Field mice, gophers, and rabbits eat the bark of young fruit trees and kill those which are not carefully protected. In some parts of our country the apple and peach tree borers are a serious menace to young orchards. Grasshoppers occasionally come in dense swarms and eat the leaves from every tree or plant in their path.
The valuable sugar pine of the Western mountains is not seeding itself as rapidly as it should, and we fear it will become extinct. The beautiful silver-gray squirrel loves the nuts of this pine, and it is said that he eats so many that few are left to sprout and make new trees. For this reason some people would like to make it lawful to kill all the gray squirrels that one wished. This would be too bad, for we do not believe the gray squirrel is the cause of the trouble. It is more likely that the lack of young sugar pines is due partly to its struggle in the forest with more rapidly growing trees and partly to the less frequent occurrence of forest fires to burn off the humus on the ground. We know that the seeds of certain trees find difficulty in sending their roots down through the humus to the soil beneath.
H. W. Fairbanks
An avalanche has passed through this forest.
The narrow-leaved or cone-bearing trees, which are the main source of our lumber, also have other enemies. The most destructive of these are the little pine beetles which lay their eggs in the bark of the yellow pine, sugar pine, and tamarack pine. From these eggs there hatch worms which burrow under the bark until they cut off the flow of the sap. This kills the trees. The trees that are young and strong are sometimes able to pour out enough sap into the wounds to drown the insects, but many thousands of trees in the Western mountains are destroyed every year by these insects.
Wind and lightning are both enemies of the forests. Hundreds of forest fires are set every summer by thunder storms, but the rangers usually discover such fires soon enough to put them out before they have done much harm.
The pasturing of forests by stock does great injury, because of the browsing and trampling underfoot of the young trees. Sheep and goats are the worst of all the animals and should be kept out of those forests where the surface particularly needs protection and where the young trees require all the encouragement that Nature can give them in order to make a successful start in life.
We have learned something about the many enemies of the trees, but the worst one has not yet been mentioned. Can you guess what it is? This terrible enemy is man,—not savage man or Indian, but civilized man. Although man has more need for forest trees than has any other animal, he is at the same time more ruthless in his treatment of them. Man destroys more trees every year, as a result of fires which he sets and of his wasteful methods of lumbering, than all the other enemies of the trees put together.
The forest area of the world is constantly growing smaller, and we must soon learn to treat the trees with more care or they may, like many of the wild creatures, nearly disappear from parts of the earth where they are most needed.