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There's a biology professor in Tennessee who can distinguish trees by their sounds.

Wind, rain, wildlife, and how they interact with the different sizes and shapes of leaves and branches all make up what David George Haskell calls the "distinct voices" of trees.

The Sewanee university professor spoke with As it Happens host Carol Off about his new book, The Songs of Trees. Here's part of their conversation:

CAROL OFF: How did you come to realize that trees have their own voices?

DAVID GEORGE HASKELL: I came to that realization, first, through my studies of birds and my work with students — teaching them bird sounds. As part of that, we tried to open our ears to the whole acoustic environment, and after several years of doing that, it became very clear to me that trees around me had their own distinct voices and all sorts of stories were tied up in those voices.

CO: What do you think it is that makes the noise or the song or the voice of the tree?

DGH: The most obvious voice of a tree is when the wind blows through the tree and, of course, the tree then responds by vibrating, and shaking, and tearing apart the air as it passes through the twigs and the leaves. And each tree has its own architecture. Each leaf has its own degree of stiffness and floppiness and shape.

Just as a cello sounds very different from a violin, because of the scale and tautness of the springs and how large the wood is, so too do the leaves and branches on trees. And those voices change through the seasons as well.

CO: For anyone who doubts that trees make sounds and have voices ... you did some recordings of trees. Here's one, I believe, that comes from the Amazon rainforest:

DGH: That recording was made underneath the ceibo tree in the rainforest in Ecuador. And if you hear the little tapping sound, we're hearing the large raindrops coming from the overstory onto the plants below.

Every species has its own rain song, its own rain sound. The big tough leaves of some plants have a much deeper bass note than the tight little snap drum of the smaller leaves ... We can see botanical diversity through our eyes, but if we open our ears that diversity is sonified. Each plant has its own sound as the rain falls on it.

I do think a tree is not really an individual, it's a community. It's formed in a network. - David George Haskell

CO: I want to play another one of yours ... This is in Ontario, in the boreal forest.

CO: A lot of birds competing there. So, what are we hearing?

DGH: The birds are in fact part of the tree's song. Of course, the trees disperse their seeds and are protected from herbivores by the activities of birds. So, I do think a tree is not really an individual, it's a community. It's formed in a network.

What we're hearing here is a balsam fir — the wind passing over the balsam fir in the winter time. The fir sound is softened by deep snow. That recording was from western Ontario, and the forest in western Ontario is fascinating because it's growing on some very, very old rocks. Those rocks have the oldest known fossils of life forms. And what's extraordinary to me is that those life forms are also networked in the way that modern forests are. So there's connection between different organisms — organisms being made from relationships is a theme that goes right back to the very first cellular remains, fossil remains, of life on the planet. We hear that song then echoed up through the ages, now leaping out of the canopy of the beautiful boreal forest in western Ontario.

CO: When you tell people you're headed off into the woods to listen to the trees — and not just the woods, you go to cities to hear trees and listen to them as well — do people ask you what you're smoking?

DGH: I've never been asked about the smoking. But, I have had some interesting conversations at customs. When I flew into Thunder Bay to visit the fir trees, the customs agent asked me, "What are you coming here for?" And, I said, "Well, I'm coming to listen to some trees." He then started a more vigorous line of question about exactly what I was really coming to do." So, I've learned to say, "Well, I've come to visit some parks and natural areas and go hikings." Which is true. But, my intent on those hikes is to listen to the wonderful soundscapes of different places in the world.

CO: What advice would you give to people for how you can tune your ears to listen to trees?

Without judgment, just be present for the physical experience of sounds flowing into our consciousness. Do that over and over again and the trees will befriend you. - David George Haskell

DGH: Go outside and don't go to a special place. Just go into your neighbourhood and repeatedly, over and over again, open your ears and harvest the sounds all around you. Whether those are tree sounds or car sounds or bird sounds. Without judgment, just be present for the physical experience of sounds flowing into our consciousness. Do that over and over again and the trees will befriend you — or come into your consciousness and teach you some of what they're saying.

This story was edited for length and clarity. For more on this story, listen to our full interview with David George Haskell.