Explorer reports information on ecological communities
and systems as defined for terrestrial, marine and (in the
future) freshwater ecosystems. Developed by NatureServe
and its natural heritage member programs in collaboration
with federal, international, academic and state partners,
these classifications provide a systematic way of describing
and assessing ecological diversity. They address the need for
subnational, national and international classification standards
for ecosystems, while allowing for classification at a scale
fine enough to be used to understand, manage, and protect
natural resources on a local or site-by-site basis. The
standards can be applied to define ecosystems anywhere in the
world; but the emphasis of the classifications are for
types that occur in North, Central and South America.
International Vegetation Classification
U.S. National Vegetation Classification
Canadian National Vegetation Classification
has developed two, inter-related terrestrial classifications, the
International Vegetation Classification (IVC), which provides
a hierarchical ordering of vegetation around the globe, from broad
formations or biomes to fine scale alliances and associations, and
the International Terrestrial Ecological Systems Classification,
which provides a single, mid-scale level unit suitable for classification
and mapping of ecosystems at a scale relevant to many conservation
and resource management applications. The IVC and Systems are linked
at mid-scales based on the shared vegetation patterns, but Systems
integrate associated abiotic factors and ecological processes that
allow for alternative ecological arrangements of ecosystem patterns,
and facilitates mapping. Together they provide valuable tools for
inventory, monitoring and assessment.
International Vegetation Classification
International Vegetation Classification (IVC) (formerly called the
International Classification of Ecological Communities or ICEC) is
based on vegetation as it currently exists on the landscape.
Landforms, soils, and other features are not directly considered as
part of the classification criteria, but ecological and
biogeographical information help guide the structure of the
classification. Because of conservation objectives, classification
efforts focus on natural and semi-natural types of vegetation, and
NatureServe Explorer reports only these types. However, the
system can be used to classify any vegetation as it currently exists
across the landscape, including natural, modified, agricultural and
urban vegetation types.
classification system has won broad acceptance within the NatureServe
network as well as among our partners. In North America, the IVC
consists of the U.S. National Vegetation Classification (USNVC) and
the Canadian National Vegetation Classification (CNVC). The IVC has
also been developed for the Caribbean region and many parts of Latin
America. The upper levels of the IVC cover the entire globe, mid-levels
are comprehensive across the western Hemisphere and various other
parts of the globe, and lower levels are most complete in the U.S. and
Canada. Partnerships with other compatible classification efforts,
such as those of the Braun-Blanquet tradition, will facilitate its use
in Europe and other regions.
the Classification Hierarchy
Ecological Community Names
Development Status of the International Classification of
Ecological Communities and NatureServe Explorer Data
references for the International Vegetation Classification
Faber-Langendoen, D., T. Keeler-Wolf, D. Meidinger, C. Josse, A. Weakley, D. Tart, G. Navarro, B. Hoagland, S. Ponomarenko, J.-P. Saucier, G. Fults, E. Helmer. 2012. Classification and description of world formation types. Part I (Introduction) and Part II (Description of formation types). Hierarchy Revisions Working Group, Federal Geographic Data Committee, FGDC Secretariat, U.S. Geological Survey. Reston, VA, and NatureServe, Arlington, VA.
D. Faber-Langendoen, T. Keeler-Wolf, D. Meidinger, D. Tart, C. Josse, G. Navarro, B. Hoagland, S. Ponomarenko, J.-P. Saucier, A. Weakley, P. Comer. 2012. Guidelines for a Vegetation - Ecologic Approach to Vegetation Description and Classification. Hierarchy Revisions Working Group, Federal Geographic Data Committee. FGDC Secretariat, U.S. Geological Survey, Reston, VA, and NatureServe, Arlington, VA. (in prep).
- Types are based on full floristic and growth form composition,
with supporting ecological and biogeographic information.
- Natural and cultural vegetation have separate treatments.
- Vegetation is characterized using plot data, with supporting
- Vegetation is classified based on existing vegetation criteria,
organized around ecological factors and biogeography:
diagnostic and dominant species
diagnostic and dominant growth forms
full floristic composition
- Hierarchy is structured using physiognomy, floristics,
- Levels of the hierarchy are both independent (i.e. no one level
is more fundamental than another), and inter-connected
(patterns at one level coordinate with other levels).
