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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In physical geography, tundra is an area where the tree growth is hindered by low temperatures and short growing seasons. The term "tundra" comes from Kildin Sami tūndâr "uplands, tundra, treeless mountain tract". There are two types of tundra: Arctic tundra (which also occurs in Antarctica), and alpine tundra. In tundra, the vegetation is composed of dwarf shrubs, sedges and grasses, mosses, and lichens. Scattered trees grow in some tundra. The ecotone (or ecological boundary region) between the tundra and the forest is known as the tree line or timberline.

Arctic tundra

Arctic tundra occurs in the far Northern Hemisphere, north of the taiga belt. The word "tundra" usually refers only to the areas where the subsoil is permafrost, or permanently frozen soil. (It may also refer to the treeless plain in general, so that northern Sápmi would be included.) Permafrost tundra includes vast areas of northern Russia and Canada. The polar tundra is home to several peoples who are mostly nomadic reindeer herders, such as the Nganasan and Nenets in the permafrost area (and the Sami in Sápmi).

The Arctic tundra is a vast area of stark landscape, which is frozen for much of the year. The soil there is frozen from 25–90 cm (9.8–35.4 inches) down, and it is impossible for trees to grow. Instead, bare and sometimes rocky land can only support low growing plants such as moss, heath, and lichen. There are two main seasons, winter and summer, in the polar tundra areas. During the winter it is very cold and dark, with the average temperature around , sometimes dipping as low as . However, extreme cold temperatures on the tundra do not drop as low as those experienced in taiga areas further south (for example, Russia's and Canada's lowest temperatures were recorded in locations south of the treeline). During the summer, temperatures rise somewhat, and the top layer of the permafrost melts, leaving the ground very soggy. The tundra is covered in marshes, lakes, bogs and streams during the warm months. Generally daytime temperatures during the summer rise to about but can often drop to or even below freezing. Arctic tundras are sometimes the subject of habitat conservation programs. In Canada and Russia, many of these areas are protected through a national Biodiversity Action Plan.

The tundra is a very windy area, with winds often blowing upwards at 48–97 km/h (30–60 miles an hour). However, in terms of precipitation, it is desert-like, with only about 15–25 cm (6–10 inches) falling per year (the summer is typically the season of maximum precipitation). During the summer, the permafrost thaws just enough to let plants grow and reproduce, but because the ground below this is frozen, the water cannot sink any lower, and so the water forms the lakes and marshes found during the summer months. Although precipitation is light, evaporation is also relatively minimal.

The biodiversity of the tundras is low: 1,700 species of vascular plants and only 48 land mammals can be found, although thousands of insects and birds migrate there each year for the marshes. There are also a few fish species such as the flat fish. There are few species with large populations. Notable animals in the Arctic tundra include caribou (reindeer), musk ox, arctic hare, arctic fox, snowy owl, lemmings, and polar bears (only the extreme north).

Due to the harsh climate of the Arctic tundra, regions of this kind have seen little human activity, even though they are sometimes rich in natural resources such as oil and uranium. In recent times this has begun to change in Alaska, Russia, and some other parts of the world.

A severe threat to the tundras, specifically to the permafrost, is global warming. The melting of the permafrost in a given area on human time scales (decades or centuries) could radically change which species can survive there.

Another concern is that about one third of the world's soil-bound carbon is in taiga and tundra areas. When the permafrost melts, it releases carbon in the form of carbon dioxide, a greenhouse gas. The effect has been observed in Alaska. In the 1970s the tundra was a carbon sink, but today, it is a carbon source.

