Researchers map effects of drought on giant sequoias

Anthony Ambrose/Courtesy

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In the wake of prolonged drought conditions, researchers are looking at the effects and impacts on giant sequoias.

By collecting ground and aerial data, the researchers are creating maps that will inform conservation tactics, watershed management, and biodiversity and animal habitat protection. A total of 50 trees in four locations throughout Sequoia and Kings Canyon National Parks were carefully climbed and equipped with monitoring devices in early August.

The study is a collaboration among UC Berkeley, United States Geological Survey, National Park Service and Carnegie Institution for Science at Stanford, all of which funded their own respective research projects. Separately but working together, the researchers will compile data to create the conservation maps.

Last year, Gov. Jerry Brown declared a state of emergency because of severe drought. Although Californians went beyond Brown’s 25 percent conservation mandate, the drought increased the risks of damage to the sequoias.

“Watersheds are critical here because that’s where all our water is coming from, and forests have a critical role to play in how well when we get rain and where it will go,” said Greg Asner, an ecologist from the Carnegie Institution for Science. “Forests act as sponges, and so when snow falls in the Sierras and it melts or it rains, the forest picks it up and releases it at a rate through the landscape … that is conducive to us collecting it with a reservoir.”

Last October, USGS ecologist Nathan Stephenson noticed that giant sequoias were showing signs of foliage dieback in Kings Canyon National Park. His observations spurred the National Park Service to fund research. Stephenson then recruited Asner for the project.

In a lab-equipped plane, Asner and his team scour up and down California with precise laser technology to create 3-D renditions of the forests. The remotely sensed data collected from Asner’s trips can tell scientists about the chemical condition of the trees, including their levels of water, nitrogen and carbon dioxide. Based on that data, the computers on board determine which areas have trees with high stress and which ones are surviving despite drought conditions.

“From the air, we’re uniquely capable of seeing the 3-D structure and chemical composition of the forest like a blood test,” Asner said. “At the same time, we have field people from Berkeley collaborating and accessing the connection to other aspects of the tree we can’t see from the air. Once the connection is made, we can map really big areas, applying it to the giant sequoias but also applying it to the entire state.”

The 3-D maps will be calibrated to the information collected by ground researchers such as UC Berkeley postdoctoral researcher and tree biologist Anthony Ambrose, who led most of the field work and just finished rigging the 50 giant sequoia trees in order to study sequoia leaves.

“We’re concerned that with increasing climate change, it could be a tipping point,” Ambrose said. “(It could be) a threshold that these trees cannot recover from if the drought is severe and long enough.”

Ambrose said that while some sequoia trees are absolutely fine, those with less access to water are stressed and shedding a significant amount of foliage, which he suspects is an adaptation tactic. The research should give scientists a better understanding of the sequoia’s resiliency and give park management the data needed to make prioritized and informed decisions when it comes to conservation.

According to Koren Nydick, an ecologist from the National Park Service, the research will tell where park management can make the biggest positive impact in the forest and allow them to alert the public if sequoias are in danger. By striving to understand the tree’s behavior during dry seasons, Nydick said, the scientists may be able to make a difference.

“Giant sequoias aren’t your normal tree. They’re awe-inspiring, and they mean a lot to people,” Nydick said. “We’ve been given the responsibility to protect them, among other things, because we don’t want to be counting dead sequoias.”

Contact Jamie Nguyen at [email protected].

A previous version of this article might have implied that UC Berkeley took a minor role in the sequoia research. In fact, UC Berkeley researchers are among the collaborators, and Anthony Ambrose led the field work effort for the project.