Take, for example, the umbrella thorn acacia in the African Savannah, whose leaves are the preferred diet of the towering giraffe. Within minutes of the first nibble, the tree starts to pump ethylene gas into the leaves so as to prevent them all from being devoured. The giraffe moves on, not to the next tree, but to a tree at least a 100 yards away.
The gas is not only toxic to the feeding giraffe, but a signal to neighbouring trees to emit the same gas so as to prevent the giraffe from nibbling on them too. It seems, then, that trees communicate for the benefit of their friends.
How is it that other trees, such as the spruce or oak “know” that they are being nibbled on, say by a caterpillar? Can it feel pain or discomfort? We have no way of recording such pain, but it is known that once bitten an electrical signal is slowly sent throughout the tree inviting defensive compounds that ward off the pest. Other trees emit pheromones summoning the exact friendly predators needed to deal with a specific pest.
Secrets of the forest underground expose a complex of roots that, once again, illustrate the community nature of forests, especially those that are old. Roots do not simply grow around each other in some tangled jumble, but often grow into each other, so that roots of a weaker tree can be nurtured or given water by another that is healthier or growing in better soil. Even stumps of long cut trees have been shown to have life in them because they remain connected to this network of roots.