Tundra

For other uses, see Tundra (disambiguation).

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 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.

Arctic tundra on Wrangel Island, Russia

Arctic tundra

Tundra coastal vegetation in Alaska, during the summer

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 Lapland 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 Lapland).

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 -28 °C (-18.4°F), sometimes dipping as low as -70 °C (-94°F). During the summer temperatures rise and the top layer of the permafrost melts, leaving the ground very soggy. The tundra is covered in marshes, lakes, bogs and streams. Generally temperatures during the summer rise to about 12°C (53.6°F) but can often drop to 3°C (37.4°F). 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 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 (mostly of snow). 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.

The biodiversity of the tundras is low: 1,700 species of flora 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. Permafrost is essentially a frozen bog - in the summer, only its surface layer melts. 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

Tundra on the Kerguelen Islands

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 tundra. Its 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 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

Typical alpine tundra

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 does not map directly to specific WWF 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 found in all areas of alpine tundra.

Some animals of alpine tundra environments include the Kea parrot, marmot, Mountain goats, chinchilla, and pika.

Climatic classification

See also: Alpine climate

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 of 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.

FLORA The Arctic tundra is, by definition, treeless. However, although the tree line in atlases is depicted as a firm line between green conifers and brown tundra, in practice it is often difficult to locate the boundary to within 200 km (124 mi) in the field. Deciding what constitutes a tree is not as straightforward as it might seem, for species which occur as tall specimens in the taiga may occur as stunted, shrub-like, and dwarfed forms within the forest/tundra transition zone. Trees are arbitrarily defined as those tall enough to stand proud of the winter snows, a convention which allows boundaries to be plotted for each of the dozen or so species typically found at the forest edge, and an average tree line to be calculated. Even so, tongues and isolated rafts of trees penetrate far into the tundra in sheltered valleys and hollows, while elevated or swampy ground isolates islands of tundra vegetation within the forest edge.

The number of species of plant on the tundra proper is usually small compared with temperate regions. Arctic tundra is characterized by tough, low-growing dwarf shrubs, including heather, birch, willow, bilberry, and crowberry, and a carpet of sedges, grasses, rushes, mosses, and lichens. Sedges and mosses tend to dominate between hummocks whereas, on slightly elevated sites, often only 15 cm to 60 cm (6 in to 24 in) above the waterlogged soils, willows, grasses, and rushes are more common. Low temperatures combined with a short growing season limit annual primary (plant) productivity to 0.1-0.4 kg/sq m, a level similar to that of many deserts.

Alpine tundra communities consist of mat-forming and cushion-forming plants adapted to heavy snows, gusting winds, and widely fluctuating temperatures. In higher mountain areas, mosses and lichens manage to grow on exposed rock surfaces. Vascular plants usually die out at or just below the line of permanent snow. Annual primary productivity varies from 0.05 kg/sq m in windswept habitats, to 0.15 kg/sq m in alpine meadows, and 0.3 kg/sq m in dwarf shrub communities. [MSN ENCARTA]

FAUNA

The same or closely related species of animal tend to be found in tundra environments around the world. Musk oxen, caribou, and reindeer are the main large grazers feeding on grasses, sedges, willows, and lichens. Hares and lemmings are common consumers of grasses and sedges, while predators include polar bears, wolves, lynxes, foxes, eagles, hawks, falcons, and owls. Many migratory birds breed on the tundra during the brief summer, feeding on the flush of seeds and berries and/or the rapidly emerging populations of mosquitoes, black flies, blow flies, springtails, weevils, beetles, and spiders. Alpine tundra supports mountain goats, bighorn sheep, ibex, chamois, foxes, wildcats, pikas, marmots, ground squirrels, rabbits, voles, many summer-visiting birds, and the resident ptarmigan, a high-altitude version of the red or willow grouse that feeds mainly on willow buds and the succulent parts of other dwarf shrubs. Flies are scarce on alpine tundra, but butterflies, beetles, and grasshoppers are often abundant.

