Climbing to study ways redwoods resist drought
UC Berkeley ecologists go high in the Big Sur canopy to understand how forest giants retain water
Wendy Baxter shimmied up the black climbing rope, pushing her the last few feet toward her goal. The jingle of her harness echoed in the silence as she gazed across the green valley with an unobscured view of the Pacific Ocean. More than 150 feet in the air, she rested in the crown of an enormous redwood tree, glimpsing wisps of morning fog rolling in from the Big Sur coast.
Lonely redwoods like this one — at the very southern end of the species’ habitat range — may hold the key to understanding how these beloved trees
respond to changing drought conditions — and how they might respond to future climate change.
Baxter and her climbing partner, Anthony Ambrose, are tree ecologists from UC Berkeley. They’ve made this corner of the forest near the Landels-Hill Big Creek Reserve — a vast, mountainous expanse of lupine, wild poppies, oak trees, shrubbery and the occasional, isolated grove of redwoods — the site of their next exploration into the health of California’s iconic trees.
Baxter used to be afraid of heights, but quickly fell under the spell of California’s redwood trees after being hired as an assistant field researcher at UC Berkeley.
“It’s kind of grounding in a way, even though I’m off the ground,” the 37-year-old Baxter said with a laugh.
She and Ambrose are concerned that “edge groves” like this one will soon disappear, burdened by prolonged drought and a scarcity of water.
“Conditions are projecting that the Big Sur coast is going to be experiencing much hotter, drier conditions under climate change scenarios,” said Ambrose, 47.
Louis Santiago, a professor of physiological ecology at UC Riverside, shares Ambrose’s concern. “If the water supply was to change, it could change the redwoods’ distribution, and the Big Sur area would be the first to suffer,” he said.
Baxter noted how important the redwoods are to California’s forest ecosystem. “They sequester atmospheric carbon, help clean water and provide habitat for species like spotted owls and endangered marbled murrelets,” she said.
Keystone species
Redwoods are a keystone species, Santiago said. “If they disappear, the ecosystem drastically changes. You might get a grassland, or you might get some other tree that forms the canopy.”
Ambrose, who sports a black Patagonia and a single, tasteful earring, said he has been studying redwoods for more than 20 years.
“As the tallest trees in the world, and some of the oldest, they’re amazingly beautiful but also interesting scientifically,” he said. “How do they get to be 300-plus feet tall and live for thousands of years?”
The purpose of this recent trip was to “rig” five redwoods of similar age and height that dominate the canopy in the grove. Rigging involves ascending into the crown of the tree, setting up webbing to hold equipment, and leaving behind a reliable line to climb on future expeditions.
Ambrose and Baxter expect to return to the site multiple times in the coming months to place sensors high above the tree canopy and collect unprecedented data about these trees’ dayto-day lives. Being able to make it to the grove at all, they said, is a matter of good luck. Their plans for earlier trips were stymied by a fierce rainy season that washed huge swaths of Highway 1 into the ocean.
The recent Paul’s Slide presented similar obstacles for the scientists’ return to Big Sur, but Ambrose said that the duo can still access the reserve via NacimientoFergusson Road through Limekiln State Park.
For the current study, Ambrose will be installing sensors that will monitor and measure the environmental conditions that these Big Sur redwoods are experiencing, particularly light, fog, humidity and temperature.
The solar-powered sensors will log data every 10 minutes for months at a time — also keeping track of how much water is flowing through the trunks, how much water the trees are using, and when they get thirsty. The information will then be relayed back to Ambrose’s office in Berkeley.
“These sensors will revolutionize how we monitor constantly changing conditions,” he said. “It’s the equivalent of us sitting in the tree 24-7.”
Other scientists studying this secluded grove include Elliott Campbell, an environmental engineer from UC Merced. He’s leading a three-year collaborative effort called the Summen Project — “summen” means redwood in Ohlone — with the hopes of understanding the interaction of redwood trees and the fog that rolls in from the ocean.
“Redwoods depend on fog. They need it to survive in summer,” Campbell said. “We want to understand how the forest will be affected if the fog declines because of climate change.”
According to Campbell and Ambrose, fog helps reduce redwoods’ water stress during the dry times of the year. That’s because redwoods can absorb fog water directly through their leaves once it condenses. The scientists want to understand if these gentle giants get more of their water from fog or groundwater creeks in the summertime.
Campbell’s project collects flasks of air from around the crowns of the trees and then analyzes what chemical isotopes, such as carbon and oxygen, are present.
“These gases are indicators of the health of these trees,” he said. “The trees are in conversation with the atmosphere.”
Todd Dawson, a UC Berkeley professor of integrative biology and Ambrose’s longtime mentor, supports the approach of climbing trees to glean better information about how they live and survive in more inhospitable areas like Big Sur. Dawson oversees much of the redwood ecology research that’s happening across California, and Ambrose now works as his research associate at the university.
Go where leaves are
Dawson said climbing is simply part of scientists’ “tool kits.” In order to measure the microclimate that impacts the leaves, he said, you have to go where the leaves are.
“Most of the action happens up in the massive crowns well above the ground,” he said. “You cannot complete this work and do it safely without knowing how to rig and climb trees safely like Wendy and Anthony do.”
The duo knows the data they’re collecting by climbing these trees will be critical to understanding and predicting if this redwood grove can survive an impending global warming.
Ambrose also knows that the southern end of the species may disappear at some point. Redwoods stretch from Big Sur as far north as Oregon’s Chetco River.
“In the next several decades, the suitable habitat conditions in terms of temperature and precipitation are going to be shifting north and coastward,” he said.
But despite an uncertain future, he remains hopeful. “These trees are kind of an enigma,” Ambrose said. “They’re very vulnerable and yet very tough at the same time.”
As Baxter began her climb out of the canopy, birdsong permeated the sun-dappled grove. The massive redwoods, with their fuzzy branches and bark charred black from past fires, dominated her view as she looked down to plan her descent.
“Being such a small, short-lived organism myself, it’s pretty cool to climb around on such a huge, long-lived tree,” she said after reaching the ground. “It just makes you think about your place in the world.”