ARI SHAPIRO, HOST:
Giant sequoias live up to their name, soaring hundreds of feet into the sky. They are also some of the longest-living organisms on the planet. Some are more than 3,000 years old.
MARY LOUISE KELLY, HOST:
But last summer, the Castle Fire ripped through California's southern Sierra Nevada and killed unprecedented numbers of the trees.
CHRISTY BRIGHAM: There's too many to count. And we'll probably never know how old they were or how many, you know, multiple thousand years of living history were lost in this fire.
SHAPIRO: Christy Brigham and her colleagues at the National Park Service have now attempted to count what's been lost with preliminary surveys. They say as many as 10,000 giant sequoias may have died in that single fire. That's one-tenth of all the giant sequoias living today.
KELLY: To see so many sequoias killed by fire is tragic but also paradoxical because the trees actually need fire to survive.
BRIGHAM: They actually rely on fire to open their cones and create small openings in the canopy and clear the soil for their seedlings to grow.
KELLY: In the past, low-intensity fires danced along the forest floor. Today they have grown much more severe and are destroying the forest canopy.
BRIGHAM: What we think is happening is that a hundred years of fire suppression, combined with climate change-driven hotter droughts, has changed the structure of the forest. The forest is more dense, and that has really changed the way fires are burning in the Sierra Nevada.
SHAPIRO: Brigham says the fire destroyed not only these trees but all the useful services they provided, too.
BRIGHAM: They are structure for birds and mammals. They're shading the soil. They're helping - their roots are helping keep the soil in place. They are sequestering carbon, taking carbon out of the atmosphere.
SHAPIRO: Ten thousand dead trees is such a large number that Brigham says it should serve as a wake-up call.
BRIGHAM: It is a reason to double-down on increasing the forest health and making the remaining groves and the forest as a whole resilient to wildfire, and when we have fire, as we will, we don't have these devastating losses.
KELLY: The hope is to bring back gentler fires that spawn new life and preserve these ancient guardians of the Sierra Nevada.
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