Howard Silverman is Ecotrust’s Senior Writer and Analyst. Working with the organization since 1999, he has guided the development of Ecotrust communications and publications in a wide variety of media. Silverman provides strategic support in creative direction, messaging, editing, writing, and public engagement. His areas of professional expertise include writing, editing, publishing, public speaking, creative direction, new media, history and evolution of environmentalism and sustainability, natural resource economies, community-based social change, and systems analysis.
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- Green groups clash over reliability of forest-based carbon offsets
Introduction
Temperate rain forests have been recognized as a distinct biome throughout the 20th century, although ecologists have not used the term uniformly. Most vegetation classification schemes use vegetation structure (and, secondarily, unique fauna) to define biomes, but temperate rain forests can be structurally similar to nearby forest types. Temperate rain forests are also difficult to define floristically because they share species with warmer and drier forest types.
Studying the temperate rain forests of North America, ecologist Paul Alaback defined the most widely recognized criteria for the biome: over 1,400 millimeters annual precipitation, cool summers stemming from an equable year-round climate, mean annual temperature between 4 and 12 degrees Celsius, and infrequent fire.
Location and General Description
Temperate rain forests are coniferous or broadleaf forests that occur in mid-latitude areas of high rainfall. Most temperate rain forests occur where mountain ranges are close to the coast, giving rise to the term “coastal temperate rain forest.” Coastal temperate rain forests occur in the oceanic moist climates of western North America, southwestern South America, Western Europe, southeastern Australia and western New Zealand and possess remarkable ecological similarities.
Worldwide, coastal temperate rain forests are scarce. Of the world’s estimated 1.3 billion hectares of temperate forest, the historic extent of coastal temperate rain forest totaled thirty to forty million hectares (2–3 percent), scarcely one-thousandth of the earth’s land surface. Tropical rain forests once covered roughly forty times more land. Though both forest types have been drastically reduced, over 30 hectares of tropical rain forest stand for every intact hectare of coastal temperate rain forest.
The largest contiguous coastal temperate rain forest traces the northwestern maritime margin of North America: from Kodiak Island in Alaska south through British Columbia to California’s redwood fogbelt. This region includes about half the remaining worldwide distribution of coastal temperate rain forest. The coastal temperate rain forests in Oregon and Washington have a distinctive dry summer season. In these forests, catastrophic fires occur every 3 to 6 centuries. By contrast, the temperate rain forests of southeastern Alaska and northern British Columbia have high annual precipitation distributed throughout the year. In this perhumid zone, wind is the dominant natural disturbance regime, while fire is comparatively rare. This zone also encompasses some of the largest remaining intact landscapes outside of the tropics.
Biodiversity Features
While tropical rain forests contain a diversity of plant and animal species vastly disproportionate to the area they occupy, coastal temperate rain forests contain a similarly disproportionate share of biological production. Coastal temperate rain forests accumulate and store more organic matter than any other forest type — as much as 500–2,000 metric tons of wood, foliate, leaf litter, moss, other living plants, and soil per hectare.
Temperate rain forests include some of the longest-lived and massive tree species in the world, such as coastal redwood in California, red gum in Australia and alerce in Chile. Some individual trees in temperate rain forests have grown for two millennia and surpass six meters in diameter.
All temperate rain forests have thick layers of epiphytes — plants that drape the bark, twigs and branches of dominant trees. Most of the world’s temperate rain forests are evergreen — needle-leaved in the northern hemisphere and broadleaved in the southern hemisphere — which allows these trees to actively grow throughout much of the year and minimizes nutrient demands.
The marine waters adjacent to temperate rain forests are productive as well. The upwelling zones and coldwater currents that bathe the edges of coastal temperate rain forests account for a substantial share of the biological production of the oceans. The productivity of coastal temperate rain forest ecosystems is enhanced by the nutrients and organic debris washed out of coastal watersheds, epitomizing the concept ecologists call “ecotones” — zones of transition between adjacent ecological systems. The seven anadromous species of Pacific salmon and trout, which range widely in the North Pacific before returning to their natal coastal rain forest streams to spawn, dramatically demonstrate the reciprocity of forest and sea.