The acacia has been caught “talking“ to its neighbours. When animals start to eat it, the tree produces some poison and “tells“ other acacias to do likewise.

People sometimes wonder what plants would say if they could talk. Probably, like animals, their most important messages would be warnings about danger. A threat to life needs to be communicated by most species.

Some plants protect themselves by bearing thorns. Tannin makes the acacia leaves taste unpleasant too. But the acacia goes one step further.

It releases a gas, when animals nibble a leaf, which drifts on to other leaves. In response, these leaves produce toxic levels of the chemical tannin to stop themselves being eaten too. Most surprisingly, though, the tree's gas reaches other trees up to 60 metres away. These trees quickly produce high levels of tannin, so protecting themselves from the advancing herds.

This discovery was made following the mysterious death of thousands of kudu, a type of African antelope, on game ranches in South Africa. Scientists found that the animals had been poisoned by tannin from acacia trees. In the wild, kudu will browse only for a short time on acacia, and they usually eat in small groups. But the game kudu were fenced in. They had only acacia to feed on, and many animals were forced to eat the same trees. The result was that the trees, under such a big attack, produced very high levels of tannin, which proved fatal for the kudu.

Professor Wouter Van Hoven, of Pretoria University, believes that browsing animals that live where acacias grow have evolved to be solitary or to move in small groups. This is partly because of this tree's chemical alarm bells.