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A map of the Amazon rainforest ecoregions. The yellow line encloses the ecoregions per the World Wide Fund for Nature.
A map of the Amazon rainforest ecoregions. The yellow line encloses the ecoregions per the World Wide Fund for Nature.
A map of North America's bioregions
A map of North America's bioregions

An ecoregion (ecological region) is an ecologically and geographically defined area that is smaller than a bioregion, which in turn is smaller than an ecozone. All three of these are either less or greater than an ecosystem.[citation needed][clarification needed] 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 (largely undefined at this point).

Three caveats are appropriate for all bio-geographic mapping approaches. Firstly, no single bio-geographic framework is optimal for all taxa. Ecoregions reflect the best compromise for as many taxa as possible. Secondly, ecoregion boundaries rarely form abrupt edges; rather, ecotones and mosaic habitats bound them. Thirdly, most ecoregions contain habitats that differ from their assigned biome. Biogeographic provinces may originate due to various barriers. Some physical (plate tectonics, topographic highs), some climatic (latitudinal variation, seasonal range) and some ocean chemical related (salinity, oxygen levels).

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  • Edwards Plateau Eco-Region- Texas Parks and Wildlife- [Official]
  • Gulf Coast Prairies Eco-Region- Texas Parks and Wildlife- [Official]
  • 20-Year Change in Growing Season Maximum NDVI By Ecoregion
  • Keep Texas Wild: Blackland Prairie - Texas Parks and Wildlife [Official]


