tundra, treeless plains of N North America and N Eurasia, lying principally along the Arctic Circle, on the coasts and islands of the Arctic Ocean, and to the north of the coniferous forest belt. The tundra area is widest in N Siberia on the Kara Sea and reaches as far south as 60° N at the neck of the Kamchatka peninsula. Although sometimes called the Arctic steppe and situated mainly within the Arctic Circle, it reaches southward into the Scandinavian, Timan, and Ural mts. For most of the year the mean monthly temperature is below the freezing point; winters are long and severe. The summers are short and relatively warm, but even in July the mean monthly temperature does not rise above 50°F; (10°C;). Although high temperatures may be reached during a summer day, the subsoil is perpetually frozen. During summer, sedges, mosses, and lichens appear in abundance, along with some flowering plants. Among the few large animal species found in the tundra are the caribou, the arctic fox, the snowshoe rabbit, and occasionally the polar bear. Precipitation is spread evenly during the year and is slight, varying from 8 to 12 in. (20-30 cm). Evaporation is low, and much of the flat ground in areas of poor drainage becomes swampy during the summer months. Because there are very few species of flora and fauna, the destruction of the tundra is a simple process. The elimination of a single species or the disruption of the permanently frozen subsoil (permafrost) may severely damage this fragile ecosystem. Russia's tundra supports a small human population mostly consisting of the Nensty (Samoyedes) and the Komi. Eskimos inhabit the North American tundra.

Treeless, level or rolling ground above the taiga in polar regions (Arctic tundra) or on high mountains (alpine tundra), characterized by bare ground and rock or by such vegetation as mosses, lichens, small herbs, and low shrubs. Animal species are limited by harsh environmental conditions. In the Arctic tundra they include lemmings, the Arctic fox, the Arctic wolf, caribou, reindeer, and musk-oxen. In the alpine tundra many animals, including mountain sheep and wildcats, descend to warmer zones during winter. The climate of alpine tundra is more moderate and has a higher amount of rainfall than does Arctic tundra. The freezing climate of the Arctic produces a layer of permanently frozen soil (permafrost). An overlying layer of soil alternates between freezing and thawing with seasonal temperature variations. Alpine tundras have a freeze-thaw layer but no permafrost. Because Arctic tundras receive extremely long periods of daylight and darkness (lasting between one and four months), biological rhythms tend to be adjusted more to variations in temperature than to variations in sunlight. Arctic tundra covers about one-tenth of the earth's surface. Alpine tundras begin above the timberline of spruce and firs. Because of the small number of plant and animal species and the fragility of the food chains in tundra regions, natural or mechanical damage to any element of the habitat affects the whole ecosystem.

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