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Altitudinal zonation (or elevational zonation) in mountainous regions describes the natural layering of ecosystems that occurs at distinct elevations due to varying environmental conditions.
Temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...
,
humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depe ...
,
soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
composition, and
solar radiation Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre (W/m ...
are important factors in determining altitudinal zones, which consequently support different vegetation and animal species. Altitudinal zonation was first hypothesized by geographer
Alexander von Humboldt Friedrich Wilhelm Heinrich Alexander von Humboldt (14 September 17696 May 1859) was a German polymath, geographer, naturalist, explorer, and proponent of Romantic philosophy and science. He was the younger brother of the Prussian minister, p ...
who noticed that temperature drops with increasing elevation. Zonation also occurs in
intertidal The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of Marine habitat, habitats with var ...
and
marine environment Marine habitats are habitats that support marine life. Marine life depends in some way on the saltwater that is in the sea (the term ''marine'' comes from the Latin ''mare'', meaning sea or ocean). A habitat is an ecological or environmental ...
s, as well as on
shore A shore or a shoreline is the fringe of land at the edge of a large body of water, such as an ocean, sea, or lake. In physical oceanography, a shore is the wider fringe that is geologically modified by the action of the body of water past a ...
lines and in
wetlands A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...
. Scientist
C. Hart Merriam Clinton Hart Merriam (December 5, 1855 – March 19, 1942) was an American zoologist, mammalogist, ornithologist, entomologist, ecologist, ethnographer, geographer, naturalist and physician. He was commonly known as the 'father of mammalogy', a ...
observed that changes in vegetation and animals in altitudinal zones map onto changes expected with increased latitude in his concept of
life zones The life zone concept was developed by C. Hart Merriam in 1889 as a means of describing areas with similar plant and animal communities. Merriam observed that the changes in these communities with an increase in latitude at a constant elevation ar ...
. Today, altitudinal zonation represents a core concept in
mountain research Mountain research or '' montology'', traditionally also known as ''orology'' (from Greek ''oros'' ὄρος for 'mountain' and ''logos'' λόγος), is a field of research that regionally concentrates on the Earth's surface's part covered by m ...
.


Factors

A variety of environmental factors determines the boundaries of altitudinal zones found on mountains, ranging from direct effects of temperature and
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
to indirect characteristics of the mountain itself, as well as biological interactions of the species. The cause of zonation is complex, due to many possible interactions and overlapping species ranges. Careful measurements and statistical tests are required prove the existence of discrete communities along an elevation gradient, as opposed to uncorrelated species ranges.


Temperature

Decreasing air temperature usually coincides with increasing elevation, which directly influences the length the growing season at different elevations of the mountain. For mountains located in deserts, extreme high temperatures also limit the ability of large
deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, aft ...
or coniferous trees to grow near the base of mountains. In addition, plants can be especially sensitive to soil temperatures and can have specific elevation ranges that support healthy growth.


Humidity

The humidity of certain zones, including precipitation levels, atmospheric humidity, and potential for
evapotranspiration Evapotranspiration (ET) is the combined processes by which water moves from the earth’s surface into the atmosphere. It covers both water evaporation (movement of water to the air directly from soil, canopies, and water bodies) and transpi ...
, varies with elevation and is a significant factor in determining altitudinal zonation. The most important variable is precipitation at various elevations. As warm, moist air rises up the windward side of a mountain, the air temperature cools and loses its capacity to hold moisture. Thus, the greatest amount of rainfall is expected at mid-altitudes and can support
deciduous forest In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, aft ...
development. Above a certain elevation the rising air becomes too dry and cold, and thus discourages tree growth. Even though rainfall may not be a significant factor for some mountains, atmospheric humidity or
aridity A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ar ...
can be more important climatic stresses that affect altitudinal zones. Both overall levels of precipitation and humidity influence soil moisture as well. One of the most important factors that control the lower boundary of the Encinal or forest level is the ratio of
evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...
to soil moisture.


Soil composition

The nutrient content of soils at different elevations further complicates the demarcation of altitudinal zones. Soils with higher nutrient content, due to higher decomposition rates or greater weathering of rocks, better support larger trees and vegetation. The elevation of better soils varies with the particular mountain being studied. For example, for mountains found in the tropical rainforest regions, lower elevations exhibit fewer terrestrial species because of the thick layer of dead fallen leaves covering the forest floor. At this latitude more acidic, humose soils exist at higher elevations in the
montane 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 f ...
or
subalpine 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 f ...
levels. In a different example,
weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...
is hampered by low temperatures at higher elevations in the
Rocky Mountain The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...
of the western United States, resulting in thin coarse soils.


