Roe deer may seem innocuous, but for maples (Acer pseudoplatanus) and young beeches (Fagus sylvatica) they could be lethal. By feeding on the buds of...
trees, the deer could inhibit or completely block the tree's growth. A recent study, published in <a href="http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12717/abstract">Functional Ecology</a>, discovered that the trees apply an interesting defense mechanism. Their buds recognize the saliva of the roe deers, and when a deer attempts to feed on them, they increase the production of tannins which repel the deers and make them lose their appetite.</p>
<p>This defense mechanism is effective, but apparently other trees are much more aggressive. In South Africa <a href="https://spectregroup.wordpress.com/2010/01/08/acacia-self-defense/">researchers discovered</a> that local acacias not only increase the production of tannins when being nibbled by antelopes, but also emit a gas called ethylene into the air. This gas can travel up to 150 feet from the original acacia, and upon sensing it the other acacias also increase their production of tannins.</p>
<p>The unique mechanism was discovered 25 years ago by the zoologist Wouter Van Hoven, who was asked to investigate the sudden death of 3,000 South African antelopes. Van Hoven found that the cause of death was excessive consumption of the acacia tannins, and that other animals in the area actively circumvented this defense mechanism - local giraffes nibble only on one acacia tree in ten, and mostly avoid downwind trees.</p>