Two-thirds of the world's temperate rainforests are found along North America's northwest coast. Temperate rainforests also occur in Chile, New Zealand and southern Australia. Tropical rainforests, which are much more extensive, are found between the latitudes of twenty degrees north and twenty degrees south. Unlike other temperate rainforests, conifers dominate pacific northwestern rainforests. Logging and other human interactions threaten both types of rainforests.
Although temperate rainforests can be found from northern California to southern Alaska the forests in each region are unique. A variety of factors such as temperature, rainfall, and altitude determine the types of trees and other vegetation that grow in the forest. Unlike the tropical rainforests, which have rapid growth and decay rates, the cold winter temperatures and the lack of light limit the growing season in temperate rainforests. The topsoil in the temperate rainforest forest is very thick and rich in nutrients since the detritivores work very slowing in this environment. Light is necessary for photosynthesis, the process that plants use to produce the sugars that can be converted to the cellulose needed for plant growth.
Trees that fall in temperate rainforests decay very slowly. Over time mosses, lichens, and seedlings cover these fallen trees. Many of these nurse logs are decades old. Epiphytes are also characteristic of the temperate rainforests.
Fallen trees create openings in the forest canopy. Many young trees, especially Douglas firs, require sunlight to grow. Once they are established, they grow rapidly and enter the canopy where sunlight is abundant. Unlike western red cedars and western hemlocks, these fast growing trees have a less well developed root system and are more likely to become future "blow overs."
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