Forest scientist and Oregon State University alumnus Steve Sillett studies and climbs the largest trees in the world. Since 1987, he’s climbed more than 1,000 trees, many of which reached heights greater than 200 feet tall and diameters upwards of 20 feet. Sillett’s study of old-growth forests and in particular redwood forest canopies has led him to some of the oldest and largest trees in existence, and what he’s learned about them has changed the way scientists view aged trees.
Sillett holds the Kenneth L. Fisher Chair in Redwood Forest Ecology at Humboldt State University in Arcata, Calif., where he spends time both teaching and researching. His arboreal research has been featured in National Geographic six times since 1997. He last appeared in the December 2012 issue of the magazine, in which he discussed climbing the second-largest tree in the world in the Sierra Nevada. Recently, Sillett answered some of our questions about his research and what it’s like to climb and see trees more than 3,000 years old in ways they’ve never been experienced before.
You were the first scientist to enter the old-growth redwood forest canopy — what first inspired you to leave the ground and take measurements of all parts of the tree?
I was first inspired to reach the canopy because I could not see what was going on high above the ground in tall forests. Arriving there revealed a world of unknowns, which required careful measurements. During the first four years of scientific exploration in the redwood canopy, I found a new phenomenon just about every time I climbed!
What is it like to climb such large trees?
Each large tree is unique structurally and requires many hours to explore. For example, my team spent a total of 320 hours mapping the President tree for National Geographic, and I never even saw about a third of its crown! The main trunk is like a wall blocking your view of the other side, so you have to go up, over, and around just to see what’s going on over there. In redwood rain forests, it’s even more complicated because there are so many juicy microhabitats tucked away in hard-to-reach places.
What do you learn about the trees through direct contact, observing every inch of them, that can’t be learned from the ground?
You cannot see the vast majority of a giant tree’s surface from the ground, so climbing and directly measuring each appendage is really the only way to get accurate numbers for important quantities like bark, wood and leaves at the whole-tree level. New methods like light detection and ranging (LiDAR) and motion capture now permit better quantification of tree structure than ever before, but much of a large tree’s crown is still invisible to these methods.
You discovered that older, larger trees actually create wood at a faster rate than they do when they’re younger — an idea that goes against previous assumptions. How significant is this to the way old trees are viewed and valued?
Well, it has long been understood that larger, older trees produce more wood than smaller, younger trees. What has been misunderstood is the effect of old age on a tree’s rate of wood production. Of course, like all earthlings, every tree eventually dies, but in long-lived species like Sequoia sempervirens and Sequoiadendron giganteum, a tree’s annual rate of wood production continues to increase for a very long time. For example, a 2000-year-old Sequoiadendron tree is growing faster than ever!
What impact could cultivating large, old trees have on human communities, animal habitats and the environment?
Even in the most massive old-growth forests, a few large trees per hectare harbor the bulk of arboreal biodiversity (e.g., epiphytes). They also do much of the forest’s work in the form of carbon sequestration, transpiration, nutrient cycling and moisture interception, so large trees have value to humans apart from wood production and aesthetics. Getting large trees back into our forested landscapes will require a long-term commitment to uneven-age management.
When you started out as a biology student, what led you to focus on trees as the organism you wanted to learn about most?
I became obsessed with tree climbing in college as a way to relieve the stress of laboratory work, and I soon became captivated by the organisms growing on tree surfaces, especially lichens and bryophytes. The more I studied these epiphytes, the more I wondered about the tree itself. Eventually my scientific interests shifted to trees entirely.
What role has your background and education at Oregon State played in the work that you do now?
My training at Oregon State and other universities has been critical to my success as a scientist. At Oregon State I had ample opportunities to work independently, make mistakes and learn from those mistakes. I was encouraged every step of the way by a great set of professors, especially Bill Denison, Bruce McCune, Pat Muir, Mark Wilson and Don Zobel.
What do you hope to see your work accomplish?
I hope to inspire a deeper understanding of trees and forests that will enable our society to better protect and utilize forest resources. Forestry has largely ignored the capabilities of large, old trees, viewing them more as commodities than as critical parts of a functioning ecosystem. The notion that old-growth forests are decadent and barely growing anymore is utterly false! The battle to save old growth from clearcutting has already been fought and mostly lost, and we now have only small remnants to remind us of these once vast forests. Instead of admitting defeat and suffering the permanent loss of forest giants and the excellent heartwood and ecosystem services they provide, however, we can rebuild great forests through careful management.
– Kayla Harr