Lush forest, generally composed of tall, broad-leaved trees and usually found in wet tropical regions around the Equator. Despite increased awareness of the rainforests' importance during the late 20th century, they continue to be cleared. Rainforests grow mainly in South and Central America, West and Central Africa, Indonesia, parts of Southeast Asia, and tropical Australia, where the climate is relatively humid with no marked seasonal variation. Depending on the amount of annual rainfall, the trees may be evergreen or mainly deciduous. The former require more water. Temperatures are high, usually about 86 °F (30 °C) during the day and 68 °F (20 °C) at night. Soil conditions vary with location and climate, though most rainforest soils tend to be permanently moist and not very fertile, because the hot, humid weather causes organic matter to decompose rapidly and to be absorbed quickly by tree roots and fungi. Rainforests have several layers. The highest continuous layer, called the canopy, extends across the treetops at a height of 100–165 ft (30–50 m). Most animals live among the leaves and branches. Below the canopy is a thick understory filled with small trees, lianas, and epiphytes. The space directly above the ground can be occupied by tree branches, twigs, and foliage, but, contrary to popular belief, the rainforest floor is not impassable. Rather, it is bare except for a thin layer of humus and fallen leaves. Animals inhabiting this layer (e.g., gorillas, elephants, jaguars, and bears) are adapted to walking or climbing for only short distances. Burrowing animals, such as armadillos and caecilians, are found in the soil, as are microorganisms that help decompose and recycle the organic litter accumulated by other plants and animals from all layers. The climate of the ground layer is unusually stable because the upper stories of tree canopies and the lower branches filter out sunlight, retain heat, and reduce wind speeds, keeping the temperature fairly even.
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Annual precipitation ranges from 3.6 to 4.2 m (12 to 14 feet). Summers are relatively dry, but only by comparison to the rest of the year. The late fall, winter and spring floods cause the Hoh River to regularly erode its banks, change its course, and deposit fresh terraces of alluvium that are soon colonized by Red Alder. Giant trees topple into the river increasing the diversity of aquatic habitats.
The dominant species in the rain forest are Sitka Spruce and Western Hemlock; some grow to tremendous size, reaching 95 m (over 300 feet) in height and 7 m (23 feet) in circumference. Coast Douglas-fir, Western Redcedar, Bigleaf Maple, Red Alder, Vine Maple, and Black Cottonwood are also found throughout the forest.
The Hoh Rainforest is home to a U.S. Park Service ranger station, from which backcountry trails extend deeper into the national park. A short, popular trail near the visitor center is the Hall of Mosses, which gives visitors a feel for the local ecosystem.