Humans Are The Leading Cause Of Wildfires In The U.S. : The Two-Way More than 8 in 10 fires are started by people. Researchers say humans are not only causing the vast majority of wildfires, they're extending the normal fire season around the U.S. by three months.

What's The Leading Cause Of Wildfires In The U.S.? Humans

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There are two ways that wildfires can start - the natural way, like lightning, and the unnatural way, a cigarette flicked in the brush. New research shows just how many wildfires are started by people. NPR's Christopher Joyce reports.

CHRISTOPHER JOYCE, BYLINE: Skyline Drive in Virginia offers an Appalachian panorama, rolling mountains carpeted in deep oak and pine forests. But it's not all green, as fire ecologist Melissa Forder points out from the side of the highway.

MELISSA FORDER: We are at the Two-Mile Run Overlook at Shenandoah National Park.

JOYCE: And right below us a lot of burned trees.

FORDER: Yes. We can see where it started. I believe that's Rocky Mount.

JOYCE: Last year's Rocky Mount fire burned over 10,000 acres. Jeff Koenig is the park's fire manager.

JEFF KOENIG: We were probably 10 plus days without rain, so, you know, it was expected. It's that time of year that you can expect fire activity.

JOYCE: It was April, and spring and fall are when the forests in the East usually burn. Forder, also with the Park Service, explains.

FORDER: To have a fire you need the fuel, which is available every spring and fall, with the leaf litter, which is constantly here, and an ignition source. And then weather conditions that would allow the fire to burn.

JOYCE: That ignition source at Rocky Mount is thought to have been people. There was no lightning at the time. Most lightning fires happen during summer storms. Forder says about 60 percent of fires in national parks are caused by humans.

FORDER: Intentionally set fires, buildings burning and spreading into the forest, smoking, equipment malfunctions and campfires.

JOYCE: But the average for all forests is even higher. New research shows that nationwide, humans cause 84 percent of wildfires, more than 8 in 10.

JENNIFER BALCH: We are playing a really substantial role in shifting fire around.

JOYCE: Jennifer Balch is a fire ecologist at the University of Colorado. She looked at the big picture, records of 1.5 million wildfires. Balch says people are starting fires where and when nature normally doesn't. As a result, people have extended the normal fire season around the country by three months.

BALCH: I think acknowledging that fact is really important, particularly right now when we have evidence that climate is changing and climate is warming and that fires are increasing in size and the fire season is increasing.

JOYCE: Writing in the Proceedings of the National Academy of Sciences, Balch says there is a solution. Ironically, it means starting more fires. Prescribed fires are intentionally lit. They burn off leaf litter and underbrush that would otherwise fuel bigger wildfires. Controlled fires also help germinate the seeds of many tree species. But people don't like them nearby. They're smoky and sometimes get loose.

BALCH: Now the question is, can we live with the amount of prescribed fire that we need in ecosystems? Can we live with the smoke that comes off of those fires?

JOYCE: The research, she says, suggests that the alternative is a year-round season of bigger, more damaging fires. Christopher Joyce, NPR News.

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