Alpine tundra

Alpine tundra

Overview
Alpine tundra is a natural region that does not contain trees because it is at high altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...

. Alpine tundra is distinguished from arctic tundra, because alpine soils are generally better drained than arctic soils. Alpine tundra transitions to subalpine forests below the tree line; stunted forests occurring at the forest-tundra ecotone
Ecotone
An ecotone is a transition area between two biomes but different patches of the landscape, such as forest and grassland. It may be narrow or wide, and it may be local or regional...

 are known as Krummholz
Krummholz
Krummholz or Krumholtz formation — also called Knieholz — is a particular feature of subarctic and subalpine tree line landscapes. Continual exposure to fierce, freezing winds causes vegetation to become stunted and deformed...

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Alpine tundra occurs in mountains worldwide.
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Encyclopedia
Alpine tundra is a natural region that does not contain trees because it is at high altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...

. Alpine tundra is distinguished from arctic tundra, because alpine soils are generally better drained than arctic soils. Alpine tundra transitions to subalpine forests below the tree line; stunted forests occurring at the forest-tundra ecotone
Ecotone
An ecotone is a transition area between two biomes but different patches of the landscape, such as forest and grassland. It may be narrow or wide, and it may be local or regional...

 are known as Krummholz
Krummholz
Krummholz or Krumholtz formation — also called Knieholz — is a particular feature of subarctic and subalpine tree line landscapes. Continual exposure to fierce, freezing winds causes vegetation to become stunted and deformed...

.

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 the low air pressure, and is similar to polar climate
Polar climate
Regions with a polar climate are characterized by a lack of warm summers . Regions with polar climate cover over 20% of the Earth. The sun shines 24 hours in the summer, and barely ever shines at all in the winter...

.

Geography


Alpine tundra occurs at high enough altitude at any latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

. Portions of Montane grasslands and shrublands
Montane grasslands and shrublands
Montane grasslands and shrublands is a biome defined by the World Wildlife Fund. The biome includes high altitude grasslands and shrublands around the world....

 ecoregions worldwide include alpine tundra. Large regions of alpine tundra occur in the American Cordillera
American cordillera
The American Cordillera is a cordillera that consists of an essentially continuous sequence of mountain ranges that form the western "backbone" of North America, Central America, South America and Antarctica. From north to south, this sequence of overlapping and parallel ranges begins with the...

 in North and South America, the Alps
Alps
The Alps is one of the great mountain range systems of Europe, stretching from Austria and Slovenia in the east through Italy, Switzerland, Liechtenstein and Germany to France in the west....

 and Pyrenees
Pyrenees
The Pyrenees is a range of mountains in southwest Europe that forms a natural border between France and Spain...

 of Europe, the Rift Mountains of Africa, and a large portion of the Tibetan Plateau
Tibetan Plateau
The Tibetan Plateau , also known as the Qinghai–Tibetan Plateau is a vast, elevated plateau in Central Asia covering most of the Tibet Autonomous Region and Qinghai, in addition to smaller portions of western Sichuan, southwestern Gansu, and northern Yunnan in Western China and Ladakh in...

.

Alpine tundra/grasslands occupy high-mountain summits, slopes, and ridges above timberline. Aspect plays a role as well: the treeline often occurs at higher elevations on warmer sun-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.

Climate


Alpine climate is the average weather (climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

) for the alpine tundra. The climate becomes colder at high elevation
Elevation
The elevation of a geographic location is its height above a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface ....

s—this characteristic is described by the lapse rate of air: air tends to get colder as it rises, since it expands. The dry adiabatic lapse rate is 10 °C per km of elevation or altitude. Therefore, moving up 100 meters on a mountain is roughly equivalent to moving 80 kilometers (45 miles or 0.75° of latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

) towards the pole. This relationship is only approximate, however, since local factors such as proximity to ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

s can drastically modify the climate.

Typical high-elevation growing seasons range from 45 to 90 days, with average summer temperatures near 50° F (10° C). Growing season temperatures frequently fall below freezing, and frost occurs throughout the growing season in many areas. Precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...

 occurs mainly as winter snow, but soil water availability is highly variable with season, location, and topography. For example, snowfields commonly accumulate on the lee sides of ridges while ridgelines may remain nearly snow free due to redistribution by wind. Some alpine habitats may be up to 70% snow free in winter. High wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...

s are common in alpine ecosystems, and can cause significant soil erosion and be physically and physiologically detrimental to plants. Also, wind coupled with high solar radiation can promote extremely high rates of evaporation
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....

 and transpiration
Transpiration
Transpiration is a process similar to evaporation. It is a part of the water cycle, and it is the loss of water vapor from parts of plants , especially in leaves but also in stems, flowers and roots. Leaf surfaces are dotted with openings which are collectively called stomata, and in most plants...

.

