Alpine tundra

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Alpine meadows
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"Alpine meadows" redirects here. For other uses, see Alpine meadow (disambiguation).
White Mountains
of New Hampshire, much of which is in the alpine zone.
Alpine tundra in the Venezuelan Andes

Alpine tundra is a type of natural region or biome that does not contain trees because it is at high elevation, with an associated harsh climate. As the latitude of a location approaches the poles, the threshold elevation for alpine tundra gets lower until it reaches sea level, and alpine tundra merges with polar tundra.

The high elevation causes an adverse climate, which is too cold and windy to support tree growth. Alpine tundra transitions to sub-alpine forests below the tree line; stunted forests occurring at the forest-tundra ecotone are known as krummholz. With increasing elevation it ends at the snow line where snow and ice persist through summer.

Alpine tundra occurs in mountains worldwide. The flora of the alpine tundra is characterized by dwarf shrubs close to the ground. The cold climate of the alpine tundra is caused by

adiabatic cooling of air, and is similar to polar climate
.

Geography

Alpine tundra occurs at high enough altitude at any

Scandinavian mountains.[5][6]

Alpine tundra occupies high-mountain summits, slopes, and ridges above timberline. Aspect plays a role as well; the

treeline often occurs at higher elevations on warmer equator-facing slopes. Because the alpine zone is present only on mountains, much of the landscape is rugged and broken, with rocky, snowcapped peaks, cliffs, and talus slopes, but also contains areas of gently rolling to almost flat topography.[7]

Averaging over many locations and local microclimates, the treeline rises 75 meters (245 ft) when moving 1 degree south from 70 to 50°N, and 130 meters (430 ft) per degree from 50 to 30°N. Between 30°N and 20°S, the treeline is roughly constant, between 3,500 and 4,000 meters (11,500 and 13,100 ft).[8]

Climate

Summer in Northern Sweden's Tarfala Valley with its alpine climate

dry adiabatic lapse rate is 10 °C per km (5.5 °F per 1000 ft) of elevation or altitude. Therefore, moving up 100 meters (330 ft) on a mountain is roughly equivalent to moving 80 kilometers (45 miles or 0.75° of latitude) towards the pole.[9] This relationship is only approximate, however, since local factors such as proximity to oceans
can drastically modify the climate.

In the alpine tundra, trees cannot tolerate the environmental conditions (usually cold temperatures, extreme snowpack, or associated lack of available moisture).

solar radiation can promote extremely high rates of evaporation and transpiration.[7]

Quantifying the climate

Alpine tundra just above the tree line in Kosciuszko National Park, Australia

There have been several attempts at quantifying what constitutes an alpine climate.

Climatologist Wladimir Köppen demonstrated a relationship between the Arctic and Antarctic tree lines and the 10 °C summer isotherm; i.e., places where the average temperature in the warmest calendar month of the year is below 10 °C cannot support forests. See Köppen climate classification for more information.

Otto Nordenskjöld theorized that winter conditions also play a role: His formula is W = 9 − 0.1 C, where W is the average temperature in the warmest month and C the average of the coldest month, both in degrees Celsius (this would mean, for example, that if a particular location had an average temperature of −20 °C (−4 °F) in its coldest month, the warmest month would need to average 11 °C (52 °F) or higher for trees to be able to survive there).

In 1947, Holdridge improved on these schemes, by defining

biotemperature: the mean annual temperature, where all temperatures below 0 °C are treated as 0 °C (because it makes no difference to plant life, being dormant). If the mean biotemperature is between 1.5 and 3 °C (34.7 and 37.4 °F),[11]
Holdridge quantifies the climate as alpine.

Flora

Main article: Alpine plant
Silky phacelia (Phacelia sericea, blooming) and spreading phlox (Phlox diffusa) are species of alpine regions of western North America.

