Massive Fire Threatens Yosemite’s Sequoias

As the Rim Fire sears through California, it has incinerated over 180,000 acres and sent more than 4,000 firefighters scrambling to tame its roaring flames. Although the fire is currently 23 percent contained, it has been moving deeper into Yosemite National Park, threatening beloved sequoia groves. “And rightly so, because they are amazing,” ecologist Stephen C. Sillett told National Geographic. As Brian Clark Howard reports for the magazine’s Daily News section, thick, fibrous bark on full-grown sequoias helps the massive trees weather milder wildfires, which were common hundreds of years ago. In fact, they have evolved to benefit from these types of wildfires:

A single sequoia can play host to more than 100,000 cones, said Sillett. The cones are green when living, meaning they carry out photosynthesis, producing some of the sugars that they need for their own growth. Each cone can live 10 to 20 years. It then dies, opens up, and drops its seeds.

When there is a fire, it kills a large percentage of the cones, causing them to drop their seeds en masse. Normally, it takes some time for the cones to open up. By the time the seeds hit the forest floor, the fire has moved on, and the earth has cooled.

The Rim Fire has burned nearly 200,000 acres and is now threatening Yosemite's sequoias.

But this fire is neither mild nor beneficial for sequoias. Instead of a moderate ground fire—which the trees’ bark can defend against—the Rim Fire is burning the forest canopy, too, damaging the more delicate leaves. Trees have a much harder time surviving crown fires, and if they do, they’re often severely damaged. Here’s Kurtis Alexander writing for the San Francisco Chronicle:

The blaze is rapidly approaching two of Yosemite’s three renowned sequoia sites, the Tuolumne and Merced groves, and firefighters are doing all they can to give the redwoods a leg up should fire strike.

“Normally we would say that fire is good for a sequoia grove. But a fire that is burning too hot is not healthy for any tree,” said Tom Medema, Yosemite’s chief of interpretation and education.

The Rim Fire, which started Aug. 17 in the Stanislaus National Forest and has since crept into the national park, is fueled by bone-dry forest and is spreading unusually fast through the treetops. Medema said strict fire suppression policies of the past have left a surplus of fuel to burn and, as a result, made the Rim Fire burn with more intensity and heat.

Foresters have been struggling to reduce fuel loads on forest floors in recent years, often using controlled burns to clear it out. But that strategy can’t be used everywhere, especially near people and houses. As a result, the Rim Fire has grown so large that you can see it from space. For a closer look, check out this video taken onboard a CAL FIRE plane.