| |
 The tundra, named from the Finnish word tunturia meaning "treeless plain," is a vast habitat that covers more than 15% of the earth's land area. It is the coldest biome (ecological community), with average winter temperatures of -30 F (-34 C) and average summer temperatures of 37-54 F (3-12 C). Different tundra zones include High (mostly restricted to islands), Middle (found on the coastal plain), and Low (inland, the most common habitat). There is also a discontinuous zone of patchy permafrost where the tundra meets the taiga or boreal forest.
 The key factor in the tundra is permafrost, a subsoil layer that is frozen all year around. Above the permafrost, a thin active layer thaws and melts in the summer, supporting a simple, rugged community: life forms adapted to the low temperatures, scarce precipitation, and short growing season, conditions resembling a cold desert. With poor drainage, no room for deep root systems, and limited nutrients, the tundra cannot support the growth of trees. Still, a wide variety (1,700 species) of plants grow there, including low shrubs such as willow, birch, and berry-bearing heaths; sedges, reindeer moss, liverworts, and tussock-forming grasses; numerous varieties of lichen; and 400 types of flowers. Some flowers concentrate heat in their blooms to attract pollinating insects.
 A diverse animal population begins with insects, sometimes in enormous swarms: mosquitoes, flies, grasshoppers, moths, and Arctic bumblebees are common. Fish such as cod and flatfish inhabit the coastal waters, with trout and salmon in the innumerable ponds, lakes, and streams. Migratory birds abound, featuring snowy owls, falcons, ravens, gulls, terns, sandpipers, loons, swans, ptarmigan, and buntings. The dominant grazing mammals, lemmings and voles, support most of the predators; fluctuations in their numbers lead to oscillating populations and migrations of the species that prey on them. Other herbivorous mammals include squirrels, hares, and caribou. Carnivorous mammals are primarily wolves, Arctic foxes, and (during the summer) polar bears.
Tundra animals are adapted for survival in many ways. Birds and mammals are insulated by layers of fat and thick coats of feathers or fur; some also migrate to warmer winter habitats where food is more plentiful. Insects produce natural "antifreeze" chemicals in their bodies. All inhabitants breed and raise their young quickly to take advantage of the short, intense summers.
|
|