[Narration] The Edwards Plateau eco-region is the Texas hill country. Bordering the Rolling Plains to the North and the Trans-Pecos to the West, this eco-region stretches as far South as the border of Mexico, and the cities of San Antonio and Austin to the East. [Terry Turney] The Edwards Plateau ecoregion is about 24 million acres, or 7 million 8 hundred thousand hectares. It's about the size of West Virginia. Early historical accounts have it as a mid to tall grass prairie with oak savannahs, scattered oak trees throughout. With hardwoods and some ashe juniper on the bottoms in what we call the drainages or the gullies. [Narration] The Edwards Plateau is transected by a number of rivers, sinkholes, caves and rocky out-croppings. This Karst topography hosts some of the most specialized species in the world. [Terry Turney] The Edwards Plateau is known internationally across the globe for its karst topography, endemic species that are found here, the golden-cheeked warbler for example only nests in Texas. The cave dwelling species, from the invertebrates to the bat communities that we have are truly amazing. [Narration] Just Northwest of San Antonio, Bracken Cave is said to host over twenty million Mexican Free-tail Bats, noted as the largest concentration of mammals at any one cave in the world. The Edwards Plateau also supports much smaller species like the federally endangered Barton Springs Salamander near Austin. [John Davis] Karst habitats and the species that inhabit them are extremely vulnerable, for several reasons. Number one due to their extreme locality. They may be abundant in one location and not found anywhere else. They are also highly vulnerable due to water quality issues. Many of the species that exist in these karst environments are dependent upon pure water, and this water may be polluted from a city that may be miles and miles away. [Narration] As new housing developments sprawl beyond the suburbs and into the Texas hill country, the resulting land fragmentation is gradually decreasing wildlife habitats. [Terry Turney] The Edwards Plateau is one of the fastest growing areas in the nation. People are moving in from all over the country. The problem is that we're breaking up large historical ranches into smaller and smaller pieces. [Narraion] Creating urban like neighborhoods in the hill country often brings with it urban land use practices. Some of those practices can produce damaging ripple effects for wildlife. [Terry Turney] The fragmentation is bad enough but when they go in and clear off all the native species and put introduced species, plant species in, there's no utilization by wildlife. When that happens the wildlife that is there is pushed out into smaller and smaller habitats, therefore overcrowding, overpopulations result. We've got a tremendous overpopulation of white-tailed deer. [Kelly Bender] Unfortunately White-Tailed Deer aren't very discriminating in their tastes and will eat just about anything from ground level up to about five feet and that completely eliminates the understory vegetation for other wildlife to use. When they do that they prevent the forest from regenerating itself and lots of different species require that understory in order to nest or roost. You have the same issue with allowing livestock to overgraze an area. With overgrazing we start to see a change in the habitat. We see brush starting to grow like mesquite and ashe juniper, and we see erosion begin. [Narration] Along with impacts of an increased deer population and overgrazing by livestock, the absence of natural fire has also contributed to brush growth in the Edwards Plateau. [Terry Turney] That fire kept the brush species suppressed. When modern man, early settlers moved in, the suppression of fire caused an increase in brush species, that along with introduction of livestock on the Edwards Plateau, both cattle, sheep and goats. They took out the grasses, erosion happened at an alarming rate, ashe juniper is the winner, so to say. It just basically out competes. Ashe juniper offers very little in the way of food source, there are a few songbirds that take its seed and that helps spread it obviously. If offers shelter for all wildlife species, some nesting substrate, obviously golden-cheeked warbler depend on its shredding bark of the mature ashe juniper for their nesting materials. But - what we call the second growth cedar, or the cedar under 10, 12, 14 feet is what we consider the invasive plants. [Narration] Uncontrolled growth of cedar has hydrological impacts as well. [John Davis] The thing about cedar trees is they've been shown to intercept a tremendous amount of moisture from the atmosphere when it rains and they evapo-transpire this moisture back into the atmosphere. What that means is, rainfall that used to penetrate the ground no longer penetrates the ground when you have a heavy cover of cedar trees. [Narration] By removing dense areas of cedar, landowners can lessen the strain on the Edwards Aquifer, the region's largest groundwater supply. Two bird species hardest hit by this continued urban sprawl in the Edwards Plateau are the Golden-cheeked Warbler and the Black Capped Vireo. [Terry Turney] The Golden-cheeked Warbler's listed as an endangered species because of land fragmentation, loss of habitat, the cutting of mature ashe juniper by early settlers. Deciduous hardwoods, the oaks, had been cleared in some areas for agricultural practices. And land fragmentation, development, we're losing many, many acres to land development to people moving out into the Edwards Plateau. The Black-capped Vireo is unique species. It's about 4 inches tall, the males are a real distinct black, color on their head, striping with a greenish-yellow body, gray tones mixed in. It's a songbird, they come here in March and set up their territories. The males can be found singing throughout the nesting season. [Narration] With continued development in the Edwards Plateau, protecting habitats for the Golden-cheeked Warbler and the Black-capped Vireo is a priority. [Terry Turney] The Texas Parks and Wildlife Department and US Fish and Wildlife service along with the other non-governmental organizations and agencies, both federal and state, have done an excellent job of educating landowners and developers in what is Golden-cheeked Warbler habitat and what is not. And doing all we can to minimize those impacts. Habitat conservation plans offset or mitigate for the damages done to Golden-cheeked Warbler habitat and in some instances Black-capped Vireo habitat also. There are numerous land trusts and conservation easement holders throughout the Edwards Plateau. Without these, public lands just wouldn't be able to recover a species or maintain a population of species on its own. [Narration] Cooperation and partnerships between private landowners and conservation professionals will continue to be a priority for ensuring the availability of existing and future habitats for fish and wildlife in the Edwards Plateau. [Kelly Bender] One of the most important things we can do for the Edwards Plateau is that we can monitor our grazing regimes and incorporate those techniques that will best preserve the prairies that are in the Edwards Plateau. One of these management techniques could be the high-intensity low frequency rotation system. The benefit of that is that while grasses are well adapted to occasional grazing, they're not well adapted to continuous grazing so by breaking up that grazing intensity, you can really increase the value of your grasslands to wildlife. [Terry Turney] Our population is expected to double in the next 20 to 30 years. With all that being said, we see the bright side of the Edwards Plateau and the species that are dependent on it. Everything that's been put in the Texas Wildlife Action Plan is to benefit the species throughout the Edwards Plateau. The implementation of this plan by both Texas Parks and Wildlife personnel and all the other individuals involved- the landowners, the consultants, the federal agencies, all will see the benefits to the wildlife species throughout the Plateau.



The history of the term is somewhat vague as it was used in many contexts: forest classifications (Loucks, 1962), biome classifications (Bailey, 1976, 2014), biogeographic classifications (WWF/Global 200 scheme of Olson & Dinerstein, 1998), etc.[1][2][3][4][5]

The concept of ecoregion of Bailey gives more importance to ecological criteria, while the WWF concept gives more importance to biogeography, that is, distribution of distinct biotas.[4]

Definition and categorization

The Ötztal Alps, a mountain range in the central Alps of Europe, are part of the Central Eastern Alps, and can both be termed as ecoregions.
The Ötztal Alps, a mountain range in the central Alps of Europe, are part of the Central Eastern Alps, and can both be termed as ecoregions.
A conifer forest in the Swiss Alps (National Park).
A conifer forest in the Swiss Alps (National Park).

