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A biome // is a community 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.
While a biome can cover large areas, a microbiome is a mix of organisms that coexist in a defined space on a much smaller scale. For example, the human microbiome is the collection of bacteria, viruses, and other microorganisms that are present on or in a human body.
A 'biota' is the total collection of organisms of a geographic region or a time period, from local geographic scales and instantaneous temporal scales all the way up to whole-planet and whole-timescale spatiotemporal scales. The biotas of the Earth make up the biosphere.
The term was suggested in 1916 by Clements, originally as a synonym for biotic community of Möbius (1877).Later, it gained its current definition, based on earlier concepts of phytophysiognomy, formation and vegetation (used in opposition to flora), with the inclusion of the animal element and the exclusion of the taxonomic element of species composition. In 1935, Tansley added the climatic and soil aspects to the idea, calling it ecosystem. The International Biological Program (1964–74) projects popularized the concept of biome.
However, in some contexts, the term biome is used in a different manner. In German literature, particularly in the Walter terminology, the term is used similarly as biotope (a concrete geographical unit), while the biome definition used in this article is used as an international, non-regional, terminology—irrespectively of the continent in which an area is present, it takes the same biome name—and corresponds to his "zonobiome", "orobiome" and "pedobiome" (biomes determined by climate zone, altitude or soil).
In Brazilian literature, the term "biome" is sometimes used as synonym of "biogeographic province", an area based on species composition (the term "floristic province" being used when plant species are considered), or also as synonym of the "morphoclimatic and phytogeographical domain" of Ab'Sáber, a geographic space with subcontinental dimensions, with the predominance of similar geomorphologic and climatic characteristics, and of a certain vegetation form. Both include many biomes in fact.
To divide the world in a few ecological zones is a difficult attempt, notably because of the small-scale variations that exist everywhere on earth and because of the gradual changeover from one biome to the other. Their boundaries must therefore be drawn arbitrarily and their characterization made according to the average conditions that predominate in them.
A 1978 study on North American grasslandsfound a positive logistic correlation between evapotranspiration in mm/yr and above-ground net primary production in g/m2/yr. The general results from the study were that precipitation and water use led to above-ground primary production, while solar irradiation and temperature lead to below-ground primary production (roots), and temperature and water lead to cool and warm season growth habit. These findings help explain the categories used in Holdridge's bioclassification scheme (see below), which were then later simplified by Whittaker. The number of classification schemes and the variety of determinants used in those schemes, however, should be taken as strong indicators that biomes do not fit perfectly into the classification schemes created.
Holdridge classified climates based on the biological effects of temperature and rainfall on vegetation under the assumption that these two abiotic factors are the largest determinants of the types of vegetation found in a habitat. Holdridge uses the four axes to define 30 so-called "humidity provinces", which are clearly visible in his diagram. While this scheme largely ignores soil and sun exposure, Holdridge acknowledged that these were important.
The principal biome-types by Allee (1949):
The principal biomes of the world by Kendeigh (1961):
Whittaker classified biomes using two abiotic factors: precipitation and temperature. His scheme can be seen as a simplification of Holdridge's; more readily accessible, but missing Holdridge's greater specificity.
Whittaker based his approach on theoretical assertions and empirical sampling. He was in a unique position to make such a holistic assertion because he had previously compiled a review of biome classifications.
Whittaker's distinction between biome and formation can be simplified: formation is used when applied to plant communities only, while biome is used when concerned with both plants and animals. Whittaker's convention of biome-type or formation-type is simply a broader method to categorize similar communities.
Whittaker, seeing the need for a simpler way to express the relationship of community structure to the environment, used what he called "gradient analysis" of ecocline patterns to relate communities to climate on a worldwide scale. Whittaker considered four main ecoclines in the terrestrial realm.
Along these gradients, Whittaker noted several trends that allowed him to qualitatively establish biome-types:
Whittaker summed the effects of gradients (3) and (4) to get an overall temperature gradient and combined this with a gradient (2), the moisture gradient, to express the above conclusions in what is known as the Whittaker classification scheme. The scheme graphs average annual precipitation (x-axis) versus average annual temperature (y-axis) to classify biome-types.
The multiauthored series Ecosystems of the world, edited by David W. Goodall, provides a comprehensive coverage of the major "ecosystem types or biomes" on earth:
The eponymously-named Heinrich Walter classification scheme considers the seasonality of temperature and precipitation. The system, also assessing precipitation and temperature, finds nine major biome types, with the important climate traits and vegetation types. The boundaries of each biome correlate to the conditions of moisture and cold stress that are strong determinants of plant form, and therefore the vegetation that defines the region. Extreme conditions, such as flooding in a swamp, can create different kinds of communities within the same biome.
