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Can we save forests by listening to trees?

Column: Two scientific discoveries could help reduce forest fires and prevent bug infestations.

By Robert C. CowenColumnist for The Christian Science Monitor / October 2, 2008

A maple tree shows early fall color in Richmond, Vt.

Toby Talbot/AP

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An old Broadway song laments, "I talk to the trees, but they don't listen to me." Now researchers are finding it pays to let the trees "talk" to them.

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Humans have lived with trees for millennia. Yet two recent studies reveal that we still have a lot to learn about the subtleties of how they function. It's knowledge scientists need to better understand how trees fit into Earth's ecosystems. That understanding is crucial to estimating how much we can count on trees to soak up some of the global warming-related carbon dioxide humans are putting into the air.

One study involves listening to the ultrasonic complaints of drought-stricken, beetle-infested piƱon pines, yielding new insights into the tree's plight. In another line of research, investigators have solved the mystery of how trees produce low-level electrical power. This opens the way to using trees' own electricity to power sensors that can provide early fire detection in even the most remote forest regions.
Shuguang Zhang at the Massachusetts Institute of Technology and co-workers recently explained tree electricity in the PloS ONE, an online journal from the Public Library of Science.

None of the obvious suspects such as tapping into emissions from power lines or broadcast radio waves turned out to be responsible. Trees generate electricity from an imbalance in acidity between a tree and the soil. As the MIT announcement last week noted, this is the same simple process that generates electricity from a potato or lemon at high school science fairs.

Dr. Zhang explains that, while tree power is weak, it can supply a "trickle charge" that "just like a dripping faucet, can fill a bucket over time." Thus trees can be a reliable power source to recharge batteries in embedded sensors.

The US Forest Service uses a sparse network of automated weather stations to monitor forest conditions and help in predicting fire dangers. A wider, denser network of tree-powered sensors that didn't need periodic battery replacement would be a major improvement. These sensors would relay data to the nearest weather station, which, in turn, would send them to the central processing center. Four instrumented trees per acre should do the job. An experimental 10-acre plot will begin testing such a system next spring.

The MIT group won't be asking the trees' opinion of that test. But James Crutchfield with the University of California at Davis and David Dunn, who heads the Art and Science Laboratory in Santa Fe, N.M., are listening to trees in their research into the effect of climate change on forest infestations. They described their ongoing work two years ago on the Santa Fe Institute website. The journal Leonardo will carry an updated version.

The two found that trees stressed by drought emit sounds pitched too high for human hearing. The researchers suspect that bark beetles detect these sounds and thus locate weakened trees to attack. The beetles also emit ultrasounds with which they communicate among themselves. This, too, may attract more beetles to a tree under attack. Dr. Crutchfield is quoted in Science News as warning that these hypothesizes now need to be thoroughly tested. If true, it may be possible to use ultrasound to divert and confuse the beetles and thus protect vulnerable trees.

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