How to save a forest by burning it down

GEORGETOWN, Calif. Waves of fire swept through the Sierra Nevada forest, kicking up smoke and leaving charred vegetation, all under the watchful eye of a high-powered drone. Instruments around the perimeter took samples of the scorched particles that were thrown into the air.

Prescribed burning, an ancient practice that removes small trees, brush and other matter that can fuel wildfires, is getting a 21st-century update.

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

“Fire has made us civilized, but we still don’t fully understand it,” said Tirtha Banerjee of the University of California, Irvine, looking at a tall pile of dead burning tree branches.

As useful as prescribed burns can be in maintaining forests, they are difficult to carry out: they are expensive, labor-intensive and dependent on shrinking windows of favorable weather. And even well-planned burns can turn disastrous, as when a fire started by the US Forest Service this spring was transformed by gusty winds into the largest wildfire on record in New Mexico.

Scientists think we can do better. Several teams recently met at the Blodgett Forest Research Station, northeast of Sacramento, an area filled with towering Ponderosa pines, Douglas firs and frankincense cedars. A planned burn at Blodgett was a precious opportunity to collect data in the field, and researchers loaded up equipment, including GoPro cameras, drone-mounted sensors to map the terrain in detail, a sonic anemometer to measure wind, and a variety of machines. that collects particles in the air.

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

Preemptive drawdown could allow more wind to pass during a burn, producing hotter flames and making the flames more difficult to control. But it could also help the burn consume more of the remaining forage, creating a longer-lasting buffer against wildfires.

“I think that in the case of prescribed fires, everything remains to be explored,” said Dr. Banerjee.

When Prometheus stole fire from the gods and gave it to humans, he probably didn’t imagine how complicated it would be to manage on a planet heated by burning fossil fuels.

Global warming has brought more extremely hot and dry conditions that can turn wildfires into deadly catastrophes. Blazes as ferocious as last year’s Dixie Fire, which scorched nearly a million acres 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 mathematical models to predict how wildfires spread.

Scientists have been “totally blown away by 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 not up to the task of global warming. The agency’s investigation into the unfortunate spring fire in New Mexico found that, despite being well planned, the resulting fire turned out to be more dangerous and quicker than anticipated.

To help teach land managers how to burn in increasingly volatile landscapes, J. Kevin Hiers, a fire scientist with the United States Geological Survey and the Tall Timbers Research Station in Tallahassee, Fla., has spent years working with other researchers on the fire equivalent of a flight simulator: a video game-like training system that would be “a Minecraft-like experience for burned-out bosses,” as Dr. Hiers calls it.

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

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

Dr. Banerjee and his team of graduate students and postdoctoral researchers flew their drone repeatedly over the area, mapping it with lidar, a technology for capturing detailed three-dimensional 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, Dr. Banerjee’s team was able to pinpoint exactly how the fire had transformed the forest floor.

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

In another patch of woods, Dr. Randerson and Audrey Odwuor, Ph.D. candidate in Irvine, he placed twigs and pine needles in Ziploc bags, as if he were gathering crime scene evidence. They planned to burn the material in their laboratory to analyze the chemical composition of the resulting emissions. Instruments had also been brought to Blodgett to collect smoke samples. One day, Ms Odwuor said, such methods could help assess how effectively a prescribed burn had burned the fuels it was supposed to get rid of.

Dr. York, who works much of the year at Blodgett, led investigators through an area of ​​forest that he said had not burned in three years. Burning now would help keep the plot in a healthy, natural state, even if all the planning, coordination, and effort that went into it were anything but natural.

The morning of the burn was sunny and hot. Investigators donned fire-resistant shirts and helmets, and Dr. York, as chief burn officer, led the group to an elevated area. He lowered the drip torch, and a thin stream of fuel spewed out and caught the flame in the torch wick. A wisp of fire erupted from the dead brown ground. The burning had started.

Dr. York and a small experienced team walked perpendicular to the forest slope, using their torches to draw lines of flame burning up the slope. The landscape was rapidly transformed. Tall trees cast dramatic, diaphanous shadows on the whitish-gray curtains of smoke. A dense mist scattered the sunlight, bathing the forest in a deep orange glow. The crackle of burning bushes mingled with the low mechanical whine of the buzz from above.

For a time, the flames had a meek, almost delicate quality; the vegetation was too wet to burn very fiercely. But as the day heated up, fires began to blacken the slopes at a rapid rate. Scientists watched the scene warily as their machines collected data.

By late afternoon, Dr. York and his team had burned about 13 acres and sat down to take a breather. His face was slick with sweat and grime. The forest burned around him.

Dr. Randerson took a moment to admire the raw, brutal power of the fire they were studying, a natural, but also unnatural, way of safeguarding the earth. “The older I get,” he said, “the more I appreciate how much science is like an art.”

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