Tundra vegetation is composed of dwarfshrubs,sedges,grasses,mosses, andlichens. Scattered trees grow in some tundra regions. Theecotone (or ecological boundary region) between the tundra and the forest is known as thetree line or timberline. The tundra soil is rich innitrogen andphosphorus.[2] The soil also contains large amounts of biomass and decomposed biomass that has been stored asmethane andcarbon dioxide in thepermafrost, making the tundra soil acarbon sink. As global warming heats the ecosystem and causes soil thawing, thepermafrost carbon cycle accelerates and releases much of these soil-contained greenhouse gases into the atmosphere, creatinga feedback cycle that contributes toglobal warming.
Arctic tundra occurs in the farNorthern Hemisphere, north of thetaiga belt. The word "tundra" usually refers only to the areas where the subsoil ispermafrost, or permanently frozen soil. (It may also refer to the treeless plain in general so that northernSápmi would be included.) Permafrost tundra includes vast areas of northern Russia and Canada.[2] The polar tundra is home to several peoples who are mostly nomadic reindeer herders, such as theNganasan andNenets in the permafrost area (and theSami inSápmi).
Arctic tundra contains areas of stark landscape and is frozen for much of the year.[5] The soil there is frozen from 25 to 90 cm (10 to 35 in) down, making it impossible for trees to grow there. Instead, bare and sometimes rocky land can only support certain kinds ofArctic vegetation, low-growing plants such as moss, heath (Ericaceae varieties such ascrowberry andblack bearberry), andlichen.[6][7]
There are two main seasons, winter and summer, in the polar tundra areas. During the winter it is very cold, dark, and windy with the average temperature around −28 °C (−18 °F), sometimes dipping as low as −50 °C (−58 °F). However, extreme cold temperatures on the tundra do not drop as low as those experienced in taiga areas further south (for example, Russia's, Canada's, and Alaska's lowest temperatures were recorded in locations south of the tree line). During the summer, temperatures rise somewhat, and the top layer of seasonally-frozen soil 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 12 °C (54 °F) but can often drop to 3 °C (37 °F) or even below freezing. Arctic tundras are sometimes the subject ofhabitat conservation programs. In Canada and Russia, many of these areas are protected through a nationalBiodiversity Action Plan.
Tundra tends to be windy, with winds often blowing upwards of 50–100 km/h (31–62 mph). However, it is desert-like, with only about 150–250 mm (6–10 in) of precipitation falling per year (the summer is typically the season of maximum precipitation). Although precipitation is light, evaporation is also relatively minimal. 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, so the water forms the lakes and marshes found during the summer months. There is a natural pattern of accumulation of fuel and wildfire which varies depending on the nature of vegetation and terrain. Research in Alaska has shown fire-event return intervals (FRIs) that typically vary from 150 to 200 years, with dryer lowland areas burning more frequently than wetter highland areas.[8]
A small herd ofmuskoxen in the Kakagrak Hills, Alaska
Due to the harsh climate of Arctic tundra, regions of this kind have seen little human activity, even though they are sometimes rich in natural resources such aspetroleum,natural gas, anduranium. In recent times this has begun to change inAlaska, Russia, and some other parts of the world: for example, theYamalo-Nenets Autonomous Okrug produces 90% of Russia's natural gas.
Permafrost thawing can cause slumping in the landscape
A severe threat to tundra isglobal warming, which causespermafrost to thaw. The thawing of the permafrost in a given area on human time scales (decades or centuries) could radically change which species can survive there.[13] It also represents a significant risk to infrastructure built on top of permafrost, such as roads and pipelines.