- Changes to the classification are coordinated by a Panel,
through a peer review process, responding to changes from
individuals or work groups, who may either conduct original
analyses, or integrate information available in the
Defining the Classification
International Vegetation Classification and the U.S. National
Vegetation Classification share the same principles and structure,
as described below. A first version of the hierarchy was developed
in 1997-1998, which was revised in 2008 (see U.S. National
Vegetation Classification (USNVC). The most current units of
the IVC are maintained on the NatureServe Explorer website,
with USNVC units also posted on the
hierarchy addresses the following issues, among others: uses
vegetation criteria to define all types (de-emphasizing explicit
abiotic criteria, such as hydrologic regimes in wetland types), b)
provides a clear distinction between natural (including semi-natural)
and cultural vegetation
wherever these can be observed from broad growth form patterns
(rather than combining natural and cultural vegetation initially and
separating them at lower levels), c) for natural vegetation, defines
the upper levels based on broad growth form patterns that reflect
ecological relationships (rather than detailed structural criteria,
which are more appropriate lower down in the hierarchy), d) provides
a new set of middle-level natural units that bridge the large
conceptual gap between alliance and formation, e) integrates the
physiognomic and floristic hierarchy levels based on ecologic
vegetation patterns, rather than developing the physiognomic and
floristic levels independently and then forcing them into a hierarchy,
f) provides detailed standards for plot data collection, type
description and classification, data management and peer review of
natural vegetation, and g) for cultural vegetation provides an
independent set of levels that addresses the particular needs of
Criteria for Natural
physiognomic criteria are the primary properties of natural vegetation
used to define all units of the classification. The choice of how
these criteria are used is integrated with ecological and biogeographic
considerations. The IVC includes criteria for all of the new and
revised levels, as shown in Table 1.
Summary of IVC Revised Hierarchy Levels and Criteria for Natural
plays a predominant role
L1 Formation Class
combinations of general dominant growth forms that are
adapted to basic temperature (energy budget), moisture,
and substrate/aquatic conditions.
L2 Formation Subclass
Combinations of general dominant and diagnostic growth
forms that reflect global macroclimatic factors driven
primarily by latitude and continental position, or that
reflect overriding substrate/aquatic conditions.
Combinations of dominant and diagnostic growth forms that
reflect global macroclimatic factors as modified by
altitude, seasonality of precipitation, substrates, and
and physiognomy play predominant roles
Combinations of dominant and diagnostic growth forms and
a broad set of diagnostic plant species that reflect
biogeographic differences in composition and continental
differences in mesoclimate, geology, substrates,
hydrology, and disturbance regimes.
Combinations of moderate sets of diagnostic plant species
and diagnostic growth forms, that reflect biogeographic
differences in composition and sub-continental to regional
differences in mesoclimate, geology, substrates,
hydrology, and disturbance regimes.
Combinations of relatively narrow sets of diagnostic plant
species (including dominants and co-dominants), broadly
similar composition, and diagnostic growth forms that
reflect regional mesoclimate, geology, substrates,
hydrology and disturbance regimes.
Floristics plays a predominant role
species, including some from the dominant growth form or
layer, and moderately similar composition that reflect
regional to subregional climate, substrates, hydrology,
moisture/nutrient factors, and disturbance regimes.
species, usually from multiple growth forms or layers, and
more narrowly similar composition that reflect topo-edaphic
climate, substrates, hydrology, and disturbance regimes.
The variety of vegetation criteria can be summarized as follows
(FGDC 2008, see also Mueller-Dombois and Ellenberg 1974, p.
Physiognomic and structural criteria include 1) Diagnostic
combinations of growth forms; 2) Ecological patterns of either
dominant growth forms or combinations of growth forms (growth
forms of similar ecological (habitat) and dynamic significance, or
growth forms of similar geographical distribution), and 3)
Vertical stratification (layering) of growth forms (complexity in
structure as produced by arrangement of growth forms).
