Classification of Ecological Communities
 
 
  
 
 
 
 
 
  
 
 

Ecological Classifications

NatureServe 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.

Terrestrial

International Vegetation Classification

U.S. National Vegetation Classification

Canadian National Vegetation Classification

Other Regions

Coastal Marine

Freshwater

TERRESTRIAL

NatureServe 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

The 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.

The 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.

Standard References

Guiding Principles

Defining the Classification Hierarchy

Understanding Ecological Community Names

Development Status of the International Classification of
Ecological Communities and NatureServe Explorer Data

Standard References

The standard references for the International Vegetation Classification system are:

Website: explorer.natureserve.org

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).

Guiding Principles

  1. Types are based on full floristic and growth form composition, with supporting ecological and biogeographic information.

  2. Natural and cultural vegetation have separate treatments.

  3. Vegetation is characterized using plot data, with supporting ecological data.

  4. 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

  5. Hierarchy is structured using physiognomy, floristics, ecology.

  6. 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).

  7. 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 literature.

Defining the Classification Hierarchy

Currently the 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 usnvc.org website.

The revised 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 cultural vegetation.

Criteria for Natural Vegetation

Floristic and 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.

Table 1. Summary of IVC Revised Hierarchy Levels and Criteria for Natural Vegetation

Hierarchy Level

Criteria

Upper:

Physiognomy plays a predominant role

L1 — Formation Class

Broad 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.

L3 — Formation

Combinations of dominant and diagnostic growth forms that reflect global macroclimatic factors as modified by altitude, seasonality of precipitation, substrates, and hydrologic conditions.

Middle:

Floristics and physiognomy play predominant roles

L4 — Division

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.

L5 — Macrogroup

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.

L6 — Group

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.

Lower:

Floristics plays a predominant role

L7 — Alliance

Diagnostic 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.

L8 — Association

Diagnostic 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. 154-155):

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).

Vegetation classification criteria

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 disturbance regimes.

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.

Table 2. Example of the IVC Hierarchy

Revised Hierarchy for
Natural Vegetation

Example

Upper Levels

1 — Formation Class

Scientific Name: Mesomorphic Tree Vegetation
Colloquial Name: Forest and Woodland

2 — Formation Subclass

Scientific Name: Temperate Forest Vegetation
Colloquial Name: Temperate Forest

3 — Formation

Scientific Name: Cool Temperate Tree Vegetation
Colloquial Name: Cool Temperate Forest

Mid Levels

4 — Division

Scientific Name: PseudotsugaTsugaPiceaPinus Forest
Colloquial Name: Rocky Mountain Cool Temperate Forest

5 — Macrogroup

Scientific Name: Pseudotsuga menziesii — Abies concolor — Picea pungens — Pinus ponderosa Forest
Colloquial Name: Southern Rocky Mountain Lower Montane Forest

6 — Group

Scientific 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

Lower Levels

7 — Alliance

Scientific Name: Abies concolor — Pseudotsuga menziesii Woodland
Colloquial Name: White Fir — Douglas-fir-Woodland

8 — Association

Scientific Name: Abies concolor — Pseudotsuga menziesii / Acer glabrum Forest
Colloquial Name: White Fir — Douglas-fir / Rocky Mountain Maple Forest

Criteria for Cultural Vegetation

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 types.

Table 3. Hierarchy for Cultural Vegetation with Examples

Hierarchy for Cultural Vegetation

Example

Example

Upper

Level 1 — Cultural Class

Agricultural & Developed Vegetation

Agricultural & Developed Vegetation

Level 2 — Cultural Subclass

Herbaceous Agricultural Vegetation

Woody Agricultural Vegetation

Level 3 — Cultural Formation

Cultivated Crop

Woody Horticultural Crop

Level 4 — Cultural Subformation

Row Crop

Orchard

Mid

Level 5 — Cultural Group [optional]

Temperate and Tropical Row Crop

Temperate and Tropical Orchard

Level 6 — Cultural Subgroup

Corn

Fruit - Orchards

Lower

Level 7 — Cultural Type

Sweet Corn

Apple

Level 8 — Cultural Subtype [optional]


    Upper level (physiognomic-ecological) units:

  1. 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.
  2. Cultural Subclass: A cultural vegetation classification unit of high rank (2nd level) defined by combinations and degree of herbaceous versus woody growth forms.
  3. 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.
  4. 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.

