North, until we
finally come to the land called the _Barren Lands_ or _tundras_, where
the trees become stunted and at last disappear--a land where they cannot
longer fight against the cold and live?

Fortunately such a long journey is not necessary. All we have to do is
to climb a great mountain range, like the Sierra Nevadas, to pass
through all the different climates which we would experience on a long
journey to the arctic regions.

It is only a few miles from the hot San Joaquin Valley, at the base of
the Sierras, where it is so dry that irrigation is necessary, to the
summit of the range, where the winter climate is as cold as it is in the
arctic regions.

In going up the mountains we first come to the foothills, where there is
a little more rain than in the valley. Here we find oak trees growing.
Farther up there is still more rain and we come to the pines. Soon we
reach the most wonderful coniferous forest in all the world. Here not
only is there a great variety of trees, but because of the favorable
climate they grow to a great size. As we approach the summit of the
mountains the trees become smaller, and at an elevation of about two
miles they shrink to the size of little bushes and finally disappear.
They can no longer stand the fierce winds and cold storms of this arctic
region.

[Illustration: _George J. Young_
East Vidette, King's River Country, California, showing how, as we
approach the summit of the mountains, the trees become smaller.]

We have learned now that the trees do not grow haphazard over our
country, but that the rain, the temperature, and the soil determine
where they can live.

Within the heart of the forest the trees will come again if we cut them
down, but upon its borders, where the air is drier, it is more difficult
for them to spring up anew. If we cut them down carelessly and allow
fires to burn over the surface, and the water to wash away the soil,
they may never come back.

It is important, then, that we understand why trees grow in some places
and not in others, in order that we may know how to take care of them.

CHAPTER SIXTEEN

WHAT ARE THE ENEMIES OF THE TREES?

Every living thing is engaged in a struggle for air to breathe and for
something to eat. Those that make their homes on the land also have to
struggle for water. The stronger rob the weaker; for, among all of them
except man, might always makes right. Men are learning that
unselfishness is t