Floristic criteria include 1) Diagnostic combinations of
species (differential and character species, constant species,
dominant species), 2) Ecological combinations of species
(indicator species of similar ecological (habitat) and/or dynamic
significance, species of similar geographical distribution), 3)
Vertical stratification (layering) of species (species patterns
found in the dominant growth forms or strata, species patterns
found between strata (overstory/understory), and 4) Numerical
relation criteria (community coefficients, such as indices of
similarity among plots within a type).
Too often vegetation classifiers rely solely on physiognomic or
floristic criteria. The IVC focuses on being a scientific natural
vegetation classification, using multiple vegetation criteria to
achieve the most natural groupings of vegetation types as
possible. The revised IVC is more likely to be compatible with
other multi-factor ecosystem classifications. Still, habitat
factors (e.g., climate, soil type) or management activities are not
an explicit part of the hierarchy; rather, they are used to help
interpret the patterns expressed through the vegetation (Fig. 1).
Figure 1. Vegetation classification criteria (from FGDC 2008)
The diagram portrays the five vegetation criteria used to classify
vegetation at all levels of the IVC hierarchy. These criteria are
arranged from the most fine-scaled on the left to the most
broad-scaled on the right. The five criteria are derived from
stand attributes or plot data (inside oval) and reflect the
ecological context (outside oval) of the stand or plot. The
ecological context includes environmental factors and biogeography
considered at multiple scales, as well as natural and human
The question is how to structure these criteria across the different
levels of the hierarchy. The criteria are weighted more towards
physiognomy-ecologic at higher levels, combinations of physiognomy
and floristics at mid levels, (guided by biogeographic, climatic and
other ecological factors), and more strongly floristic-ecologic
criteria for the lowest levels (see Table 1). The intent is to
provide as "natural" a classification of vegetation as possible. An
example of the types across the levels is provided in Table 2.
Example of the IVC Hierarchy
Revised Hierarchy for
1 Formation Class
Name: Mesomorphic Tree Vegetation
Colloquial Name: Forest and Woodland
2 Formation Subclass
Name: Temperate Forest Vegetation
Colloquial Name: Temperate Forest
Name: Cool Temperate Tree Vegetation
Colloquial Name: Cool Temperate Forest
Name: Pseudotsuga Tsuga
Picea Pinus Forest
Colloquial Name: Rocky Mountain Cool Temperate Forest
Name: Pseudotsuga menziesii Abies concolor Picea pungens
Pinus ponderosa Forest
Colloquial Name: Southern Rocky Mountain Lower Montane Forest
Name: Pseudotsuga menziesii Abies concolor
Picea pungens Mesic Southern Rocky Mountain Forest Group
Colloquial Name: Rocky Mountain Douglas-fir White Fir
Blue Spruce Mesic Forest
Name: Abies concolor Pseudotsuga menziesii Woodland
Colloquial Name: White Fir Douglas-fir-Woodland
Name: Abies concolor Pseudotsuga menziesii /
Acer glabrum Forest
Colloquial Name: White Fir Douglas-fir / Rocky Mountain Maple Forest
Criteria for Cultural
The cultural vegetation hierarchy consists of eight levels (see
Table 3). These levels are different from the natural vegetation
hierarchy, by providing an additional physiognomic level (level 4),
placing less emphasis on broad-scale, biogeographic and climate
patterns, but still providing for multiple scales of floristically
and physiognomically defined agricultural and developed vegetation
Hierarchy for Cultural Vegetation with Examples
Hierarchy for Cultural
Level 1 Cultural Class
Agricultural & Developed Vegetation
Agricultural & Developed Vegetation
Level 2 Cultural Subclass
Herbaceous Agricultural Vegetation
Woody Agricultural Vegetation
Level 3 Cultural Formation
Woody Horticultural Crop
Level 4 Cultural Subformation
Level 5 Cultural Group [optional]
Temperate and Tropical Row Crop
Temperate and Tropical Orchard
Level 6 Cultural Subgroup
Fruit - Orchards
Level 7 Cultural Type
Level 8 Cultural Subtype [optional]
Upper level (physiognomic-ecological) units:
- Cultural Class: A cultural vegetation classification unit of high rank (1st level) defined by a characteristic combination of dominant growth forms adapted to relatively intensive human manipulations, as reflected in relatively rapid changes in structure and/or composition.
- Cultural Subclass: A cultural vegetation classification unit of high rank (2nd level) defined by combinations and degree of herbaceous versus woody growth forms.
