18 May 2018

Tree-listener brings the hidden world of trees alive

Tune in to the sounds beneath the bark with Alex Metcalf's tree-listening microphones.

By Sandra Howard

Shine shines through the trees at the Woodlands in wakehurst

“Watching the incredible reactions on people’s faces when they listen to the sounds of water surging up through a trees trunk, is what makes my work a complete privilege,” explains Alex Metcalf, the world’s first tree-listener.

Alex, who always appreciated the natural world, began to wonder whether it was possible to hear the inner workings of a tree when he was studying for an MA in Product Design at the Royal College of Art in 2005-7.

After discussing his ideas with his tutors, Alex came up with the idea of designing a unique tree listening device - which looks rather like an old-fashioned hearing trumpet. He designed and built the instrument as part of his Master’s degree assignment.

After pressing the listening trumpet against numerous trees Alex was amazed by how well it worked.

“You will hear a quiet popping sound that is produced by the water passing through the cells of the Xylem tubes and cavitating as it mixes with air on its way upwards. In the background is a loud deep rumbling noise that is produced by the tree moving and vibrating,”

He added: “It is this water movement that keeps the tree alive by providing the leaves with the necessary water to turn into sugar as a source of food, and as part of its cooling system on a hot sunny day.”

Tree-listening at Wakehurst

Beneath the bark

To be certain that what he was hearing really was the water moving Alex took his creation to Royal Botanic Gardens, Kew.

Here he was introduced to Steven Jansen, a Kew scientist who had a PhD in the cavitation of water in the xylem tubes.

Alex said: “Steven was the expert but even he had never actually heard the water move before. He was blown away by the idea. After much discussion we took a tree branch into one of the science laboratories at Kew.

Steven made the water travel through the branch at 2 bar / 30 psi. He pushed the water through using a pressure bomb and using my listening trumpet I could confirm that the noises I could hear was the water moving behind the bark."

Alex had to display his work at the Royal College of Art along with that of other students.

But rather than stand his trumpet on a plinth he came up with the novel idea of recording what he was hearing and then hanging lots of headphones from the lower branches of a tree in nearby Kensington Gardens and linked them to the recording.

Alex stood by the tree housing his installation for two weeks and recorded more than a thousand people queuing to hear the hidden life inside this metropolitan tree. He encouraged people to stand close to the bark and look up into the canopy.

Emmenopterys henry
Emmenopterys henry

A global trend

“Standing under the branches with the headphones on gives you a physical connection with the tree and makes it a really immersive experience.”

Now, Alex shares these sounds at country shows and workshops  throughout the year. He has been all over the world demonstrating his device.

Alex has a permanent installation in the Natural History Museum in LA and has been to Italy to listen to the water inside a tree located inside of a volcano.

In December last year Alex appeared in the BBC programme Judi Dench: my love of trees.

Alex said that Dame Judi was completely overcome by the experience. “She was so emotional when she heard what was really going on beneath the bark. It was a moving moment for all of us.” He added: “Judi said she would never look at trees in the same way again!”

Alex Metcalf will be sharing his Tree Listening Project at Wakehurst’s Wild Wood Festival, 26 – 28 May 2018.

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