Blaze near Yosemite, mostly under control, shows limits to the parks' 'let it burn' policy.
If a blaze didn't threaten homes or people, park officials would let it burn. The idea was to let natural processes take over and prevent wildland from becoming too overgrown and vulnerable to a conflagration.
Forty years on, this strategy – known as "fire management" – is in place in wilderness areas across the West despite constant revision after a catastrophic miscalculation in the late 1980s at Yellowstone National Park in Wyoming. But as this year's extraordinary wildfire season in northern California shows, the strategy isn't always practical.
Firefighters at Yosemite National Park, for instance, normally let fires burn thousands of acres each year, sometimes for weeks. This year, the epidemic of nearby wildfires has caused so much pollution that Yosemite allowed only four fires to burn because of smoke regulations.
The strategy of using fire to prevent future fires "is a luxury," especially given the restrictions regarding its use, says Jan van Wagtendonk, a federal fire researcher who works at Yosemite. Still, he says, "it's the most natural way to allow the ecosystem to perpetuate itself."