I finally got round to watching a little of Autumn Watch tonight. It was very interesting, learning all about beavers, grey seals, red deer and much much more. Then a very interesting and rather odd report came on about the sound of trees. I've neer thought trees would have a sound, it's not like you can hear sound coming from the trees when you're walking through a forest right? However Alex Metcalf used listening devices (see picture) against various trees and recorded the sounds to play through some hanging headphones for passers by to listen to (see picture)
Apparently "you will hear the water being pulled up from the roots to the leaves through the xylem tubes.
The clicking sound that you will hear is produced by the water passing through the cells and cavitating."