In some parts of the United States forestry experts can tell
where they are by the local tree growth. For example, in the
extreme northern districts the spruce and the balsam fir are
native. As one travels farther south these give way to little
Jack pine and aspen trees. Next come the stately forests of white
and Norway pine. Sometimes a few slow-growing hemlock trees
appear in the colder sections. If one continues his journey
toward the equator he will next pass through forests of
broad-leaved trees. They will include oak, maple, beech,
chestnut, hickory, and sycamore.

In Kentucky, which is a centre of the broad-leaved belt, there
are several hundred different varieties of trees. Farther south,
the cone-bearing species prevail. They are followed in the march
toward the Gulf of Mexico by the tropical trees of southern
Florida. If one journeys west from the Mississippi River across
the Great Plains he finally will come to the Rocky Mountains,
where evergreen trees predominate. If oak, maple, poplar, or
other broad-leaved trees grow in that region, they occur in
scattered stands. In the eastern forests the trees are close
together. They form a leafy canopy overhead. In the forests of
the Rockies the evergreens stand some distance apart so that
their tops do not touch. As a result, these Western forests do
not shade the ground as well as those in the east. This causes
the soils of these forests to be much drier, and also increases
the danger from fire.

The forests of western Washington and Oregon, unlike most
timberlands of the Rocky Mountain Region, are as dense as any
forests in the world. Even at midday it is as dark as twilight in