- Cultural Formation: A cultural vegetation classification unit of high rank (3rd level) defined by whether or not canopy structure of dominant growth forms is annually converted or heavily manipulated / harvested.
- Cultural Subformation: A vegetation classification unit of intermediate rank (4th level) defined by the spatial structure of the vegetation, including whether in swards, rows, and degree of manipulation to the canopy.
Mid-level (physiognomic-floristic) units:
- Cultural Group: A cultural vegetation classification unit of intermediate rank (5th level) defined by a common set of growth forms and many diagnostic plant taxa sharing a broadly similar region and climate, and disturbance factors.
- Cultural SubGroup: A cultural vegetation classification unit of intermediate rank (6th level) defined by a common set of growth forms and diagnostic species (taxa) preferentially sharing a similar set of regional edaphic, topographic, and disturbance factors.
Lower-level (floristic) units:
- Cultural Type: A vegetation classification unit, of moderately low rank (7th level) defined by one or more dominant or co-dominant species, as well as habitat conditions, and physiognomy.
- Cultural Subtype: A vegetation classification unit, of low rank (8th level) defined on the basis one or more dominant or co-dominant species, in conjunction with a characteristic set of associated species, habitat conditions and physiognomy.
Floristic and physiognomic criteria are the primary properties of cultural vegetation used to define all units of the classification, but assessed in light of human activities that govern these properties. Thus, choice of how these criteria are used should be evaluated in light of human management needs. Excluded from these criteria are properties from outside the current vegetation, such as explicit habitat factors (e.g., climate, soil type) or land use activities (e.g., grazed pasture versus ungrazed pasture), except as these are expressed in the vegetation cover. Some types are difficult to place in terms of natural versus cultural vegetation (e.g., forest plantation, pastures), and the user may need to look in both parts of the hierarchy to determine the type’s location. The broad criteria for classifying cultural vegetation may be summarized as follows (Table 3):
(crop or managed species) criteria
- Growth form criteria
- Diagnostic patterns of growth forms
- Ecologic and managed patterns of growth forms
- Growth forms of similar management significance (e.g., crop types)
- Growth forms of similar ecology and habitat
- Vertical stratification (layering) of growth forms
- Diagnostic combinations of species/crop or managed types
- Ecologic and managed combinations of species/crop or managed types
Vertical stratification (layering) of species
- Species of similar management significance (e.g., crop types)
- Species of similar ecology and habitat
All type concepts based on these criteria should be derived from field observations, in which the crop or managed species, growth forms, and their abundance, along with the field observation record, overall vegetation structure, and habitat setting are described. These field data provide the fundamental information for the description of types. All types at all levels should be described and characterized. Initially, the new upper and mid levels may have only brief characterizations, but shall be elaborated over time.
Plant species that are dominant (cover the greatest area) and diagnostic (found consistently in some vegetation types but not others) are the foundation of alliance and association names. At least one species from the dominant and/or uppermost stratum is included in each name. The following guidelines apply to alliance and association names:
- A hyphen ("-") indicates species occurring in the same stratum.
- A slash ("/") indicates species occurring in different strata.
- Species that occur in the uppermost stratum are listed first, followed successively by those in lower strata.
- Order of species names generally reflects decreasing levels of dominance, constancy, or indicator value.
- Parentheses around species name indicate species less consistently found either in all associations of an alliance, or in all occurrences of an association.
Alliance names include a term relevant to the class or formation in which they belong (e.g., "Forest," "Woodland," "Grassland", "Marsh"), and, if needed, can be followed by the word "alliance" to distinguish them from associations. The lowest possible number of species is used for an alliance name, up to a maximum of four.
of alliance names:
menziesii Forest Alliance
grandifolia - Magnolia grandiflora Forest Alliance
palustris / Quercus spp. Woodland Alliance
gerardii - (Calamagrostis canadensis, Panicum virgatum)
Association names include a term relevant to the class or formation in which they are classified. The lowest possible number of species is used in an association name. Up to four species may be necessary to define types with very diverse vegetation, relatively even dominance, and variable total composition.
