Redwoods are made to survive fire, but they don't live alone in the forest

When four of the five largest wildfires in California's history were ablaze simultaneously late last summer, it certainly felt apocalyptic for the state's coastal redwoods. 

Beyond burning more than 2 million acres and destroying thousands of homes and structures, the fires swept through pristine redwood groves, many with old-growth trees that had been standing before non-native settlers arrived on the West Coast hundreds of years ago. The images of flames climbing some of the largest and oldest living things on Earth were sobering, as was an assessment from state officials that Big Basin Redwoods, California's oldest state park, had been extensively damaged.

But six months later, the news from the embers isn't hopeless. Kristen Shive, the now former director of science for the Save the Redwoods League (Shive left her position just after we spoke for this story) says redwoods are sturdy trees that have evolved to survive fire. Though 2020's ferocious fires were incredibly destructive to infrastructure on public lands, other trees and wildlife, the redwoods themselves fared relatively well.

"The most important thing to understand is that coast redwoods really are some of the most resilient species on the planet," she said. "That's why they live as long as they do. And they actually are adapted to both low and high severity fire."

Bark of armor

You don't need to be a scientist like Shive to understand why redwoods have this resiliency. Instead, all you need to do is feel one with your hand. Unlike the tough, impenetrable bark on other trees, a redwood's trunk feels soft and spongy, with stringy fibers you can peel away.

It may feel counterintuitive for a tree that can grow almost 400-feet high to have such soft skin, but the bark is a redwood's suit of armor, resisting not just fire, but also decay and parasites. As Sam Hodder, the president and CEO of Save The Redwoods League told me in 2019, "We can't find anything that kills a redwood."

Watch this: Saving California's redwoods, one tree at a time

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Redwoods die when they fall over, which repeated fires can indirectly cause. As they burn at a redwood's base over hundreds of years, fires can create cavities called basal hollows. The tallest trees continue to stand even with basal hollows large enough to fit a group of people, but over time a hollow can grow too big.

"Sometimes it's just one too many fires, and [the redwood] is no longer structurally stable," Shive said. "But the fire itself doesn't really kill them."

Redwoods also have a powerful ability to regenerate after a fire, either through new sprouts at a tree's base (a growth called a fairy ring) or buds that grow inside the trunk and sprout higher up closer to the tree's crown. Even higher-severity fires that can completely consume other coniferous trees nearby aren't as damaging to a redwood because they're so tall. 

"It's actually kind of hard for fire to get up into the canopy unless you have more extreme conditions," Shive said. "In a way, the redwoods themselves will be fine … A few will fall down, but most will recover and still be there."

Indirect effects

Shive admits, though, that a few redwoods falling down is a problem considering how small the present range of the trees is. Two hundred years ago, redwoods blanketed the Northern California coast, including the now thickly populated hills surrounding the San Francisco Bay Area. But today, after extensive logging in the latter half of the 19th century, just 5%, or about 115,000 acres, of those old growth trees remain. 

"My big concern is that there's so little old growth left," Shive said. "Close to 10,000 acres of that burned [in 2020]. That's nearly 10% in just a couple of fires."

Redwoods also don't live by themselves in the forest. They're a home to endangered birds like the marbled murrelet, and they're surrounded by other trees like Douglas firs that lack a redwood's resiliency. 

"Fires have consequences for the broader ecosystem," Shive said. "Douglas firs don't sprout back. So, if they have a total loss of their foliage, they're dead. That's another tree the marbled murrelet really loves, and they're an equally important component of the forest."

On public lands, fires also can destroy infrastructure for visitors and forest maintenance. Big Basin Redwoods State Park in Santa Cruz County remains closed until at least the autumn after the visitor center, headquarters and museum burned to the ground. And though fire crews were able to save the facilities and redwoods at Armstrong Woods State Natural Reserve in Sonoma County, including the 1,400-year-old Colonel Armstrong tree, that park also remains closed due to other damage. 

"It's all a mixed bag," Shive said. "One thing that's utterly devastating is the impact to infrastructure. [Big Basin] is a state park that's really beloved, and it lost virtually all of its infrastructure. That's going to take so much work to rebuild."

Good fire

As drought and climate change increase fire severity and the length of the fire season in California, the outlook for the future of the state's forests can appear grim. 

But fire is also essential for a forest's health. Low-intensity blazes clear dead trees, leaves and vegetation from the forest floor and they remove weak and diseased trees so new plants can grow. A thinner forest means there are fewer trees competing for sunlight (already a precious commodity on the Northern California coast). 

The key, Shive says, is to keep fires at a low-intensity by conducting regular controlled burns in forests to reduce the combustible material that causes blazes to get out of control. That's happening on private land, but less so on public land where resources are scarce. In California the federal government owns about 58% of its 33 million acres of forestlands, according to the governor's office. The state owns 3%, with the rest in private hands.

"What we really need to do is to get our forests in a condition where they're resilient to fire so that when a wildfire does come through, it burns at lower severity," Shive said. "The way to do that is to reduce fuel by things like prescribed fire."