Thus in 1740 and the two following years the larva of a moth (Phalaena graminis) committed such destruction in many of the meadows of Sweden that the grass was greatly diminished in quantity, and many plants which were before choked by the grass sprang up, and the ground became variegated with a multitude of different species of flowers.

The introduction of goats into the island of St.Helena led to the entire destruction of the native forests, consisting of about a hundred distinct species of trees and shrubs, the young plants being devoured by the goats as fast as they grew up.

The camel is a still greater enemy to woody vegetation than the goat, and Mr.Marsh believes that forests would soon cover considerable tracts of the Arabian and African deserts if the goat and the camel were removed from them.[6] Even in many parts of our own country the existence of trees is dependent on the absence of cattle.

Mr.Darwin observed, on some extensive heaths near Farnham, in Surrey, a few clumps of old Scotch firs, but no young trees over hundreds of acres.

Some portions of the heath had, however, been enclosed a few years before, and these enclosures were crowded with young fir-trees growing too close together for all to live; and these were not sown or planted, nothing having been done to the ground beyond enclosing it so as to keep out cattle.