Earth Operative: Anthony Ambrose, Redwoods, and Climate Change
In order to determine how 400-foot, 2,000-year-old Redwoods are fairing in our changing climate, this Berkeley researcher puts on his climbing harness.
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The Yosemite Rim Fire is currently blazing around California’s giant sequoias, but they’ve survived thousands of years of fire just fine. And a study released this month shows that they and California’s ancient coastal redwoods are surviving climate change, as well—so far. In fact, the massive trees are in the midst of a growth spurt. The $2.5 million, multiyear research project, is funded through the 95-year-old conservation group Save the Redwoods League and conducted by a consortium of forest ecologists from Northern California universities. We talked to one of these researchers, Anthony Ambrose, PhD, from UC Berkeley’s Department of Integrative Biology, about what it’s like to scale a three hundred-foot redwood in the name of science.
OUTSIDE: Before we get into talking about tree-climbing, what is the main takeaway from the new report on redwoods? A lot of media reports focus on the rising temperatures in the Sierra Nevada range providing a longer growing season, and reductions in coastal fog providing more sunset, which links climate change to the growth spurt.
ANTHONY AMBROSE: Since the 1970s there has been a growth surge in a lot of the trees in the places we studied. One important point is: that’s good news in that we’re not seeing a decline in the growth rates of these trees but it also raises the question of why this is happening and how long this trend can continue. These trees go through natural fluctuations. The growth could be caused by climate change but we can’t attribute any causal mechanism – it could be temperature, it could be CO2, it could be other factors. And we don’t know how long it will continue. If it is attributable to increasing temperatures, then if the temperatures continue to rise they could surpass a physiological threshold for the trees. Another factor is that redwood trees need more water than most trees on the planet – an individual giant sequoia needs 2,000 liters of water a day. So if they don’t get enough water, the temperature and CO2 levels won’t matter.
Plus, the trees we studied were old growth in optimal sites for the two species. There are a lot of marginal habitats that might be experiencing stress or not—we don’t know what the species as a whole are doing. That’s the next step in our research.
So we’re cautiously optimistic, but we have a lot more work to do to understand what the mechanisms are that are causing this. The good news is that the trees we studied have not experienced any negative impacts from climate change, which is what we were concerned about when we went into the study.
Can you describe the rigging and climbing process?
We identify which trees we want to study and we have high-powered crossbows with rubber tipped arrows. We have fishing line attached to the arrow and from the ground we find nice big branches in the crown and an open spot where we can shoot the arrow. We shoot, the arrow goes up and over some large branches and falls to the ground. Then we tie a light, strong nylon cord to the fishing line, pull that up and over the branch and then attach a static climbing rope to that pull that up and over and tie it to an adjacent tree or other safe anchor.
We wear tree climbing saddles that are similar to rock climbing harnesses but have much more padding and are made for hanging in the tree for a long period of time. We use mechanical ascenders, similar to what’s used on big wall climbing, to climb up the rope. Then we use a shorter rope system called lanyards to pull ourselves up to higher positions until we get to the top of the tree. We use the lanyards to move around the crown.
When you are taking samples, what’s the process?
It depends on what we’re measuring. For this project we took a lot of what are called increment cores. For that we take an auger-like device that we screw into the tree and extract a pencil-wide core that has the whole tree-ring record as far as we can go into the tree—the deepest we have from this project are 32 inches. We use the lanyard system to collect leaf samples, which we use to analyze morphology and stable isotope composition, from different parts of the crown, at different heights. To measure the diameter of the branches we use laser range finders and other tools. Sometimes we have to set up a porta-ledge at the top of the tree to use set up equipment that collect physiological measurements, or to measure the water status of the plant.
Sometimes we start taking measurements pre-dawn, so we’re up there all night. We might start a measurement at 4 am and then take it again throughout the day until after dark [to see how the tree reacts to changes in the environment].
It’s very a challenging environment to be doing scientific work as you can imagine, because you’re hanging at 300 feet and you have all this heavy, expensive equipment and samples that you don’t want to drop.
So sometimes you go up there the night before and try to get some ZZs?
Yeah we use tree hammocks. It’s cool, but it’s not the most comfortable sleep, because you’re in your harness, but it’s definitely a really special, magical place to sleep. The trees move around quite a bit during the day, if there are storms, but it’s generally calm at night when we go up there. You can hear owls and sometimes they land on a branch nearby. This hasn’t happened to me personally, but some of my colleagues have been visited by what we think might be raccoons or flying squirrels, checking them out.
You also rock climb. Did you get inspired to get into that through your tree-climbing?
It happened kind of in parallel, but separate. I got into forest ecology and realized that in order to understand a lot of the really cool things about these trees you needed to get up into the crowns. I started to tree climb as part of my Masters research. It was only in the last four or so years that I started technical rock climbing—I had been doing non-technical climbing since I was a teenage—so I go out to South Lake Tahoe, Tuolumne and Bishop, bouldering and climbing as much as I can.