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.cite web |title=The Tundra Biome |work=The World's Biomes |url=http://www.ucmp.berkeley.edu/glossary/gloss5/biome/tundra.html |accessdate=2006-03-05] 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 convert|-28|°C|°F|abbr=on|lk=on, sometimes dipping as low as convert|-50|°C|°F|abbr=on|lk=off. 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 convert|12|°C|°F|abbr=on|lk=off but can often drop to convert|3|°C|°F|abbr=on|lk=off 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). [cite web |title=Tundra |work=Blue Planet Biomes |url=http://www.blueplanetbiomes.org/tundra.htm |accessdate=2006-03-05]

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. [cite web |title=Tundra Threats |work=National Geographic |publisher= |url=http://science.nationalgeographic.com/science/earth/habitats/tundra-threats.html |accessdate=2008-04-03]

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. cite journal | last = Oechel | first = Walter C. | authorlink = | coauthors = "et al." | year = 1993 | month = | title = Recent change of Arctic tundra ecosystems from a net carbon dioxide sink to a source | journal = Nature | volume = 361 | issue = 6412 | pages = 520–523 | doi = 10.1038/361520a0 | url = | accessdate = | quote = ]

= 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 [cite web |title=Terrestrial Plants |work=British Antarctic Survey: About Antarctica |url=http://www.antarctica.ac.uk/About_Antarctica/Wildlife/Plants/index.html |accessdate=2006-03-05] 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. [cite web |title=Protocol on Environmental Protection to the Antarctic Treaty |work=British Antarctic Survey: About Antarctica |url=http://www.antarctica.ac.uk/About_Antarctica/Treaty/protocol.html |accessdate=2006-03-05]

Tundra also occurs on Tierra del Fuego and southern Argentina. [cite journal |last=Brancaleoni |first=Lisa |coauthors=Jorge Strelin, Renato Gerdol |year=2003 |title=Relationships between geomorphology and vegetation in subantarctic Andean tundra of Tierra del Fuego |journal=Polar biology |volume=26 |issue=6 |pages=404–410 |doi=10.1007/s00300-003-0499-7] 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.

ee also

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


External links

* [http://www.panda.org/about_wwf/where_we_work/ecoregions/about/habitat_types/selecting_terrestrial_ecoregions/habitat11.cfm WWF Tundra Ecoregions]
* [http://www.cotf.edu/ete/modules/msese/earthsysflr/tundra.html The Arctic biome at Classroom of the Future]
* [http://www.ulapland.fi/home/arktinen/tundra/tundra.htm Arctic Feedbacks to Global Warming: Tundra Degradation in the Russian Arctic]
* [http://www.antarctica.ac.uk/about_antarctica/wildlife/plants/ British Antarctica Survey]

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