It’s a sound you will probably never hear, a sickened tree

sending out a distress signal. But a group of scientists has heard

the cries, and they think some insects also hear the trees and are

drawn to them like vultures to a dying animal.


Researchers with the u.s. Department of Agriculture’s Forest (line 5)

Service fastened sensors to the bark of parched trees and

clearly heard distress calls. According to one of the scientists,

most drought-stricken trees transmit their plight in the 50- to 500

kilohertz range. (The unaided human ear can detect no more than

20 kilohertz.) Red oak, maple, white pine, and birch all make (line 10)

slightly different sounds in the form of vibrations at the surface of the wood.

The scientists think that the vibrations are created when

the water columns inside tubes that run the length of the tree break,

a result of too little water flowing through them. These fract