This movement of water is what keeps the tree alive. It provides the leaves with the necessary water to turn into sugar as a source of food, and is part of its cooling system on a hot and sunny days.
When a tree is in leaf there is a constant flow of water moving up from the roots to the leaves through the xylem tubes. As the leaves lose water through evaporation the cells become drier and they in turn pull water from the next cell. The water molecules cling together to form a water chain from the leaves to the root; this is called tension-cohesion. In hot dry conditions the leaves can lose more water than the roots and water columns can supply, which brings air into the system. When the air and water meet and mix this causes an audible pop, known as cavitation.
Using the headphones you will hear a quiet clicking sound. This is produced by the water passing through the cells of the xylem tubes and the cavitation process as this mixes with air on its way upwards. In the background is a deep rumbling sound. This is the whole tree vibrating. You are listening to a recording of the water moving in this oak tree and Metcalf is currently researching technologies that will allow the audience to listen to this process ‘live’. Alex Metcalf is an artist and designer who creates installations and artworks that engage participants in natural processes.