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Redwoods Growing at Remarkable Rates

Some coastal redwoods are growing faster than expected and scientists aren’t completely certain why

Many redwoods in Northern California are growing at unexpected—even record-breaking—rates. While redwoods only remain in a tiny portion of the world, they appear to be in good health.

“People talk about saving the redwoods,” Humboldt State University Professor of Forest Ecology Steve Sillett said. “The redwoods, as long as we don’t cut them down, are doing just fine. The question is, can they help save us?”

The answer is complicated.

“The Redwoods and Climate Change Initiative found that one Del Norte County redwood put on 2,811 pounds in 2014, a record-breaking annual growth.”

Many coastal redwoods are growing faster today than they have in the last thousand years, according to a 2019 report from the ongoing Redwoods and Climate Change Initiative.

The RCCI, a research partnership studying redwood health since 2013, found surprising growth in redwoods located away from dry forest fringes or recent fires.

By estimating tree weight through calculations based on the tree’s measured width, height and volume, the RCCI found that one Del Norte County redwood put on 2,811 pounds in 2014, a record-breaking annual growth.

The cause of the increased growth is uncertain. Professor Sillett sat in his lab beside tree rings which he used to measure age and growth. He noted that climate change may or may not be playing a role in the increased growth. Sillett said the Clean Air Act of 1970 may have cleaned the air enough to cast more sunlight light on the trees, resulting in more growth.

“What happened is, the air cleared,” Sillett said “And with clear air, you get more light, and so it could very well be that this increase in growth rate that we see very strikingly in some of these trees, starting in the late sixties and early seventies to present, is just because of increasing air quality.”

Beyond climate and air quality, Sillett said multiple factors likely contribute to increasing growth. Sillett also noted that the growth won’t necessarily last.

“I think that there’s very much a limit to what redwoods or any vegetation can achieve,” Sillett said.

A redwood tree ring in HSU Professor Stephen Sillett’s lab on Aug. 28. | Photo by James Wilde

A sudden spread of redwood forest also seems unlikely, said Lucy Kerhoulas, an assistant professor of Forest Physiology. Kerhoulas said redwoods already work hard to reproduce via seed. Climate change may make reproduction even more difficult.

“Successful seedling germination and establishment might be really challenging under a warming and drying climate,” Kerhoulas said.

In other words, redwoods are doing well, but they’re not about to reclaim their lost forests.

Professor Sillett emphasized that many living redwoods are maintaining their normal growth despite less successful reproduction.

“It’s not the case that they’re responding uniformly,” Sillett said. “But what we do see is that in the prime parts of their range, which is, say, north of San Francisco and relatively close to the coast, the rates of wood production are higher than they were in the not-too-distant past.”

Although redwoods store large amounts of carbon, especially in their prime ranges, Professor Sillett said redwoods won’t offset the carbon dioxide produced by humans.

“There’s not enough land in the world to plant with redwood forest that would allow them to save us from what we’re doing to the atmosphere’s chemistry,” Sillett said.

Today, when the future of humanity is ever-uncertain, the redwoods are productive as ever. The redwood forests have been resilient since the Cretaceous period but we’ll have to do more than plant trees to save ourselves.

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