Mountain Ecosystem

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Mountain Ecosystem

Mountains occur on all continents, in all latitude zones, and within all the world’s principal biome types – from hyperarid hot desert and tropical moist forest to arid polar icecaps – and support a correspondingly wide variety of ecosystems.

Mountain ecosystems tend to be important for biological diversity, particularly in the tropics and warmer temperate latitudes.

Although richness declines with altitude, lower elevation slopes often hold a wide range of habitat types within a relatively short distance.

Isolated mountain blocks are often rich in endemics.

Polar mountains may be entirely without vegetation; at other high latitude sites, mountains may bear only sparse tundra-like scrub. On low elevation mountains at lower latitudes, vegetation may be broadly similar to that of surrounding lowlands, often with coniferous or broadleaf forest. With increasing elevation, the effects of temperature, precipitation and wind combine to induce an altitude-related zoning in vegetation. As elevation increases, the availability of moisture – as rain or condensation from cloud or fog – tends to increase (up to a level that varies with latitude and between continents).

In arid regions such as the Horn of Africa, this can allow tree growth near the top of mid elevation mountains that emerge from treeless semi-desert plains. In more humid regions, shortstature epiphyte-rich evergreen forest (cloud forest) may flourish above more seasonal forest types.

Ultimately, temperature and moisture availability decrease, and windspeed increases, to a point where tree growth cannot be sustained. Above this point, low herbaceous vegetation, often including tussock grassland, takes over, to be succeeded by largely bare rock or snow. Such montane grasslands are often important for livestock grazing, as exemplified by the páramo zone of the northern Andes. This is an extensive tract of grass and shrub, lying between the upper limit of cultivation (around 3,250 m) and the high summits (> 4,000 m).

Distinctive giant forms of groundsel and lobelia (whose widespread relatives are small herbaceous plants) occur above the treeline on high mountains in tropical Africa, while giant bromeliads and large composites occur on the Andean páramo. In many hill and mountain regions the present treeline has been pushed downslope from its potential level by burning and agricultural activity.

The vegetation zones encountered with increasing elevation on an idealized tropical mountain tend to resemble the biome types found with increasing latitude. Vegetation types similar to those that succeed one another through more than 80° of latitude and 3 000 km distance – tropical moist forest, deciduous forest, coniferous forest, shrub and grassland, or ice – may be compressed onto the slopes of a mountain perhaps 5,000 m high.

Despite superficial resemblance in vegetation, there are fundamental differences between elevational gradients in the tropics and latitudinal gradients. In tropical regions, the sun is high overhead throughout the year, whereas seasonality increases with increasing latitude. At high arctic latitudes, permafrost is common and there is little shortage of water during the short growing season, whereas alpine environments are less seasonal, with high light levels and daytime warming through much of the year.

The absence of permafrost means that soil water is readily lost through downslope drainage, leading to water stress.


Also See

Reference

  1. Mountain Watch Defining Mountain Regions [1]

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