Ancient sequoia trees suffering in California drought

California’s four-year drought has killed millions of trees in the Sierra Nevada mountain range and has scientists worrying about the region’s giant sequoias.

The famous thousand-year-old trees require more water than any other species on Earth, but warm conditions during the past two winters have reduced the snowpack that provides their main source of water.

Sequoias pull water from the soil all the way up to the tops of the trees, according to University of California, Berkeley researcher Wendy Baxter. Examining how much tension the water is under as it travels upwards and into each leaf tells researchers the level of stress each tree is experiencing.

The greater the pressure required to push the water out, the more stressed the tree becomes. Less water causes air bubbles to form and prevents the water from moving up the tree. If this happens, cell after cell collapses and the tree eventually dies.

Nathan Stephenson, a biologist with the U.S. Geological Survey, said he has noticed brown foliage on some of the giant sequoias in the park, something no one has reported before.

While a lot of the park’s sequoias appear healthy, many also show symptoms of stress. Scientists aboard the Carnegie Airborne Observatory use instruments to study the sequoias’ water content and determine which park regions are in the most distress.

One option to help the giant trees is to burn part of the forest, which would reduce the number of trees and give the burn-resistant sequoias more access to water, according to Sequoia & Kings Canyon National Park ecologist Koren Nydick.

“There’s less competition for the larger trees that remain behind,” Nydick said. “So the larger trees have more access to water and nutrients and helps them get through the drought.”

Stephenson said researchers hope to avoid unnatural actions like burning or drip irrigation to help the trees, but continuation of the drought and other global warming effects may leave them no choice.

Vocab

• giant sequoia — a type of redwood that can grow hundreds of feet tall and live for thousands of years, found primarily in California
• greenhouse gas — a gas that contributes to global warming by absorbing infrared radiation, e.g., carbon dioxide and chlorofluorocarbons