Biological forces

In addition to physical forces, biological forces may also produce zonation. For example, a strong competitor can force weaker competitors to higher or lower positions on the elevation gradient. The importance of competition is difficult to assess without experiments, which are expensive and often take many years to complete. However, there is an accumulating body of evidence that competitively dominant plants may seize the preferred locations (warmer sites or deeper soils). Two other biological factors can influence zonation:
grazing In agriculture, grazing is a method of animal husbandry whereby domestic livestock are allowed outdoors to roam around and consume wild vegetations in order to convert the otherwise indigestible (by human gut) cellulose within grass and other ...
and mutualism. The relative importance of these factors is also difficult to assess, but the abundance of grazing animals, and the abundance of
mycorrhiza   A mycorrhiza (from Greek μύκης ', "fungus", and ῥίζα ', "root"; pl. mycorrhizae, mycorrhiza or mycorrhizas) is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plant ...
l associations, suggests that these elements may influence plant distributions in significant ways.


Solar radiation

Light is another significant factor in the growth of trees and other
photosynthetic Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...
vegetation. The earth's atmosphere is filled with water vapor, particulate matter, and gases that filter the radiation coming from the sun before reaching the earth's surface. Hence, the summits of mountains and higher elevations receive much more intense radiation than the basal plains. Along with the expected
arid A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ar ...
conditions at higher elevations, shrubs and grasses tend to thrive because of their small leaves and extensive root systems. However, high elevations also tend to have more frequent cloud cover, which compensates for some of the high intensity radiation.


Massenerhebung effect

The physical characteristics and relative location of the mountain itself must also be considered in predicting altitudinal zonation patterns. The
Massenerhebung effect The Massenerhebung effect (German for "mountain mass elevation") describes variation in the tree line based on mountain size and location. In general, mountains surrounded by large ranges will tend to have higher tree lines than more isolated mount ...
describes variation in the tree line based on mountain size and location: mountains surrounded by large ranges will tend to have higher tree lines than more isolated mountains due to heat retention and wind shadowing. This effect predicts that zonation of rain forests on lower mountains may mirror the zonation expected on high mountains, but the belts occur at lower elevations. A similar effect is exhibited in the
Santa Catalina Mountains The Santa Catalina Mountains, commonly referred to as the Catalina Mountains or the Catalinas, are north and northeast of Tucson in Arizona, United States, on Tucson's north perimeter. The mountain range is the most prominent in the Tucson area, w ...
of Arizona, where the basal elevation and the total elevation influence the elevation of vertical zones of vegetation.


Other factors

In addition to the factors described above, there are a host of other properties that can confound predictions of altitudinal zonations. These include: frequency of disturbance (such as fire or monsoons), wind velocity, type of rock, topography, nearness to streams or rivers, history of tectonic activity, and latitude.


Elevation levels

Elevation models of zonation are complicated by factors discussed above and thus the relative elevations each zone begins and ends is not tied to a specific elevation. 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 elevation, which is called ''vegetation inversion''. * Nival level (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: 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 The Cyperaceae are a family of graminoid (grass-like), monocotyledonous flowering plants known as sedges. The family is large, with some 5,500 known species described in about 90 genera, the largest being the "true sedges" genus ''Carex'' wit ...
and rush heaths typical of arctic zones . Snow is found in this region for part of the year. ** Treeless alpine (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: Extends from the mid-elevation 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 forest Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All exta ...
s often dominate. * Lowland layer: 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 In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, which ...
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
List of life zones by region The climate and ecology of different locations on the globe naturally separate into life zones, depending on elevation, location, and latitude. The generally strong dependency on elevation is known as altitudinal zonation: the average temperatur ...
.


Treeline

The most decisive biogeographic and climatic boundary along elevation gradients is the climatic high-elevation treeline. The treeline separates the
montane 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 f ...
from the
alpine zone Alpine tundra is a type of natural region or biome that does not contain trees because it is at high elevation, with an associated harsh climate. As the latitude of a location approaches the poles, the threshold elevation for alpine tundra gets ...
and marks the potential for tree growth, irrespective of whether trees are present or not. So when trees had been cut or burnt, and thus, are absent from the treeline, it is still in place as defined by the treeline isotherm. At the tree line, tree growth is often sparse, stunted, and deformed by wind and cold
krummholz ''Krummholz'' (german: krumm, "crooked, bent, twisted" and ''Holz'', "wood") — also called ''knieholz'' ("knee timber") — is a type of stunted, deformed vegetation encountered in the subarctic and subalpine Montane ecosystems are fou ...
(German for "crooked wood"). The tree line often appears well-defined, but it can be a more gradual transition. Trees grow shorter and often at lower densities as they approach tree line, above which they cease to exist.


