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La '''tundra''' (del vocablo [[lenguas saami|sami kildin]] en letra o caracteres [[alfabeto cirílico|cirílicos]] : "тӯндар" [''tūndar''], "páramo elevado", en su [[genitivo]] "тӯндра" [''tūndra'']) es un terreno abierto y llano, de [[clima]] [[subglacial]] y subsuelo helado ([[permafrost]]), falta de vegetación arbórea o en todo caso árboles "[[bonsái]]" naturales debido a la poca [[heliofanía]] y el estrés de frío glacial; los suelos están cubiertos de [[musgo]]s y [[liquen|líquenes]], y son pantanosos con [[turbera]]s en muchos sitios. Se extiende principalmente por el [[Hemisferio Norte]]: en [[Siberia]],<ref name="berkeley">{{Cita web |título=The Tundra Biome |obra=The World's Biomes |url=http://www.ucmp.berkeley.edu/glossary/gloss5/biome/tundra.html |fechaacceso=5 marzo 2006}}</ref> [[Alaska]], norte de [[Canadá]], sur de [[Groenlandia]] y la costa [[ártico|ártica]] de [[Europa]].<ref name="berkeley" /> En el [[Hemisferio Sur]] se manifiesta con temperaturas mucho más parejas durante el año y en lugares como el extremo sur de [[Chile]] y [[Argentina]], [[islas subantárticas]] como [[Georgia del Sur]] y [[Kerguelen]], y en pequeñas zonas del norte de la [[Antártica]]<ref>{{Cita web |título=Terrestrial Plants |obra=British Antarctic Survey: About Antarctica |url=http://www.antarctica.ac.uk/About_Antarctica/Wildlife/Plants/index.html |fechaacceso=5 marzo 2006}}</ref> cercanas al nivel del mar.
La tundra ocupa aproximadamente un quinto de la superficie emergida de la Tierra, subiendo las latitudes en dirección a ambos [[polo]]s [[antípoda|antipodales]] del planeta comienzan (en los hemisferios N y S entre los 45 y 60°) las zonas de tundra, bajando estas latitudes se suelen encontrar [[bosque]]s de [[conífera]]s (en el Hemisferio Norte [[picea]]s) con algunas [[abedul|betulaceas]] enanas (es decir la [[taiga]]), en el Hemisferio Sur con bosques y [[selva húmeda fría]] antiboreal de [[fagácea]]s seguidos de coníferas australes.<ref>{{cita publicación|apellido=Brancaleoni |nombre=Lisa |coautores=Jorge Strelin, Renato Gerdol |año=2003 |título=Relationships between geomorphology and vegetation in subantarctic Andean tundra of Tierra del Fuego |revista=Polar biology |volumen=26 |número=6 |páginas=404–410 |doi=10.1007/s00300-003-0499-7}}</ref>
La tundra ocupa aproximadamente un quinto de la superficie emergida de la Tierra, subiendo las latitudes en dirección a ambos [[polo]]s [[antípoda|antipodales]] del planeta comienzan (en los hemisferios N y S entre los 45 y 60°) las zonas de tundra, bajando estas latitudes se suelen encontrar [[bosque]]s de [[conífera]]s (en el Hemisferio Norte [[picea]]s) con algunas [[abedul|betulaceas]] enanas (es decir la [[taiga]]), en el Hemisferio Sur con bosques y [[selva húmeda fría]] antiboreal de [[fagácea]]s seguidos de coníferas australes.<ref>{{cita publicación|apellido=Brancaleoni |nombre=Lisa |coautores=Jorge Strelin, Renato Gerdol |año=2003 |título=y carnívoros:[[oso blanco]] (en el extremo norte) [[lobo]], [[halcón gerifalte]], [[oso kodiak]], [[búho nival]] y el [[zorro ártico]] ; los [[salmones]],son en gran medida la base de la [[red trófica]] 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--------------------vTundra |obra=Blue Planet Biomes |url=http://www.blueplanetbiomes.org/tundra.htm |fechaacceso=5 marzo 2006}}</ref>
También existe [[bioma]]s semejantes a los de tundra por efecto de altura ([[páramo|páramos montanos]]) , como en el [[Tíbet]] y en diversos niveles de las montañas alrededor del mundo como ocurre en zonas tropicales de [[Perú]] y [[Bolivia]].