In cases where diagnostic species are unknown or in question, a more general term (such as "Prairie Forbs" is currently allowed as a "placeholder." An environmental or geographic term (for example, "Northern"), or one that is descriptive of the height of the vegetation ("Dwarf"), can also be used as a modifier when such a term is necessary to adequately characterize the association. When confidence in the circumscription of the association is low, the name is followed by the term "[Provisional]".
of association names:
lasiocarpa / Vaccinium scoparium Forest
toxiferum - Eugenia foetida - Krugiodendron ferreum
- Swietenia mahagoni /Capparis flexuosa Forest
macrocarpa - (Quercus alba - Quercus
velutina) / Andropogon gerardii Savanna
- In North America, the IVC is being widely applied by NatureServe, federal, academic and state partners through the USNVC and CNVC classifications. Many mapping and classification products are available (see www.natureserve/publications).
USNVC development began in the late 1980s and a first
approximation was published in 1997-98 (FGDC 1997, Grossman
et al. 1998, Anderson et al.
1998). Challenges in the use of that hierarchy led to a complete overhaul of all levels, and a revised version was released in 2008 (FGDC 2008), based on input from national and international vegetation ecologists (Table 3). The most current units of the USNVC are
now maintained on the NatureServe Explorer
website and on the usnvc.org website. The USNVC is currently a jurisdictional subset
of the IVC; that is, all units defined and described
for the U.S. contain range-wide information, as best
as that can be determined through the review process.
The USNVC is being developed by NatureServe and its natural heritage member programs in partnership with the Federal Geographic
Data Committee Vegetation Subcommittee (FGDC), the
Ecological Society of America Vegetation Classification
Panel (see Jennings et al. 2009)
and federal partners, many of whom are represented
on the Subcommittee and the Panel. See the IVC description above for more information on the USNVC hierarchy.
The structure of the USNVC hierarchy is a substantial revision of the 1997 hierarchy, which relied heavily on the UNESCO (1973) physiognomic hierarchy for all levels above the alliance (see Franklin et al 2012 and Faber-Langendoen et al. 2009 for a comparison of the two hierarchies). The newly adopted national vegetation hierarchy consists of eight levels, organized into three upper levels, three middle levels, and two lower levels (see Table 1 above).
Standard References for the USNVC
Websites: usnvc.org, explorer.natureserve.org.
Faber-Langendoen, D., D.L Tart, and R.H.Crawford. 2009. Contours of the revised U.S. National Vegetation Classification standard. Bulletin of the Ecological Society of America 90:87-93.
Faber-Langendoen, D., J. Drake, S. Gawler, M. Hall, G. Kittel, S. Menard, C. Nordman, M. Pyne, M. Reid, L. Sneddon, K. Schulz, J. Teague, M. Russo, K. Snow, P. Comer. 2012. Macrogroups and Groups for the U.S. National Vegetation Classification. NatureServe, Arlington, VA. + Appendices.
FGDC. 2008. National Vegetation Classification Standard, Version 2 FGDC-STD-005-2008 (version 2). Vegetation Subcommittee, Federal Geographic Data Committee, FGDC Secretariat, U.S. Geological Survey. Reston, VA. 55 pp. + Appendices.
Jennings, M.D., D. Faber-Langendoen, O.L. Loucks, R.K. Peet, and D. Roberts. 2009. Standards for Associations and Alliances of the U.S. National Vegetation Classification. Ecological Monographs 79: 173-199.
Peet R.K. 2008. A Decade of Effort by the ESA Vegetation Panel Leads to a New Federal Standard. Bulletin of the Ecological Society of America: Vol. 89, No. 3 pp. 210-211
FGDC. 1997. Vegetation Classification Standard. FGDC-STD-005. Vegetation Subcommittee, Federal Geographic Data Committee, FGDC Secretariat, U.S. Geological Survey. Reston, VA. 58 pp.
Grossman D.H., Faber-Langendoen D., Weakley A.S., Anderson M., Bourgeron P., Crawford R., Goodin K., Landaal S., Metzler K., Patterson K.D., Pyne M., Reid M., and Sneddon L. 1998. International classification of ecological communities: terrestrial vegetation of the United States. Volume I, The National Vegetation Classification System: development, status, and applications. The Nature Conservancy: Arlington, VA.