Animal zonation

Animals also exhibit zonation patterns in concert with the vegetational zones described above. Invertebrates are more clearly defined into zones because they are typically less mobile than vertebrate species. Vertebrate animals often span across altitudinal zones according to the seasons and food availability. Typically animal species diversity and abundance decrease as a function of elevation above the montane zone because of the harsher environmental conditions experienced at higher elevations. Fewer studies have explored animal zonation with elevation because this correlation is less defined than the vegetation zones due to the increased mobility of animal species.


Land-use planning and human utilization

The variability of both natural and human environments has made it difficult to construct universal models to explain human cultivation in altitudinal environments. With more established roads however, the bridge between different cultures has started to shrink. Mountainous environments have become more accessible and diffusion of ideas, technology, and goods occur with more regularity. Nonetheless, altitudinal zonation caters to agricultural specialization and growing populations cause
environmental degradation Environmental degradation is the deterioration of the environment (biophysical), environment through depletion of resources such as quality of air, water and soil; the destruction of ecosystems; habitat destruction; the extinction of wildlife; an ...
.


Agriculture

Human populations have developed agricultural production strategies to exploit varying characteristics of altitudinal zones. Elevation,
climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...
, and soil fertility set upper limits on types of crops that can reside in each zone. Populations residing in the
Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
Mountain region of South America have taken advantage of varying altitudinal environments to raise a wide variety of different crops. Two different types of adaptive strategies have been adopted within mountainous communities. * Generalized Strategy – exploits a series of microniches or
ecozone An Ecozone may refer to: * Ecozone (Canada), one of 15 first-level ecological land classifications in Canada * Biogeographic realm, the broadest biogeographic division of Earth's land surface (referred to as ''ecozone'' by BBC) * Biome, a large c ...
s at several elevational levels * Specialized Strategy – focuses on a single zone and specializes in the agricultural activities suitable to that elevation, developing elaborate trade relationships with external populations With improved accessibility to new farming techniques, populations are adopting more specialized strategies and moving away from generalized strategies. Many farming communities now choose to trade with communities at different elevations instead of cultivating every resource on their own because it is cheaper and easier to specialize within their altitudinal zone.


Environmental degradation

Population growth is leading to environmental degradation in altitudinal environments through
deforestation Deforestation or forest clearance is the removal of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. The most concentrated d ...
and
overgrazing Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. It can be caused by either livestock in poorly managed agricultural applications, game reserves, or nature res ...
. The increase in accessibility of mountainous regions allows more people to travel between areas and encourage groups to expand commercial land use. Furthermore, the new linkage between mountainous and lowland populations from improved road access has contributed to worsening environmental degradation.


Debate on continuum versus zonation

Not all mountainous environments exhibit sudden changes in altitudinal zones. Though less common, some tropical environments show a slow continuous change in vegetation over the altitudinal gradient and thus do not form distinct vegetation zones.


See also

*
Biome A biome () is a biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate. Biomes may span more than one continent. Biome is a broader ...
*
Habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
*
Montane ecosystem Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures lapse rate, fall as elevation increases, causing the ecosystem to stratify. This stratification is ...


Examples

*
Life zones of central Europe Central Europe contains several life zones, depending on location and elevation. Geographically, Central Europe lies between the Baltic Sea and the Apennine and Balkan peninsulas. It includes the plains of Germany and Poland; the Alps; and ...
* Life zones of the Great Basin of North America *
Life zones of the Mediterranean region The climate and ecology of land immediately surrounding the Mediterranean Sea is influenced by several factors. Overall, the land has a Mediterranean climate, with mild, rainy winters and hot, dry summers. The climate induces characteristic Medit ...
* Life zones of the North Cascades in the Pacific Northwest of America * Life zones of the Sierra Nevada in California *
Life zones of Peru When the Spanish arrived, they divided Peru into three main regions: the coastal region (11.6% of Peru), that is bounded by the Pacific Ocean; the highlands (28.1% of Peru), that is located on the Andean Heights, and the jungle, that is located on ...


References


Sources

* * * * * * * * * * * * * * * , note: 1st Edition (his dissertation of 1940); ''Las ocho regiones naturales del Perú'', Boletín del Museo de Historia Natural „Javier Prado“, n° especial, Lima, 1941, 17, pp. 145–161. * * * * * * * * * {{DEFAULTSORT:Altitudinal Zonation Montane ecology