DAVID GREENE, HOST:
When you're more than a thousand years old, you have seen a lot. That can certainly be said for the giant Sequoias, redwood trees that tower up towards the sky. When you're among these trees in a place like California's Sequoia National Park, you can almost feel like you're in a fairy tale. But even if these trees have seen it all, scientists are worried that nothing prepared them for the awful drought in California right now. Here's Ezra David Romero from Valley Public Radio.
EZRA DAVID ROMERO, BYLINE: Anthony Ambrose is on the hunt in the giant forest in Sequoia National Park, but not for deer. He's aiming a crossbow at a tree 30 feet around and 300 feet tall.
ANTHONY AMBROSE: A lot of it is luck.
ROMERO: Ambrose connects fishing line to a plastic pipe arrow and mounts it into the crossbow.
AMBROSE: It's not, like, super precise. You can kind of get a good idea of where it's going to go. Did it come down?
UNIDENTIFIED MAN: Yeah.
ROMERO: Ambrose, a UC Berkeley tree biologist, isn't trying to harm the agent sequoias. He wants to help them. He shoots a line over a limb so a climber can eventually scale the tree. On a hike last summer, a scientist noticed the leaves of the giant sequoias were browning and more sparse than usual. This finding got ecologists like Ambrose thinking. Did the drought cause this?
AMBROSE: We're just trying to get a better understanding of how giant Sequoia trees respond to severe drought. We have very little understanding of, like, well, how severe of a drought does it take to, like, kill a giant Sequoia tree.
ROMERO: This notion that the giant sequoias could die because of drought has brought together multiple agencies for the first health-related study on the giant sequoia. Some of these trees are over 3,000 years old and have faced many droughts in their lifespans. But perhaps this drought is too much for them.
KOREN NYDICK: 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.
ROMERO: Koren Nydick is the lead scientist behind the study. More than 40 trees are in the process of being analyzed for stress from four years of drought and warming temperatures.
NYDICK: That's the kind of stress that eventually could kill a tree.
ROMERO: Researchers want to compare data from healthy sequoias with those showing signs of decay. Gathering all this information is labor-intensive. Tree biologists like Wendy Baxter are trying to understand how these sequoias respond to drought conditions.
WENDY BAXTER: We're going to assess the water status of those samples that we collect. So that's sort of an instantaneous measurement of the water status of the tree at that point in time.
ROMERO: This is how it works - after a researcher loops that rope over a branch hundreds of feet high, tree biologists like Baxter attach themselves to the line and literally hoist themselves into the branches.
BAXTER: Hey, Anthony, I'm about to start heading up this tree.
AMBROSE: Copy that.
ROMERO: At the moment, the scientists are setting up rainfall sensors in the branches themselves. 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.
BAXTER: All right. I'm coming down.
ROMERO: Researchers will also study the sprigs of foliage in the laboratory. The goal of this study is twofold. Scientists like Ambrose want to figure out how the drought is harming these historic trees. And he says they want to be able to fly over the forest, look at the color of the leaves and understand how stressed these areas are.
AMBROSE: Being able to relate the measurements that we get on the ground to the airborne data, and assuming we get a nice relationship, then they'll just be able to fly periodically over the whole forest and get, like, a spatial map of tree water status or tree stress levels.
ROMERO: But for now, the researchers are rushing to collect data in case a strong El Nino brings a large amount of rain and snow this fall. For NPR News, I'm Ezra David Romero in Sequoia National Park.
NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.