Do Trees Talk? Some Scientists Think They Do

Do Trees Talk? Some Scientists Think They Do

By Mr Ghaz, January 17, 2010

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Do Trees Talk? Some Scientists Think They Do

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“Stones have been known to move and trees to speak,”said Shakespeare’s Macbeth, voicing an old superstition. Today a team of scientists at the University of Washington in Seattle, led by Professor David F. Rhoades, claim to have evidence that proves that trees really do “talk.’’ Humans cannot hear their conversations, but one can be understood by another.

Under the weather

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The scientists gathered their evidence in the course of experiments on the effects of stress on trees. Plant stress can be caused by drought, frost, pollution, or lack of nutrients in the soil. Under such conditions they are move vulnerable to attacks by insects and another plant-eating creature because their natural defenses are low. This vulnerability is much like people caching a load when they have been soaked by rain: it is not a rain that causes the cold, but the fact that the soaking lowers the body’s resistance to any cold viruses.

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Stress in plants is accompanied by chemical changes, just as it in humans. The scientists discovered that when under stress, plants produce more nutrients, such as amino acids, and smaller amounts of the chemical that help to protect them against the ravages of insects.

The scientists then began a series of experiments with willows, placing hungry caterpillars on some trees but not on others. The latter were the controls. At first the caterpillars flourished. But before long it became apparent that they were doing surprisingly little damage to the trees. Analysis showed that after the initial attack the trees produced more defensive chemicals such as proanthocyanidin, a kind of natural insecticide.

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Then came the surprise. After a few weeks the control trees were also producing more proanthocyanidin. They were defending themselves in advance of attack. It seemed that the affected trees were somehow signaling to the others:”There is danger around here!”

Professor Rhoades and his colleagues wondered if the trees were ‘communicating’ through the roots and the soil. But experiments in and out of the laboratory proved conclusively that this was not so. In any case, the trees were apparently “talking” over a distance of more than 100 yards.

The scientists then proposed that airborne pheromones might hold the clue. These chemical substances given off by plants and animals act as signals between members of the same species.

Although present in very small quantities, pheromones are amazingly powerful. For example, the pheromones emitted by female moths will attract male hundreds of yards away.

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After further tests professor Rhoades and his colleagues came to the conclusion that the pheromone hydrocarbon ethylene, emitted by trees through the leaves, was a likely carrier of the danger signal from one three to another. Research along these lines is still continuing.

Vocal or Dumb?

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Not all scientists are convinced by this evidence, however. Two British biologists from York University, Dr Simon, V. Fowler professor John H. Lawton, maintain that the suppositions of the U.S. team can be explained equally well by the spread of infectious diseases carried by the caterpillars themselves. The two scientists conducted their own experiments with birch trees. Their finding: no evidence that trees: “talk.”

The story is still unfinished. Both sides are very cautious in their claims. But as Professor Rhoades points out, if trees really do “talk” to each other, we may have reassess our view that trees are totally inanimate.