A biome ( ) is a distinct geographical region with specific climate, vegetation, animal life, and an ecosystem. It consists of a biological community that has formed in response to its physical environment and regional climate.;Meira Neto, J. A. A. (Org.). Fitossociologia no Brasil: métodos e estudos de caso. Vol. 1. Viçosa: Editora UFV. pp. 44–85. . Earlier version, 2003, . In 1935, Arthur 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.Box, E.O. & Fujiwara, K. (2005). Vegetation types and their broad-scale distribution. In: van der Maarel, E. (ed.). Vegetation ecology. Blackwell Scientific, Oxford. pp. 106–128, .
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 the Brazilian literature, the term biome is sometimes used as a 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.
Classifications To divide the world into a few ecological zones is difficult, 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 grasslands found 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 (1947, 1964) life zones
In 1947, the American botanist and climatologist Leslie 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.
Allee (1949) biome-types The principal biome-types by Allee (1949): Tundra Taiga Deciduous forest Grasslands Desert High plateaus Tropical forest Minor terrestrial biomes
Kendeigh (1961) biomes The principal biomes of the world by Kendeigh (1961): Terrestrial Temperate deciduous forest Coniferous forest Woodland Chaparral Tundra Grassland Desert Tropical savanna Tropical forest Marine Oceanic plankton and nekton Balanoid-gastropod-thallophyte Pelecypod-annelid Coral reef
Whittaker (1962, 1970, 1975) biome-types
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 had previously compiled a review of biome classifications.
Key definitions for understanding Whittaker's scheme Physiognomy: sometimes referring to the plants' appearance; or the biome's apparent characteristics, outward features, or appearance of ecological communities or species – including plants. Biome: a grouping of terrestrial ecosystems on a given continent that is similar in vegetation structure, physiognomy, features of the environment and characteristics of their animal communities. Formation: a major kind of community of plants on a given continent. Biome-type: grouping of convergent biomes or formations of different continents, defined by physiognomy. Formation-type: a grouping of convergent formations.
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 a broader method to categorize similar communities.
Whittaker's parameters for classifying biome-types Whittaker 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. Intertidal levels: The wetness gradient of areas that are exposed to alternating water and dryness with intensities that vary by location from high to low tide Climatic moisture gradient Temperature gradient by altitude Temperature gradient by latitude
Along these gradients, Whittaker noted several trends that allowed him to qualitatively establish biome-types: The gradient runs from favorable to the extreme, with corresponding changes in productivity. Changes in physiognomic complexity vary with how favorable of an environment exists (decreasing community structure and reduction of stratal differentiation as the environment becomes less favorable). Trends in the diversity of structure follow trends in species diversity; alpha and beta species diversities decrease from favorable to extreme environments. Each growth-form (i.e. grasses, shrubs, etc.) has its characteristic place of maximum importance along the ecoclines. The same growth forms may be dominant in similar environments in widely different parts of the world.
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.
Biome-types
Tropical rainforest Tropical seasonal rainforest deciduous semideciduous Temperate giant rainforest Montane rainforest Temperate deciduous forest Temperate evergreen forest needleleaf sclerophyll Subarctic-subalpine needle-leaved forests (taiga) Elfin woodland Thorn forest Thorn scrub Temperate woodland Temperate shrublands deciduous heath sclerophyll subalpine-needleleaf subalpine-broadleaf Savanna Temperate grassland Alpine grasslands Tundra Tropical desert Warm-temperate desert Cool temperate desert scrub Arctic-alpine desert Bog Tropical fresh-water swamp forest Temperate fresh-water swamp forest Mangrove swamp Salt marsh WetlandWhittaker, R. H. (1970). Communities and Ecosystems. Toronto, pp. 51–64, .
Goodall (1974–) ecosystem types The multi-authored series Ecosystems of the World, edited by David W. Goodall, provides a comprehensive coverage of the major "ecosystem types or biomes" on Earth:
Walter (1976, 2002) zonobiomes 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.
Number 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) eco-zones Schultz (1988, 2005) defined nine ecozones (his concept of ecozone is more similar to the concept of biome than to the concept of ecozone of BBC):Schultz, J. Die Ökozonen der Erde, 1st ed., Ulmer, Stuttgart, Germany, 1988, 488 pp.; 2nd ed., 1995, 535 pp.; 3rd ed., 2002; 4th ed., 2008; 5th ed., 2016. Transl.: The Ecozones of the World: The Ecological Divisions of the Geosphere. Berlin: Springer-Verlag, 1995; 2nd ed., 2005, .
polar/subpolar zone boreal zone humid mid-latitudes dry mid-latitudes subtropics with winter rain subtropics with year-round rain dry tropics and subtropics tropics with summer rain tropics with year-round rain
Bailey (1989) ecoregions 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 four domains (polar, humid temperate, dry, and humid tropical), with further divisions based on other climate characteristics (subarctic, warm temperate, hot temperate, and subtropical; marine and continental; lowland and mountain). [With map of land-masses of the world, "Ecoregions of the Continents – Scale 1 : 30,000,000", published as a supplement.] 100 Polar Domain 120 Tundra Division (Köppen: Ft) M120 Tundra Division – Mountain Provinces 130 Subarctic Division (Köppen: E) M130 Subarctic Division – Mountain Provinces 200 Humid Temperate Domain 210 Warm Continental Division (Köppen: portion of Dcb) M210 Warm Continental Division – Mountain Provinces 220 Hot Continental Division (Köppen: portion of Dca) M220 Hot Continental Division – Mountain Provinces 230 Subtropical Division (Köppen: portion of Cf) M230 Subtropical Division – Mountain Provinces 240 Marine Division (Köppen: Do) M240 Marine Division – Mountain Provinces 250 Prairie Division (Köppen: arid portions of Cf, Dca, Dcb)