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Carbon dating machine gives glimpse into the past and future of redwood trees

Small green sprouts rise out of brown, dead needles at the base of a burned tree.
Melissa Enright
Small green sprouts rise out of brown, dead needles at Big Bend Redwoods State Park in California.

Redwoods that grow on the Pacific coast are among the largest and oldest living organisms on Earth. Yet after a wildfire, burned trees can regrow from a sprout no bigger than a pencil shaving. Scientists at Northern Arizona University have begun to investigate the enigmatic origins of these baby redwoods, using a state-of-the-art machine that offers a rare glimpse into the past. KNAU’s Melissa Sevigny reports.

Last summer, wildfires charred the Big Basin Redwoods State Park on the coast of northern California. Ecologist Andrew Richardson drove through the aftermath. “It was pretty devastating,” he remembers, “driving in on the park entrance road past the burned-out visitor center and bathrooms and picnic areas. Not a whole lot of green in the forest, until you looked carefully…”

When he looked carefully, he noticed something growing at the bottoms of the scorched trees. “What was really amazing was when we climbed the tree… tiny little sprouts, just an inch long or so, were poking out through cracks in the bark,” he says. Those sprouts were strange. They didn’t come from pinecones or roots and didn’t even need sunlight to get started. They could spring up in complete darkness by drawing on old carbon squirreled away in the trunk of the mother tree, a kind of emergency reserve.

 Looking upward, redwood trees tower to the blue sky, their needles brown and dead, but with green fuzz along the length of their trunks.
Drew Peltier
Redwood trees tower to the sky, their needles brown and dead, but with green fuzz along the length of their trunks.

Biogeochemist Mariah Carbone explains, “This is their savings and they’re going to spend that savings when they absolutely need to.” She was curious about the source of that savings account. “So the idea for this redwood study was that: These are really old trees. Do they have really old carbon pools within them that they can use to regrow after a disturbance?”

Researchers collected several hundred sprouts and brought the samples back to Northern Arizona University in Flagstaff. There, they could measure the age of the carbon in the sprouts by using a brand-new carbon dating machine installed in a science lab on campus.

A series of interconnected chambers, with wires and tubes, makes a horseshoe shape about twenty feet long.
Melissa Sevigny
The carbon dating machine at the Arizona Climate and Ecosystems Isotope Lab at NAU

Research scientist Chris Ebert explains demonstrates how to load a sample capsule, about the size of an almond, into the machine. A mechanical arm makes a clicking and whirring noise as it moves. Ebert explains, the carbon atoms in the sample first get an electrical charge. Then, guided by magnets, they ricochet through the horseshoe-shaped machine and begin to spread out, sort of like horses on a racetrack.

“They make one more turn here,” Ebert says, pointing to a curve where heavier and lighter atoms separate from each other, “and they end up getting detected in a little detector,” at the other end of the horseshoe.

Ecosystem ecologist Ted Schuur says the goal is to count the heavier, radioactive atoms called carbon-14. “Now the reason this is important, is carbon-14, because it has a radioactive decay, it acts like a clock, it measures time for us.”

Carbon-14 occurs naturally but also was created in unusual quantities by humans, half a century ago. “As far back in the 1950s and 1960s there were nuclear bomb tests in the atmosphere and those created carbon-14 atoms…. and that happened quite quickly, and those atoms having been moving into trees and ecosystems, and they imprinted a time scale of the past 10-20-30-40 years,” he says.

The machine uses this clock to tell if the carbon in a sample was made fifty thousand years ago or last summer. Built in Switzerland, it’s the first of its kind in the United States. It can answer all kinds of questions about ecology, archeology, even the human body.

A green sprout sticks up out of the bark of a charred redwood tree.
Andrew Richardson
A green sprout sticks up out of the bark of a charred redwood tree.

“This is really letting us do things we couldn’t do before,” says George Koch, an NAU ecologist involved in the redwood project. “It remains a bit of amazing phenomena that these trees can fuzz out like this and regenerate so vigorously, many of them.”

It’s a strategy for survival in a world of wildfire. And by looking into decades past, in the tiny world of the atom, scientists can get a glimpse of the future of the colossal redwood tree.

Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.