Animals have evolved a number of ecological strategies and physiological adaptations to cope with the harsh tundra environment. The most obvious strategy is to migrate to the tundra when the climate warms in the summer and when food supplies are at their maximum, and leave when temperatures begin to fall. Barren-ground caribou, for example, migrate in large herds from the fringes of the taiga to feed on the flush of plants hurriedly flowering and setting seed during the short summer growing season. Dwarf willows, blueberries (bilberries), cranberries, grasses, sedges, and carpets of lichen all develop rapidly at this time providing fodder for grazers and berries and seeds for other mammals and birds. Predatory wolves track the herds on their northward migration, while foxes clean up carrion and the sickly.

The migration of close to 100 species of breeding bird to the tundra coincides with the spring flush of vegetation and the emergence of insects from the soil and from beneath the regenerating carpet of plants. The herbivorous willow grouse makes only a short journey to the tundra from the evergreen forests to the south, but Arctic terns travel 40,000 km (25,000 mi) twice a year from the Arctic to the Antarctic and back again. Visiting birds include grouse, terns, ducks, geese, and waders that, along with rapidly multiplying populations of small rodents, draw in predatory eagles, peregrines, merlins, and owls.

The emergence of insects on which many summer visiting birds and their chicks rely is triggered by the springtime melting of ice at the soil surface that is unable to drain away because of the impermeable barrier of underlying permafrost. This creates boggy conditions ideal for invertebrate larvae, which hatch from eggs deposited in the previous year. Each small patch of tundra may be home to millions of herbivorous springtails, plant-sucking weevils, carnivorous beetles and spiders, and detritus-eating blow flies, dung beetles, and burying beetles. The most notorious insects of the tundra, however, are the mosquitoes and black flies, which rise in summer from the surface of pools and marshy areas like clouds of smoke. Female mosquitoes possess the piercing mouthparts used to suck blood from their victims. They can prove such an irritation to caribou that some individuals are driven to distraction.

A few animals are hardy enough to stay on the tundra all year round. The largest resident grazers are musk oxen, which survive the bitter Arctic winter by insulating themselves with thick layers of fur and fat. Young musk oxen are born with huge deposits of heat-producing (thermogenic) fat in their bodies and regularly hide beneath their mothers’ shaggy skirts of fur for extra protection from the penetrating winds. Adult musk oxen also huddle together in groups for warmth and, when threatened by predators, will often form a protective circle with the young calves at the centre.

Arctic foxes are also resident on the tundra, feeding mostly on the lemming population, which finds refuge in the winter beneath the insulating mantle of snow. Relative to their size, Arctic foxes have the thickest pelts in the animal kingdom and are stockier than their temperate counterparts with snub noses and tiny ears to reduce the surface area of skin in contact with the cold air. Like many other cold-climate animals, Arctic foxes have evolved an ingenious method of preventing heat escaping from their paws into the freezing snow. A fine network of blood vessels at the top of the leg called the rete mirabile (“wonderful net”) carries cool blood back to the body from the feet and warm blood in the opposite direction. The blood vessels come into such close contact in the rete that heat flows from the leg-bound blood, cooling it before it reaches the feet, while at the same time warming the ascending blood before it re-enters the torso. In this way, the paws of an Arctic fox are kept constantly at around 0o C (32° F) or slightly higher, while blood in the animal’s body remains at 38o C (100° F). Because there is little difference in temperature between paws and ground (that is, a negligible thermal gradient) little heat escapes from the animal’s legs into the environment. Caribou have similar heat-exchangers and a special type of fat in their lower legs which, unlike the fat in their bodies, remains pliable at low temperatures. Inuit have long appreciated the difference and used the marrow-fat at the top of Caribou legs as a solid food and the fat extracted from the feet as a fluid lubricant. [MSN ENCARTA]

HUMAN INFLUENCE The earliest human settlers of Arctic and tundra regions were probably the Yenisey Ostyaks of western Siberia and the Yukaghirs and Chukchi of eastern Siberia. Early inhabitants of northern Scandinavia and the White Sea region were among the first settlers of Arctic Europe, while North American Native Americans may have spread into the far north of the New World thousands of years before the Inuit. Later waves of settlers included the Finns of northern Scandinavia, the Nenets of northern Russia, and the Tungus and Yakuts of eastern Siberia. These were nomadic peoples, initially hunters, latterly herdsmen, who became increasingly dependent on following the great herds of reindeer on their migrations. About 20 ethnic groups now inhabit Arctic areas of Russia including the Yakut of the Lena River basin, the Tungus of the region east of the River Yenisey, the Yukaghir between the Indigirka and Yana Rivers, and the Chukchi of the extreme north-east of Siberia. The Chukchi are believed by many to have given rise to the Aleuts and Inuits whose descendants still live in semi-permanent settlements in Canada, Alaska, and coastal areas of Greenland.