Antarctic tundra

Antarctic tundra occurs on Antarctica and on several Antarctic and subantarctic islands, including South Georgia and the South Sandwich Islands and the Kerguelen Islands. Antarctica is mostly too cold and dry to support vegetation, and most of the continent is covered by ice fields. However, some portions of the continent, particularly the Antarctic Peninsula, have areas of rocky soil that support plant life. The flora presently consists of around 300–400 lichens, 100 mosses, 25 liverworts, and around 700 terrestrial and aquatic algae species, which live on the areas of exposed rock and soil around the shore of the continent. Antarctica's two flowering plant species, the Antarctic hair grass (Deschampsia Antarctica) and Antarctic pearlwort (Colobanthus quitensis), are found on the northern and western parts of the Antarctic Peninsula In contrast with the Arctic tundra, the Antarctic tundra lacks a large mammal fauna, mostly due to its physical isolation from the other continents. Sea mammals and sea birds, including seals and penguins, inhabit areas near the shore, and some small mammals, like rabbits and cats, have been introduced by humans to some of the subantarctic islands. The Antipodes Subantarctic Islands tundra ecoregion includes the Bounty Islands, Auckland Islands, Antipodes Islands, the Campbell Island group, and Macquarie Island.

The flora and fauna of Antarctica and the Antarctic Islands (south of 60° south latitude) are protected by the Antarctic Treaty.

Tundra also occurs on Tierra del Fuego and southern Argentina. Notable plant and lichen species of this tundra include Neuropogon aurantiaco, Azorella lycopodioides, Marsippospermum reichei, Nardophyllum bryoides, and Bolax gummifera.

Alpine tundra

Alpine tundra is an ecozone that does not contain trees because it has high altitude. Alpine tundra occurs at high enough altitude at any latitude on Earth. Alpine tundra also lacks trees, but the lower part does not have permafrost, and alpine soils are generally better drained than permafrost soils. Alpine tundra transitions to subalpine forests below the tree line; stunted forests occurring at the forest-tundra ecotone are known as Krummholz. Alpine tundra occurs in an alpine zone.

Alpine tundra does not map directly to specific World Wide Fund for Nature ecoregions. Portions of Montane grasslands and shrublands ecoregions include alpine tundra.

Because alpine tundra is located in various widely-separated regions of the Earth, there is no animal species common to all areas of alpine tundra. Some animals of alpine tundra environments include the Kea parrot, marmot, Mountain goats, chinchilla, and pika.

Large sections of the Tibetan Plateau include alpine tundra.

Climatic classification

Tundra climates ordinarily fit the Köppen climate classification ET, signifying a local climate in which at least one month has an average temperature high enough to melt snow (0°C or 32°F), but no month with an average temperature in excess of (10°C/50°F). The cold limit generally meets the EF climates of permanent ice and snows; the warm-summer limit generally corresponds with the poleward or altitudinal limit of trees, where they grade into the subarctic climates designated Dfd and Dwd (extreme winters as in parts of Siberia), Dfc typical in Alaska, Canada, European Russia, and Western Siberia (cold winters with months of freezing), or even Cfc (no month colder than -3°C as in parts of Iceland and southernmost South America). Tundra climates as a rule are hostile to woody vegetation even where the winters are comparatively mild by polar standards, as in Iceland.

Despite the potential diversity of climates in the ET category involving precipitation, extreme temperatures, and relative wet and dry seasons, this category is rarely subdivided. Rainfall and snowfall are generally slight due to the limited capacity of the chilly atmosphere to hold water vapor, but as a rule potential evapotranspiration is extremely low, allowing soggy terrain of swamps and bogs even in places that get precipitation typical of deserts of lower and middle latitudes. Scarcity or lushness (by polar standards) of native vegetation of tundra regions depends more upon the severity of the temperatures than upon the scarcity or copiousness of precipitation. The alpine tundra also lacks in precipitation compared to the Arctic tundra.

See also

• List of tundra ecoregions from the WWF
• Fellfield
• Steppe-tundra

References

External links

• WWF Tundra Ecoregions
• The Arctic biome at Classroom of the Future
• Arctic Feedbacks to Global Warming: Tundra Degradation in the Russian Arctic
• British Antarctica Survey