Prescribed Burning: an Overrated Strategy

A Forest Service employee lighting a prescribed fire on the Deschutes National Forest, Oregon. Photo George Wuerthner.

The Deschutes National Forest plans to ramp up prescribed burns across Central Oregon. However, the Forest Service exaggerates the presumed benefits of prescribed burning and ignores the problems.

One of the most important issues is that  most wildfires never encounter a fuel reduction, whether from thinning or prescribed burns. So, even if prescribed burns were effective, fires seldom occur in treated areas.

Second, the burn must be repeated every few years—forever to be effective. By removing competing vegetation, plant regrowth is rapid. Often, within a few years, there is as much or, in some cases, even more burnable biomass than before any prescribed burn.

For example, one study conducted in California Sierra Nevada found that within two years after a spring season burn, the herbaceous vegetation in the prescribed burn area did not differ from non-burned controls.

Creating more fine fuels like grasses, shrubs, and small trees exacerbates the spread of fire.

Thus the effectiveness of a prescribed burn depends on the time since its ignition, and the regrowth of plant material quickly negates its usefulness. Hence, communities will experience the harmful effects of smoke every year, even though the likelihood of a significant fire and attendant smoke may not occur in that locality for years.

For instance, in 2023, prescribed burns burned  8,950 acres.

Third, it’s essential to question the belief that Indian burning kept fuels low and contributed to “healthy forests’. This notion can be considered an urban myth.

Numerous studies have shown that Indian burning was primarily local, typically around village sites and other high-use areas, raising doubts about its effectiveness in reducing wildfires across the landscape.

Large blazes are recorded even when Native Americans occupied the landscape and were presumably active in cultural burning. A study in the Siskiyou Mountains of northern California and southern Oregon examining a 2000-year sediment record found that 77% of 68 major fires occurred before Euro-American settlement.

For instance, a study done by Cathy Whitlock in the Willamette Valley of Oregon, which had some of the densest Native American populations in the West, concluded: “The idea that Native Americans burned from one end of the valley to the other is not supported by our data … Most fires seem to have been fairly localized, and broad changes in fire activity seem to track large-scale variations in climate.”

Advocates of native burning typically suggest that cultural burns keep forests healthy. One has to ponder how ponderosa pine, which thrived as a distinct species for over 55 million years, managed to maintain its health all those millions of years before humans arrived less than 20,000 years ago.

At a landscape-scale influence, there is no evidence that Indian fires kept the forest “healthy” or reduced large-scale wildfires.

Fourth, fuel reductions may work to reduce or slow fires under ordinary fire weather conditions but are ineffective during the 1-2% of the time when large wildfires occur. These blazes are dominated by extreme fire weather conditions, particularly ignition with high winds.

For example, from 1970 to 2002, on U.S. Forest Service lands, 1 percent of all fires burned 97.5 percent of total area.

Wind is critical to all large blazes. Wind fans the flames by delivering a crucial component – oxygen – to a fire and directing the fire’s spread. High winds cause flames to heat and eventually ignite vegetation in front of it. They often carry embers to unburned areas, starting a spot fire. Extreme heat and sun will accelerate the drying of fuels, making them easier to ignite.

Under such extreme fire weather conditions, high winds loft embers through and over-prescribed burns. A 2023 paper that reviewed the “beneficial effects” of prescribed burning admits: “Under the most extreme conditions, even the best treatments may fail to prevent high-intensity fires with the potential for substantial impacts on both the ecosystem and human welfare.”

Extreme fire weather conditions cause unstoppable wildfires like the Holiday Farm, Bootleg, Ceder Creek, Eagle Creek, and other recent large Oregon conflagrations, which in one way or another have significant natural or human fuel reductions.

For instance, the Holiday Farm blaze raced down the McKenzie River, burning through and over numerous clearcuts. With the aid of high winds, the Eagle Creek blaze even crossed the mile-wide Columbia River to start ignition on the Washington side of the river.

If the barrier created by a large river won’t stop a blaze, how can anyone other than someone delusional believe that removing a small portion of the fuel with logging or burning can prevent or control a blaze?

Finally, a philosophical issue with these Forest Service fuel reduction efforts is their inability to see the forest through the trees. The agency and most researchers start by assuming that large, high-severity blazes, where most trees may be killed, damage the landscape, and must be significantly reduced, if not eliminated. However, some researchers find stand replacement blazes critical to forest ecosystem health.

After such high-severity blazes, there are mushrooms, more birds, butterflies, bees, small mammals, and even more fish in streams where the logs from the wildfire create habitat.

Snag forests and the resultant downwood store carbon for decades and centuries.

Another concern is that prescribed fires can sometimes escape containment. Prescribed burns in New Mexico triggered two major blazes in 2022, including the Hermits Peak-Calf Canyon Fire, the largest in state history.

Due to these limitations and issues, the Forest Service and governmental authorities should reconsider their strategies in an era of climate warming. To the degree that prescribed burns are implemented, they should be located near the margin of communities and burned every few years. If you can’t guarantee burning, it is better not to do them.

However, the federal strategy of “active forest management,” including forest thinning and prescribed burning, is a less effective way to protect communities. A study in California analyzed the effectiveness of Home Ignition Zone (HIZ) characteristics for about 40,000 California buildings exposed to wildfire between 2013 and 2018 to determine the most critical features in preventing structure loss. After sorting the buildings into “survived” (about 10%) and “destroyed” (about 90%), statistical comparisons of the two groups showed that “hardened home” details were most strongly associated with surviving wildfire across California during the period of study.

We need more wildfire in our ecosystems, but the idea that prescribed fire emulates natural wildfire ignitions and will significantly reduce the acreage burnt under extreme fire weather conditions is questionable.

Lastly, even the largest blazes are essentially burnt at low severity. In dry forests that historically experienced low- and moderate-severity fires, these severity levels accounted for roughly 75 percent of the acres burned during the 1985–2010 period. In other words, one large blaze reduces fuel more at low severity than dozens of prescribed fires.

George Wuerthner has published 36 books including Wildfire: A Century of Failed Forest Policy