How to save a forest by burning it

An afternoon pile burn at the Blodgett Forest Research Station in Georgetown, California, May 13, 2022. (Andri Tambunan/The New York Times)

GEORGETOWN, Calif. — Waves of fire swept through the Sierra Nevada forest, spewing smoke and leaving behind charred vegetation — all under the watchful eye of a heavy-duty drone. Instruments around the perimeter grabbed samples of particles that were thrown into the air.

Prescribed burning, an age-old practice that rids forests of small trees, brush and other matter that can’t fuel fires, is getting a 21st-century upgrade.

With climate change drying out the land and increasing wildfire risks, scientists are beginning to use cutting-edge technology and computer modeling to make controlled, low-intensity burns safer, more efficient and less disruptive to nearby communities.

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“Fire has made us civilized, but we still don’t fully understand it,” said Tirtha Banerjee of the University of California, Irvine, as she watched a tall pile of dead tree limbs burn.

As useful as prescribed burns can be for forest conservation, they are difficult to implement — expensive, labor-intensive, dependent on narrowing windows of favorable weather. And even well-planned burns can turn disastrous, as when a fire started by the U.S. Forest Service this spring was turned by gusty winds into New Mexico’s largest wildfire on record.

Scientists believe we can do better. Several groups recently gathered at the Blodgett Forest Research Station northeast of Sacramento, California, an area thick with towering ponderosa pine, Douglas fir and incense cedar. A planned burn in Blodgett was a valuable opportunity to collect data in the field, and researchers packed loads of equipment, including GoPro cameras, drone-mounted sensors to map the terrain in minute detail, an sonic anemometer to measure wind, and a variety of machinery which collected suspended particles.

While researchers have long developed advanced techniques to examine wildfire behavior, fewer have looked at questions specific to prescribed fires, such as whether debris should be removed with chainsaws and bulldozers in advance, said Robert York, a forest ecologist. at the University of California. Berkeley.

Preemptive thinning could allow more wind to flow through during a burn, producing hotter flames and making the flame more difficult to control. But it can also help the burn consume more of the remaining forage, creating a long-lasting fire buffer.

“For prescribed fire, I think it’s really all out there to explore,” Banerjee said.

When Prometheus stole fire from the gods and gave it to humans, he probably had no idea how difficult it would be to handle on a planet heated by burning fossil fuels.

Global warming has brought more of the extremely hot and dry conditions that can turn wildfires into deadly disasters. Flames as wild as last year’s Dixie fire, which burned nearly 1,563 square miles of Northern California, weren’t part of the picture for scientists half a century ago when the Forest Service and other agencies first developed their math models to predict how fires spread.

Scientists “were just completely unaware of how quickly things are changing,” said James T. Randerson, an earth scientist at the University of California, Irvine.

The Forest Service has acknowledged that its methods are failing to keep pace as the planet warms. The agency’s investigation into the unfortunate spring burn in New Mexico found that, although properly planned, the resulting fire proved more dangerous and fast-moving than expected.

To help land managers learn how to burn in increasingly unstable landscapes, J. Kevin Hiers, a fire scientist with the US Geological Survey and the Tall Timbers Research Station in Tallahassee, Florida, has spent years working with other researchers to the fire equivalent of flight. simulator — a video game-like training system that would be “a Minecraft-type experience for burnt bosses,” as Hiers calls it.

Better fire modeling is important, but so is baking that knowledge into easy-to-use tools for burn crews, he said. “We should be able to represent, in a training environment, what the fire should or can do in a very complex way, long before we hit a match.”

For the scientists who traveled to Blodgett Forest, their first two days on site were spent setting up equipment and carefully surveying the landscape before it went up in flames—something that would have been impossible if they were trying to study a fire.

Banerjee and his team of graduate students and postdoctoral researchers repeatedly flew their drone over the area, mapping it with lidar, a technology for taking detailed 3D images. a thermal camera; and a multispectral camera, which told them how dry the brush was. By comparing images from before, during and after the burn, Banerjee’s team could pinpoint exactly how the fire had transformed the forest.

In the evenings, Banerjee’s team would burn small piles of dead wood and shoot GoPro videos of the flickering flames and embers rising into the air. The footage would help the team study how embers travel, which could reveal how the fires spread out of control.

In another patch of woods, Randerson and Audrey Odwuor, a doctoral candidate at Irvine, placed branches and pine needles in Ziploc bags, as if collecting evidence from a crime scene. They planned to burn the material back to their lab to analyze the chemical composition of the resulting emissions. They had also brought instruments to Blodgett to collect smoke samples. Someday, Odwuor said, such methods could help assess how efficiently a prescribed fire had burned through the fuel it was supposed to get rid of.

York, who works for much of the year at Blodgett, led searchers to an area of ​​the forest that he said hadn’t burned in three years. Burning now would help keep the plot in a healthy, natural state, even if all the planning, coordination, and effort involved was anything but natural.

The morning of the burn was sunny and warm. The searchers donned flame-resistant shirts and hard hats, and York, as the burn boss, led the team into an area of ​​high ground. He lowered his torch and a thin stream of fuel ran out and caught the flame in the torch wick. A mouth of fire sprouted from the dead brown ground. The burn had started.

York and a small, experienced crew walked perpendicular to the forest slope, using their torches to draw lines of flame that burned uphill. The landscape quickly transformed. Tall trees cast gauzy, dramatic shadows on curtains of whitish-gray smoke. Thick fog scattered the sunlight, bathing the forest in a deep orange glow. The crackle of burning bushes mingled with the low mechanical whine from the drone overhead.

For a while, the flames had a soft, almost elegant quality. the vegetation was too wet to burn very strongly. But as the day warmed, the fires began to blacken the hillsides at a rapid clip. The scientists entered the scene cautiously as their machines collected data.

By late afternoon, York and his team had burned about 13 acres and sat down for a breather. His face was shiny with sweat and dirt. The forest fell silent around him.

Randerson took a moment to marvel at the brutal raw power of the fire they were studying—a natural, yet unnatural way of protecting the earth. “The older I get,” he said, “the more I appreciate how much science is like art.”

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