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Giant Sequoias Are Built to Withstand Fire, But Not These Fires

Giant Sequoias Are Built to Withstand Fire, But Not These Fires

Monday, 1 August, 2022 - 03:45

No sooner had one fire in Yosemite been contained than a new one erupted in a different part of the park. This summer’s Western wildfires have brought attention to the risks that climate change brings to America’s national parks and the treasures they contain — like the giant sequoia trees, the largest trees on Earth. In the last two years, fires have consumed nearly 20% of them, according to the Forest Service.

The people who know these forests told me the best place to go to understand the fate of these trees is Kings Canyon, a national park a three-hour drive south of Yosemite. What has happened there is unprecedented in natural history. In Kings Canyon, hundreds of giant sequoias have burned to death — even though these trees were built to burn and survive, and rely on fire to reproduce.

At the park’s visitor center, I met up with Tony Caprio, a fire ecologist who studies the longstanding relationship between fires and forests. The fire that caused the most trouble as it raged through the park was the KNP complex fire of 2021. A normal lightning strike became a freakish mega-fire, exacerbated human-generated climate change and our misguided attempts to control the natural cycles of fire.

Human-generated carbon emissions have contributed to the drying out of the Sierra and other mountain forests by warming the air and reducing snowfall. Since rain tends to run off slopes quickly, snow is crucial for preventing the ground and plant life from drying out. Then there’s fire suppression.

“We suppressed fire in those areas for hundred-plus years,” Caprio told me. That meant there was a tremendous amount of fuel on the ground. The drought conditions made that fuel more flammable. When it caught fire, it burned very hot.

“This is something that’s probably unprecedented in the history of sequoias.”

Standing on a ridge above the area that had burned, Redwood Canyon, he pointed to a healthy grove of the giant trees. These sequoias were saved by “prescribed” burns — planned, small fires done in 2011 and 2012. The clearing of brush and small trees from those fires acted like a wall, protecting the groves from the massive fires that devastated other parts of Redwood Canyon.

The giant sequoias thrived for centuries in a normal, natural cycle of fires. The trees have adapted so the cones open and release their seeds when heated by a fire — a fire that in turn clears the ground so that those seeds can reach soil and germinate.

Some of the trees in this grove are 3,000, even 3,400 years old. In the back of his pickup, Caprio had a core sample of a tree — a stick more than five feet long that recorded thousands of tree rings. He pointed to a section about eight inches from the outer edge, or present time. That was A.D. 1295, he said, when you could see the tree survived a fire, and then had a growth spurt. The fire happened right at the end of the Medieval warm period, and from the rings it looks to have been the worst fire for several thousand years — but it didn’t kill the tree, and the growth spurt probably resulted from the clearing away of competing plants.

We drove partway into Redwood Canyon, and Caprio removed some barriers from the road so we could enter a region that had been closed to tourists because downed trees hadn’t all been cleared. That led to a hiking path through the fire-ravaged area.

The first thing I noticed was how many trunks were black. Everything was covered in soot. But this, he assured me, was the healthier part of the area. You just had to crane your neck to see the crowns of the trees, 200 or more feet in the air, covered with live green needles. Cones were falling, sometimes piled up by squirrels. Each one contained hundreds of seeds the size of oatmeal flakes. A tiny fraction of those would sprout, and a tiny fraction of those sprouts would become new trees.

After two miles of hiking, we reached the bad part — a place called the Sugar Bowl Grove, where we were suddenly surrounded by a ring of blackened trunks. And now, if we looked up, there were no live, green branches. The fire here got so hot, and so high, that it jumped as if climbing a ladder from smaller trees to the crowns of the giants, and spread from one to another until all were dead.

This is something that’s probably unprecedented in the history of sequoias as far as we know, he told me. He was the first person to see the remains, and the one to deliver the bad news to others who worked in the park. “People cried when they saw this,” he said.

Something else is going wrong with some of these trees. Bark beetles started killing sequoias — something never seen until 2014. The beetles are native to this area, and until now, no match for the giant trees, with 15-foot diameter trunks, thick leathery bark and resin that blocks the beetles from boring in. But we’re in a prolonged drought amplified by human-generated global warming. Some of the trees are stressed, weakened.

Giant sequoias aren’t going to go extinct any time soon. Some of the oldest trees have lived in drier areas for decades and have harder wood that better withstands the beetles’ assault. But they live and reproduce so slowly that whenever they do die, they won’t be replaced for centuries, if ever.

Reducing emissions will help more trees survive in the long term. And in the shorter term, prescribed burns can mitigate the threat caused by all those decades of fire suppression and unnatural fuel build up. The downside to prescribed burns is that the smoke won’t stay in the park; it can affect nearby communities. Getting it right isn’t easy: Recent burns in New Mexico got out of control and destroyed hundreds of people’s homes.

But there’s always hope. Americans used to be so callous about these natural wonders they would chop them down for lumber. Anything to make money — even if the wood easily shattered and ended up being used for fence posts.

So we’re learning. And thanks to controlled burning in the past, the Yosemite fire is coming under control, and the sequoias there survived. On the hike back, Caprio bent down and pointed to a tiny little sprig of green sprouting from the ground. That’s an infant sequoia, he told me. And maybe, someday, it will live to be the next generation of giants.


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