MONTANE ECOSYSTEMS refers to any ecosystem found in mountains . These ecosystems are strongly affected by climate , which gets colder as elevation increases . They are stratified according to elevation. Dense forests are common at moderate elevations. However, as the elevation increases, the climate becomes harsher, and the plant community transitions to grasslands or tundra .
* 1 Life zones
* 2 Montane forests
* 2.1 Temperate climate
* 3 Subalpine zone * 4 Alpine grasslands and tundra * 5 See also * 6 References * 7 External links
A stand of mountain birch at around 750 m in
As elevation increases, the climate becomes cooler , due to a decrease in the greenhouse effect . The characteristic flora and fauna in the mountains tend to strongly depend on elevation, because of the change in climate. This dependency causes life zones to form: bands of similar ecosystems at similar altitude.
One of the typical life zones on mountains is the montane forest: at moderate elevations, the rainfall and temperate climate encourages dense forests to grow. Holdridge defines the climate of montane forest as having a biotemperature of between 6 and 12 °C (43 and 54 °F), where biotemperature is the mean temperature considering temperatures below 0 °C (32 °F) to be 0 °C (32 °F). Above the elevation of the montane forest, the trees thin out in the subalpine zone, become twisted krummholz , and eventually fail to grow. Therefore, Montane forests often contain trees with twisted trunks. This phenomenon is observed due to the increase in the wind strength with the elevation.The elevation where trees fail to grow is called the tree line . The biotemperature of the subalpine zone is between 3 and 6 °C (37 and 43 °F).
Above the tree line the ecosystem is called the alpine zone or alpine
tundra , dominated by grasses and low-growing shrubs. The
biotemperature of the alpine zone is between 1.5 and 3 °C (34.7 and
37.4 °F). Many different plant species live in the alpine
environment, including perennial grasses , sedges , forbs , cushion
plants , mosses , and lichens . Alpine plants must adapt to the harsh
conditions of the alpine environment, which include low temperatures,
dryness, ultraviolet radiation, and a short growing season. Alpine
plants display adaptations such as rosette structures, waxy surfaces,
and hairy leaves. Because of the common characteristics of these
World Wildlife Fund
Climates with biotemperatures below 1.5 °C (35 °F) tend to consist purely of rock and ice.
Montane forests occur between the submontane zone and the subalpine
zone. The elevation at which one habitat changes to another varies
across the globe, particularly by latitude . The upper limit of
montane forests, the forest line or timberline , is often marked by a
change to hardier species that occur in less dense stands. For
example, in the Sierra Nevada of
The lower bound of the montane zone may be a "lower timberline" that separates the montane forest from drier steppe or desert region.
Montane forests differ from lowland forests in the same area. The climate of montane forests is colder than lowland climate at the same latitude, so the montane forests often have species typical of higher-latitude lowland forests. Humans can disturb montane forests through forestry and agriculture . On isolated mountains, montane forests surrounded by treeless dry regions are typical "sky island " ecosystems.
Montane forests in temperate climate are typically one of temperate coniferous forest or temperate broadleaf and mixed forest , forest types that are well known from northern Europe, northern United States, and southern Canada. The trees are, however, often not identical to those found further north: geology and climate causes different related species to occur in montane forests.
Montane forests around the world tend to be more species-rich than those in Europe, because major mountain chains in Europe are oriented east-west, which blocked species migration in the last ice age.
Montane forests in temperate climate occur in Europe (the
Iranian oak scrub in the Zagros Mountains
Montane forests in
SUBTROPICAL AND TROPICAL CLIMATE
Tropical montane forest at around 2,000 m in
In the tropics, montane forests can consist of broadleaf forest in addition to coniferous forest . One example of a tropical montane forest is a cloud forest , which gains its moisture from clouds and fog. Cloud forests often exhibit an abundance of mosses covering the ground and vegetation, in which case they are also referred to as mossy forests. Mossy forests usually develop on the saddles of mountains, where moisture introduced by settling clouds is more effectively retained. Depending on latitude, the lower limit of montane rainforests on large mountains is generally between 1,500 and 2,500 metres (4,900 and 8,200 ft) while the upper limit is usually from 2,400 to 3,300 metres (7,900 to 10,800 ft).
Subalpine Fir in
Mount Rainier National Park
The subalpine zone is the biotic zone immediately below the tree line
around the world. In tropical regions of
Trees in the subalpine zone often become krummholz , that is, crooked wood, stunted and twisted in form. At tree line, tree seedlings may germinate on the lee side of rocks and grow only as high as the rock provides wind protection. Further growth is more horizontal than vertical, and additional rooting may occur where branches contact the soil. Snow cover may protect krummholz trees during the winter, but branches higher than wind-shelters or snow cover are usually destroyed. Well-established krummholz trees may be several hundred to a thousand years old.
Example subalpine zones around the world include the French Prealps
in Europe, the Sierra Nevada and Rocky
ALPINE GRASSLANDS AND TUNDRA
Alpine grasslands and tundra lie above the tree line, in a world of intense radiation, wind, cold, snow, and ice. As a consequence, alpine vegetation is close to the ground and consists mainly of perennial grasses , sedges , and forbs . Annual plants are rare in this ecosystem and usually are only a few inches tall, with weak root systems. Other common plant life-forms include prostrate shrubs , graminoids forming tussocks , and cryptogams , such as bryophytes and lichens .
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. Non-flowering lichens cling to rocks and soil. Their enclosed algal cells 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.
Alpine meadows form where sediments from the weathering of rocks has
produced soils well-developed enough to support grasses and sedges.
Alpine grasslands are common enough around the world to be categorized
as a biome by the
World Wildlife Fund
The most extensive montane grasslands and shrublands occur in the
* ^ A B C Lugo, Ariel E.; Brown, Sandra L.; Dodson, Rusty; Smith,
Tom S.; Shugart, Hank H. (1999). "The Holdridge Life Zones of the
conterminous United States in relation to ecosystem mapping" (PDF).
Journal of Biogeography. 26 (5): 1025–1038. doi
* ^ A B Körner, Christian (2003). Alpine Plant Life: Functional
Plant Ecology of High