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In physical geography, tundra is an area where tree growth is hindered by low temperatures and short growing seasons. The term "tundra" comes from the Sami language (through Russian), meaning treeless plain. There are three types of tundra: arctic tundra, antarctic tundra, and alpine tundra. In all of these types, the dominant vegetation is grasses, mosses, and lichens. Trees grow in some of the tundra. The ecotone (or ecological boundary region) between the tundra and the forest is known as the tree-line or timberline. See also:
Arctic tundraArctic 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, which contains permanently frozen water. (It may also refer to the treeless plain in general, so that northern Lapland would be included.) Permafrost tundra includes vast areas of northern Russia and Canada. The arctic tundra is home to several peoples who are mostly nomadic reindeer herders, e.g. Nganasan and Nenets in the permafrost area (and the Sami in Lapland). The biodiversity of tundra is low: there are few species with large populations. Notable animals in the arctic tundra include:
Due to the harsh climate of the arctic tundra, regions of this kind have seen little exploitation even though they are sometimes rich in natural resources such as oil and uranium. In recent time this has begun to change, and in Alaska, Russia and some other parts of the world the tundra is being ever more subjected to human interference. Global warming is a severe threat to the arctic tundra because of the permafrost. Essentially, permafrost is frozen bog. In the summer, only its surface layer melts. Should it melt completely, the entire ecosystem would be devastated. The arctic species could not adjust for such a rapid change. Another threat is that one third of the world's soil-bound carbon is in the taiga and tundra areas. When the permafrost melts, it releases carbon more than it can bind. The effect has been observed in Alaska: in the 1970's, the tundra was a carbon sink, but today, it's a carbon source. This aggravates the problem of global warming even further. Antarctic tundraAntarctic 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 tundra. Its flora presently consists of around 250 lichens, 100 mosses, 25-30 liverworts, around 700 terrestrial and aquatic algal 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, 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 flora and fauna of Antarctica and the Antarctic Islands (south of 60º south latitude) are protected by the Antarctic Treaty. Alpine tundra Alpine tundra occurs at high enough altitude at any latitude on Earth. Alpine tundra also lacks trees, but does not usually have permafrost, and alpine soils are generally better drained than permafrost soils. Alpine tundra transitions to subalpine forests or Montane grasslands and shrublands below the tree-line; stunted forests occurring at the forest-tundra ecotone are known as Krummholz. Notable animals in the alpine tundra include:
Tundra ecoregions
External link
da:Tundra de:Tundra es:Tundra eo:Tundro fi:Tundra fr:toundra it:Tundra ja:ツンドラ nl:Toendra |
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