Because of the harsh climate, long, dark winter months, and low productivity, the impact of humans on Arctic tundra ecosystems has been relatively mild until recently. However, exploitation of oil, coal, and minerals (such as nickel, iron, apatite, gold, tin, mica, tungsten, lead, zinc, and molybdenum) in the last few decades has resulted in a number of undesirable effects. Low productivity coupled with peaty soils that are easily compressed during the summer thaw renders the tundra very sensitive to heavy vehicles. Traffic has led to local erosion in many areas, particularly those targetted for oil extraction. Lines to guide engineers taking seismic readings have also been bulldozed across the tundra at regular intervals causing extensive damage. Even where this damage does not lead to erosion, the slow-growing tundra vegetation may take many years to recover. Environmental organizations have pointed out these negative effects and forced many companies active on the tundra into developing landscape management and wildlife conservation plans. Many access and distribution roads are now constructed on thick cushions of gravel up to 2 m (7 ft) deep to prevent melting of the permafrost, movement of the soil, and the initiation of erosion.

A less predictable consequence of oil-prospecting and extraction is the threat of oil spillage from the distribution network, particularly from ocean-going tankers. In 1989, 250,000 barrels of oil spilled from the tanker Exxon Valdez causing extensive pollution of coastal habitats and the death of large numbers of sea birds. The long-term effects of the spillage, if any, are the subject of continuing research.

The construction of long pipelines to carry oil across the North American tundra has led to some disruption of caribou movements as herds are prevented from following their traditional seasonal migration routes. The growing human presence in the region, however, has led to a marked reduction in the density of wolves, a benefit to the caribou population that traditionally suffers heavy losses to these predators. However, an increase in caribou numbers could lead to overgrazing of tundra vegetation and degradation of the typical plant communities. Striking a balance between caribou, wolves, and the perceived threat to human and domestic populations will require careful planning and population management.

Radioactive pollution from nuclear testing and reactor accidents is also a cause of considerable concern. Dust ejected from the failing Chernobyl nuclear power station in 1986 (see Chernobyl Accident) contained large amounts of radioactive caesium, which was washed out of the atmosphere and subsequently accumulated in the snow and ice of Greenland and other Arctic lands at such high levels that it can still be detected in the accreting ice masses of glaciers. The uptake of radioactive material and other chemical pollutants by slow-growing lichens has had severe repercussions, for these plants are a major source of food for reindeer and caribou which, in turn, are hunted and eaten by indigenous people. Consumption of food contaminated with radioactive substances may increase the risk of developing diseases such as cancer and may also contribute to the risk of birth defects. The slow turnover of nutrients by the relatively unproductive tundra vegetation suggests that the problems of radioactive contamination and its accumulation in food chains will be acute for many years to come.

There is also concern about the release of chemicals such as chlorofluorocarbons (CFCs) into the atmosphere and the effect on the ozone layer at polar latitudes. The major concern at the moment is the large ozone hole that opens over the southern polar landmass of Antarctica each spring, permitting increases in ultraviolet radiation possibly to levels that may endanger living organisms in places such as Australia and New Zealand. Although small temporary holes have been detected over the Arctic and caused some concern, the ozone layer at northern latitudes appears to be much more resilient than in the south. The issue of chemical contamination of the upper atmosphere and the effects on the ozone layer at both poles is the subject of continuing monitoring and research. [MSN ENCARTA]

See also

• List of tundra ecoregions from the WWF
• Fellfield

External links

• Tundra biome information from the University of California
• WWF Tundra Ecoregions
• The Arctic biome at Classroom of the Future
• Arctic Feedbacks to Global Warming: Tundra Degradation in the Russian Arctic