In locations where dead vegetation andpeat have accumulated, there is a risk of wildfire, such as the 1,039 km2 (401 sq mi) of tundra which burned in 2007 on the north slope of theBrooks Range in Alaska.[14] Such events may both result from and contribute to global warming.[15]
Carbon emissions from permafrost thaw contribute to the same warming which facilitates the thaw, making it apositive climate change feedback. The warming also intensifies Arcticwater cycle, and the increased amounts of warmer rain are another factor which increases permafrost thaw depths.[16]
TheIPCC Sixth Assessment Report estimates that carbon dioxide and methane released from permafrost could amount to the equivalent of 14–175 billion tonnes of carbon dioxide per 1 °C (1.8 °F) of warming.[17] For comparison, by 2019,annual anthropogenic emission of carbon dioxide alone stood around 40 billion tonnes.[17] A 2018 perspectives article discussingtipping points in the climate system activated around 2 °C (3.6 °F) of global warming suggested that at this threshold, permafrost thaw would add a further 0.09 °C (0.16 °F) to global temperatures by 2100, with a range of 0.04–0.16 °C (0.07–0.29 °F)[18]
Antarctic tundra occurs on Antarctica and on several Antarctic and subantarctic islands, includingSouth Georgia and the South Sandwich Islands and theKerguelen Islands. Most of Antarctica is too cold and dry to support vegetation, and most of the continent is covered by ice fields or cold deserts. However, some portions of the continent, particularly theAntarctic Peninsula, have areas of rocky soil that support plant life. The flora presently consists of around 300–400 species of lichens, 100 mosses, 25liverworts, 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, theAntarctic hair grass (Deschampsia antarctica) andAntarctic pearlwort (Colobanthus quitensis), are found on the northern and western parts of the Antarctic Peninsula.[19]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. TheAntipodes Subantarctic Islands tundraecoregion includes theBounty Islands,Auckland Islands,Antipodes Islands, theCampbell Island group, andMacquarie Island.[20] Species endemic to this ecoregion includeCorybas dienemus andCorybas sulcatus, the only subantarctic orchids; theroyal penguin; and theAntipodean albatross.[20]
There is some ambiguity on whetherMagellanic moorland, on the west coast ofPatagonia, should be considered tundra or not.[21]PhytogeographerEdmundo Pisano called it tundra (Spanish:tundra Magallánica) since he considered the low temperatures key to restrict plant growth.[21] More recent approaches have since recognized it as atemperate grassland, restricting southern tundra to coastal Antarctica and its islands.[22][23][24]
The flora and fauna of Antarctica and the Antarctic Islands (south of 60° south latitude) are protected by theAntarctic Treaty.[25]
Alpine tundra does not contain trees because the climate and soils at high altitude block tree growth.[26]: 51 The cold climate of the alpine tundra is caused by the low air temperatures, and is similar topolar climate. Alpine tundra is generally better drained than arctic soils.[7] Alpine tundra transitions tosubalpine forests below the tree line; stunted forests occurring at the forest-tundraecotone (thetreeline) are known asKrummholz. Alpine tundra can be affected bywoody plant encroachment.[27]
Alpine tundra occurs in mountains worldwide. The flora of the alpine tundra is characterized by plants that grow close to the ground, includingperennial grasses,sedges,forbs,cushion plants,mosses, andlichens.[28] The flora is adapted to the harsh conditions of the alpine environment, which include low temperatures, dryness, ultraviolet radiation, and a short growing season.
Tundra region with fjords, glaciers and mountains. Kongsfjorden,Spitsbergen.
Tundra climates ordinarily fit theKöppen climate classificationET, signifying a local climate in which at least one month has an average temperature high enough to melt snow (0 °C (32 °F)), but no month with an average temperature in excess of 10 °C (50 °F).[29] The cold limit generally meets theEF climates ofpermanent ice and snows; the warm-summer limit generally corresponds with the poleward or altitudinal limit of trees,[30] where they grade into thesubarctic climates designatedDfd,Dwd andDsd (extreme winters as in parts ofSiberia),Dfc typical in Alaska, Canada, mountain areas ofScandinavia,European Russia, andWestern Siberia (cold winters with months of freezing).[31]
Despite the potential diversity of climates in theET 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 lowvapor pressure of water in the chilly atmosphere, but as a rulepotential 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.[6] The amount of native tundra biomass depends more on the local temperature than the amount of precipitation.[32]
^Elliott-Fisk, D.L. (2000). "The Taiga and Boreal Forest". In Barbour, M.G.; Billings, M.D. (eds.).North American Terrestrial Vegetation (2nd ed.).Cambridge University Press.ISBN978-0-521-55986-7.
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