Giant Sequoias Are Built To Withstand Fire, But Not These Fires
People who know these forests have told me that the best place to go to understand the fate of these trees is Kings Canyon, a national park three hours south of Yosemite. What happened there is unprecedented in natural history. In Kings Canyon, hundreds of giant sequoias have been burned alive, even though these trees were built to burn and survive, and depend on fire to reproduce.
At the park visitor center, I met Tony Caprio, a fire ecologist who studies the long-standing relationship between fires and forests. The fire that caused the most trouble as it raged through the park was the 2021 KNP Complex Fire. A normal lightning strike turned into a freak mega-fire, exacerbated climate change generated by man and our misguided attempts to control the natural cycles of fire.
Human-generated carbon emissions have helped dry out the Sierra and other mountain forests by warming the air and reducing snowfall. As rain tends to run off slopes quickly, snow is essential to prevent soil and vegetation from drying out. Then there is fire suppression.
“We’ve been putting out the fire in these areas for over a hundred years,” Caprio told me. This meant that there was a huge amount of fuel on the ground. Drought conditions have made this fuel more flammable. When it caught fire, it burned very hard.
“This is something that is probably unprecedented in the history of redwoods.”
Standing on a ridge above the area that had burned, Redwood Canyon, he pointed to a healthy grove of giant trees. These redwoods were saved by “prescribed” burns – small planned fires in 2011 and 2012. The clearing and small trees from these fires acted like a wall, protecting the groves from the massive fires that devastated other parts of Redwood Canyon.
Giant Sequoias have thrived for centuries in a normal, natural cycle of fires. The trees have adapted so that the cones open and release their seeds when heated by a fire – a fire which in turn clears the soil so that those seeds can reach the ground and germinate.
Some of the trees in this grove are 3,000 or even 3,400 years old. In the back of his pickup, Caprio had a core sample of a tree – a stick over five feet long that recorded thousands of tree rings. He indicated a section about eight inches from the outer edge, or present time. It was 1295 AD, he said, when you could see the tree survived a fire and then had a growth spurt. The fire happened just at the end of the Medieval Warm Period, and from the rings it appears to have been the worst fire in several thousand years – but it didn’t kill the tree, and the growth spurt probably resulted from the release of competing plants.
We drove halfway through Redwood Canyon and Caprio removed some road barriers so we could enter an area that had been closed to tourists because the downed trees hadn’t all been cleared. This led to a hiking trail 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 healthiest part of the region. You only had to crane your neck to see the treetops, 200 feet or more in the air, covered in living green needles. Cones fell, sometimes piled up by squirrels. Each contained hundreds of seeds the size of oatmeal. A tiny fraction of these would sprout, and a tiny fraction of those shoots would grow into new trees.
After two miles of hiking, we reached the wrong part – a place called the Sugar Bowl Grove, where we were suddenly surrounded by a ring of blackened logs. And now, if we looked up, there were no more living green branches. The fire here got so hot and so high that it leaped as if climbing a ladder from smaller trees to the tops of the giants, and spread from one to another until until all are dead.
This is something that is probably unprecedented in the history of redwoods that we know of, he told me. He was the first person to see the remains and the one to break the bad news to others working in the park. “People cried when they saw that,” he said.
Something else is wrong with some of these trees. The bark beetles began killing redwoods – something not seen until 2014. The beetles are native to this region, and so far no match for the giant trees, with trunks 15 feet in diameter, a thick leathery bark and resin that keeps the beetles bored But we are in a prolonged drought amplified by human-caused global warming. Some trees are stressed, weakened.
The giant sequoias aren’t going away anytime soon. Some of the oldest trees have lived in drier areas for decades and have harder wood that is more resistant to beetle attacks. But they live and reproduce so slowly that each time they 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 lessen the threat caused by all those decades of fire suppression and unnatural fuel buildup. The disadvantage of prescribed burns is that the smoke does not stay in the park; this may affect nearby communities. It’s not easy to get it right: recent fires in New Mexico have spiraled out of control and destroyed hundreds of homes.
But there is always hope. Americans were so oblivious to these natural wonders that they cut them down to make wood. Anything to make money – even if the wood broke easily and ended up being used for fence posts.
So we learn. And thanks to controlled burning in the past, the Yosemite fire is being brought under control and the redwoods have survived it. On the way back, Caprio bent down and pointed to a tiny sprig of greenery sticking out of the ground. It’s a baby redwood, he told me. And maybe one day he will live to be the next generation of giants.
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Faye Flam is a Bloomberg Opinion columnist covering science. She hosts the “Follow the Science” podcast.
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