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Catégorie
Étage montagnard
Résumé
Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial factor in shaping plant community, biodiversity, metabolic processes and ecosystem dynamics for montane ecosystems. Dense montane forests are common at moderate elevations, due to moderate temperatures and high rainfall. At higher elevations, the climate is harsher, with lower temperatures and higher winds, preventing the growth of trees and causing the plant community to transition to montane grasslands and shrublands or alpine tundra. Due to the unique climate conditions of montane ecosystems, they contain increased numbers of endemic species. Montane ecosystems also exhibit variation in ecosystem services, which include carbon storage and water supply.
As elevation increases, the climate becomes cooler, due to a decrease in atmospheric pressure and the adiabatic cooling of airmasses. In middle latitudes, the change in climate by moving up 100 meters on a mountain is roughly equivalent to moving 80 kilometers (45 miles or 0.75° of latitude) towards the nearest pole. 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 elevation.
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 , where biotemperature is the mean temperature considering temperatures below to be . 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.
Source officielle
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