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.[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
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).
2 Definition and categorization
7 See also
10 External links
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.
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.
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
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". 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".
"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
North America by the Commission for Environmental
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
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.
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
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
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.
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.
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
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.
See also: Large marine ecosystem
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." They have been defined by The Nature Conservancy (TNC)
World Wildlife Fund
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. 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.
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
Marine ecoregions for a full list of marine
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). 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
Tropical Eastern Pacific,
Temperate South America,
Temperate Southern Africa,
Temperate Australasia, Southern Ocean.
A similar system of identifying areas of the oceans for conservation
purposes is the system of large marine ecosystems (LMEs), developed by
National Oceanic and Atmospheric Administration
National Oceanic and Atmospheric Administration (NOAA).
Amazon River in Brazil.
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.
A map of Freshwater
Ecoregions of the World, released in 2008, has 426
ecoregions covering virtually the entire non-marine surface of the
World Wildlife Fund
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
Lists of ecoregions
^ Loucks, O. L. (1962). A forest classification for the Maritime
Provinces. Proceedings of the Nova Scotian Institute of Science,
25(Part 2), 85-167.
^ Bailey, R. G. 1976.
Ecoregions of the United States (map). Ogden,
Utah: USDA Forest Service, Intermountain Region. 1:7,500,000.
^ Bailey, R. G. 2002. Ecoregion-based design for sustainability. New
York: Springer, .
^ a b Bailey, R. G. 2014. Ecoregions: The
Ecosystem Geography of the.
Oceans and Continents. 2nd ed., Springer, 180 pp., .
^ 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.
^ Brunckhorst, D. (2000). Bioregional planning: resource management
beyond the new millennium. Harwood Academic Publishers: Sydney,
^ Omernik, J. M. (2004). Perspectives on the Nature and Definition of
Ecological Regions. Environmental Management. p. 34 - Supplement
Biomes - Conserving
Biomes - WWF".
^ 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. CS1 maint: Multiple names: authors list (link)
^ Olson and Dinerstein 1998 and 2002
^ a b "Marine
Ecoregions of the World". World Wide Fund for
^ 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.
Ecoregions of the World". WWF.
Sources related to the WWC scheme:
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, .
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
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Russia and Indo-Pacific
Krever, V., Dinerstein, E., Olson, D. and Williams, L. 1994.
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Morrison, J. L. Lamoreux, M. McKnight, and P. Hedao. 2002. Terrestrial
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Busch, D.E. and J.C. Trexler. eds. 2003. Monitoring Ecosystems:
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Island Press. 447 pages.
Wikimedia Commons has media related to Ecoregions.
WWF WildFinder (interactive on-line map of ecoregions with additional
information about animal species)
WWF Map of the ecozones
Activist network cultivating Ecoregions/Bioregions
Sierra Club - ecoregions
Montane grasslands and shrublands
Broadleaf and mixed forests
Grasslands, savannas, and shrublands
Moist broadleaf forests
Dry broadleaf forests
Grasslands, savannas, and shrublands
Mediterranean forests, woodlands, and scrub
Deserts and xeric shrublands
Flooded grasslands and savannas
Temperate Northern Pacific
Tropical Eastern Pacific
List of ecoregions
Global 200 ecoregions
Ecological land classification