Coniferous Forest

Coniferous forest is dominated by conifers—evergreen, cone-bearing, needle-leaved trees such as spruce (Picea), fir (Abies), hemlock (Tsuga), or pine (Pinus). Larch (Larix), a deciduous conifer that drops its leaves in winter, may be common in some coniferous forests, especially in more northern latitudes. Conifers are the signature tree species of coniferous forests, but some broad-leaved deciduous tree species, such as birch (Betula) and aspen (Populus), are minor components of coniferous forests.

Coniferous forests are largely confined to the Northern Hemisphere and consist of several types. The world's largest expanse of coniferous forest is the boreal forest or taiga, covering over 18 million square kilometers. Taiga occurs as a broad circumpolar belt located between 50 degree and 70 degree north latitude, including parts of North America, Europe, and Asia. Montane coniferous forest occurs at higher elevations and covers over 3 million square kilometers in temperate North America, Europe, and Asia. Wet coastal coniferous forest—temperate rain forest—occurs in a narrow strip of northwestern North America from Alaska to northern California and in Japan. Local coniferous forest types such as the pitch pine (Pinus rigida) coastal plain forests are also recognized in the northeastern United States, among others. Many coniferous forests in warmer climates are successional, such as the extensive pine forests of the southeastern United States. In the absence of human or natural disturbance—especially fire—successional coniferous forests are replaced in time by deciduous forests.

Climate plays a key role in determining the distribution, composition, and productivity of coniferous forests. The taiga climate is the most extreme, with a growing season of 50–100 days, and winter temperatures that often drop below −30 degrees C. The annual precipitation is low, ranging from 40–50 centimeters, and falling mainly in summer when temperatures range from 12 degrees C to 15 degrees C. The climate of the montane coniferous forest is generally milder and wetter than that of the taiga, but topography, elevation, and aspect create a diversity of climatic conditions. In the European Alps, annual precipitation varies between 80–260 centimeters, winter temperatures range between 0 degrees C and 5 degrees C, and summer temperatures average 10 degrees C to 18 degrees C.

In the North American Rockies, annual precipitation varies from 40–120 centimeters, with winter and summer temperatures ranging from −5 degrees C to −10 degrees C and 15 degrees C to 20 degrees C, respectively, depending on latitude. North America's wet coastal coniferous forests have the mildest climate with a frost-free period that can exceed 240 days and winter temperatures that rarely surpass −5 degrees C. Annual precipitation ranges from 40–200 centimeters and is often embellished by sea fog. North America's wet coastal coniferous forest is the most productive on the continent, harboring species like coast redwood (Sequoia sempervirens) that may grow 100 meters tall and reach 2,000 years in age.

Humans have exploited coniferous forests for food, timber, fuel, and fiber for millennia. Today, many coniferous forests are intensely managed for timber and pulpwood, like the pine forests of the southeastern United States. Other coniferous forests, like the taiga of Russia and Canada—which contain 50 percent of the world's old-growth forests—are under increasing human pressure for harvest and oil development. The peat soils of the taiga are an important global carbon sink and heavy development may influence global warming rates.

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