A decent level of physical fitness, a fondness for climbing, an intimate knowledge of giant old-growth tree species, and being handy with a crossbow: If you possess this most unusual of skill sets, then tree-climbing botanist may be the job you never realised you were born to do.
Wendy Baxter and her partner and colleague Anthony Ambrose have said skill set and more. The scientists, based out of the University of California in Berkeley, have spent years accessing and exploring the crowns and canopies of some of the biggest, oldest, and tallest trees on the planet: California’s coastal redwoods and giant sequoias. Their research over the last six years has revealed insights into previously unknown aspects of both species, such as how they combat drought and exactly how much water they need to survive.
Baxter’s journey to a career ascending to heights of over 91.44m to study some of the most impressive organisms on Earth began when she saw an unusual job advertisement, shortly after completing a masters degree studying butterflies in the Netherlands.
“I have been involved in science for many years and was looking for job and saw something at UC Berkeley and it said must be interested in climbing very tall trees and I thought ‘wow that sounds amazing’,” she told Earther.
Baxter was hired by Ambrose in 2010, who helped her develop her extant rock-climbing skills into tree-scaling skills. He himself had spent time living among and studying redwoods before he decided to take it to the next level, quite literally, by doing a course in forest canopy biology back in 1997.
Nine years down the line the duo spend as much time as they can up in the branches. If it’s not for work, then they climb for leisure in one of the state’s national forests. “It’s pretty addictive really,” Baxter said.
Coastal redwoods and sequoias have are endemic to narrow pockets of California and Oregon and protected within the national parks. So revered are they that many have their own names, like 2,200-year-old General Sherman, the biggest living sequoia. (The General’s trunk is nearly 30.48m in circumference. If he needed a hug, it would take about 20 people with their arms outstretched to give him one).
Baxter and Ambrose believe working in the crowns of such giants provides scientific and ecological insights that cannot be obtained any other way. “Being able to get an idea of how much they’re growing depends on how big the branches are and how many branches they have and how much leaf area they have,” Ambrose told Earther. “You can’t really do that in intact trees from the ground.”
In order to reach the crown, a budding tree climber firstly must use a crossbow to shoot a blunt-tipped arrow over the highest reachable branch trailing a fishing line. That is used to run over a nylon cord which is strong enough to run a rope over. One end of the rope is then tied to a nearby tree, while the other hangs free and can be clipped onto and climbed up. The climber uses grips that slide up but not down, one attached to a climbing harness, another to a pair of foot slings. Then you’re ready to go.
As the lowest branches of the taller trees are often 30.48m or so off the ground, the initial ascent is often the toughest. It’s not for the acrophobic, nor for novice climbers. “It probably selects for people who are interested in climbing and aren’t afraid of heights,” Baxter confirmed. “We have colleagues who we trained to climb but they never got to the point where they felt comfortable doing it themselves.”
Baxter and Ambrose’s studies of the redwoods and sequoias coincided with unprecedented drought in California between 2011 and 2016. For Baxter and Ambrose it has provided an opportunity to look more into how exactly such water-dependent species respond. In 2015, they initiated a long-term study called “Leaf to Landscape” to look at any long-term effects the drought had on the giant trees.
This involved the installation of weather stations in the canopy, the use of drones, remote sensing, and overflights as well as scores of trips up trees to take core and foliage samples and measurements. By looking at the foliage for signs of drought stress, scientists can determine how the tree’s water supply as a whole is faring. The cores allow them to study the tree’s growth rings and as Ambrose put it that reveals “thousands of years of history right here,” offering insights into their response to past droughts.
This work is still ongoing. While today, Baxter and Ambrose have support from eager volunteers and institutions including Stanford and the U.S. Geological Survey, the early days of the project saw a lot of hard work and long days beginning at two thirty in the morning and involving numerous treks to and from their vehicle and many escalations up and down trees to install their instruments.
“It was intense and a great weight loss program!” Baxter said.
The hard labour has borne scientific fruit. Ambrose and other colleagues noticed in 2015 that trees stressed by prolonged drought will sometimes deliberately drop their foliage, which helps them reduce them amount of water they’re losing to the atmosphere. “They have all sorts of different adaptations and adjustments they make under conditions of water limitation, or drought, that allows them to persist under those conditions,” Ambrose said.
While these giant species have had to endure prolonged drought before in their climatic history, there are reasons to be concerned about their future, say Ambrose and Baxter. Both coastal redwoods and giant sequoias are resistant to wildfires, but the scientists say human fire suppression activities have allowed many smaller trees, that would be cleared out naturally by fire, to grow into the understory of the giant ones, rendering it easier for flames to carry up into their canopy.
And because both species have small and specific ranges, a changing climate could have impacts. The giant sequoias are confined to about 75 groves in the Sierra Nevada, and Ambrose says as they chug through an estimated two to four thousand litres of water, per day, per tree, they are entirely dependent on the snow in the area—which is diminishing.
For coastal redwoods it is the coastal fogs that are key. If a drier future climate means the fog moves or disappears (a possibility that some research supports), that combined with snowfall declines could cause the trees to start to dying off.
“We don’t know when that might happen or on what time scale but there is definitely cause for concern,” Ambrose said. Still, he feels, there’s little risk of the ancient trees completely disappearing, and the two species are planted worldwide in such numbers that there is no risk of extinction.
For now, there is still much to learn about these fascinating organisms, including what’s going on beneath the ground, giving the researchers plenty of reasons to keep climbing.
“We just know so very little and these trees are so complex and not only the individual trees but the whole ecosystem they are a part of,” said Ambrose. “There is so much more than we can learn about them and that is so cool from a scientific perspective. We have a lifetime of questions to ask.”