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.
DRAPERIES OF CLUBMOSS HANG FROM LIMBS IN THE RAIN FOREST.
RAIN FOREST
An extraordinary forest has developed along the western slopes of the Coast Range where moisture is available in the greatest abundance. The most typical and beautiful expression of this coastwise forest is found in the western valleys and on the coastal plain of the Olympic Peninsula. It is the most luxuriant growth in any temperate climate and may properly be called a rain forest. This temperate-climate rain forest, however, is not like the rain forests of the hot, superhumid tropics. Here, there are tall conifers instead of broad-leaved trees; there are mosses and ferns on the ground instead of an understory of vines.
The rain forest is principally distinguished by the presence of Sitka spruce. This tree grows only in a narrow belt along the coast from northern California to Alaska. The other trees of the rain-forest community have much wider distribution.
The trees of this forest are among the largest in the world. Many of them have trunks that exceed 10 feet in diameter at 4½ feet above the ground, and are up to 300 feet tall. The largest known trees in the park for the most common species are: western redcedar, 21 feet 4 inches in diameter; Sitka spruce, 13 feet 4 inches; Douglas-fir, 14 feet 5 inches; western hemlock, 9 feet; and Pacific silver fir, 6 feet 10 inches.