It looks like a fairy tale story copied from "Lord of the rings" or from a science fiction story, but scientists proved that trees do communicate.
One chemist made an experiment: he investigated how willows react when attacked by a caterpillar, so he assigned them to two lots: one which he invaded with caterpillars and another as a witness, leaving it "untouched".
After 14 days,
he picked up leaves from the two plots to feed in the lab some other caterpillars. He found that the larvae that ate small amounts of leaves were growing very slowly. But what was more puzzling is that leaves from both plots were equally "unpleasant" for the caterpillars.
Both willow groups filled their leaves with a chemical that proved to be repulsive for the insects.
A similar experiment was made on poplars. On similar plots, one was doused with chemicals contained by insects eating on the trees. Both groups of poplars developed repulsive compounds, but when the two plots of young trees were separated in different rooms, only the doused plot synthesized the chemicals.
In both experiments, the tress in different plots did not communicate through their roots or other organs, the only conclusion being that they communicated with each other by air, employing warning pheromones. Thus, plants are not passive, at the mercy of natural phenomena and attackers.
Other experiments also showed that plants can contra-attack in group, and this is done using vegetable pheromones. When informed about an occurring attack, till 50 % of the compounds synthesized by a tree can be defense products, like tannins, alkaloids and peptides, mostly in leaves, their most vulnerable organ.
But trees were found to communicate not only for defense, but also to time their blooming. In fact, blooming at the same time can also be a defense mechanism, as the consumers will not have enough time to eat too many flowers, as it would happen if trees bloomed one after another.
Recently, parasite plants were even found to sniff their host-plants, selecting the preferred ones! Some corn varieties defend themselves against the root worm (Diabrotica virgifera) emitting chemicals that attract minute nematode worms that kill the root worms, which are in fact the larvae of a beetle.