Leaf It Alone

Giraffes move from tree to tree instead of eating off only one or two because the trees “communicate” with each other. When a giraffe (or elephant or other large species) eats the leaves, it causes stress on the tree. The tree then secretes a noxious chemical that makes the leaves taste bad. Once a tree starts secreting this chemical, it signals surrounding trees to produce the same chemical. (Kind of like how one rotting apple will cause the others to spoil.) Giraffes always start with the tallest tree that is upwind, then take a few bites before moving to the next tree, and thereby largely avoiding the chemical deterrent.

(Info lifted from seadaze.com)