The trees are most likely talking over your head. ©Henry H. Holdsworth

If you’ve ever walked in a forest or a grove on a breezy or windy day, you’ve probably experienced that bit of an unsettling feeling that says to you that the trees are “talking” above your head. With every moan and retort of the wood, you’d almost swear that you could hear rumblings. Much like the trees in the film the Wizard of Oz that get annoyed with Dorothy after she picks an apple from one of them and then they begin to throw apples back at her, the trees surrounding you on your walk seem to be whispering to each other about the propriety of your presence.

Turns out that your intuition may not be so far from the truth. Scientists are now discovering that plants have similar senses to ours and that they “talk” to each other—not through their roots, but as we do: through the air.

Defense talks

We’ve known for a long time that plants are sensitive to their environments, reacting to changes in temperature, soil conditions and light. Their senses, like ours, are quite developed: the Venus flytrap catches its dinner by snapping shut when an insect touches the tiny hairs on its leaves, and some farmers believe that sounds louder than the human voice stimulate the germination and rapid growth of some vegetables. But the confirmation that plants of the same species are able to talk with each other through the air is a new development.

These aspens are probably discussing the moose in their midst. ©Henry H. Holdsworth

In one recent research project, scientists took note of when the first gypsy moth larvae landed on a mature oak tree that resided in a grove with other oaks. By analyzing the chemistry of the mature oak tree’s leaves, they were able to determine that within a very short period of time, the tree had added a bitter tannin to all of its leaves. The tannin made the tree an unattractive lunch option for the gypsy moth larvae. But what was more astounding was that all the other oak trees in the grove changed the chemistry of their leaves, too, making them unappetizing as well.

It took a few years for the scientists to understand just how the trees in the rest of grove had gotten word that the gypsy moths were in town. It was found that the trees did not communicate through their roots—instead, they released a special gas (or pheromone) to warn their neighbors of the danger.

Willow witnesses

It’s not only the oak trees that are chatting. We now have proof that willows, too, are talking with each other through the air. A chemist investigating how willows react when attacked by tent caterpillars provides verification.

The Great Bear Rain Forest, the largest remaining intact coastal temperate rain forest in the world, deserves our respect and protection. ©Candice Gaukel Andrews

The chemist subjected two groups of willows to different conditions: one group was allowed to be invaded with tent caterpillars, while the second group was left to act as “witnesses”; in other words, left untouched. After 14 days, he picked up leaves from willows in both groups to feed to tent caterpillars, which this time were in the lab. He found that the lab caterpillars that ate small amounts of leaves from the willows that had had caterpillars were growing very slowly. But what was puzzling was that leaves from the untouched or “witness” group of willows were equally unpleasant for and caused the same result in the lab caterpillars.

Further analysis showed that both willow groups had filled their leaves with a chemical that proved to be repulsive for the insects. The message about the influx of tent caterpillars had been transported from willow group to willow group by ethylene, a gas normally produced during the reaping of fruits but also released by a willow’s harmed or irritated tissues.

These new reports are especially appropriate for this International Year of Forests. Now that we know for sure that trees talk through the air like we do, we have to wonder what they say about us as we press into their territories and begin to deforest the land, starting at one edge of the woods and working our way through to the other. Do the trees cut first shout to the others on the opposite end to run? Or are they whispering to us, asking that we be more mindful of the consequences?

Here’s to finding your true places and natural habitats,