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.
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.
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): • 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). •
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) • 260 Mediterranean Division (Köppen:
Cs) • M260 Mediterranean Division – Mountain Provinces •
300 Dry Domain • 310 Tropical/Subtropical Steppe Division • M310 Tropical/Subtropical Steppe Division – Mountain Provinces • 320 Tropical/Subtropical Desert Division • 330 Temperate Steppe Division • 340 Temperate Desert Division •
400 Humid Tropical Domain • 410 Savanna Division • 420 Rainforest Division
Olson & Dinerstein (1998) biomes for WWF / Global 200 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. ==== Biogeographic realms (
marine) ==== •
Arctic •
Temperate Northern Atlantic •
Temperate Northern Pacific •
Tropical Atlantic •
Western Indo-Pacific •
Central Indo-Pacific •
Eastern Indo-Pacific •
Tropical Eastern Pacific •
Temperate South America •
Temperate Southern Africa •
Temperate Australasia •
Southern Ocean Biomes (terrestrial) •
Tropical and subtropical moist broadleaf forests (tropical and subtropical, humid) •
Tropical and subtropical dry broadleaf forests (tropical and subtropical, semihumid) •
Tropical and subtropical coniferous forests (tropical and subtropical, semihumid) •
Temperate broadleaf and mixed forests (temperate, humid) •
Temperate coniferous forests (temperate, humid to semihumid) •
Boreal forests/taiga (subarctic, humid) •
Tropical and subtropical grasslands, savannas, and shrublands (tropical and subtropical, semiarid) •
Temperate grasslands, savannas, and shrublands (temperate, semiarid) •
Flooded grasslands and savannas (temperate to tropical, fresh or brackish water inundated) •
Montane grasslands and shrublands (alpine or montane climate) •
Tundra (Arctic) •
Mediterranean forests, woodlands, and scrub or
sclerophyll forests (temperate warm, semihumid to semiarid with winter rainfall) •
Deserts and xeric shrublands (temperate to tropical, arid) •
Mangrove (subtropical and tropical, salt water inundated) • Large
lakes • Large
river deltas • Polar
freshwaters • Montane
freshwaters • Temperate
coastal rivers • Temperate floodplain rivers and
wetlands • Temperate
upland rivers • Tropical and subtropical
coastal rivers • Tropical and subtropical floodplain rivers and
wetlands • Tropical and subtropical
upland rivers • Xeric freshwaters and
endorheic basins •
Oceanic islands Biomes (marine) Biomes of the coastal and
continental shelf areas (
neritic zone): • Polar • Temperate shelves and sea • Temperate
upwelling • Tropical
upwelling •
Tropical coral Summary of the scheme •
Biosphere •
Biogeographic realms (terrestrial) (8) •
Ecoregions (867), each characterized by a biome, a major habitat type (14) •
Ecosystems (
biotopes) •
Biosphere •
Biogeographic realms (freshwater) (8) •
Ecoregions (426), each characterized by a biome, a major habitat type (12) •
Ecosystems (biotopes) •
Biosphere • Biogeographic realms (marine) (12) • (
Marine provinces) (62) •
Ecoregions (232), each characterized by a biome, a major habitat type (5) •
Ecosystems (biotopes) Example: •
Biosphere •
Biogeographic realm:
Palearctic •
Ecoregion:
Dinaric Mountains mixed forests (PA0418); biome type:
temperate broadleaf and mixed forests •
Ecosystem:
Orjen, vegetation belt between 1,100 and 1,450 m, Oromediterranean zone, nemoral zone (temperate zone) •
Biotope:
Oreoherzogio-Abietetum illyricae Fuk. (
Plant list) • Plant: Silver fir (
Abies alba) == Other biomes ==