The following essay is reprinted with permission from The Conversation, an online publication covering the latest research.
Coast redwoods – enormous, spectacular trees, some reaching nearly 400 feet, the tallest plants on the planet – thrive mostly in a narrow strip of land in the Pacific Northwest of the United States. Most of them grow from southern Oregon down into northern California, snugged up against the rugged Pacific coast.
They have grown by slowly responding to moisture and rich alluvial soil over millennia, combined with a genetic payload that pushes them to the upper limits of tree height. They are at risk – down to perhaps 70,000 individuals, falling from at least a half-million trees before humans arrived – but that’s not a new story, for we are all at risk.
Redwoods, like all trees, are engineered marvels. People don’t tend to think of natural things as “structures,” leaving that term to stand in for buildings, bridges and dams. But although trees were not built by humans, they didn’t just happen. They have come into their own through the inexorably turning wheels of natural selection and evolution, responding to environmental pressures, genetic drift and mutation.
They even have two kinds of leaves that help the trees adapt to both wet and dry conditions. They are born to change, just as humans are born to change.
Evolution is usually a very slow process, although sometimes it’s surprisingly quick. New, intense pressures of a warming and changing climate are speeding things up.
I teach environmental humanities and history courses at Caltech and work as a senior curator at The Huntington – a research institution in nearby San Marino. It includes one of the world’s most renowned botanical gardens, comprising more than 130 acres and visited by over a million people annually.
Researchers and horticulturists at the botanical gardens are thinking about trees, and how to integrate them into larger landscapes, in new ways. Our approach to climate change resilience, our increased reliance on technologies like geographic information systems, and our new engagements with local communities all continue to shape our attitudes about trees.
There are differences as well as similarities between human-made edifices and trees. A structure or building typically is a sort of island unto itself, separate from its neighbors; in contrast, the coast redwood is an ecosystem with enormously broad consequences for other life forms.
Life is folded in and among the redwoods, below and within and about them. The trees are integrators, bringing together many life forms. Some of these life forms rely on the tree; others on occupants in and around the tree.
The coast redwood hosts so many different ecological interactions that it’s faintly ridiculous. Consider Aneides vagrans, the wandering salamander, which usually spends its entire life high in the canopy, but sometimes must jump out to escape predators. Without wings or gliding, it falls for as long as two full minutes, only to land perfectly unharmed on the ground.
It took scientists dropping these creatures into a wind tunnel and filming them with high-speed cameras to understand why they didn’t end up as a wet splat on the forest floor. As it turns out, the salamander’s body shape does the work, with a torso that’s just sufficiently flattened, and large feet with long toes, that create just enough drag and balance for a soft landing.
Redwoods are so large that one reportedly was found to house a Sitka spruce (Picea sitchensis), 8 feet tall, growing far off the ground within the larger tree. Redwoods also have served for millennia as nesting habitat for huge California condors (Gymnogyps californianus), whose wingspan is nearly 10 feet. A big bird needs a big home.
There’s also a place for the tiny, living side by side with all of the largeness tucked in the complex, secret interstices of these trees. Nestled into extensive mats of ferns that grow high up in redwood canopies, researchers find aquatic crustaceans called copepods that normally would live in larger bodies of water. No one knows how they got into the trees, but the fern mats trap enormous quantities of moisture from rain and fog, creating wetlands in the sky.
Enduring but not static
Even species as enduring as coast redwoods are affected by climate change. Diminished moisture stresses the trees, making them grow with less vigor. New fire dangers put them at risk, and more frequent floods erode the big trees’ footing. But redwoods also are adapting.
A 2018 survey of nine large redwood trees found a total of 137 species of lichen growing on the trees, including several that were new to science. One was Xylopsora canopeorum, whose specific name celebrates the canopy where it was discovered.
This lichen seems to be unique to the warmer and drier forests in California’s Sonoma and Santa Cruz counties, in the southern part of coast redwoods’ range. This is an exciting finding, for it provides evidence that new forms of life – ecosystem partners – may be evolving in sync with trees that are also evolving in the face of climate change.
Scientists are finding more new organic redwood partners every year. Since these trees are so networked and interconnected, the sum is greater than its parts and isn’t easy to quantify.
As I write in my forthcoming book, “Twelve Trees: The Deep Roots of Our Future,” there’s something congregational about the redwoods in their groves, like “a group of worshippers, petitioners standing solemnly, upright before an even higher power than themselves: the calculus of wind, rain, sun, oxygen, carbon dioxide, and time.” Experiencing them stimulates one’s senses with scent, sight and sound, along with a tincture of the most essential ingredient of all – memory.
A pair of redwoods grow just outside my office at the Huntington, which is some 700 miles south of the coast redwood’s usual range. I’ve resisted giving names to this duo, although many giant redwoods have monikers like Adventure, Brutus, Nugget, Paradox and Atlas – most named by the scientists who first quantified their extreme heights.
The redwoods outside my window are perhaps 100 feet tall – puny by comparison to their northern brethren. But they are healthy, and will continue to be shaped by their immediate environments. They’ve traveled far to get to here, planted more than a half-century ago by an earlier generation of horticulturalists, and they’re thriving in their new home. We should all be so lucky.