Trees Cry Out

Carl Blechen (July 29, 1798 – July 23, 1840), Young Oak
Carl Eduard Ferdinand Blechen (1798 – 1840)


When drought hits, trees suffer—a process that makes sounds.
Scientists have known for decades that microphones can pick up the sounds that trees make.
Now, scientists may have found the key to understanding these particular cries for help.
In the lab, a team of French scientists has captured the ultrasonic noise made by bubbles forming inside water-stressed trees.
Because trees also make noises that aren’t related to drought impacts, scientists hadn’t before been able to discern which sounds were most worrisome.

The findings could lead to the design of a handheld device that allows people to diagnose stressed trees using only microphones.
Such a device may be particularly important as droughts become more common and more severe.

Across western North America, from Mexico to Alaska, forest die-off is occurring on an extraordinary scale, unprecedented in at least the last century-and-a-half — and perhaps much longer. All told, the Rocky Mountains in Canada and the United States have seen nearly 70,000 square miles of forest — an area the size of Washington state — die since 2000.

In 2005 Colorado researchers noticed that aspens were suddenly dying in large numbers. The die-off is called Sudden Aspen Death, or SAD.
It’s growing at an exponential rate – and killing not only mature trees, but the root mass as well.
An aspen grove is the offspring of a large single underground clonal mass, which sends up shoots.  “The whole organism is disappearing and it has profound implications,” said Wayne Shepperd, of the Forest Service. “When the roots die, groves that are hundreds or thousands of years old aren’t going to be there anymore.”

A study published in Nature last fall suggested that trees in many places—from tropical rain forests in South America to arid woodlands in the U.S. West—already “live on the edge,” meaning their cavitation rate is almost as high as they can sustain.
Sizeable areas of forest in Australia, Russia, France, and other countries have experienced die-offs, most of which appears to have been caused by drought, high temperatures, or both.

Shifts in rainfall patterns and increasing temperatures associated with climate change are likely to cause widespread forest decline in regions where droughts are predicted to increase in duration and severity