Trees can make noises when short on water

Like a person gasping for air when it's in short supply, living trees make noises when they are running out of water, and a team of French scientists is a step closer to pinpointing the noises.

Lab experiments at Grenoble University in France have isolated ultrasonic pops, which are 100 times faster than what a human can hear, in slivers of dead pine wood bathed in a hydrogel to simulate the conditions of a living tree.

Researchers exposed the gel to an artificially dry environment and listened for the noises that occurred as air bubbles built up, similar to what occurs to trees during droughts. Air bubbles form when a tree is trying to suck moisture out of dry ground during droughts. As leaves on a tree collect carbon dioxide, they open their pores, a process that leaves them vulnerable to water loss.

Evaporation from the leaves pulls water up the trees in a state of tension. The tree vacuums up water from the ground through its root system, pulling it up through tubes. There are thousands of them in a typical tree, connected by pit membranes (sort of like a two-way valve). Tension in the xylem tubes increases in times of drought, then cavitates.Douglas firs and pine trees can repair this damage as frequently as every hour, said Katherine McCulloh, a plant ecophysiologist at Oregon State University, in a past Our Amazing Planet interview. The bubbles are deadly for other species, however, if the bubbles block the water's flow