That is not the only time trees make a noise â€" they do it when they are scared, in pain, cold… A team of French scientists at Grenoble University in France led by Physicist Alexandre Ponomarenko have separated these sounds and analysed those that they need to know. (After all if they helped us understand how trees scream when they are being cut, it would be bad for business).
How do trees take in water? Essentially, they drink from a really long straw. Inside tree trunks are bundles of specialized tubes called xylem, which lift liquid to the highest leaves and branches.
Because trees are so tall, the liquid in the xylem can be under intense pressure -Imagine using a straw to slurp the last few drops from the bottom of your glass: You have to increase the pressure. In drought-stricken trees, this increased pressure can cause the water column to break, allowing dissolved air to form bubbles that block water flow.
These events are called cavitation and while trees can withstand some, too many can be deadly. In simple terms: one of the main functions of wood is to transport water and when a plant or tree is under stress, the water transport system stops working.
Microphones can pick up the noises that cavitations make. When the tree is getting less water, the noise of the cavitations and the bubbles increase. The sound waves of a tree in water-distress are distinct. This discovery could help scientists figure out when trees are parched and need emergency watering. Imagine a device attached to a tree that could listen for sounds of thirst and then trigger an emergency-watering system. Two companies of geologists in Arizona are building a low-cost acoustic detector drawn by the age-old allure of communicating with plants. They hope to be able to decode the language that says 'I'm thirsty' to the one that says 'I'm cold' to the one that says 'ouch , you're hurting me'.
Britain's Royal Botanical Kew Gardens has an exhibit that allows visitors to don head phones and listen to the inner rumblings of a eucalyptus tree, a project funded by the Natural Environment Research Council. Researchers are looking at the differences in sounds between various tree species. By comparing trees that grow in similar conditions, the research can reveal which trees are most efficient at transporting water through their trunks. This is going to be important as the earth grows warmer and droughts increase. A study printed in the magazine 'Nature' says that trees in many placesâ€"from tropical rain forests in South America to arid desertsâ€"already 'live on the edge,' meaning their cavitation rate is almost as high as they can sustain.
Certain species, like pine trees and Douglas firs, can repair the damage, filling the embolisms on a daily or even an hourly basis. Trees considered the most drought-tolerant, such as junipers, are found to be the worst at repairing embolisms. Broad-leaf plants are better at fixing the damage caused by dry pipes. In future, during the predicted severe droughts, the plants that have a harder time repairing embolisms are more likely to die. It's the plants that can repair embolisms which are going to survive.
