Altitudinal zonation

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Altitudinal zonation (or elevational zonation [1] ) in mountainous regions describes the natural layering of ecosystems that occurs at distinct elevations due to varying environmental conditions. Temperature, humidity, soil composition, and solar radiation are important factors in determining altitudinal zones, which consequently support different vegetation and animal species. [2] [3] Altitudinal zonation was first hypothesized by geographer Alexander von Humboldt who noticed that temperature drops with increasing elevation. [4] Zonation also occurs in intertidal and marine environments, as well as on shorelines and in wetlands. Scientist C. Hart Merriam observed that changes in vegetation and animals in altitudinal zones map onto changes expected with increased latitude in his concept of life zones. Today, altitudinal zonation represents a core concept in mountain research.

Contents

Factors

Heating of solids, sunlight and shade in different altitudinal zones (Northern hemisphere) Altitudinal zonation VVP.svg
Heating of solids, sunlight and shade in different altitudinal zones (Northern hemisphere)

A variety of environmental factors determines the boundaries of altitudinal zones found on mountains, ranging from direct effects of temperature and precipitation 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. [6]

Temperature

Decreasing air temperature usually coincides with increasing elevation, which directly influences the length the growing season at different elevations of the mountain. [2] [7] For mountains located in deserts, extreme high temperatures also limit the ability of large deciduous or coniferous trees to grow near the base of mountains. [8] In addition, plants can be especially sensitive to soil temperatures and can have specific elevation ranges that support healthy growth. [9]

Humidity

The humidity of certain zones, including precipitation levels, atmospheric humidity, and potential for evapotranspiration, varies with elevation and is a significant factor in determining altitudinal zonation. [3] The most important variable is precipitation at various elevations. [10] 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 development. Above a certain elevation the rising air becomes too dry and cold, and thus discourages tree growth. [9] Even though rainfall may not be a significant factor for some mountains, atmospheric humidity or aridity can be more important climatic stresses that affect altitudinal zones. [11] 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 to soil moisture. [12]

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. [3] At this latitude more acidic, humose soils exist at higher elevations in the montane or subalpine levels. [3] In a different example, weathering is hampered by low temperatures at higher elevations in the Rocky Mountain of the western United States, resulting in thin coarse soils. [13]

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. [14] 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). [15] [16] Two other biological factors can influence zonation: grazing and mutualism. The relative importance of these factors is also difficult to assess, but the abundance of grazing animals, and the abundance of mycorrhizal associations, suggests that these elements may influence plant distributions in significant ways. [17]

Solar radiation

Light is another significant factor in the growth of trees and other photosynthetic 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. [18] Hence, the summits of mountains and higher elevations receive much more intense radiation than the basal plains. Along with the expected arid conditions at higher elevations, shrubs and grasses tend to thrive because of their small leaves and extensive root systems. [19] 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. [3] The Massenerhebung effect describes variation in the tree line based on mountain size and location. 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. [3] A similar effect is exhibited in the Santa Catalina Mountains of Arizona, where the basal elevation and the total elevation influence the elevation of vertical zones of vegetation. [12]

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. [2] [3]

Elevation levels

Altitudinal zonation in the Alps Altitudinal zones of Alps mountains-extended diagram.svg
Altitudinal zonation in the Alps

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. [20] 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.

Altitudinal zonation of Grand Teton in the Rocky Mountains (note change in vegetation as elevation increases) Grand Tetons11.jpg
Altitudinal zonation of Grand Teton in the Rocky Mountains (note change in vegetation as elevation increases)

For detailed breakdowns of the characteristics of altitudinal zones found on different mountains, see List of life zones by region.

Treeline

The most decisive biogeographic and climatic boundary along elevation gradients is the climatic high-elevation treeline. The treeline separates the montane from the alpine zone and marks the potential for tree growth, irrespective of whether trees are present or not. [24] 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. [25] At the tree line, tree growth is often sparse, stunted, and deformed by wind and cold krummholz (German for "crooked wood"). [26] 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. [27]

Animal zonation

Animals also exhibit zonation patterns in concert with the vegetational zones described above. [7] 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. [7]

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. [28] 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.

