How Is A 1,600-Year-Old Tree Weathering California's Drought?

Oct 27, 2016
Originally published on October 27, 2016 7:00 pm

It's been a brutal forest fire season in California. But there's actually a greater threat to California's trees — the state's record-setting drought. The lack of water has killed at least 60 million trees in the past four years.

Scientists are struggling to understand which trees are most vulnerable to drought and how to keep the survivors alive. To that end, they're sending human climbers and flying drones into the treetops, in a novel biological experiment.

From a distance, the forests of the Sierra Nevada look blotchy, with patches of dead trees standing right next to healthy green ones.

Nate Stephenson, an ecologist with the U.S. Geological Survey, says the drought and high heat combine to do things he hasn't seen before. "We don't really understand a lot of things," he says, "like exactly how a drought kills a tree, or what's going on underground. Where is the water flowing in areas we can't see?"

Stephenson and his team of ecologists pull into a designated spot in the mountains, near Sequoia National Park, with truckloads of equipment they'll have to carry in. Their mission: to find out what separates the surviving trees from the dead. Their ultimate destination is down a steep slope — through a blanket of pine needles, rotting tree limbs and a few yellow-jacket nests they are careful not to walk on.

The walk is worth it. Looming above is Odin, a green and thriving giant sequoia that's more than 1,600 years old. The top is 250 feet up. Its base is as wide as a city street. Odin was a sapling when Rome was still an empire and, for some reason, it and many other sequoias are resisting this drought.

In hopes of finding clues to Odin's survival, Cameron Williams, a researcher with the University of California, Berkeley, is heading up to the top.

"I consider myself a forest canopy biologist," Williams says as he buckles on a climbing harness festooned with clips, carabiners, and an ascender — a kind of a clamp attached to the rope he will use to climb up.

He practices his emergency communication system: "Aaaaaaaaahhhhhhhhhhhhhhh," he yells, then laughs. Williams can joke because he's done this so many times. He and his climbing partner, Rikke Naesborg, also a research scientist at UC Berkeley, have spent hundreds of hours up in this tree. They take meticulous measurements, limb by limb, as though studying a patient etherized on a table. "Every single branch," says Naesborg.

She takes notes dangling from the rope. "You get used to it," she says. They check the tree's growth rate, and how much moisture is in each branch and in the needles and cones.

"It's very, very laborious," Williams says.

Todd Dawson, the plant ecologist from UC Berkeley who is in charge of the expedition, says what's happening to these forests is shocking and abnormal.

"There are a lot more dead trees in this forest than I've ever seen since we've been working here — since 2008," Dawson says.

Dawson is like an epidemiologist — studying disease in a large population. In this case, the patients are trees. There are far too many to be able to climb each one, so while some members of the team take Odin's measurements, Dawson is going to experiment with another approach. He'll fly a drone around the giant sequoia — carefully avoiding branches on every side — and take detailed images.

"This is the first time for all of us," says drone jockey Tom Jennings, who works for a company called CloudD8TA. "So we're taking our time and trying to be very cautious. We're dealing with the canopy, and that's a new hazard that I'm not used to."

The drones will fly to the top of the tree and then down around it in a spiral, taking many different sorts of images.

What the team hopes to do is compare what the climbers see with what the drones reveal. If drones can diagnose a tree as well as a climber can, they could cover a whole forest much faster.

The black drone rises from the ground, equipped with sophisticated cameras. It's about 3-feet square and looks like something Darth Vader would have on his desk.

It records, basically, the reflected light off the canopy," Dawson explains. "And that reflected light give us the health of the crown itself — water content and other chemicals like chlorophyll content, which is related to photosynthesis and nitrogen content." These readings reflect how stressed the tree is.

As the drone slowly descends from the top of Odin, Williams pulls himself up the tree, on a rope the size of his pinky finger. He narrates his climb into a microphone clipped to his shirt.

"So we just reached 160ish feet above the ground," Williams says. "Looks like a long way down there, and I can hear a drone overhead. Sounds like a giant bee's nest. Looking around the landscape you can really see a lot of dead trees. Wow. There are hundreds — potentially thousands — of dead trees I can see in this one view."

Already, from these sorts of measurements, Dawson has found that forests at low and mid-elevations — pine trees, fir, cedar — are suffering the most.

Drought and heat can choke a tree to death, scientists have found, by causing gas bubbles to form in the trunk, and block the flow of water. The stressed trees also close their stomata — the pores they respire through in the leaves and needles. That conserves moisture, but at a high cost. They can't take in the carbon dioxide they need to survive. In other cases, beetles detect the weak trees and single them out — like predators taking wounded prey on the Serengeti.

So how are giant sequoias like Odin different? It could be that sequoias tend grow where there's more groundwater, Dawson says. Or maybe it's the way they shed needles when stressed.

Understanding how different species of trees respond is already helping scientists focus their rescue efforts.

For starters, you might thin the forest in places, removing some small trees and underbrush, Stephenson says. Having fewer straws sucking water out of the ground, means more water, more light and more nutrients for the biggest trees in the landscape, he says. And that would help the survivors weather future environmental stresses.

California's current drought is disaster, but also a huge natural experiment, the forest ecologists say. Any lessons they can glean from studying Odin — going strong despite the drought — could help them save the rest of the forest.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.

KELLY MCEVERS, HOST:

It's been a brutal fire season in California, but the record-setting drought is actually a greater threat to the state's forests. Over the past four years, the drought has killed at least 60 million trees. Scientists are struggling to find ways to keep the survivors alive, and as NPR's Christopher Joyce discovered, they're trying some completely new ideas.

