Redwoods Growing at Remarkable Rates

Some coastal redwoods are growing faster than expected and scientists aren’t 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.

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 based on the tree’s measured width, height and volume, the RCCI found 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. Sillett, who sat in his lab beside tree rings which he used to measure age and growth, said climate change may or may not play a role in the increased growth. Sillett said the Clean Air Act of 1970 may have cleaned the air enough to allow more sunlight on the trees.

“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 60s and early 70s to present, is just because of increasing air quality.”

Beyond climate and air quality, Sillett said multiple factors likely contribute to increased growth. Sillett also said 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 sudden spread of redwood forest also seems unlikely, Lucy Kerhoulas, an assistant professor of forest physiology, said. Kerhoulas said redwoods already have to work hard to reproduce via seed. Climate change might 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.

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.”

Redwoods store large amounts of carbon, especially in their prime ranges, but Sillett said that won’t offset the carbon dioxide produced by humans.

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