Agriculture

Altitudinal zones of Andes Mountains and corresponding communities of agriculture and livestock raised Hoehenstufen der anden.en.PNG
Altitudinal zones of Andes Mountains and corresponding communities of agriculture and livestock raised

Human populations have developed agricultural production strategies to exploit varying characteristics of altitudinal zones. Elevation, climate, and soil fertility set upper limits on types of crops that can reside in each zone. Populations residing in the Andes Mountain region of South America have taken advantage of varying altitudinal environments to raise a wide variety of different crops. [11] Two different types of adaptive strategies have been adopted within mountainous communities. [29]

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. [28]

Environmental degradation

Population growth is leading to environmental degradation in altitudinal environments through deforestation and overgrazing. 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. [28]

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. [30]

See also

Examples

Related Research Articles

Biome Plants and animals associated with an environment

A biome is a collection of plants and animals that have common characteristics for the environment they exist in. They can be found over a range of continents. Biomes are distinct biological communities that have formed in response to a shared physical climate. Biome is a broader term than habitat; any biome can comprise a variety of habitats.

Alpine tundra Biome found at high altitudes

Alpine tundra is a type of natural region or biome that does not contain trees because it is at high elevation. As the latitude of a location approaches the poles, the threshold elevation for alpine tundra gets lower until it reaches sea level, and alpine tundra merges with polar tundra.

Great Basin Desert Desert in the United States

The Great Basin Desert is part of the Great Basin between the Sierra Nevada and the Wasatch Range. The desert is a geographical region that largely overlaps the Great Basin shrub steppe defined by the World Wildlife Fund, and the Central Basin and Range ecoregion defined by the U.S. Environmental Protection Agency and United States Geological Survey. It is a temperate desert with hot, dry summers and snowy winters. The desert spans a large part of the state of Nevada, and extends into western Utah, eastern California, and Idaho. The desert is one of the four biologically defined deserts in North America, in addition to the Mojave, Sonoran, and Chihuahuan Deserts.

Tree line Edge of the habitat at which trees are capable of growing

The tree line is the edge of the habitat at which trees are capable of growing. It is found at high elevations and high latitudes. Beyond the tree line, trees cannot tolerate the environmental conditions. The tree line is sometimes distinguished from a lower timberline or forest line, which is the line below which trees form a forest with a closed canopy.

Alpine plant Plants that grow at high elevation

Alpine plants are plants that grow in an alpine climate, which occurs at high elevation and above the tree line. There are many different plant species and taxon that grow as a plant community in these alpine tundra. These include perennial grasses, sedges, forbs, cushion plants, mosses, and lichens. Alpine plants are adapted to the harsh conditions of the alpine environment, which include low temperatures, dryness, ultraviolet radiation, wind, drought, poor nutritional soil, and a short growing season.

Páramo

Páramo can refer to a variety of alpine tundra ecosystems. Some ecologists describe the páramo broadly as "all high, tropical, montane vegetation above the continuous timberline". A more narrow term classifies the páramo according to its regional placement in the northern Andes of South America and adjacent southern Central America. The páramo is the ecosystem of the regions above the continuous forest line, yet below the permanent snowline. It is a "Neotropical high mountain biome with a vegetation composed mainly of giant rosette plants, shrubs and grasses". According to scientists, páramos may be "evolutionary hot spots" and among the fastest evolving regions on Earth.

Global Observation Research Initiative in Alpine Environments

The Global Observation Research Initiative in Alpine Environments (GLORIA) established an international long-term monitoring program and site-based network dealing with high-mountain vegetation and its biological diversity. Its purpose is the in-situ observation and comparative assessment of alpine biodiversity patterns under the impact of accelerating anthropogenic climate change. GLORIA involves sets of permanent plots established at pristine or near-natural sites set aside and monitored to observe the migration of plant species due to climate change. Founded in 2001, the program has grown to more than 120 sites around the world, distributed from the poles to the tropics."

Scandinavian montane birch forest and grasslands Tundra ecoregion in Scandinavia


The Scandinavian montane birch forests and grasslands is a tundra ecoregion in Norway, Sweden, and Finland. It is one of the terrestrial ecoregions determined and defined by the World Wildlife Fund.

Dwarf forest A type of forest ecosystem

Dwarf forest, elfin forest, or pygmy forest is an uncommon ecosystem featuring miniature trees, inhabited by small species of fauna such as rodents and lizards. They are usually located at high elevations, under conditions of sufficient air humidity but poor soil. There are two main dwarf forest ecosystem types, involving different species and environmental characteristics: coastal temperate and montane tropical regions. Temperate coastal dwarf forest is common for parts of Southern California. Montane tropical forests are found across tropical highlands of Central America, northern South America and Southeast Asia. There are also other isolated examples of dwarf forests scattered across the world, while the largest dwarf forest is found in the Philippines.

Puna grassland

The puna grassland ecoregion, of the montane grasslands and shrublands biome, is found in the central Andes Mountains of South America. It is considered one of the eight Natural Regions in Peru, but extends south, across Bolivia, as far as northern Argentina and Chile. The term puna encompasses diverse ecosystems of the high Central Andes above 3200–3400 m.