Since the habitat of alpine vegetation is subject to intense radiation, wind, cold, snow, and ice, it grows close to the ground and consists mainly of

cushion plants; and cryptogams, such as bryophytes and lichens.[12]

Relative to lower elevation areas in the same region, alpine regions have a high rate of

adaptations, both of new species and the dispersal of pre-existing species.[12]

Though tundra covers only a minority of the Earth's surface (17-20%), the biodiversity of plant species is important to human nutrition. Of the 20 plant species that make up 80% of human food, 7 of them (35%) originated in this region.[13]

Alpine flora at 11,500 feet (3500 m) on the Flat Tops plateau in the Colorado Rocky Mountains U.S.A

Plants have adapted to the harsh alpine environment. Cushion plants, looking like ground-hugging clumps of moss, escape the strong winds blowing a few inches above them. Many flowering plants of the alpine tundra have dense hairs on stems and leaves to provide wind protection or red-colored pigments capable of converting the sun's light rays into heat. Some plants take two or more years to form flower buds, which survive the winter below the surface and then open and produce fruit with seeds in the few weeks of summer.[14] In various areas of alpine tundra, woody plant encroachment is observed.[15][16][17]

Alpine areas are unique because of the severity and complexity of their environmental conditions. Very small changes in

saturation, several intermediate environments may exist all within a few yards of each other, depending on topography, substrate, and climate. Alpine vegetation generally occurs in a mosaic of small patches with widely differing environmental conditions. Vegetation types vary from cushion and rosette plants on the ridges and in the rock crannies; to herbaceous and grassy vegetation along the slopes; dwarf shrubs with grasses and forbs below the melting snowdrifts; and sedges, grasses, low shrubs, and mosses in the bogs and along the brooks.[7]

An alpine mire in the Swiss Alps

Alpine meadows form where sediments from the weathering of rocks has produced soils well-developed enough to support grasses and sedges. Non-flowering

photosynthesize at any temperature above 0 °C (32 °F), and the outer fungal layers can absorb more than their own weight in water. The adaptations for survival of drying winds and cold may make tundra vegetation seem very hardy, but in some respects the tundra is very fragile. Repeated footsteps often destroy tundra plants, allowing exposed soil to blow away; recovery may take hundreds of years.[14]

Fauna

The Himalayan tahr

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, marmot, mountain goat, bighorn sheep, chinchilla, Himalayan tahr, yak, snow leopard, and pika.[18]

See also

References

  1. ISBN 978-1-925039-32-0
    . Retrieved 2023-07-05.
  2. ^ "The Alpine Biome". Archived from the original on 19 January 2010. Retrieved 2009-12-19.
  3. ISSN 0362-4331
    . Retrieved 2021-05-31.
  4. ^ "South Island montane grasslands". Terrestrial Ecoregions. World Wildlife Fund.
  5. JSTOR 3683770
    .
  6. PMID 26811780
    .
  7. ^ a b c d Public Domain This article incorporates public domain material from Grassland Habitat Group (PDF). Bureau of Land Management. Archived from the original (PDF) on 2008-07-24.
  8. S2CID 8647814. Archived from the original
    (PDF) on 2006-09-11. Retrieved 2018-07-30.
  9. ISBN 978-1-899628-20-9. Archived from the original
    (PDF) on 2013-10-14.
  10. ISBN 978-0-521-55986-7
    .
  11. ^ "Biodiversity lectures and practicals of Allan Jones". dundee.ac.uk. Archived from the original on 2007-09-29.
  12. ^
    S2CID 41723233
    .
  13. ISBN 978-1-77041-435-8
    .
  14. ^ a b Public Domain This article incorporates public domain material from Rocky Mountain National Park: Alpine Tundra Ecosystem. National Park Service.
  15. S2CID 225314620
    .
  16. JSTOR 1478919
    .
  17. S2CID 245267638
    .
  18. ^ "The tundra biome". ucmp.berkeley.edu. Retrieved 2023-12-31.

External links

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