At Wilder Ranch outside of Santa Cruz, the fire starts slowly. Forest managers clad in yellow protective gear use drip torches to light the grass, still damp from the previous day’s rain. Huge columns of smoke quickly obscure the sun and ash rains down. At first it smells like a campfire, but soon the smoke is choking, even as the breeze carries it toward the Santa Cruz Mountains.
Prescribed burns, used to limit destructive wildfires, are growing in frequency at California State Parks. But as the smoke swirls around the firefighters and drifts into neighboring residential areas, it’s easy to see why many Californians are concerned about the health impacts of deliberately set fires.
“I have asthma. My eyes were burning, my lungs were burning, it wasn’t affecting me kindly,” said Michael Brokaw, who lives in Scotts Valley, 6 miles from the Wilder Ranch burn. “I couldn’t go outside.”
FILE – Hikers make their way along a path on the ocean side of Highway 1 at Wilder Ranch State Park as a thick cloud of smoke rises from a prescribed burn at an inland section of the park. (Shmuel Thaler/Santa Cruz Sentinel)
Few studies have directly compared the effects of breathing smoke from wildfires and prescribed burns. But preliminary findings indicate that deliberate burns are less dangerous, partly because they burn less intensely and over a shorter period of time — and those living nearby are typically notified in advance.
Prescribed burns also seem to contain lower concentrations of harmful particulates, the microscopic matter in our atmosphere, and are less likely to contain toxic chemicals released when a wildfire engulfs everything in its path.
Still, breathing any smoke is bad for you.
“You’ll quickly find that if you breathe smoke, it hurts,” said Josh Dougherty, a forestry aide with California State Parks, who helped light the fire at Wilder Ranch.
Californians are going to have to get used to smoke, as state and federal agencies fight fire with fire in an effort to reduce the accumulated vegetation that — together with drought and a warming climate — has fueled the intense wildfire seasons of recent years. In January of 2021, the California Wildfire and Forest Resilience Task Force outlined a goal of using prescribed fires on 400,000 acres across the state annually by 2025, compared to about 50,000 acres in 2023.
“You have to understand that [fire] is a part of California’s forest history,” said task force director Patrick Wright. Low-intensity fires used to burn almost constantly in California, which prevented larger all-consuming fires, he said. Indeed, the 400,000-acre target for prescribed burns is just a small fraction of the area that burned in California each year in the days before European colonization — one study put that figure at more than 4.5 million acres.
Prescribed burns can also help preserve vulnerable ecosystems such as the rare coastal prairies at Wilder Ranch. Without fire, bushes can quickly crowd out the more fragile grasslands and the species they support.
“I can’t make it rain, but I can use prescribed fire,” said Tim Hyland, senior environmental scientist for California State Parks. “It’s the most powerful landscape tool we have.”
FILE – A California State Parks employee maintains a vigilant presence on the Eucalyptus Loop at Wilder Ranch State Park on Nov. 3, 2022 as State Parks began five weeks of prescribed burns. The fires were part of the state’s program for vegetation management, hazardous fuel load reduction and wildlife habitat improvement. (Shmuel Thaler – Santa Cruz Sentinel)
Another advantage is that exposure to smoke can be reduced when people are alerted to prescribed burns in advance — although the process is far from perfect, as Brokaw’s experience demonstrated. He said he had no idea the prescribed burns were planned at Wilder Ranch this fall. It took him four phone of calls, including to 911, to find out why smoke was blanketing Scotts Valley. “Their communication with the community is awful,” Brokaw said.
Eventually, his calls brought him to Hyland, who manages prescribed fires on State Parks lands in Santa Cruz County. He was able to give Brokaw an explanation, and even warn him ahead of time before the next burn on the property.
Hyland said the online prescribed fire schedule for Santa Cruz County is updated regularly. News releases also go out to local daily news outlets in advance of a burn.
With prescribed burns on the rise, in April 2022 the American Lung Association and PSE Healthy Energy, a nonprofit research institute based in Oakland, released a report assessing the health effects of wildfires and prescribed burns. “While prescribed fire may also result in harmful smoke exposure, the overall air quality and health impacts are estimated to be lower than that of wildfire smoke,” the report concluded.
All smoke carries tiny particles known as PM2.5, less than 2.5 microns in diameter — or about a fiftieth the thickness of a human hair. They can permeate deep into the lungs, causing microscopic tearing and inflammation. Even brief exposure to PM2.5 can trigger asthma attacks and increase hospital admissions for heart or lung disease. Children and older adults with preexisting heart or lung conditions are especially vulnerable.
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In 2019, a team led by Mary Johnson, then at Stanford University, published a study of children in Fresno, who had blood drawn three months after being exposed to either smoke from a wildfire or a prescribed burn, each about 70 miles away. Levels of PM2.5 and other pollutants in Fresno were lower for the prescribed burn. The blood samples also revealed that the children exposed to wildfire smoke had fewer of an important type of cell involved in healthy immune responses compared to those exposed to smoke from a prescribed burn.
“A prescribed burn is done slowly and with more control, so you’re not going to reach the same levels of PM 2.5 as you would with one of these out-of-control wildfires,” said Johnson, who is now at Harvard University.
That’s because fire managers purposefully burn at low intensities and on days when the wind is least likely to carry smoke into heavily populated areas. In another study, scientists estimated the exposure of people to elevated levels of PM2.5 from fires that burned in the central and southern Sierra Nevada from 2010 to 2016, based on satellite observations of their smoke plumes. Per acre burned, they found that prescribed burns caused about 64% less harmful exposure than low-intensity wildfires, and 93% percent less than high-intensity wildfires.
Unless they get out of control, prescribed burns should consume only natural vegetation–and hopefully prevent exposure to something more dangerous.
“The challenge of wildfire is that it consumes anything in its path. It creates this toxic stew, and we can’t place what’s in that smoke. It could be chemicals, metal, plastic, anything,” said Will Barrett, national senior director of advocacy and clean air with the American Lung Association. “Smoke is bad to begin with, but with these additions, it’s far worse.”