Quantifying the climate



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

Climatologist Wladimir Köppen
Wladimir Köppen
Wladimir Peter Köppen was a Russian geographer, meteorologist, climatologist and botanist. After studies in St. Petersburg, he spent the bulk of his life and professional career in Germany and Austria...

 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
Köppen climate classification
The Köppen climate classification is one of the most widely used climate classification systems. It was first published by Crimea German climatologist Wladimir Köppen in 1884, with several later modifications by Köppen himself, notably in 1918 and 1936...

 for more information.

Otto Nordenskiöld
Otto Nordenskiöld
Nils Otto Gustaf Nordenskjöld was a Finnish and Swedish geologist, geographer, and polar explorer.-Biography:...

 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 in its coldest month, the warmest month would need to average 11 °C 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 °C and 3 °C, Holdridge quantifies the climate as alpine.

Flora




In a world of intense radiation, wind, cold, snow, and ice, alpine vegetation is close to the ground and consists mainly of perennial grasses, sedges
Cyperaceae
Cyperaceae are a family of monocotyledonous graminoid flowering plants known as sedges, which superficially resemble grasses or rushes. The family is large, with some 5,500 species described in about 109 genera. These species are widely distributed, with the centers of diversity for the group...

, forb
Forb
A forb is a herbaceous flowering plant that is not a graminoid . The term is used in biology and in vegetation ecology, especially in relation to grasslands and understory.-Etymology:...

s, and low-growing shrubs with prominent inclusions of lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...

s and moss
Moss
Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...

es. Compared to ecosystems at lower elevations, the alpine tundra contains few plant species; usually there are no more than 200 to 300 species present in the alpine zone of a given mountain range. Perennial herbs (including grasses, sedges, and low woody or semi-woody shrubs) dominate the alpine landscape; they have much more root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

 and rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

 biomass than that of shoots, leaves, and flowers. The roots and rhizomes not only function in water and nutrient absorption but also play a very important role in over-winter carbohydrate storage. Annual plants are rare in this ecosystem and usually are only a few inches tall, with weak root systems.

Plants have adapted to the harsh alpine environment. Cushion plant
Cushion plant
A cushion plant is a compact, low growing, mat forming plant that is found in alpine, subalpine, arctic, or subarctic environments around the world...

s, 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
Anthocyanin
Anthocyanins are water-soluble vacuolar pigments that may appear red, purple, or blue according to pH...

 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.

Alpine areas are unique because of the severity and complexity of their environmental conditions. Very small changes in topography
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...

 [as small as 1 foot (0.3 m) or less] may mean the difference between a windswept area or an area of snow accumulation, changing the potential productivity
Productivity
Productivity is a measure of the efficiency of production. Productivity is a ratio of what is produced to what is required to produce it. Usually this ratio is in the form of an average, expressing the total output divided by the total input...

 and plant community drastically. Between these extremes of drought
Drought
A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...

 versus saturation
Saturation (chemistry)
In chemistry, saturation has six different meanings, all based on reaching a maximum capacity...

, 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.
Alpine meadows form where sediments from the weathering of rocks has produced soils well-developed enough to support grass
Grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...

es and sedges
Cyperaceae
Cyperaceae are a family of monocotyledonous graminoid flowering plants known as sedges, which superficially resemble grasses or rushes. The family is large, with some 5,500 species described in about 109 genera. These species are widely distributed, with the centers of diversity for the group...

. Non-flowering lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...

s cling to rocks and soil. Their enclosed algal cells
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

 can 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, leaving exposed soil to blow away, and recovery may take hundreds of years.

Fauna


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
Kea
The Kea is a large species of parrot found in forested and alpine regions of the South Island of New Zealand. About long, it is mostly olive-green with a brilliant orange under its wings and has a large narrow curved grey-brown upper beak. The Kea is the world's only alpine parrot...

 parrot, marmot
Marmot
The marmots are a genus, Marmota, of squirrels. There are 14 species in this genus.Marmots are generally large ground squirrels. Those most often referred to as marmots tend to live in mountainous areas such as the Alps, northern Apennines, Eurasian steppes, Carpathians, Tatras, and Pyrenees in...

, mountain goat
Mountain goat
The Mountain Goat , also known as the Rocky Mountain Goat, is a large-hoofed mammal found only in North America. Despite its vernacular name, it is not a member of Capra, the genus of true goats...

s, chinchilla
Chinchilla
Chinchillas are crepuscular rodents, slightly larger and more robust than ground squirrels, and are native to the Andes mountains in South America. Along with their relatives, viscachas, they make up the family Chinchillidae....

, woodland caribou, and pika
Pika
The pika is a small mammal, with short limbs, rounded ears, and short tail. The name pika is used for any member of the Ochotonidae, a family within the order of lagomorphs, which also includes the Leporidae . One genus, Ochotona, is recognised within the family, and it includes 30 species...

.