Such resilience highlights a seeming contradiction: The coast redwood and its cousin the giant sequoia are, respectively, the tallest and largest trees on the planet, and they are among the longest-lived. Why, then, are they found only in small slices of the world, as if they are too delicate and finnicky to grow anywhere else? A likely answer, experts told me, is that today’s redwood groves are the remnants of forests that covered vast swaths of the Northern Hemisphere millions of years ago. Judging by the fossil record, redwood varieties once grew in Europe, East Asia and across upper North America. Some scientists think that starting about 56 million years ago, as the world gradually cooled and dried after an extremely warm period, the optimal habitat for coast redwood shrank. Similar climatic trends may have pushed the giant sequoia westward from the continent’s interior. As the Sierra Nevada began to rise, they created a rain shadow, a dry area, to their east. According to one theory, the trees, which at that point grew as far east as Idaho, migrated toward the sea, seeking moisture.
Despite their narrow ranges, the species themselves are not in immediate danger of going extinct in the literal sense. Partly that’s because they have already been planted elsewhere. New Zealand is home to forests of coast redwood. Some of the tallest trees in continental Europe are redwoods, both giant sequoias and coast, planted in the 19th century. Such relocations highlight something that’s often glossed over in the debate over assisted migration. People have for centuries been relocating trees around the globe for reasons unrelated to climate change. According to several scientists I spoke with, the question is not whether redwoods are in danger of disappearing but how climate change might alter the native communities they shape and are, in turn, shaped by — and whether portions of the iconic redwood forests might look very different in the future.
Coast redwoods are well adapted to fires of moderate intensity — their thick bark protects them from the flames — but in recent years, fires have become more intense, especially around the southern groves in Big Sur. Stephen Sillett expects the southern redwood forests to become increasingly stunted. He speculates that, at some point in the future, the tree’s prime habitat in far Northern California, the place where they grow largest, which is characterized by cool nights and abundant moisture, could shift north. But that change doesn’t have to mean a death knell. Millions of years ago the trees lived much further north than where they do now. “They were pushed out of the north by glaciation,” Sillett says. “Humans can definitely help them move back.”
For giant sequoia, the picture is slightly grimmer, if far from hopeless. Historically the trees were less often logged than the coast redwood; their brittle wood tended to shatter when felled, reducing its commercial appeal. About 70 percent of the original old-growth sequoia groves are thought to remain. But in the past decade or so, one disaster after another has befallen them. In the 2010s, the most intense droughts on record caused a loss of foliage. Then came the wildfires. The tree is exquisitely adapted to fire: In fact, it needs fire to complete its reproductive cycle; green cones can stay on higher branches for decades, until fire dries them and coaxes them to open. But the intensity of recent wildfires along the southern Sierra overwhelmed many old sequoias. Nathan Stephenson, a forest ecologist with the U.S. Geological Survey who has studied the trees for decades and who lives about 30 miles away from one grove that caught fire, recalls burned sequoia needles raining down on his deck in 2020. That’s when he understood that, for the first time in his experience, the fire had reached the trees’ crowns. Between 13 and 19 percent of the world’s sequoias were lost in recent fires. “They’ve been there thousands of years,” Stephenson says, “and they just sort of burned up in the blink of an eye.”
In the face of this and other threats, like beetle infestations, many people are taking steps to protect the trees. The nonprofit organization Save the Redwoods League, for example, is replanting sequoias. Anthony Ambrose, the executive director of the Ancient Forest Society, another nonprofit, collects cones for seed banking. There’s also renewed emphasis on fighting fire with fire. It has escaped no one’s notice that groves recently subject to prescribed burns, in which the underbrush and detritus that acts as kindling has been deliberately burned off, did not suffer the same catastrophic losses as untreated groves.