Our continent has a variety of climates, and each climatic area has its
appropriate vegetation. Generally, the interiors of continents do not
have forests, but have grass or desert vegetation. The most luxuriant
forests develop near oceans where climate is sufficiently moist. This is
true of other continents as well as North America.
The differences in the general character of our natural vegetation from
coast to coast and border to border are apparent despite three centuries
of man’s disturbance in the East and one century in the West. Sizeable
samples of some of the many kinds of original vegetation are preserved
in national parks and monuments. These are precious remnants of our
plant heritage that become more valued year by year in proportion to
their scarcity elsewhere.
The mild, humid climate of the northern half of the Pacific slope is
unusually favorable for forest growth. The most luxuriant of the western
forests developed here in unbroken stretches. The forests that girdle
the Olympic Peninsula represent the best development of this evergreen
forest domain. Its ultimate composition is of western hemlock and
western redcedar in dense stands, with trunks commonly 4 to 6 feet in
diameter and 125 to 200 feet tall. Their crowns shut out most of the
sunlight, but enough gets through to the bottom of the forest for the
growth of mosses and ferns. Shrubs grow dense and tall, in places
becoming almost impenetrable to hikers. Fallen trees of all sizes soon
are enveloped by the lush growth in the damp shade, and in time return
to the soil through decay.
Hemlock and redcedar seedlings take root in the forest litter or on
prostrate, moss-covered trunks. They are able to live in the deep shade.
The most hardy of them outstrip their rivals, and when a vacancy occurs
in the forest canopy their growth speeds up. Thus a forest of hemlock
and redcedar is maintained. This is the climax forest in the lowlands of
the northwest coast. It is the kind of forest the climate here will
produce and maintain in the absence of interference.
Interference has been the rule, however, both before and since the
coming of man. Therefore, the climax forest is less common than the
subclimax in which Douglas-fir is the dominant tree. Forest fires have
repeatedly exposed the forest floor to sunlight and thus allowed the
development of Douglas-fir, by far the most abundant and widespread tree
in northwest forests. In the regeneration of a forest after fire,
logging, or other disturbance, it is Douglas-fir that is ever present.
The northwest coast is an evergreen land. This may not be apparent in
summer, however, when all plants are green. Not counting the numerous
mosses that are always green, there are 73 species of evergreen plants
on the Olympic Peninsula.
[Illustration: DRAPERIES OF CLUBMOSS HANG FROM LIMBS IN THE RAIN
FOREST.]