An ecoregion is a "recurring pattern of ecosystems associated with characteristic combinations of soil and landform that characterise that region".[6] Omernik (2004) elaborates on this by defining ecoregions as: "areas within which there is spatial coincidence in characteristics of geographical phenomena associated with differences in the quality, health, and integrity of ecosystems".[7] "Characteristics of geographical phenomena" may include geology, physiography, vegetation, climate, hydrology, terrestrial and aquatic fauna, and soils, and may or may not include the impacts of human activity (e.g. land use patterns, vegetation changes). There is significant, but not absolute, spatial correlation among these characteristics, making the delineation of ecoregions an imperfect science. Another complication is that environmental conditions across an ecoregion boundary may change very gradually, e.g. the prairie-forest transition in the midwestern United States, making it difficult to identify an exact dividing boundary. Such transition zones are called ecotones.

Ecoregions can be categorized using an algorithmic approach or a holistic, "weight-of-evidence" approach where the importance of various factors may vary. An example of the algorithmic approach is Robert Bailey's work for the U.S. Forest Service, which uses a hierarchical classification that first divides land areas into very large regions based on climatic factors, and subdivides these regions, based first on dominant potential vegetation, and then by geomorphology and soil characteristics. The weight-of-evidence approach is exemplified by James Omernik's work for the United States Environmental Protection Agency, subsequently adopted (with modification) for North America by the Commission for Environmental Cooperation.

The intended purpose of ecoregion delineation may affect the method used. For example, the WWF ecoregions were developed to aid in biodiversity conservation planning, and place a greater emphasis than the Omernik or Bailey systems on floral and faunal differences between regions. The WWF classification defines an ecoregion as:

A large area of land or water that contains a geographically distinct assemblage of natural communities that:

(a) Share a large majority of their species and ecological dynamics;
(b) Share similar environmental conditions, and;
(c) Interact ecologically in ways that are critical for their long-term persistence.

According to WWF, the boundaries of an ecoregion approximate the original extent of the natural communities prior to any major recent disruptions or changes. WWF has identified 867 terrestrial ecoregions, and approximately 450 freshwater ecoregions across the Earth.

Terrestrial Ecoregions of the World (Olson et al. 2001, BioScience)
Terrestrial Ecoregions of the World (Olson et al. 2001, BioScience)


The use of the term ecoregion is an outgrowth of a surge of interest in ecosystems and their functioning. In particular, there is awareness of issues relating to spatial scale in the study and management of landscapes. It is widely recognized that interlinked ecosystems combine to form a whole that is "greater than the sum of its parts". There are many attempts to respond to ecosystems in an integrated way to achieve "multi-functional" landscapes, and various interest groups from agricultural researchers to conservationists are using the "ecoregion" as a unit of analysis.

The "Global 200" is the list of ecoregions identified by WWF as priorities for conservation.

Ecologically based movements like bioregionalism maintain that ecoregions, rather than arbitrarily defined political boundaries, provide a better foundation for the formation and governance of human communities, and have proposed ecoregions and watersheds as the basis for bioregional democracy initiatives.


WWF terrestrial ecoregions
WWF terrestrial ecoregions

Terrestrial ecoregions are land ecoregions, as distinct from freshwater and marine ecoregions. In this context, terrestrial is used to mean "of land" (soil and rock), rather than the more general sense "of Earth" (which includes land and oceans).

WWF (World Wildlife Fund) ecologists currently divide the land surface of the Earth into 8 major ecozones containing 867 smaller terrestrial ecoregions (see list). The WWF effort is a synthesis of many previous efforts to define and classify ecoregions. Many consider this classification to be quite decisive, and some propose these as stable borders for bioregional democracy initiatives.[8]

The eight terrestrial ecozones follow the major floral and faunal boundaries, identified by botanists and zoologists, that separate the world's major plant and animal communities. Ecozone boundaries generally follow continental boundaries, or major barriers to plant and animal distribution, like the Himalayas and the Sahara. The boundaries of ecoregions are often not as decisive or well recognized, and are subject to greater disagreement.

Ecoregions are classified by biome type, which are the major global plant communities determined by rainfall and climate. Forests, grasslands (including savanna and shrubland), and deserts (including xeric shrublands) are distinguished by climate (tropical and subtropical vs. temperate and boreal climates) and, for forests, by whether the trees are predominantly conifers (gymnosperms), or whether they are predominantly broadleaf (Angiosperms) and mixed (broadleaf and conifer). Biome types like Mediterranean forests, woodlands, and scrub; tundra; and mangroves host very distinct ecological communities, and are recognized as distinct biome types as well.


View of Earth, taken in 1972 by the Apollo 17 crew. Approximately 72% of the Earth's surface (an area of some 361 million square kilometers) consists of ocean.
View of Earth, taken in 1972 by the Apollo 17 crew. Approximately 72% of the Earth's surface (an area of some 361 million square kilometers) consists of ocean.