Anderson, M., P. Bourgeron, M. T. Bryer, R. Crawford, L. Engelking, D. Faber-Langendoen, M. Gallyoun, K. Goodin, D. H. Grossman, S. Landaal, K. Metzler, K. D. Patterson, M. Pyne, M. Reid, L. Sneddon, and A. S. Weakley. 1998. International classification of ecological communities: terrestrial vegetation of the United States. Volume II. The National Vegetation Classification System: list of types. The Nature Conservancy, Arlington, Virginia, USA. 502 p.
CNVC development began in 2000, when partners in Canada,
together with NatureServe and the Network in Canada,
agreed to collaborate on a framework and principles
compatible with the IVC (Alvo
and Ponomarenko 2003). The potential for integration
of existing provincial and territorial classification
information into the CNVC and IVC was described by
Ponomarenko and Alvo (2001).
Forest and woodland associations are being developed
first, led by the Canadian
Forest Service's Canadian Forest Ecosystem Classification
(CFEC) project, which began in 1998. The Canadian Forest Service and Parks Canada are key partners in the overall CNVC development, along with provincial forest ecosystem classification programs,the CDC network, and NatureServe. The Canadian National Vegetation Classification is separate from, but linked to, existing provincial, territorial, regional, and international classifications. It is specifically derived to serve Canadian national needs. Wherever possible, definitional conventions of the USNVC and IVC are applied in the CNVC to facilitate international exchange of ecological information.
The mandate of the Canadian National Vegetation Classification (CNVC) is to define and describe the vegetation of Canada at various levels of generalization, using standardized criteria and terminology. The CNVC can be thought of as a "dictionary" or "encyclopedia" of Canadian vegetation types. It integrates knowledge of plant community composition and structure in relation to environmental gradients, such as regional climate and site-specific moisture and nutrients.
Standard references for the CNVC
Website: http:// cnvc-cnvc.ca.
Ponomarenko, S., and R. Alvo. 2001 Perspectives on developing a Canadian classification of ecological
communities. Canadian Forest Service, Information
Report ST-X-18E, Ottawa. 50 pp.
Alvo, R, and S. Ponomarenko. 2003. Vegetation Classification Standard for Canada Workshop: May 31-June 2 2000 (Hull, Quebec). Canadian Field Naturalist 117(1):125-139.
The IVC is being applied and testing throughout Latin America, parts of Africa, Europe. In addition, a global classification of grasslands has been completed using the IVC (Faber-Langendoen and Josse 2010)
Faber-Langendoen, D. and C. Josse. 2010. World Grasslands and Biodiversity Patterns. NatureServe, Arlington, VA. + Appendices.
International Terrestrial Ecological System Classification
NatureServe and its natural heritage program members, have completed a working classification of terrestrial ecological systems in the conterminous United States, southern Alaska, and adjacent portions of Mexico and Canada. NatureServe's terrestrial ecological system classification defines groups of plant communities that tend to co-occur within landscapes with similar ecological processes, substrates, and/or environmental gradients. They are intended to provide a "meso-scale" classification unit that is readily mappable, often from remote imagery, and readily identifiable in the field. Approximately 600 terrestrial ecological system units are described in a comprehensive classification for the lower 48 United States and adjacent Canada (Comer et al 2003). This number compares with some 1,800 alliances and over 6,000 associations in the same area.
Defining the Ecological System Classification
Understanding ecological system names
Development status of the International
Terrestrial Ecological System Classification
and NatureServe Explorer Data
The standard reference for the terrestrial ecological system classification for the United States is:
P., D. Faber-Langendoen, R. Evans, S. Gawler, C. Josse,
G. Kittel, S. Menard, M. Pyne, M. Reid, K. Schulz,
K. Snow, and J. Teague. 2003. Ecological Systems
of the United States: A Working Classification of
U.S. Terrestrial Systems. NatureServe, Arlington,
Comer, P., and K. Schulz. 2007. Standardized ecological classification for meso-scale mapping in Southwest United States. Rangeland Ecology and Management 60: 324-335.
Vascular plant names used in describing ecological systems generally follow:
Kartesz, J.T. 1999. A synonymized checklist and atlas with biological attributes for the vascular flora of the United States, Canada, and Greenland. First edition. In: Kartesz, J.T. and C.A. Meacham. Synthesis of the North American flora [computer program]. Version 1.0. North Carolina Botanical Garden: Chapel Hill, NC.