  5. Mid-level (physiognomic-floristic) units:

  6. 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.
  7. 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.

  8. Lower-level (floristic) units:

  9. 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.
  10. 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):

  1. Growth form criteria
    1. Diagnostic patterns of growth forms
    2. Ecologic and managed patterns of growth forms
      • Growth forms of similar management significance (e.g., crop types)
      • Growth forms of similar ecology and habitat
    3. Vertical stratification (layering) of growth forms
  2. (crop or managed species) criteria
    1. Diagnostic combinations of species/crop or managed types
    2. Ecologic and managed combinations of species/crop or managed types
      • Species of similar management significance (e.g., crop types)
      • Species of similar ecology and habitat
    3. Vertical stratification (layering) of species

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.

Understanding Ecological Community Names

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.

Examples of alliance names:

  • Pseudotsuga menziesii Forest Alliance
  • Fagus grandifolia - Magnolia grandiflora Forest Alliance
  • Pinus palustris / Quercus spp. Woodland Alliance
  • Andropogon gerardii - (Calamagrostis canadensis, Panicum virgatum) Grassland Alliance

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]".

Examples of association names:

  • Abies lasiocarpa / Vaccinium scoparium Forest
  • Metopium toxiferum - Eugenia foetida - Krugiodendron ferreum - Swietenia mahagoni /Capparis flexuosa Forest
  • Rhododendron carolinianum Shrubland
  • Quercus macrocarpa - (Quercus alba - Quercus velutina) / Andropogon gerardii Savanna

Development Status of the International Vegetation Classification and NatureServe Explorer Data

  • 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).

U.S. National Vegetation Classification (USNVC)

The 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

1997 Version

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.

Canadian National Vegetation Classification (CNVC)

The 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.

Other Regions

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)

References:

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.

Standard References

Defining the Ecological System Classification

Meso-Scale Ecosystems

Diagnostic Classifiers

Understanding ecological system names

Development status of the International
Terrestrial Ecological System Classification
and NatureServe Explorer Data

Standard References

The standard reference for the terrestrial ecological system classification for the United States is:

Comer, 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, Virginia.

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.

By 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.

A 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:

  1. The unit is explicitly scaled to represent
       a. spatial scales of 10s to 1000s of hectares.
       b. temporal scales of 50 to 100 years
  2. 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.
  3. 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.
  4. 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.

Meso-Scale Ecosystems

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.

Diagnostic Classifiers

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.

Diagnostic Classifiers
(Categories and Examples)
Ecological Divisions
- Continental Bioclimate and Phytogeography
Bioclimatic Variables
- Regional Bioclimate
Environment
- Landscape Position, Hydrogeomorphology
- Soil Characteristics, Specialized Substrate
Ecological Dynamics
- Hydrologic Regime
- Fire Regime
Landscape Juxtaposition
- Upland-Wetland Mosaics
Vegetation
- 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.

Biogeographical 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).

Vegetation 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 after Environment.

Environment: 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 and Composition.

Examples:
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

Development status of the International Terrestrial Ecological System Classification and NatureServe Explorer Data

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). All of these ecological systems are served here on NatureServe Explorer.

Terrestrial ecological systems have also been developed and described comprehensively for Latin America and the Caribbean (Josse 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.

COASTAL MARINE

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.

FRESHWATER

NatureServe relies on other partners for freshwater classifications.



 

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State and Provincial Distribution data sources. US ESA and Canada COSEWIC national status. The Heritage Conservation Status Rank System and definitions.