he 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.

[Illustration: _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 savag