ACACIA trees pass on an ‘alarm signal’ to other trees when antelope

browse on their leaves, according to a zoologist from Pretoria University.

Wouter Van Hoven says that acacias nibbled by antelope produce leaf tannin

in quantities lethal to the browsers, and emit ethylene into the air which

can travel up to 50 yards. The ethylene warns other trees of the impending

danger, which then step up their own production of leaf tannin within just

five to ten minutes.

Van Hoven made his discovery when asked to investigate the sudden death

of some 3000 South African antelope, called kudu, on game ranches in the

Transvaal. He noticed that giraffe, roaming freely, browsed only on one

acacia tree in ten, avoiding those trees which were downwind. Kudu, which

are fenced in on the game ranches, have little other than acacia leaves

to eat during the winter months. So the antelope continue to browse until

the tannin from the leaves sets off a lethal metabolic chain reaction in

their bodies.

Van Hoven’s research is to be published in the Journal of African Zoology.

He described his results at a recent conference in France. Claude Edelin

of the National Scientific Research Centre (CNRS) described the discovery

as ‘terribly exciting’.

Fifteen years ago, a French scientist at the CNRS, Paul Caro, found

that oak trees attacked by caterpillars reacted by stepping up the quantity

of tannin and phenol produced in their leaves. Caro observed that the trees’

defence mechanism inhibited the growth of the larvae.