Trees Can Sing

February 1, 2010

Ever since I spent a week filming the pistachio, almond, and pomegranate harvest for my documentary, I have been interested in the inner life of a tree. I know it sounds completely ridiculous and lord knows I’m probably losing my mind, but keep with me here just for a minute.

In my interviews of everyone working the harvest, from the business-y type ranch managers to immigrant field hands, I asked if they felt a special relationship with the trees that gave them everything — their jobs, and everything that those jobs provide for their lives. Literally, without the orchards in the southern end of the Central Valley, the scale of its economy would be unfathomably smaller.

I can’t say I was surprised by the responses I heard. The suits had no idea what the hell I was talking about, and when I asked one if they had ever read Shel Silverstein’s classic children’s book “The Giving Tree” — about the bond forged between a person and a tree over each others’ lifespans — he had no recollection of such a book existing. On the other hand, the field hands I spoke with, the ones who spent virtually all hours of the day in the orchards, felt a kinship. “Well, I am like a tree, in that I have life, I give, and then I die,” a recent immigrant tells me. He sang to the tree while using a bamboo rod to knock the last nuts from the tree’s highest limbs.

It turns out that the tree was probably singing back. According to a study by Dr. Bernie Krause, trees actually sing. Dr. Krause, a former musician who was in the Greenwich Village proto-folk group The Weavers (he replaced Pete Seeger) and later introduced the moog to the world with the only electronic music performance at the Monterey Pop Festival and an album called “The Nonesuch Guide to Electronic Music,” now studies natural soundscapes. He outlines the basics of his research and theories in this terrific lecture delivered at the California Academy of Sciences.

Krause makes two fascinating points in this lecture that really stood out to me. One concerns the human impact on the environment as measured through images of sonic frequencies. Fast forward about 15 minutes in for evidence of the invisible impact of human inpositions on the environment. It seems totally obvious, but it’s the evidence in sound recordings — the clicks and hums of insects and animals of the habitat before and after — that shows how important the sense of hearing is to our appreciation and understanding of nature. For instance, his study on the synchronization of bullfrog sounds in the Mono Lake Basin before and after a military jet flyover shows both how all those ribbits have their own logic, and the details of how artificial noise destroys that natural process will blow your mind.

The second point concerns the voice of a tree. One really needs to hear his recording from inside the trunk of a tree to believe it (it begins about 34 minutes in). Here is my transcription of the part of the lecture about it. (Sorry if there are spelling errors concerning scientific terminology.)

Trees also sing. We were recording bats, and had a bat detector. Bats send out pings of echo-location to locate insects and other things to eat. We were holding the detector in our hand in Utah and as we got closer to a Cottonwood Tree, we started to receive a constant signal, which was unusual because bats don’t normally emit a constant signal, and as we got closer to the tree, the signal got stronger. We drilled a hole into the trunk and installed a hydrophone and recorded a 70 kHz sound. When I got back to the studio, I slowed it up by a factor of seven and this is what I got (we hear an erie and delightful rhythmic drum beat). Now dang if that ain’t weird.
Now what’s happening here? What we think is happening, is the cells in the xylem and pholum (sp? sorry, I just don’t know these words) are trying to maintain osmotic pressure even when theres no rain, and when there’s no rain for a time they suck in air. So when they suck in too much air, the cells dry up and die, and they burst — which is what you’re hearing. When the cells die they create the rings on the tree, and also when they die, the tree exudes a sap, which draws insects and birds to the tree. So it’s a whole microhabitat created by sound.
I think he’s making a bit of a leap in logic with that final point about the sound creating the microhabitat. But it’s fascinating theory nonetheless. As I think about those millions of trees and acres and acres and acres of orchards artificially transposed onto a desert, I think about what they’re thinking sometimes. But I just never thought that they might actually be saying something.
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