhotos

This article was originally featured on High Country News.

Western forests are a modern artifact. Gaze upward, and you’ll see needles overlapping needles, blocking out the sky. Peer around, and you won’t see far through the congestion of shrubs, young trees and vines. Look down, and you will see duff, debris and non-native plants. Primeval forests, by contrast, were a patchwork of varying densities, often sparsely populated by leviathan trees lording over a healthy, diverse and fruitful understory.

The strange new state of modern forests makes them more flammable.

Severe wildfire —which kills most of the trees in its path — has increased eightfold in 30 years. The burned forest is often replaced by shrubland, extinguishing a once-magnificent ecosystem.

Decades of scientific research and field practice have landed on a powerful tool for preventing severe wildfire — and helping forests become more resilient to climate change: fuels reduction. This term includes both thinning, the mechanical removal of shrubs and small trees, and prescribed burning, the purposeful introduction of fire under favorable conditions.

Wildfire ecologists almost universally support fuels reduction — especially in forests that used to flourish under frequent ground fires, such as the ponderosa pine forests of the Southwest. There is no sizeable cohort of scientific dissent, but forest managers still struggle to put it into practice. Thinning is the target of prolific misinformation, while nearby residents may see prescribed burning as a nuisance or threat, sometimes with good reason. 

Here’s a brief rundown on fuels reduction, wildfires, and what most scientists think we should do to protect forests and homes:

Thinning is not logging. To its opponents, thinning is a form of “silviculture by stealth,” as wildfire historian Stephen Pyne put it. Pyne, however, says thinning is more like “woody weeding.” Logging, he explained, harvests large, mature trees over large areas, while thinning mostly removes small trees. Logging makes money; thinning almost always costs money. “When you hear something like ‘fuels reduction logging,’ that’s a classic conflation,” said Gavin Jones, research ecologist with the U.S. Forest Service and lead author of a paper on wildfire misinformation published last September in Frontiers in Ecology and the Environment.

Thinning does not make wildfires more destructive. One line of misinformation claims thinning creates “hotter, drier, and windier conditions that favor the spread of flames.” “Yes, but they favor the spread of flames on the surface,” said Pyne, “and that’s where you want it.”

Thinning followed by frequent ground fire is generally beneficial; it promotes nutrient cycling and maintains an open forest structure that won’t get dense enough to invite a crown fire.

Thinning is not a climate change risk. Detractors say thinning contributes to climate change by depleting carbon reserves in the form of forests. That’s not entirely inaccurate, but it overlooks an important point: Forests in need of thinning are already “pretty darn at risk of total loss from wildfire and drought,” said Jones. Thinning sacrifices a portion of the carbon reserves in order to save the ecosystem and the remaining carbon reserves.

Thinning should be followed by prescribed fire. “If you don’t follow it up with the right fire, then it’s worthless, and in many cases may have made it worse,” said Pyne. Thinning and prescribed burning are the one-two punch that will knock out many severe wildfires. Prescribed fires do have drawbacks: They are complicated to plan and execute, they dump unwanted smoke on communities, they’re subject to litigation, and in rare instances they can spark destructive burns. Nevertheless, they are sorely needed, and without them, thinning rarely succeeds. Updated policies, funding and new programs could reduce the risks and increase the use.

The vast majority of scientists approve of thinning, though a quick Google search may seem to show otherwise. Chad Hanson, director of the John Muir Project, is thinning’s most vocal opponent. His opinions have appeared in dozens of news clips, reports, letters to Congress, lawsuits, op-eds, webinars, books and interviews. In 2019, Jones co-authored a paper criticizing Hanson’s methods and conflicts of interest in the journal Frontiers in Ecology and the Environment.

Jones argued Hanson and his coauthors were guilty of unscientific practices, including “mixing science and litigation without disclosing potential conflicts of interest,” “pressuring scientists and graduate students with different research findings to retract their papers,” and “selectively using data that support their agendas.”

In 2021, a group of more than 20 fire ecologists led by Susan Prichard, Keala Hagmann, and Paul Hessburg published a trio of scientific reviews in the journal Ecological Applications, refuting some of the most persistent misinformation about wildfire. In answer to the question, “Are (fuels reduction) treatments unwarranted and even counterproductive?” they argued the evidence was clear: No.

Still, misinformation and confusion surround fuels reduction. For example, thinning, which by definition happens before a burn, is at times conflated with salvage logging, or harvesting mature but dead trees after a wildfire or a disease outbreak. While there are practical and ecological reasons for salvage logging, such as road safety or avoiding future wildfires in downed dead trees, the trade-offs between benefits and ecological detriments are less clear. Many scientists say more research is needed to employ salvage logging for ecological benefit.

“All these decimated towns were not taken out by tsunamis of flame raging through the woods — they were taken out by embers.”

Fuels reduction also has its limits. It can help save forests from obliteration — but it might not protect the towns nestled within them. This is because even low-intensity fires can ignite human-built structures from afar.

“All these decimated towns were not taken out by tsunamis of flame raging through the woods — they were taken out by embers,” said Pyne. “They come in as a kind of blizzard of sparks. Once a house or two gets started, then it spreads structure to structure.” Fuels reduction can help save forests, but saving towns means using fire-savvy construction: ignition-resistant building materials, ember-trapping ventilation systems, and defensible space around structures.

In short, thinning and prescribed fire are critical for preserving Western forests. But they won’t save forests on their own: Climate action is imperative, too.