Is The Drought Killing The Giant Sequoias?

Aug 4, 2015

The Giant Sequoias in the Sierra Nevada are one of America’s treasures.  But for the first time in the parks history the trees are showing visible signs of exhaustion due to the drought:  thin and browning leaves. Valley Public Radio’s Ezra David Romero hikes into one of the largest groves of Giant Sequoias and finds a crew of scientists rushing to gather data by scaling the monstrous trees.

In order to gather data Anthony Ambrose has to hook a Giant Sequoia by shooting a pipe arrow with fishing wire over a limb of the tree.
Credit Ezra David Romero / Valley Public Radio

Anthony Ambrose is on the hunt in the Giant Forest in Sequoia National Park, but not for deer or wild boar.

He’s aiming a cross bow at a Giant Sequoia tree 30 feet around and 300 feet tall.

“A lot of it is luck,” Ambrose says.

Fishing line is connected to a plastic pipe arrow and a reel is jimmy rigged to the cross bow.

“It’s not like super precise,” says Ambrose. “You can kind of get a good idea of where it’s going to go.”

He shoots the arrow with fishing line connected to it at a limb of the giant tree over 250 feet in the air.

Unlike a hunter, Ambrose, a UC Berkeley Tree Biologist, isn’t trying to harm the ancient trees. He wants to help them. He shot a line over a limb so a climber could eventually scale the tree.

The researchers are scaling trees in four different areas of Sequoia National Park.
Credit Ezra David Romero / Valley Public Radio

On a hike last summer a scientist noticed the leaves of the Giants Sequoias were browning and sparser than usual. This finding got scientists thinking. Did the drought cause this?

“We’re just trying to get a better understanding of how Giant Sequoia trees respond to severe drought,” Ambrose says.  “We have very little understanding of like well how severe a drought it takes to kill a Giant Sequoia tree.”

Koren Nydick and Anthony Ambrose are leading the project.
Credit Ezra David Romero / Valley Public radio
"The good 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 we haven't seen documented before in the parks." - Koren Nydick

This notion that the Giant Sequoias could die because of drought has brought together agencies like the National Park Service, UC Berkeley, Stanford, the US Forest Service and others for the first health related study on the Giant Sequoia. The U.S. Geological Survey and the Carnegie Airborne Observatory are also involved in the research. 

Some of these trees are over 3,000 years old and have faced many droughts in their lifespan. But perhaps this drought is too much for them. While a lot of these trees look healthy, many of the are under stress.

“The good 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 we haven’t seen documented before in the parks,” says Koren Nydick the lead scientist behind the study with the 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,” says Nydick.

It’s these groups goal to avoid tree die off by comparing data of healthy Giant Sequoias to those showing signs of decay.

Gathering all this data is a labor intensive task.

This is how it works. A researcher climbs the rope previously looped over a branch over 250 feet high. And then tree biologists like Wendy Baxter attach themselves to the line and literally hoist themselves up a rope into the branches of the tree.”

“Hey Anthony, I’m about to start heading up this tree,” says Baxter.
“Copy that,” says Ambrose.

At the moment the scientists are setting up rainfall sensors in the monstrous trees. At the end of August they’ll return and take clippings from different heights for testing in a pressurized chamber to measure water content in the leaves and the stress the drought has put on the tree.

“We’re going to assess the water status of those samples that we collect,” Baxter says. “That’s sort of an instantaneous measurement of the water status of the tree at that point in time.”

Some Giant Sequoias are more than 3,000 years old.
Credit Ezra David Romero / Valley Public Radio

Researchers will also study the sprigs of foliage in the laboratory.  The goal of this study is two-fold. The scientists want to figure out how the drought is harming these historic trees. They also want to be able to fly over the forest, look at the color of the leaves and understand how stressed those trees are. They’ll do this by pairing the data they collect with aerial data.

“Being able to relate the measurements that we get on the ground to the airborne data assuming we get a nice relationship, then they’ll just be able to fly periodically over the whole forest and get a map of tree stress levels,” Ambrose says.

But for now the researchers are rushing to collect data in case a strong El Nino brings large amounts of rain and snow this the fall.

"Alright, I'm coming down," says Baxter.