Ancient Forest Society performs health checkup of General Sherman Tree in Sequoia National Park

by Allison Kidder

Ancient Forest Society (AFS) was recently hired by Sequoia National Park to inspect the General Sherman tree’s canopy for bark beetle activity and to perform a general health checkup of the tree. The General Sherman tree is the largest tree in the world by volume and is located within the Giant Forest grove in the park. 

Soaking in the significance of the job ahead, Anthony Ambrose, the Executive Director and co-founder of AFS, hesitated a moment in contemplation before starting to climb into the canopy. He was eventually joined by AFS Program Director and co-founder Wendy Baxter. The tree is so large that Ancient Forest Society enlisted two other tree- canopy researchers to help with the inspection, Cameron Williams, a botanist and tree ecophysiologist, and Rikke Naesborg, a lichenologist and tree-canopy researcher with the Santa Barbara Botanic Garden.

As far as anyone knows, they are the first people to climb this giant tree in its 2,200 years of life. (Spoiler alert: the tree is in great shape!).

The Bark Beetle Situation

Bark beetles (Phloeosinus sp.) are native to California and often live on phloem sap in conifers. This liquid is transported through the tree in the cambium layer just under the bark and contains nutrients and hormones generated through photosynthesis in the tree’s leaves (needles). Under normal conditions, bark beetles are present in small numbers. Trees are generally able to fend them off by exuding large amounts of the sticky sap to plug the beetles’ entrance holes and prevent entry into the wood, a process known as a “pitch response.”

When trees are stressed from conditions such as multi-year droughts or overly-intense fires, they are no longer able to repel their attackers, and they can succumb to beetle infestations. The multi-year drought of the past decade, in combination with intense fires, was a vivid example. Giant sequoias were no longer able to access water supplies they’d long relied upon and could therefore no longer generate enough pitch to close the bark-beetle bore holes. This allowed the beetles to freely enter the wood and multiply in their nuptial chambers.

In 2017, researchers started seeing giant sequoia trees in Sequoia National Park and other areas die from the combination of drought, fire, and bark-beetle attacks. When giant sequoias in the same grove as the General Sherman tree started dying from bark-beetle attacks, the National Park Service could not ignore the threat. They could not risk damage to such a globally-important tree, so they brought in the Ancient Forest Society team to inspect the General Sherman tree for bark- beetle damage.

The Inspection

During the climb of the General Sherman tree, everyone within the drip line of the tree was required to wear a helmet. Debris, foliage, and small branches can rain down from the canopy onto unsuspecting onlookers. The drip line is defined by the area directly upward from the outermost tips of the branches.

Once all four researchers were in the canopy, they began their carefully choreographed inspection, with each researcher covering certain parts of the tree. Given its age, the tree has extremely large branches that grow outward and then eventually upward within its canopy. Each of these branches, the size of a large tree itself, needed to be inspected. 

Tree scientists look for five signs of beetle damage when performing bark-beetle inspections.

1. Entrance holes created by adult beetles into the bark and wood. These are at an oblique angle.

2. Exit holes created by the larvae. These holes are often perpendicular to the surface of the branch or trunk.

3. The presence of sawdust from beetles burrowing into the wood.

4. Beetle frass (insect poop).

5. Globs of pitch or sap that the tree has exuded to close off the holes.

Foliage dieback can occur when bark-beetle activity is high enough that the tree can no longer transport water and nutrients to the top of its canopy. 

Novel climatic conditions are requiring novel research methods, and these methods were on display during the climb. While the four AFS researchers were inspecting the General Sherman tree’s canopy, researchers with the U.S. Forest Service and National Park Service flew a drone (officially termed an unmanned aerial vehicle, or UAV) with a powerful camera that could zoom in on the tiny bark beetle entrance holes pointed out by the researchers. What a fantastic event and location to test-run the method!  

During the inspection, the researchers reported their findings on a radio to help guide the drone operators to photograph specific locations within the canopy. The ability of the drone to successfully identify bark-beetle activity on branches in the canopy means a new and vital tool has been added to the tree management toolbox.  

The Scientists Report Back After the Climb

After the climb, there was a media event sponsored by the Giant Sequoia Lands Coalition, which is a collaboration of federal, tribal, state, and local agencies, organizations, academic institutions, and nonprofits to coordinate conservation and stewardship of remaining giant sequoia groves. Ancient Forest Society is one of the partners of the Coalition. During the media event, representatives of the media (ABC, NBC, Associated Press, Los Angeles Times, Sacramento Bee, Porterville Reporter, and more) asked questions of the Ancient Forest Society researchers, Sequoia National Park staff, and drone operators.

Anthony Ambrose, who had led the climb up the General Sherman tree, shared his observations after the climb. “I have good news to report. There does appear to be some level of beetle activity in the General Sherman tree, which is not surprising. We found some evidence of entry holes into some of the branches . . . . The adult beetles that are trying to burrow into the bark don’t seem to be making it very deep into the bark. And in some cases where they do get down into the live bark, the tree seems to pitch them out. Overall, there doesn’t seem to be any impacts to the tree. It seems to be successfully fending them off. The tree seems to be very vigorous; the foliage is very healthy.” Phew!

The Future of Giant Sequoias

Ancient Forest Society researchers have been regularly climbing high into giant sequoia canopies throughout the species’ range to study its response to increasingly intense wildfires, droughts, and bark beetle attacks. For the bark-beetle research, they are collaborating with scientists from Colorado State University and are funded by the Forest Health Research Program of the California Department of Forestry and Fire Protection (also known as CAL FIRE).

Stay tuned as the Ancient Forest Society team continues their mission to study and protect the majestic and ancient giant sequoia trees.

Our contributing writer, Allison Kidder, has been a Board Member of Ancient Forest Society since 2023. She has a PhD in plant ecophysiology from UC Berkeley and has been a docent and Managing Editor at the East Bay Regional Parks Botanic Garden since 2017.

Welcome our newest addition to the team!

We are happy to announce that we have brought in a new Program Associate to the team, Erin Burk. Erin is a forester who strives to apply modern silvicultural techniques and forest operations technology to retain and restore old-growth characteristics across the Sierra Nevada. Using her expertise in site preparation forestry and mechanical thinning operations as a precursor to prescribed fire, she is excited to help develop a landscape-scale approach to our mission of studying and protecting old-growth forests. As an experienced climber, digital illustrator, and science communicator based in South Lake Tahoe, California, she is happy to have found a home for all of her diverse interests and skill sets. She has already begun to join us in our fieldwork and we are excited to have her join the team. Welcome Erin!