California redwoods 'killed' by wildfire come back to life with 2,000-year-old buds

After a massive wildfire swept through California's Big Basin Redwood State Park in 2020, the state's iconic trees appeared to be dying. But then, something incredible happened: Tiny sprouts began to peek through the charred remains.

Now, a new study shows how the trees sprouted new growth: They tapped into ancient carbon reserves and bud tissues that formed centuries ago.

Trees respirate using photosynthesis, in which they convert carbon dioxide from the atmosphere into oxygen and sugars. Although the energy can be used for growth, metabolism and reproduction, trees can also store it for later. These carbon stores may be integral to how trees survive challenges such as droughts or fires that destroy the tree's foliage and, as a result, its ability to photosynthesize.

For the study, published Nov. 30 in the journal Nature Plants, Drew Peltier, an ecophysiologist at Northern Arizona University at the time of the study and currently an assistant professor in the School of Life Sciences at the University of Nevada, Las Vegas, and colleagues analyzed the sprouts from burnt redwood trees.

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"What we found was that the trees used very old carbon reserves on the order of 50 to 100 years ago, which is by far the oldest observations of carbon reserves being used for something," he told Live Science.

To accurately date the carbon being used to fuel new growth in the coast redwoods (Sequoia sempervirens) the researchers used a form of radiocarbon dating. A specific isotope of atmospheric carbon, known as carbon-14, spiked in the early 1960s due to thermonuclear bomb testing, before slowly depleting over time. Carbon-14 from this period was absorbed by the redwoods, along with carbon-12 isotopes that were in the atmosphere after nuclear tests were banned.

The trees' stores of carbon include a mix of this newer and older carbon. By assuming that trees use up newer carbon more quickly, scientists can estimate the age of the carbon reserves being used by the sprouts.

The paper compares this to checking and savings accounts: Newer carbon is absorbed and used faster, and whatever is left is saved up and left relatively untouched.

Building a simulation based on this assumption, they found that some of the carbon found in new growth was photosynthesized more than half a century ago. Specifically, the new growth sprouted from previously dormant buds buried deep in the pit of the burnt redwoods. These ancient buds likely would have formed when the trees were still saplings.

"These giant trees are 5 meters [16 feet] in diameter at the base, and some are 2,000 years old — which means that the bud tissue is 2,000 years old," Peltier said.

The team was unsure whether the redwood trees could survive a disastrous forest fire that could burn all the way up to the tree canopies, Peltier said. Such extreme weather events could become more frequent with climate change.  Research published in 2022 found tree cover in California decreased by 6.7% between 1985 and 2021, with an increase in wildfires being the primary driver.

The latest findings suggest the state's redwoods are more resilient to wildfires than previously thought.

"In addition to having really thick bark and extreme tree height, this is just one of those additional adaptations that redwood trees have that make them super-resilient to fire," he said.

Researching how other trees store carbon over time could also be vital to understanding how trees act as a local and global carbon sink. Trees can act as net sinks for carbon because they can absorb carbon dioxide from the atmosphere and convert it into biomass or energy stores, which only get released if they are burned or cut down.

The goal is to continue studying large, old tree species like the giant sequoia (Sequoiadendron giganteum), which is closely related to coast redwood, but is a different species of tree and does not resprout after a forest fire.