Marine ecoregions are: "Areas of relatively homogeneous species composition, clearly distinct from adjacent systems….In ecological terms, these are strongly cohesive units, sufficiently large to encompass ecological or life history processes for most sedentary species."[9] They have been defined by The Nature Conservancy (TNC) and World Wildlife Fund (WWF) to aid in conservation activities for marine ecosystems. Forty-three priority marine ecoregions were delineated as part of WWF's Global 200 efforts.[10] The scheme used to designate and classify marine ecoregions is analogous to that used for terrestrial ecoregions. Major habitat types are identified: polar, temperate shelves and seas, temperate upwelling, tropical upwelling, tropical coral, pelagic (trades and westerlies), abyssal, and hadal (ocean trench). These correspond to the terrestrial biomes.

The Global 200 classification of marine ecoregions is not developed to the same level of detail and comprehensiveness as that of the terrestrial ecoregions; only the priority conservation areas are listed.

See Global 200 Marine ecoregions for a full list of marine ecoregions.[11]

In 2007, TNC and WWF refined and expanded this scheme to provide a system of comprehensive near shore (to 200 meters depth) Marine Ecoregions of the World (MEOW).[11] The 232 individual marine ecoregions are grouped into 62 marine provinces, which in turn group into 12 marine realms, which represent the broad latitudinal divisions of polar, temperate, and tropical seas, with subdivisions based on ocean basins (except for the southern hemisphere temperate oceans, which are based on continents).

Major biogeographic realms, analogous to the eight terrestrial ecozones, represent large regions of the ocean basins: 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.[9]

A similar system of identifying areas of the oceans for conservation purposes is the system of large marine ecosystems (LMEs), developed by the US National Oceanic and Atmospheric Administration (NOAA).


A freshwater ecoregion is a large area encompassing one or more freshwater systems that contains a distinct assemblage of natural freshwater communities and species. The freshwater species, dynamics, and environmental conditions within a given ecoregion are more similar to each other than to those of surrounding ecoregions and together form a conservation unit. Freshwater systems include rivers, streams, lakes, and wetlands. Freshwater ecoregions are distinct from terrestrial ecoregions, which identify biotic communities of the land, and marine ecoregions, which are biotic communities of the oceans.[12]

A map of Freshwater Ecoregions of the World, released in 2008, has 426 ecoregions covering virtually the entire non-marine surface of the earth.[13]

World Wildlife Fund (WWF) identifies twelve major habitat types of freshwater ecoregions: 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, and oceanic islands. The freshwater major habitat types reflect groupings of ecoregions with similar biological, chemical, and physical characteristics and are roughly equivalent to biomes for terrestrial systems.

The Global 200, a set of ecoregions identified by WWF whose conservation would achieve the goal of saving a broad diversity of the Earth's ecosystems, includes a number of areas highlighted for their freshwater biodiversity values. The Global 200 preceded Freshwater Ecoregions of the World and incorporated information from regional freshwater ecoregional assessments that had been completed at that time.

See also


  1. ^ Loucks, O. L. (1962). A forest classification for the Maritime Provinces. Proceedings of the Nova Scotian Institute of Science, 25(Part 2), 85-167.
  2. ^ Bailey, R. G. 1976. Ecoregions of the United States (map). Ogden, Utah: USDA Forest Service, Intermountain Region. 1:7,500,000.
  3. ^ Bailey, R. G. 2002. Ecoregion-based design for sustainability. New York: Springer, [1].
  4. ^ a b Bailey, R. G. 2014. Ecoregions: The Ecosystem Geography of the. Oceans and Continents. 2nd ed., Springer, 180 pp., [2].
  5. ^ Olson, D. M. & E. Dinerstein (1998). The Global 200: A representation approach to conserving the Earth's most biologically valuable ecoregions. Conservation Biol. 12:502–515.
  6. ^ Brunckhorst, D. (2000). Bioregional planning: resource management beyond the new millennium. Harwood Academic Publishers: Sydney, Australia.
  7. ^ Omernik, J. M. (2004). Perspectives on the Nature and Definition of Ecological Regions. Environmental Management. p. 34 - Supplement 1, pp.27–38.
  8. ^ "Biomes - Conserving Biomes - WWF".
  9. ^ a b Spalding, Mark D., Helen E. Fox, Gerald R. Allen, Nick Davidson; et al. Marine Ecoregions of the World: A Bioregionalization of Coastal and Shelf Areas. Bioscience Vol. 57 No. 7, July/August 2007, pp. 573–583.
  10. ^ Olson and Dinerstein 1998 and 2002
  11. ^ a b "Marine Ecoregions of the World". World Wide Fund for Nature.
  12. ^ Hermoso, Virgilio; Abell, Robin; Linke, Simon; Boon, Philip (2016). "The role of protected areas for freshwater biodiversity conservation: challenges and opportunities in a rapidly changing world". Aquatic Conservation: Marine and Freshwater Ecosystems. 26 (s1): 3–10. doi:10.1002/aqc.2681.
  13. ^ "Freshwater Ecoregions of the World". WWF.


