these forests. The trees are gigantic. They tower 150 to 300 feet
above the ground. Their trunks often are 6 feet or larger in
diameter. They make the trees of the eastern forests look
stunted. They are excelled in size only by the mammoth redwood
trees of northern California and the giant Sequoias of the
southern Sierras.

[Illustration: THE SEQUOIAS OF CALIFORNIA]

Differences of climate have largely influenced tree growth and
types in this country. The distribution of tree families is
changing all the time. It shifts just as the climate and other
conditions change. Trees constantly strive among themselves for
control of different localities. For a time one species will
predominate. Then other varieties will appear and displace the
ones already established. The distribution of trees changes very
remarkably from one century to another. For example, in some
sections, the red and black oaks are replacing the white oaks.
Some trees are light-lovers. They require much more sunlight than
others that do well under heavy shade. Oak trees require plenty
of light; maples or beeches thrive on little light.

The seed of trees requiring little light may be scattered in a
dense forest together with that of trees which need plenty of
daylight in order to make normal growth. The seedlings that like
shade will develop under such conditions while those that need
light will pine away and die. Gradually the shade-loving trees
will replace the light-loving trees in such a forest stand. Even
the different trees of the same family often strive with one
another for light and moisture. Each tree differs from every