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The Sounds of Thirsty Trees


And if you're just joining us, this is WEEKENDS on ALL THINGS CONSIDERED from NPR News. I'm Jacki Lyden.

Remember this scene from "Lord of the Rings: The Two Towers?" Treebeard, Pippin and Merry come upon the wasted forests of Isengard. Treebeard, a giant tree himself, laments...


JOHN RHYS-DAVIES: (as Treebeard) Many of these trees were my friends, creatures I had known from nut and acorn.

BILLY BOYD: (as Pippin) I'm sorry, Treebeard.

RHYS-DAVIES: (as Treebeard) They have voices of their own.

LYDEN: Voices of their own. Tolkien might've been on to something. Scientists around the world have learned that trees do indeed make sounds. And now, a team of physicists in France have determined specifically what sounds trees make when they're thirsty for water. As it turns out, there are a lot of thirsty trees out there.

Two out of three trees are dangerously parched the world over, at least that's what a study published in Nature determined late last year. Biologists looked at hundreds of tree species in 80 locations around the world and found...

DR. ALEXANDRE PONOMARENKO: If you increase a little bit of stress, potentially, a lot of trees may die from this drought even.

LYDEN: That's Dr. Alexandre Ponomarenko. Now, you can't use the human eye to detect a tree in desperate need of water. Well, water trees look virtually the same as their thirsty brethren, so Ponomarenko led a team of physicists at the University of Grenoble in France to detect trees' stress through sound.

PONOMARENKO: But we didn't know exactly where the sound is coming from, so this is where we start to work.

LYDEN: They designed a sensitive microphone to attach to the tree to monitor the sounds, and this is what they heard. Are you ready?


LYDEN: Here that? It was quick, I know. So let's take it again.


PONOMARENKO: We saw in our studies that every time there's a sound, there were a bubble appearing inside the tree.

LYDEN: And when those little bubbles appear, the tree is thirsty.

PONOMARENKO: When the bubble appear, it can trigger all the bubble around, and it's very, very bad for the tree.

LYDEN: Don't try this at home, though. These sounds are slowed down a thousand times so that they can be heard by the human ear. Not all hope is lost. Dr. Ponomarenko says that as his team compiles data, they can pinpoint exactly when trees want water. The thirstier they are, the louder they become.


LYDEN: He says one day, scientists or park rangers or anyone can carry these light, specialized microphones out into the field and know just when our forests are on the brink of disaster. Then we have to learn how to save them.

(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.