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How Controlled Burns Work

        Science | Matter

Why We Need Controlled Burns
Captain Russell Mitchell with Yosemite Fire monitors a controlled backfire along Highway 120 at the southwestern edge of Yosemite National Park. The 2013 fire was set to keep a wildfire from progressing toward the Big Oak Flat Entrance Station.
Captain Russell Mitchell with Yosemite Fire monitors a controlled backfire along Highway 120 at the southwestern edge of Yosemite National Park. The 2013 fire was set to keep a wildfire from progressing toward the Big Oak Flat Entrance Station.
Don Bartletti/Los Angeles Times via Getty Images

Nowadays, foresters make extensive use of controlled burns, in part of promote healthier forests, but largely to prevent large wildfires. By lighting fires in the right places under the right weather conditions and with fire suppression tools on hand, experts can clear out the combustible understory material that leads to out-of-control wildfires.

But even if controlled burning has the above-mentioned benefits, surely it's bad for the environment. After all, burning releases particulate matter into the air, especially greenhouse gases like carbon. So controlled burning pollutes the air and contributes to climate change, right?

Yes and no. Recent computer modeling studies have shown that wisely deployed controlled burning actually captures more carbon in trees than it releases. That's thanks, in part, to the fact that old-growth trees trap far more carbon than younger, smaller growth. Burning the little stuff helps the bigger stuff last longer and therefore hold onto more greenhouse gas. And, as previously mentioned, controlled burning helps prevent wildfires, which are big, bad emitters of carbon [source: Gearin].

And there are other reasons for controlled burning, too. Back in the 1960s, experts in Yosemite National Park were puzzling over the fact that there were no baby sequoias growing in the shadow of the giant elders. While these titans can live for thousands of years, they're not immortal. They need to reproduce. But they weren't. One researcher, a Dr. Richard Hartesveldt, suspected that fire might have something to do with it. For decades, the park service had been diligently suppressing wildfires to help preserve the forest according to their mandate. Hartesveldt experimented with small-scale controlled burns and discovered that his hunch was correct.

Giant sequoias are highly fire resistant. They can easily survive low-intensity fires, and it turns out they desperately need those fires to reproduce. The heat opens up the sequoia cones and releases the seeds. By clearing out undergrowth, the fires uncover bare soil in which the seeds can germinate, and the new canopy gaps allow sunlight to reach the seedlings. The park service now lights carefully supervised and controlled burns. [source: National Park Service].

Fire doesn't just destroy, it helps regenerate.