|Zonobiome||Zonal soil type||Zonal vegetation type|
|ZB I. Equatorial, always moist, little temperature seasonality||Equatorial brown clays||Evergreen tropical rainforest|
|ZB II. Tropical, summer rainy season and cooler “winter” dry season||Red clays or red earths||Tropical seasonal forest, seasonal dry forest, scrub, or savanna|
|ZB III. Subtropical, highly seasonal, arid climate||Serosemes, sierozemes||Desert vegetation with considerable exposed surface|
|ZB IV. Mediterranean, winter rainy season and summer drought||Mediterranean brown earths||Sclerophyllous (drought-adapted), frost-sensitive shrublands and woodlands|
|ZB V. Warm temperate, occasional frost, often with summer rainfall maximum||Yellow or red forest soils, slightly podsolic soils||Temperate evergreen forest, somewhat frost-sensitive|
|ZB VI. Nemoral, moderate climate with winter freezing||Forest brown earths and grey forest soils||Frost-resistant, deciduous, temperate forest|
|ZB VII. Continental, arid, with warm or hot summers and cold winters||Chernozems to serozems||Grasslands and temperate deserts|
|ZB VIII. Boreal, cold temperate with cool summers and long winters||Podsols||Evergreen, frost-hardy, needle-leaved forest (taiga)|
|ZB IX. Polar, short, cool summers and long, cold winters||Tundra humus soils with solifluction (permafrost soils)||Low, evergreen vegetation, without trees, growing over permanently frozen soils|
Schultz (1988) defined nine ecozones (note that his concept of ecozone is more similar to the concept of biome used in this article than to the concept of ecozone of BBC):
Robert G. Bailey nearly developed a biogeographical classification system of ecoregions for the United States in a map published in 1976. He subsequently expanded the system to include the rest of North America in 1981, and the world in 1989. The Bailey system, based on climate, is divided into seven domains (polar, humid temperate, dry, humid, and humid tropical), with further divisions based on other climate characteristics (subarctic, warm temperate, hot temperate, and subtropical; marine and continental; lowland and mountain).
A team of biologists convened by the World Wildlife Fund (WWF) developed a scheme that divided the world's land area into biogeographic realms (called "ecozones" in a BBC scheme), and these into ecoregions (Olson & Dinerstein, 1998, etc.). Each ecoregion is characterized by a main biome (also called major habitat type).
This classification is used to define the Global 200 list of ecoregions identified by the WWF as priorities for conservation.
For the terrestrial ecoregions, there is a specific EcoID, format XXnnNN (XX is the biogeographic realm, nn is the biome number, NN is the individual number).
The applicability of the realms scheme above - based on Udvardy (1975)—to most freshwater taxa is unresolved.
According to the WWF, the following are classified as freshwater biomes:
Biomes of the coastal and continental shelf areas (neritic zone):
Pruvot (1896) zones or "systems":
Longhurst (1998) biomes:
Other marine habitat types (not covered yet by the Global 200/WWF scheme):[ citation needed ]
Humans have altered global patterns of biodiversity and ecosystem processes. As a result, vegetation forms predicted by conventional biome systems can no longer be observed across much of Earth's land surface as they have been replaced by crop and rangelands or cities. Anthropogenic biomes provide an alternative view of the terrestrial biosphere based on global patterns of sustained direct human interaction with ecosystems, including agriculture, human settlements, urbanization, forestry and other uses of land. Anthropogenic biomes offer a new way forward in ecology and conservation by recognizing the irreversible coupling of human and ecological systems at global scales and moving us toward an understanding of how best to live in and manage our biosphere and the anthropogenic biomes we live in.
Major anthropogenic biomes:
The endolithic biome, consisting entirely of microscopic life in rock pores and cracks, kilometers beneath the surface, has only recently been discovered, and does not fit well into most classification schemes.
An ecoregion is an ecologically and geographically defined area that is smaller than a bioregion, which in turn is smaller than an ecozone. Ecoregions cover relatively large areas of land or water, and contain characteristic, geographically distinct assemblages of natural communities and species. The biodiversity of flora, fauna and ecosystems that characterise an ecoregion tends to be distinct from that of other ecoregions. In theory, biodiversity or conservation ecoregions are relatively large areas of land or water where the probability of encountering different species and communities at any given point remains relatively constant, within an acceptable range of variation.
In physical geography, a steppe is an ecoregion characterized by grassland plains without trees apart from those near rivers and lakes. Steppe biomes may include:
Temperate grasslands, savannas, and shrublands is a terrestrial habitat type defined by the World Wide Fund for Nature. The predominant vegetation in this biome consists of grass and/or shrubs. The climate is temperate and ranges from semi-arid to semi-humid. The habitat type differs from tropical grasslands in the annual temperature regime as well as the types of species found here.
A biogeographic realm or ecozone is the broadest biogeographic division of Earth's land surface, based on distributional patterns of terrestrial organisms. They are subdivided into ecoregions, which are classified based on their biomes or habitat types.
The Palearctic or Palaearctic is one of the eight biogeographic realms on the Earth's surface, first identified in the 19th century, and is still in use as the basis for zoogeographic classification. The Palearctic is the largest of the eight realms. It stretches across all of Europe, Asia north of the foothills of the Himalayas, North Africa, and the northern and central parts of the Arabian Peninsula.
