Want to know if a tree is thirsty? Listen. It'll tell you.
Wednesday, July 20, 2016, 1:50 PM - As recent weather patterns have shown, humans and animals aren't the only ones that get scorched by the sun.
The earth itself is also under heat distress when a drought hits. But while a field of grass displays more obvious signs of damage, the same couldn't be said for trees. Many will see wilting and even defoliation after a short dry spell, but more severe damage -- such as stunted growth or even death of a plant -- often happen over the long-term.
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So how can we protect aged-old trees when a hot and dry spell takes over?
Scientists say the answer is actually more obvious than we think. All we have to do is listen and understand.
Trees make a distinct noise when thirsty. Ironically, the sound they make comes from a process similar to slurping the last few drops of water from a tall glass, through a straw.
Xylem are essentially the "straws" within a tree. They're bunches of tubes that depend on the force between water molecules and those between plant and water cells used to lift liquid to the tips of tall branches and far-stretched leaves, National Geographic's Gabe Popkin explains.
It takes extreme pressure (much more intense than the atmosphere around us), to draw the water up, "but the attractive forces between neighbouring water molecules keep the water column intact," Popkin writes.
Similar to slurping the last few sips of water through a straw, sucking up liquid during a drought calls for increased pressure. The increase in pressure can lead to a water column breaking, which causes dissolved air to create bubbles, blocking water flow.
This is known as a cavitation. Trees can handle a few, but too many can be deadly Popkin says.
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A group of French scientists has captured an ultrasonic noise that generates when these bubbles form inside drought-stressed trees. It's decades-old information that microphones can pick up the sound of cavitations, but without seeing inside trees, scientists couldn't be sure of the origins of the sound.
Along with his team, physicist Alexandre Ponomarenko of France's Grenoble University discovered this by mimicking the conditions within a living tree, using a thin piece of pine wood and a gel capsule filled with liquid. Water was then evaporated from the capsule, recreating drought conditions. The wood underwent the cavitation process and the bubbles formed.
Ponomarenko told Popkin that these findings open doors for new technology to assist in diagnosing heat-stressed trees, all by use of a microphone.