Disturbances Benefit Giant Sequoias

Long-term Dynamics Following Fuel Reduction Treatment in a Giant Sequoia–Mixed Conifer Forest

High-severity treatments have boosted the growth of isolated giant sequoias in what is now Giant Sequoia National Monument. Photo by Rob York
High-severity treatments have boosted the growth of isolated giant sequoias in what is now Giant Sequoia National Monument. Photo by Rob York

Being dwarfed by Earth’s most massive tree, the giant sequoia (aka “Sierra redwood”), fills you with wonder. It’s hard to believe that a living thing can be so enormous and old. It may be alarming to see these forests on fire, but research funded by your gifts shows that disturbances such as these actually are good for giant sequoias.

Using chainsaws and controlled burns, Harold Biswell began some long-term experiments in the Sierra Nevada in the 1960s. Known to his critics as “Harry the Torch,” the University of California, Berkeley, professor established plots in which bushes, detritus and trees less than 13 feet tall were cleared away to reduce the potential for huge, catastrophic wildfires.

Some 40 years later, a research team led by University of California scientists Scott Stephens and Rob York revisited Biswell’s plots. Partly funded by Save the Redwoods League and you, our members, they examined how his “low-severity” disturbances had affected the structure of the forest. Among the evidence they collected were core samples comparing the growth rings of the plots’ giant sequoias with those of sequoias in undisturbed forests.

What the researchers found was that sequoias in the disturbed plots grew faster than undisturbed sequoias in the first six years.

“Sequoias are so big and long-lived, you might think they would be immune to competition,” York said. “But we actually found they were competing for resources with these very small trees.”

The effect was not long-lasting, however. Twelve years post-disturbance, growth rates in the two groups of trees were nearly the same. And today a tinder-filled understory has grown back.

More long-lasting effects have been created by higher-severity treatments. In the 1980s, the US Forest Service cleared out almost everything except large sequoias in plots ranging from 7 to 42 acres. Twelve years later, those sequoias had doubled their “radial growth.” Unlike Biswell’s low-severity plots (and sequoias in most of the rest of Sierra where fire has been excluded), those sequoias have also been able to establish seedlings.

The takeaway for land managers? Disturbances benefit giant sequoias. Higher-intensity disturbances enhance their growth the most, are longer lasting, and encourage reproduction. “But managers should consider a range of severities that are adjusted over time,” York said.

You can help us learn more lessons like these to understand how to best protect redwoods and what the forest’s long-term survival means to the health of people and our planet. Please donate today.

Learn more about managing giant sequoia forests with fire; check out our blog, “Setting Fire to the Forest.

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