Se pueden distinguir dos tipos de tundra la Alpina y la Artica; La alpina o alta montaña se encuentra en zonas montañosas, mientras que la Artica se encuentra en zonas mas bajas en donde se forman charcos y es en esta donde abunda la mayor vegetación.
== Situación y clima ==
Son zonas cercanas a los polos, en torno a los círculos polares donde los [[invierno]]s son extremadamente fríos, los veranos cortos y frescos.Con lluvias ligeras en [[verano]] y nevadas.
Su clima polar propicia que durante largos inviernos la temperatura
permanezca por debajo de los cero grados y que el terreno este cubierto por hielo y nieve.
En cambio durante los cortos veranos la temperatura puede variar de cero a diez grados centigrados; grandes extensiones se convierten en pantano en esta época, debido al deshielo y a que los suelos no permiten que se filtre el agua.
== Carbono ==
Un tópico valioso es que un tercio del carbono secuestrado en el suelo se encuentra en las áreas de [[taiga]] y de tundra. Cuando el permafrost funde, libera carbono como [[dióxido de carbono]], un [[gas de invernadero]]. Este efecto se ha observado en Alaska. En los años 70,la tundra era un depósito de carbono, pero en la actualidad, es una fuente de carbono gaseoso.<ref name="Oechel1993">{{cita publicación| apellido= Oechel | nombre= Walter C. | enlaceautor= | coautores= ''et al.'' | año= 1993 | mes= | título= Recent change of Arctic tundra ecosystems from a net carbon dioxide sink to a source | revista= [[Nature (journal)|Nature]] | volumen= 361 | número= 6412 | páginas= 520–523 | doi = 10.1038/361520a0 | url = | fechaaceso= | quote = }}</ref>
== Fauna ==
Algunos animales: fitófagos (heterótrofos que se alimentan de vegetales): [[caribú]], [[reno]], [[buey almizclero]], [[liebre]] ártica y [[cabra nival]] y el [[lemming]] y carnívoros:[[oso blanco]] (en el extremo norte) [[lobo]], [[halcón gerifalte]], [[oso kodiak]], [[búho nival]] y el [[zorro ártico]] ; los [[salmones]],son en gran medida la base de la [[red trófica]] para la fauna de este bioma<ref>{{Cita web |título=Tundra |obra=Blue Planet Biomes |url=http://www.blueplanetbiomes.org/tundra.htm |fechaacceso=5 marzo 2006}}</ref>
== Flora ==
Algunas plantas: [[pastos]], [[musgos]] y [[líquenes]] (que no pasan los 10 [[Centímetro|cm]] de altura, gracias a los vientos que los hacen mantenerse pegados al suelo).
Algunas plantas:
En la tundra hay poca vegetación, puesto que el suelo es muy pobre en materia orgánica, ya que está congelado casi todo el año.
Hay que aclarar que en este bioma no hay árboles, ya que el suelo no tiene suficientes nutrientes para que éstos crezcan
== Referencias ==
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== Enlaces externos ==
{{commonscat}}
*[http://www.panda.org/about_wwf/where_we_work/ecoregions/about/habitat_types/selecting_terrestrial_ecoregions/habitat11.cfm Ecorregiones de Tundra, WWF]
*[http://www.cotf.edu/ete/modules/msese/earthsysflr/tundra.html El Bioma Ártico, en Classroom of the Future]
*[http://www.ulapland.fi/home/arktinen/tundra/tundra.htm Retroalimentaciones Árticas al calentamiento Global: deegradación de la Tundra en el Ártico Ruso]
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