Altitudinal Zonation - Elevation Levels

Elevation Levels

Elevation models of zonation are complicated by factors discussed above and thus the relative altitudes each zone begins and ends is not tied to a specific altitude. However it is possible to split the altitudinal gradient into five main zones used by ecologists under varying names. In some cases these level follow each other with the decrease in altitude, which is called vegetation inversion.

• Nival level (Tierra Nevada, glaciers): Covered in snow throughout most of the year. Vegetation is extremely limited to only a few species that thrive on silica soils.
• Alpine level: The zone that stretches between the tree line and snowline. This zone is further broken down into Sub-Nival and Treeless Alpine (in the tropics-Tierra fria; low-alpine)
  • Sub-nival (Tierra helada): The highest zone that vegetation typically exists. This area is shaped by the frequent frosts that restrict extensive plant colonization. Vegetation is patchy and is restricted to only the most favorable locations that are protected from the heavy winds that often characterize this area. Much of this region is patchy grassland, sedges and rush heaths typical of arctic zones . Snow is found in this region for part of the year.
  • Treeless alpine (Tierra fria, low-alpine): Characterized by a closed carpet of vegetation that includes alpine meadows, shrubs and sporadic dwarfed trees. Because of the complete cover of vegetation, frost has less of an effect on this region, but due to the consistent freezing temperatures tree growth is severely limited.
• Montane level (Tierra templada): Extends from the mid-altitude forests to the tree line. The exact level of the tree line varies with local climate, but typically the tree line is found where mean monthly soil temperatures never exceed 10.0 degrees C and the mean annual soil temperatures are around 6.7 degrees C. In the tropics, this region is typified by montane rain forest (above 3,000 ft) while at higher latitudes coniferous forests often dominate.
• Lowland layer (Tierra caliente): This lowest section of mountains varies distinctly across climates and is referred to by a wide range of names depending on the surrounding landscape. Colline zones are found in tropical regions and Encinal zones and desert grasslands are found in desert regions.
  • Colline (tropics): Characterized by deciduous forests when in oceanic or moderately continental areas, and characterized by grassland in more continental regions. Extends from sea level to about 3,000 feet (roughly 900 m). Vegetation is abundant and dense. This zone is the typical base layer of tropical regions.
  • Encinal (deserts): Characterized by open evergreen oak forests and most common in desert regions. Evaporation and soil moisture control limitation of which encinal environments can thrive. Desert grasslands lie below encinal zones. Very commonly found in the Southwestern United States.
  • Desert grassland: Characterized by varying densities of low lying vegetation, grasslands zones cannot support trees due to extreme aridity. Some desert regions may support trees at base of mountains however, and thus distinct grasslands zones will not form in these areas.

For detailed breakdowns of the characteristics of altitudinal zones found on different mountains, see Climate zones by altitude.