The Global 200 is the list of ecoregions identified by WWF, the global conservation organization, as priorities for conservation. According to WWF, an ecoregion is defined as a "relatively large unit of land or water containing a characteristic set of natural communities that share a large majority of their species dynamics, and environmental conditions". So, for example, based on their levels of endemism, Madagascar gets multiple listings, ancient Lake Baikal gets one, and the North American Great Lakes get none.
Grasslands are areas where the vegetation is dominated by grasses (Poaceae); however, sedge (Cyperaceae) and rush (Juncaceae) families can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur naturally on all continents except Antarctica. Grasslands are found in most ecoregions of the Earth. For example, there are five terrestrial ecoregion classifications (subdivisions) of the temperate grasslands, savannas, and shrublands biome (ecosystem).
Tropical and subtropical grasslands, savannas, and shrublands is a terrestrial habitat type defined by the World Wide Fund for Nature. The biome is dominated by grass and/or shrubs located in semi-arid to semi-humid climate regions of subtropical and tropical latitudes.
Temperate broadleaf and mixed forest is a temperate climate terrestrial habitat type defined by the World Wide Fund for Nature, with broadleaf tree ecoregions, and with conifer and broadleaf tree mixed coniferous forest ecoregions.
Rangelands are grasslands, shrublands, woodlands, wetlands, and deserts that are grazed by domestic livestock or wild animals. Types of rangelands include tallgrass and shortgrass prairies, desert grasslands and shrublands, woodlands, savannas, chaparrals, steppes, and tundras. Rangelands do not include forests lacking grazable understory vegetation, barren desert, farmland, or land covered by solid rock, concrete and/or glaciers.
Miombo is the vernacular word for Brachystegia, a genus of tree comprising many tree species together with Julbernardia species in woodlands. Miombo woodland is classified in the tropical and subtropical grasslands, savannas, and shrublands biome. The biome includes four woodland savanna ecoregions characterized by the predominant presence of miombo species, with a range of climates from humid to semi-arid, and tropical to subtropical or even temperate.
The Maputaland-Pondoland bushland and thickets is one of the ecoregions of South Africa. It consists of the montane shrubland Biome. The ecoregion occupies the foothills of the Drakensberg mountains, covering an area of 19,500 square kilometers (7,500 sq mi) in South Africa's Eastern Cape and KwaZulu-Natal provinces. It is bounded on the east by the KwaZulu-Cape coastal forest mosaic, which lies in the humid coastal strip along the Indian Ocean; to the west it is bounded by the higher-elevation Drakensberg montane grasslands, woodlands and forests. To the south, it transitions to the drier Albany thickets, which are characterized by more succulent and spiny plants.
When the Spanish arrived, they divided Peru into three main regions: the coastal region, that is bounded by the Pacific Ocean; the highlands, that is located on the Andean Heights, and the jungle, that is located on the Amazonian Jungle. But Javier Pulgar Vidal (es), a geographer who studied the biogeographic reality of the Peruvian territory for a long time, proposed the creation of eight Natural Regions. In 1941, he presented his thesis "Las Ocho Regiones Naturales del Perú" at the III General Assembly of the Pan-American Institute of Geography and History.
The Holdridge life zones system is a global bioclimatic scheme for the classification of land areas. It was first published by Leslie Holdridge in 1947, and updated in 1967. It is a relatively simple system based on few empirical data, giving objective mapping criteria. A basic assumption of the system is that both soil and climax vegetation can be mapped once the climate is known.
Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affect the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. 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.
Tropical vegetation is any vegetation in tropical latitudes. Plant life that occurs in climates that are warm year-round is in general more biologically diverse that in other latitudes. Some tropical areas may receive abundant rain the whole year round, but others have long dry seasons which last several months and may vary in length and intensity with geographic location. These seasonal droughts have great impact on the vegetation, such as in the Madagascar spiny forests. Rainforest vegetation is categorized by five layers. The top layer being the upper tree layer. Here you will find the largest and widest trees in all the forest. These trees tend to have very large canopy's so they can be fully exposed to sunlight. A layer below that is the middle tree layer. Here you will find more compact trees and vegetation. These trees tend to be more skinny as they are trying to gain any sunlight they can. The third layer is the lower tree area. These trees tend to be around five to ten meters high and tightly compacted. The trees found in the third layer are young trees trying to grow into the larger canopy trees. The fourth layer is the shrub layer beneath the tree canopy. This layer is mainly populated by sapling trees, shrubs, and seedlings. The fifth and final layer is the herb layer which is the forest floor. The forest floor is mainly bare except for various plants, mosses, and ferns. The forest floor is much more dense than above because of little sunlight and air movement.
Vegetation classification is the process of classifying and mapping the vegetation over an area of the earth's surface. Vegetation classification is often performed by state based agencies as part of land use, resource and environmental management. Many different methods of vegetation classification have been used. In general, there has been a shift from structural classification used by forestry for the mapping of timber resources, to floristic community mapping for biodiversity management. Whereas older forestry-based schemes considered factors such as height, species and density of the woody canopy, floristic community mapping shifts the emphasis onto ecological factors such as climate, soil type and floristic associations. Classification mapping is usually now done using geographic information systems (GIS) software.
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