CHRISTOPHER JOYCE, BYLINE: The Sierra Nevada Mountains are known for rocky pinnacles and tall forests. These days, though, the forests are blotchy. Patches of dead trees stand right next the healthy, green ones. I went into the forest to talk to Nate Stephenson, an ecologist with the U.S. Geological Survey. He says the drought and high heat combine to do things he has not seen before.

NATE STEPHENSON: We don't really understand a lot of things, like exactly how a drought kills a tree or what's going on underground - you know, where is the water flowing in areas we can't see.

JOYCE: So a team of ecologists has come here, as well, with truckloads of equipment to find out what separates the survivors from the dead.

UNIDENTIFIED PERSON: (Unintelligible).

UNIDENTIFIED MAN: Yeah.

JOYCE: Their destination is down a steep slope, through piles of pine needles and rotting tree limbs.

STEPHENSON: Yellow jacket nests down here, so watch out.

JOYCE: Looming above is Odin, a green, thriving giant sequoia. The top is 250 feet up. Its base is as wide as a city street. Odin was a sapling when Rome was still an empire, and for some reason, it's resisting this drought. These scientists want to find out why.

CAMERON WILLIAMS: My name is Cameron Williams. I consider myself a forest canopy biologist.

JOYCE: Williams buckles on a climbing harness festooned with clips, carabiners and an ascender - a clamp attached to the rope he's now uncoiling that he will use to climb up into the canopy. I put a small microphone on his shirt, and he practices his emergency communication drill.

(SOUNDBITE OF SCREAMING)

WILLIAMS: Williams can joke because he's done this so many times. He and his climbing partner, Rikke Naesborg, have spent hundreds of hours up in this tree, measuring it like a patient etherized on a table.

RIKKE NAESBORG: Every single branch.

JOYCE: Taking notes while you're hanging from a rope?

NAESBORG: We are taking notes while we're hanging on rope, yes (laughter). Well, you get used to it.

WILLIAMS: It's very, very laborious.

JOYCE: They measure to check growth rate and how much moisture is in the branches and the needles and cones. Todd Dawson is running the show here. He's a plant ecologist from the University of California, Berkeley. Dawson says what's happening to these forests is not normal.

TODD DAWSON: There's a lot more dead trees in this forest than I've ever seen since we've been working here - since 2008.

JOYCE: Dawson is like an epidemiologist, studying disease in a large population - in this case, trees. But there are way too many trees here to climb each one, so while his climbers take Odin's measurements, Dawson is going to try something else. He's going to fly a drone around the giant sequoia, carefully avoiding branches on every side, and essentially do a botanical X-ray of it.

DAWSON: This is the first time for all of us, so we're taking our time and trying to be very cautious.

JOYCE: Tom Jennings is a drone jockey with a company called CloudD8TA.

TOM JENNINGS: We're dealing with the canopy, and that's a new hazard that I'm not used to.

JOYCE: The drones will fly to the top of the tree and then down around it, taking images.

JENNINGS: Go ahead, guys. We just figured we all should get started.

JOYCE: What the team hopes to do is compare what the climbers see with what the drones reveal. If drones can diagnose a tree as well as a climber can, they could cover a whole forest much faster.

(SOUNDBITE OF DRONE BUZZING)

JOYCE: The black drone rises from the ground. It's about three feet square and looks like something Darth Vader would have on his desk. It's carrying some very sophisticated cameras.

DAWSON: It records basically the reflected light off the canopy, and that reflected light gives us the health of the crown itself - water content and other chemicals in there, like chlorophyll content, which is directly related to photosynthesis, and nitrogen content.

JOYCE: All things that reflect how stressed the tree is.

(SOUNDBITE OF DRONE BUZZING)

JOYCE: The drone slowly descends from the treetop. Meanwhile, Cameron Williams pulls himself up a tree on a rope the size of his pinky finger.

(SOUNDBITE OF RUSTLING AND CLICKING)

WILLIAMS: Well, we just reached 160-ish feet above the ground. Looks like a long ways down there. And I can hear a drone overhead. Sounds like a giant bees' nest (laughter). Looking around at the landscape, you can really see a lot of dead trees. Wow. There's hundreds - potentially thousands - of dead trees that I can see in this one view.

JOYCE: These diagnoses are vital to understanding the drought. Already, Dawson has found that forests at low and mid-elevations - pine, fir, cedar - are getting slammed the hardest. They can choke to death. Heat and drought cause air bubbles to form in their trunks and block their flow of water. Or they die when beetles detect the weak ones and single them out like predators on the Serengeti. But the giant sequoias, like Odin, are different.

DAWSON: What is giant sequoia doing? Why is it able to be so resilient?

JOYCE: It could be that sequoias grow where there is more groundwater, or maybe it's the way they shed needles when they're stressed. Understanding how different species of trees respond will help scientists focus their rescue efforts. There are things that can be done. Forest ecologists like Nate Stephenson say, for example, you can thin out small trees and underbrush. That means fewer straws sucking water out of the ground.

STEPHENSON: That gives more water, more light, more nutrients for the biggest trees on the landscape, so they're better able to survive stresses in the future.

(SOUNDBITE OF RUSTLING)

JOYCE: The drought is a disaster, but also a huge natural experiment. And ecologists like Cameron Williams, still up in Odin's branches, say trees like this one could tell them how to help these forests survive.

WILLIAMS: Looks like this tree has been here for a long time and endured a lot of the elements that the environment has in store for it.

JOYCE: And that's exactly why these scientists think that Odin, going strong despite the drought, will help them save the rest of the forest. Christopher Joyce, NPR News. Transcript provided by NPR, Copyright NPR.