Standard references for nonvascular plant names used in describing ecological systems are the same as those listed for the nonvascular plant species presented in NatureServe Explorer.
Defining the Ecological System classification
A terrestrial ecological system is defined as a group of plant community types that tend to co-occur within landscapes with similar ecological processes, substrates, and/or environmental gradients. A given terrestrial ecological system will typically manifest itself in a landscape at intermediate geographic scales of 10s to 1,000s of hectares and persist for 50 or more years. Therefore, these units are intended to encompass common successional pathways for a given landscape setting.
plant community type, we mean a vegetation classification
unit at the association or alliance level, where these
are available in the International Vegetation Classification
(IVC) and its U.S. or Canadian components, the USNVC
and CNVC (Grossman et al. 1998,
Alvo and Ponomarenko 2003),
or, if these are not available, other comparable vegetation
units. IVC associations are used where available
to describe the component plant communities of each
terrestrial system. Ecological systems are defined
using both spatial and temporal criteria that influence
the grouping of associations. Associations that consistently
co-occur on the landscape therefore define biotic
components of each ecological system type.
set of diagnostic classifiers is used to describe
the critical ecological variables that support the
co-occurrence of plant communities. This multi-factor
approach to classification integrates knowledge of
natural disturbances such as fire and flooding along
with environmental settings, such as soil and bedrock
features or wetland characteristics. Variables describing
environmental gradients include local climate, hydrologically
defined patterns in coastal zones, arid grassland
or desert areas, or montane, alpine or subalpine zones.
Ecological processes include natural disturbances such as fire and flooding. Substrates may include a variety of soil surface and bedrock features, such as shallow soils, alkaline parent materials, sandy/gravelling soils, or peatlands. Finally, environmental gradients include local climates, hydrologically defined patterns in coastal zones, arid grassland or desert areas, or montane, alpine or subalpine zones.
NatureServe's ecological system concept is defined as follows:
- The unit is explicitly scaled to represent
a. spatial scales of 10s to 1000s of hectares.
b. temporal scales of 50 to 100 years
- The variability in the system is explicitly described in terms of a consistent list of abiotic and biotic criteria and by linking ecological systems to plant community types (associations and alliances of the IVC and NVC) that describe the biotic community variation within the system.
- Long-term sustainability and local stability are to be considered by mapping and evaluating the occurrence of ecological systems at the local site and the regional level.
- Population processes not formally included as explicit system dynamics, but through knowledge of the component plant communities, the major plant species and their dynamics within the systems can be described. Additional work could formalize the roles of additional biotic elements such as invertebrates and vertebrates.
An bio-ecological hierarchy of Ecological Systems is available through the IVC, by linking the ecological vegetation patterns of the Group level of the IVC to the Systems level.
Our conceptualization of terrestrial ecological systems includes temporal and geographic scales intermediate between those commonly considered for local stand and landscape-scale analyses, which can range from 50 to 1,000s of years and 10s to 1,000s of hectares. These "meso-scales" are intended to constrain the definition of system types to scales that are of prime interest for conservation and resource managers who are managing landscapes in the context of a region or state. More precise bounds on both temporal and geographic scales take into account specific attributes of the ecological patterns that characterize a given region.
As the definition for ecological systems indicates,
this is a multi-factor approach to ecological classification.
Multiple environmental factors - or diagnostic classifiers
- are evaluated and combined in different ways to
explain the spatial co-occurrence of IVC associations
(See below). The structure of the ecological systems classification is more "modular" in that it aggregates diagnostic classifiers in multiple, varying combinations, without a specific hierarchy. The focus is on a single set of ecological system types. This is in contrast to, for example, the framework and approach of the IVC. The nested IVC hierarchy groups associations into alliances based on common dominant or diagnostic species in the upper most canopy, validated through ecological and biogeographical relationships. This provides more of a taxonomic-ecological aggregation with no presumption that associations co-occur in a given landscape. The ecological system unit links IVC associations using multiple factors that help to explain why they tend to be found together in a given landscape due to similar ecological processes, substrates, and/or ecological gradients. Therefore, ecological systems are often more readily identified, mapped, and understood as practical ecological classification units. Diagnostic classifiers include a wide variety of factors representing bioclimate, biogeographic history, physiography, landform, physical and chemical substrates, dynamic processes, landscape juxtaposition, and vegetation structure and composition.
