A recent Bend Bulletin Editorial repeated the numerous misconceptions about prescribed burning. The commentary suggested that more prescribed burning would reduce smoke in Bend during the summer months.
While I agree that less smoke would be a great outcome, prescribed burning will not accomplish that for several reasons.
First, much of the smoke we experience in Bend is not of local origin. Smoke can drift thousands of miles from its source, and often, the smoke we get in Bend originates in Canada, Idaho, Montana, California, and other locations hundreds to thousands of miles away.
A good example of how smoke drift can affect air quality was in June of 2023 when New York City had the worst air quality of any place in the world! This was due to smoke from Canadian wildfires hundreds of miles away.
The Milli Burn on the Deschutes NF near Sisters Oregon raced across the landscape driven by high winds, and drought conditions. Photo George Wuerthner
A second reason prescribed burning is not a panacea for smoky skies is the limited nature of such burns. Climate controls wildfires far more than fuel reductions.
For instance, in 2023, when the Cascades experienced higher precipitation the previous winter and spring, only 44 acres were burned on the entire Deschutes National Forest. In other words, there was no smoke from local sources that summer.
Smoke from Pole Creek Fire obsures Green Lake in Three Sisters Wilderness, Photo George Wuerthner
Therefore, Bend may experience more smoke from prescribed burns in some years than from local wildfires.
A third reason prescribed burning may not reduce smoke is probability. Studies have shown that few wildfires encounter fuel reductions, whether resulting from thinning the forest or prescribed burns. Indeed, the percentage is often as low as 1% of all wildfires touch a fuel reduction project. So, most of these fuel reductions do nothing to alleviate wildfire smoke, but they have significant ecological and other collateral damage.
Regrowth of grass after prescribed burn creates more “fine” fuel that is flammable than prior to the burn. Photo George Wuerthner
A fourth reason prescribed burning fails to reduce local smoke is that burning shifts the plant community from shrubs and small trees to grass, which is far more flammable than the plants reduced by burning.
This was burned two years before I took this photo. Note that there is tremendous regrowth of flammable grasses and other biomass. Photo George Wuerthner
As a study on fast-moving fires concluded:
“It is also known that invasive grasses can drive increases in size, occurrence, and frequency. Because grass-fueled fires are some of the fastest, it may follow that fire speed may have also increased where vegetation transitions have occurred, for example, from forest or shrubland to invasive grassland.”
Regrowth of flammable grasses two years after a prescribed burn in this area. Deschutes NF, Oregon. To be effective, burning must be repeated frequently and forever. Photo George Wuerthner
It typically takes 2-3 years for the flammable biomass on a site to return to or exceed the amount of fuel before a prescribed burn. Thus, prescribed burning can enhance fuels and fire probability unless repeated every year or two.
Since the Forest Service seldom revisits the prescribed burn areas in which it has previously burned, the positive impact of fuel reduction, if it works at all, is transitory at best.
Most wildfires are small, burning less than a few acres. Photo George Wuerthner
First, this leads to the issue of prescribed burn effectiveness. Under most weather/climate scenarios, most wildlife are small, frequently burning less than an acre. These smaller fires account for as much as 99% of all ignitions but affect a tiny fraction of the landscape.
By contrast, under extreme fire weather conditions, particularly with high winds, almost nothing stops or slows a wildfire. Wind can blow embers miles ahead of any fire front and jump over, around, or through a prescribed burn site.
Most of the area burned in extremely large events is from the growth on a single day, which is driven by extreme fire weather.
One Forest Service study concluded:
“Extreme environmental conditions…overwhelmed most fuel treatment effects. . . This included almost all treatment methods, including prescribed burning and thinning. .. Suppression efforts had little benefit from fuel modifications.”
These “red flag” wildfires often account for less than 0.1% of all wildfires but are responsible for most acreage charred annually. So, the very fires that fuel reduction advocates hope to reduce or control are the very fires that do not respond to fuel reductions.
As a 2023 study found:
“fuel reduction appears ineffective since <1% of the treated area encounters fire each year and fires are still increasing…”
For all the above reasons, prescribed burns are unlikely to reduce summer smoke. They guarantee smoke conditions throughout the year, making it harder to avoid. For people with asthma and other breathing conditions, the presence of smoke for six months or more of the year makes living in Bend unacceptable.
Despite all of the above limitations, prescribed burns have a role. They should be strategic and immediately adjacent to communities. They must be repeated annually or bi-annually to keep fuel from regrowth. And they should be viewed as part of a more significant effort to harden communities against wildfire.
Unfortunately, if we fail to address climate warming, we can expect more wildfires around the West and, of course, the attendant smoke.
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