Sierra Nevada subalpine zone

The Sierra Nevada subalpine zone refers to a biotic zone below treeline in the Sierra Nevada mountain range of California, United States. This subalpine zone is positioned between the upper montane zone at its lower limit, and tree line at its upper limit.

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 Mediterranean forests, woodlands, and scrub vegetation. Plant life immediately near the Mediterranean is in the Mediterranean Floristic region, while mountainous areas further from the sea supports the Sub-Mediterranean Floristic province.

Ecology of the North Cascades Ecosystems of the Cascade mountain range in northern Washington state and southern British Columbia

The Ecology of the North Cascades is heavily influenced by the high elevation and rain shadow effects of the mountain range. The North Cascades is a section of the Cascade Range from the South Fork of the Snoqualmie River in Washington, United States, to the confluence of the Thompson and Fraser Rivers in British Columbia, Canada, where the range is officially called the Cascade Mountains but is usually referred to as the Canadian Cascades. The North Cascades Ecoregion is a Level III ecoregion in the Commission for Environmental Cooperation's classification system.

Natural history of Mount Kenya

The flora and fauna of Mount Kenya are diverse, due to the variation in altitude, rainfall, aspect and temperature. The mountain slopes can be divided into vegetation zones, with each zone having different dominant plant species. Although many plants on Mount Kenya have local names, here they are reported only with their English and scientific names.

Montane ecosystems

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, 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.

Rwenzori–Virunga montane moorlands montane ecoregion in central Africa

The Ruwenzori-Virunga montane moorlands is a montane grasslands and shrublands ecoregion of central Africa.

Alpine vegetation refers to the zone of vegetation between the altitudinal limit for tree growth and the nival zone. Alpine zones in Tasmania can be difficult to classify owing to Tasmania's maritime climate limiting snow lie to short periods and the presence of a tree line that is not clearly defined.

Katon-Karagay National Park

Katon-Karagay National Park is the largest national park in Kazakhstan, located on the eastern edge of the country, in the Southern Altai Mountains. The park fills the west side of the "X" where the borders of Kazakhstan, Russia, China, and Mongolia meet. The highest peak in Siberia, is on the Russian border in the Katun Range. The park is in Katonkaragay District of East Kazakhstan Region, 1,000 kilometres (620 mi) southeast of the capital city of Astana.

Altai alpine meadow and tundra

The Altai alpine meadow and tundra ecoregion is a terrestrial ecoregion covering the higher elevation of the Altai Mountains at the center of the "X" formed by the borders separating Russia, Kazakhstan, China, and Mongolia. The mountain peaks are the farthest north in Central Asia, separating the plains of Siberia to the north from the hot, dry deserts to the south. Altitudes above 2,400 meters display characteristics of tundra, with patches of alpine meadows and some trees immediately below the treeline. The ecoregion is in the montane grasslands and shrublands biome, and the Palearctic realm, with a humid continental climate. It covers an area of 90,132 square kilometres (34,800 sq mi).

References

  1. McVicar & Körner 2013
  2. 1 2 3 Daubenmire 1943
  3. 1 2 3 4 5 6 7 8 Frahm & Gradstein 1991
  4. 1 2 Salter et al. 2005
  5. Fukarek et al. 1982
  6. Shipley & Keddy 1987
  7. 1 2 3 4 5 6 Nagy & Grabherr 2009
  8. Daubenmire 1943 , pp. 345–349
  9. 1 2 Nagy & Grabherr 2009 , pp. 30–35
  10. Daubenmire 1943 , pp. 349–352
  11. 1 2 Stadel 1990
  12. 1 2 3 4 Shreve 1922
  13. Daubenmire 1943 , p. 355
  14. Keddy 2001 , p. 552
  15. Goldberg 1982
  16. Wilson 1993
  17. Keddy 2007 , p. 666
  18. Daubenmire 1943 , p. 345
  19. Nagy & Grabherr 2009 , p. 31
  20. 1 2 3 4 Troll 1973
  21. Pauli, Gottfried & Grabherr 1999
  22. Tang & Ohsawa 1997
  23. Pulgar Vidal 1941 , pp. 145–161
  24. Körner 2012
  25. Paulsen & Körner 2014
  26. Zwinger & Willard 1996 , p. 58
  27. Zwinger & Willard 1996 , p. 55
  28. 1 2 3 Allan 1986
  29. Rhoades & Thompson 1975
  30. Hemp 2006

Sources