(Categories and Examples)
- Continental Bioclimate and Phytogeography
- Regional Bioclimate
- Landscape Position, Hydrogeomorphology
- Soil Characteristics, Specialized Substrate
- Hydrologic Regime
- Fire Regime
- Upland-Wetland Mosaics
- Vertical Structure and Patch Type
- Composition of component associations
- Abundance of component association patches
Understanding ecological system names
The nomenclature for the ecological systems classification includes three primary components that communicate regional distribution (predominant Ecological Division), vegetation physiognomy and composition, and/or environmental setting. The final name is a combination of these ecological characteristics with consideration given to local usage and practicality.
Divisions: The Division-scaled units typically
form part of each classification unit's name. For
example, a "Rocky Mountain" ecological system unit
is entirely or predominantly found (>80% of its total
range) within the Rocky Mountain Division, but could
also occur in neighboring Divisions. This nomenclatural
standard is applicable to most ecological system units,
except for those types that span many several Divisions
(e.g., some tidal or freshwater marsh systems), or
that are more localized (>80% of the range) within
a subunit of the Division (e.g., Colorado Plateau,
within the Inter-Mountain Basins Division).
Structure and Composition: Vegetation structure
(e.g., Forest and Woodland, Grassland), and vegetation
composition (e.g. Pinyon-Juniper, mixed conifer) is
commonly used in the name of a system. In sparse to
unvegetated types, reference to characteristic landforms
(e.g., badland, cliff) may substitute for vegetation
structure and/or composition. It will typically come
after Biogeographical Division, but may come before or
Environmental factors (e.g., xeric, flats, montane)
can be used in conjunction with Vegetation Structure
and Composition or, on their own, to name system types.
This will typically come after Biogeographical Division,
but may come before or after Vegetation Structure
Laurentian-Acadian Pine-Hemlock-Hardwood Forest Cross
Timbers Oak Forest and Woodland Central Appalachian
Limestone Glade and Woodland Southern and Central
Appalachian Cove Forest North-Central Interior Shrub-Graminoid
Alkaline Fen Cross Timbers Oak Forest and Woodland
Western Great Plains Wooded Draw and Ravine Rocky
Mountain Foothill Grassland Chihuahuan-Sonoran Desert
Bottomland and Swale Grassland
status of the International Terrestrial Ecological
System Classification and NatureServe Explorer Data
600 terrestrial ecological system units are described
in a comprehensive classification for the lower 48
United States and adjacent Canada (Comer
et al. 2003). All of these ecological systems
are served here on NatureServe Explorer.
ecological systems have also been developed and described
comprehensively for Latin America and the Caribbean
et al. 2003). This report summarizes the nearly
700 ecological systems that currently are classified
and described in the region, emphasizing the natural
portion of the landscape. These ecological systems
are posted in Spanish on InfoNatura. Ecological system units tend to be readily mapped using areal photographs or satellite imagery, especially when combined with ancillary data, such as soil maps, elevation-derived landform models, and stream or wetland map layers. NatureServe ecological system units have become established as map legends for several federal agencies (e.g. USGS Gap Analysis programs) for new mapping efforts that depict units at fine grain (0.25 hectare) as well as intermediate grain (5 hectare). Given their utility for standardized mapping, the ecological systems classification lends itself to a wide range of mapping activities and subsequent assessments of habitat diversity and landscape conditions.
NatureServe collaborated with NOAA and leading academic experts to develop the Coastal/Marine Ecological Classification Standard (CMECS). This classification framework extends from the head-of-tides in the coastal zone to the deep ocean, encompassing estuaries, wetlands, rivers, shorelines, islands, the intertidal zone, the entire benthic zone, and the entire water column from the shore to the deep ocean. CMECS allows effective identification, monitoring, protection, and restoration of unique biotic assemblages, protected species, critical habitat, and important ecosystem components.
NatureServe relies on other partners for freshwater classifications.