Nothing may define our state more than majestic redwoods trees, from the towering coastal sequoia sempevirens to their mammoth Sierra Nevada brethren, the giant sequoias. So it's surprising, then, how little we know about how redwoods will survive in the coming global warming crisis. How will less rainfall and higher temperatures affect them? Will the world's tallest and largest trees die out? Or will their primary habitat move farther north?
UC Berkeley Professor Todd Dawson hopes to begin answering some of these questions this summer when he and his colleagues launch an in-depth study of the giant sequoias near Sequoia and Kings Canyon National Park. The study is being funded by a grant from Save the Redwoods League, a nonprofit dedicated to protecting the magnificent trees and funding research on them. Dawson and a group of ten to twelve researchers plan to spend two weeks climbing the nearly 300-foot tall giant sequoias, the world's largest trees in terms of sheer mass, and measuring their enormous branches and extensive crowns. "We'll actually spend a great deal of time up in the crowns themselves," Dawson said in a recent interview. "We're trying to understand how they will respond to future changes in their environment."
Dawson and his UC Berkeley graduate student Anthony Ambrose, along with Humboldt State University Professor Steve Sillett, will conduct their study this July in Whitaker Forest, a giant stand of old-growth sequoias managed by the University of California. Sequoias are most famous for their massive trunks — sometimes big enough to drive a car through. The best known is "General Sherman," the world's largest tree, a 275-foot-tall behemoth in Sequoia National Park that sports a girth 109 feet around.
Dawson and his colleagues begin their ascent into the sequoias' canopy by using a crossbow or a slingshot to shoot a small line over a tree's biggest branch. They then pull themselves into the crown structure, employing basic climbing techniques and being careful so as not to harm the gentle giants, the oldest of which can reach ages of 3,500 years. "We certainly don't want to damage the trees at all," Dawson said, adding that they do not use spikes or any other equipment that might affect the trees' bark.
The teams then will take meticulous measurements of every branch in about twelve to fifteen trees, along with a sampling of leaves. Dawson and his collaborators will then feed the data into complex computer models that will provide estimates of how well the sequoias can weather climate change, from increasingly smaller snow packs to longer periods of drought and more intense summer heat. The models also will allow researchers to predict how the trees will be affected by increasing amounts of greenhouse gases, and whether they will be able to digest more carbon dioxide when they have less water to drink. "It's essential information if we want to make sound predictions about how these trees are going to do in the future," Dawson said. "If snowpacks go down, and stress goes up, then these plants may not be able to cope with an increase in carbon dioxide."
The good news is that giant sequoias are incredibly resilient. Climate change, for example, is already being blamed for beetle infestations that have led to mass die-offs of pine trees in certain parts of the country. Giant sequoias, however, are "very resistant to pests," Dawson noted. But that doesn't mean the trees will escape human-caused changes to their habitats. "If the climate change keeps ramping up the way it has, then a lot of plants could be doomed, especially in Mediterranean climates like ours," Dawson said.
Save the Redwoods League also has awarded grants to two other UC Berkeley researchers, Scott Stephens and Kevin O'Hara. Stephens also will be studying in Whitaker Forest, examining how a decades-old forest-trimming plan has affected the health of the giant sequoias. The program attempted to mimic the effects of smaller fires that improve the health of forests, and involved cutting down smaller-diameter trees and removing fallen ones to allow the larger trees to become stronger and more fire resistant, said Dan Porter, director of science and planning for Save the Redwoods League. Stephens will then input the data into computer models that predict the severity of a fire, depending on the amounts of fuel in a particular forest.
O'Hara, meanwhile, will study the effects of last summer's wildfires on coastal redwood forests in Monterey, Santa Cruz, Sonoma, Mendocino, and Humboldt counties. Typically, coastal redwood forest fires tend to be mild, because the trees grow in California's fog belt and receive sixty to eighty inches of rain a year. But last year, during the drought, some of the fires were far more intense than unusual, which raised questions about whether the state's longstanding practice of allowing redwood forests to grow thick with fuel is the best idea in the coming era of climate change. "We might be at the tipping point in terms of fire suppression," Porter said. Correction: An earlier version of this story misstated Professor Dawson's first name. It is Todd -- not Ted.
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