Tundra
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 tū̄ndra, the
genitive of
tundar, "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:
Fellfields
 |
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, which means 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 down, and so it is impossible for trees to grow. Instead, bare and sometimes rocky land can only support low growing plants such as
mosses,
heaths and
lichen. There are two main seasons â€" winter and summer in the polar Tundra areas. During the winter, it is very cold and dark, with the average temperature being around -28 °C. However, when there is no sun for several weeks â€" which is a common occurrence, temperatures have been known to drop to a chilling -70 °C. There is permafrost on the ground, which never completely melts. In 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, but can often drop to 3°.
The tundra is a very windy area, with winds blowing upwards of 48â€"97 km/h (30-60 miles an hour). However in terms of precipitation, it is desert-like, with only about 150â€"250 mm (6â€"10 inches) falling a 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 tundra is low: there are 1700 species of flora and only 48 land mammals can be found, although thousands of insects and plants 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.
Global warming is a severe threat to the arctic tundra because of the permafrost. 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 would 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
.
|
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, 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,
penguins, inhabit areas near the shore, and some small mammals, like
rabbits and , 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 |
Typical 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 below the
tree-line; stunted forests occurring at the forest-tundra
ecotone are known as
Krummholz.
Notable animals in the alpine tundra include, ,
marmots,
Mountain goats, and
pika.
Alpine tundra does not map directly to specific WWF ecoregions. Portions of
Montane grasslands and shrublands ecoregions include alpine tundra. The alpine tundra also has elks,marmots, mountain goats, pikas, and sheep.
See also: Alpine climate*
Tundra biome information from the
University of California*
WWF Tundra Ecoregions*
The Arctic biome at Classroom of the Future*
List of tundra ecoregions from the
WWF
