UC Berkeley tree biologist Wendy Baxter is about to begin her ascent of a giant sequoia. For the first time in Sequoia National Park's history, the trees are showing visible signs of exhaustion due to the record drought. Photo: Ezra David Romero / Valley Public Radio

By Ezra David Romero
17 August 2015

(NPR) – The giant sequoias in the Sierra Nevada are one of America's treasures, but for the first time in Sequoia National Park's history, the trees are showing visible signs of exhaustion due to the drought.

On a hike last summer, a scientist noticed that the needles of the giant sequoias were browning and more sparse than usual. This finding got ecologists thinking: Did the drought cause this?

"We're just trying to get a better understanding of how giant sequoia trees respond to severe drought. We have very little understanding of … how severe of a drought it takes to kill a giant sequoia tree," says Anthony Ambrose, a tree biologist at University of California, Berkeley.

This notion that the giant sequoias could die because of drought has brought together multiple agencies, including the National Park Service, Stanford University, the U.S. Forest Service, the U.S. Geological Survey and the Carnegie Airborne Observatory, for the first health-related study on the giant sequoia. Ambrose is part of a team working on — and climbing up — trees in Sequoia National Park.

Some of the sequoias in the park are over 3,000 years old and have faced many droughts in their lifespans. But perhaps this drought is too much for them.

"The good news is that there were lots of trees that still seem healthy, but there was this smaller amount that seemed to be stressed — and stressed in ways that we haven't seen documented before in the parks," says the study's lead scientist, Koren Nydick, with Sequoia National Park.

More than 40 trees are in the process of being analyzed for stress from four years of drought and warming temperatures. "That's the kind of stress that eventually could kill a tree," Nydick says.

Researchers want to compare data from healthy sequoias with those showing signs of decay. [more]

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