Temperate rain forests are rain forests with coniferous or broadleaf forests that occur in the temperate zone and receive heavy rain. Temperate rain forests occur in oceanic moist regions around the world: the Pacific temperate rain forests of the North American Pacific Northwest as well as the Appalachian temperate rain forest in the Appalachian region of the United States; the Valdivian temperate rain forests of southwestern South America; the rain forests of New Zealand and southeastern Australia; northwest Europe (small pockets in Great Britain and larger areas in Ireland, southern Norway, northern Iberia and Brittany); the Eastern Korea-Manchuria continuum; Japan; the Black Sea–Caspian Sea region from the southeasternmost coastal zone of the Bulgarian coast, through Turkey, to Georgia, and northern Iran. The moist conditions of temperate rain forests generally have an understory of mosses, ferns and some shrubs and berries. Temperate rain forests can be temperate coniferous forests or temperate broadleaf and mixed forests.
Definition
For temperate rainforests of North America, Alaback's definition is widely recognized:
Annual precipitation over 140 cm (55 in) (KJ) Mean annual temperature is between 4 and 12 °C (39 and 54 °F). However, required annual precipitation depends on factors such as distribution of rain over the year, temperatures over the year and fog presence, and definitions in other regions of the world differ considerably. For example, Australian definitions are ecological-structural rather than climatic:
Closed canopy of trees excludes at least 69% of the sky. Forest is composed mainly of tree species which do not require fire for regeneration, but with seedlings able to regenerate under shade and in natural openings. Australian definitions would exclude some temperate rainforests of western North America that are Coast Douglas-fir dominant, such as parts of the Klamath Mountains in southern Oregon and northern California, the Puget Lowlands of western Washington and the Georgia Depression in British Columbia, as their dominant tree species, the Coast Douglas-fir, requires stand-destroying disturbance to initiate a new cohort of seedlings. The North American definition would in turn exclude a part of temperate rainforests under definitions used elsewhere.
Canopy level
For forests, canopy refers to the upper layer or habitat zone, formed by mature tree crowns and including other biological organisms (epiphytes, lianas, arboreal animals, etc.). The canopy level is the third level of the temperate rainforest. The trees forming the canopy, conifers, can stand as tall as 100 metres or more. A variety of species survive in the canopy. The tops of these trees collect most of the rain, moisture, and photosynthesis that the rainforest takes in. They form a canopy over the forest, covering about 95% of the floor during the summer. The canopy's coverage affects the shade tolerance levels of forest floor plants. When the canopy is in full bloom, covering about 95% of the floor, plant survival decreases. Some plant species have become shade tolerant in order to survive. The treetops take in the heavy amount of rain and keep the lower levels of the forest damp. The canopy survives through photosynthesis. The leaves provide energy and nutrients for the trees, which provide homes and food for the forest. Through satellite data, the radiation use efficiency (RUE) calculates the annual amount of photosynthesis that occurs in temperate rainforests. A diverse amount of photosynthesis occurs based on the location and microclimates of the forest.
Distribution
North America
Pacific temperate rainforests
A portion of the temperate rain forest region of North America, the largest area of temperate zone rainforests on the planet, is the Pacific temperate rain forests ecoregion, which occur on west-facing coastal mountains along the Pacific coast of North America, from Kodiak Island in Alaska to northern California, and are part of the Nearctic realm. In the different system established by the Commission for Environmental Cooperation, this same general region is classed as the Pacific Maritime Ecozone by Environment Canada and as the Marine West Coast Forest Level II ecoregion by the United States Environmental Protection Agency. In terms of the floristic province system used by botany, the bulk of the region is the Rocky Mountain Floristic Region but a small southern portion is part of the California Floristic Province.
Sub-ecoregions of the Pacific temperate rainforest ecoregion as defined by the WWF include the Northern Pacific coastal forests, Haida Gwaii ecoregion, Vancouver Island ecoregion, British Columbia mainland coastal forests, Central Pacific coastal forests, Cascades forests, Klamath-Siskiyou coastal forests, and Northern California coastal forests ecoregions. They vary in their species composition, but are all predominantly coniferous, sometimes with an understory of broadleaved trees and shrubs. Most of the precipitation occurs in winter, similar to Mediterranean climates, but in summer, fog moisture is extracted by the trees and produces a fog drip keeping the forest moist. The Northern California coastal forests are home to the Coast Redwood (Sequoia sempervirens), the world's tallest tree. In the other ecoregions, Coast Douglas-fir (Pseudotsuga menziesii var. menziesii), Sitka Spruce (Picea sitchensis), Western Hemlock (Tsuga heterophylla) and Western redcedar (Thuja plicata) are the most important tree species. A common feature of Pacific temperate rainforests of North America is the Nurse log, a fallen tree which as it decays, provides ecological facilitation to seedlings. Trees such as the Coast Douglas-fir, Western Hemlock, Western Red Cedar, Pacific Yew, and Vine Maple are more closely related to coniferous and deciduous trees in the temperate forests of East Asia.
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