Sources related to the WWC scheme:

  • Main papers:
    • Abell, R., M. Thieme, C. Revenga, M. Bryer, M. Kottelat, N. Bogutskaya, B. Coad, N. Mandrak, S. Contreras-Balderas, W. Bussing, M. L. J. Stiassny, P. Skelton, G. R. Allen, P. Unmack, A. Naseka, R. Ng, N. Sindorf, J. Robertson, E. Armijo, J. Higgins, T. J. Heibel, E. Wikramanayake, D. Olson, H. L. Lopez, R. E. d. Reis, J. G. Lundberg, M. H. Sabaj Perez, and P. Petry. (2008). Freshwater ecoregions of the world: A new map of biogeographic units for freshwater biodiversity conservation. BioScience 58:403-414, [3].
    • Olson, D. M., Dinerstein, E., Wikramanayake, E. D., Burgess, N. D., Powell, G. V. N., Underwood, E. C., D'Amico, J. A., Itoua, I., Strand, H. E., Morrison, J. C., Loucks, C. J., Allnutt, T. F., Ricketts, T. H., Kura, Y., Lamoreux, J. F., Wettengel, W. W., Hedao, P., Kassem, K. R. (2001). Terrestrial ecoregions of the world: a new map of life on Earth. Bioscience 51(11):933-938, [4].
    • Spalding, M. D. et al. (2007). Marine ecoregions of the world: a bioregionalization of coastal and shelf areas. BioScience 57: 573-583, [5].
  • Africa:
    • Burgess, N., J.D. Hales, E. Underwood, and E. Dinerstein (2004). Terrestrial Ecoregions of Africa and Madagascar: A Conservation Assessment. Island Press, Washington, D.C., [6].
    • Thieme, M.L., R. Abell, M.L.J. Stiassny, P. Skelton, B. Lehner, G.G. Teugels, E. Dinerstein, A.K. Toham, N. Burgess & D. Olson. 2005. Freshwater ecoregions of Africa and Madagascar: A conservation assessment. Washington DC: WWF, [7].
  • Latin America
    • Dinerstein, E., Olson, D. Graham, D.J. et al. (1995). A Conservation Assessment of the Terrestrial Ecoregions of Latin America and the Caribbean. World Bank, Washington DC., [8].
    • Olson, D. M., E. Dinerstein, G. Cintron, and P. Iolster. 1996. A conservation assessment of mangrove ecosystems of Latin America and the Caribbean. Final report for The Ford Foundation. World Wildlife Fund, Washington, D.C.
    • Olson, D. M., B. Chernoff, G. Burgess, I. Davidson, P. Canevari, E. Dinerstein, G. Castro, V. Morisset, R. Abell, and E. Toledo. 1997. Freshwater biodiversity of Latin America and the Caribbean: a conservation assessment. Draft report. World Wildlife Fund-U.S., Wetlands International, Biodiversity Support Program, and United States Agency for International Development, Washington, D.C., [9].
  • North America
    • Abell, R.A. et al. (2000). Freshwater Ecoregions of North America: A Conservation Assessment Washington, DC: Island Press, [10].
    • Ricketts, T.H. et al. 1999. Terrestrial Ecoregions of North America: A Conservation Assessment. Washington (DC): Island Press, [11].
  • Russia and Indo-Pacific
    • Krever, V., Dinerstein, E., Olson, D. and Williams, L. 1994. Conserving Russia's Biological Diversity: an analytical framework and initial investment portfolio. WWF, Switzerland.
    • Wikramanayake, E., E. Dinerstein, C. J. Loucks, D. M. Olson, J. Morrison, J. L. Lamoreux, M. McKnight, and P. Hedao. 2002. Terrestrial ecoregions of the Indo-Pacific: a conservation assessment. Island Press, Washington, DC, USA, [12].


  • Brunckhorst, D. 2000. Bioregional planning: resource management beyond the new millennium. Harwood Academic Publishers: Sydney, Australia.
  • Busch, D.E. and J.C. Trexler. eds. 2003. Monitoring Ecosystems: Interdisciplinary approaches for evaluating ecoregional initiatives. Island Press. 447 pages.

External links

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