This method assesses the conservation status of species and ecosystems–specifically the extinction risk of species and elimination risk of ecosystems at global scales, and their extirpation risk at national and subnational scales. NatureServe and Natural Heritage Program staff across North America collect and evaluate data for species and ecosystems of concern using these methods and tools to ensure that assigned status ranks are accurate and consistent, based on current field and remote sensing information.
Conservation status assessments are completed to produce conservation status ranks that measure extinction or extirpation risk at three geographic scales: global, national, and subnational. Global, National, and Subnational Ranks (or “G-Ranks,” N-Ranks” and “S-Ranks”) are widely used throughout the conservation community and are regarded as highly credible by scientists, government agencies and private-sector organizations. These assessments are also a valuable resource for government agencies responsible for administration of Federal, state and provincial species conservation laws. See below for rank definitions.
Determining which plants, animals and ecosystems are thriving and which are rare or declining is crucial for targeting conservation of the species, habitats and ecosystems in greatest need. NatureServe and its member Natural Heritage Programs have developed a rigorous and consistent method for evaluating the relative imperilment of both species and ecosystems based on the best available science.
The purpose of the conservation status ranks developed by NatureServe is to assess the relative risk facing a species or ecosystem and does not imply that any specific action or legal status is needed to assure its survival. NatureServe is a non-advocacy organization and is committed to providing objective and reliable scientific data.
Features & Benefits
NatureServe and its member programs and collaborators use a rigorous, consistent, and transparent methodology to assess the conservation status (extinction or extirpation risk) of species of plants, animals, and fungi, as well as the conservation status (elimination or extirpation risk) of ecosystems (ecological communities and systems).
- Eight core status rank factors are identified as relevant to risk assessments of extinction/elimination, or extirpation.
- Descriptions of each factor include the basis for its use, and its evaluation and rating criteria.
- Factors are organized into three categories (rarity, threats, trends).
- Conditional rules for use of factors are applied to ensure that adequate information is used for assessing status.
- Factors are scaled and weighted according to their impact on risk.
- Consistent factor scaling and weighting allow the use of points to effectively score the contribution of each factor to risk.
- Scores are weighted and combined by category resulting in an overall calculated rank, which is reviewed, and a final conservation status rank assigned.
- A rank calculator automates the process of assigning conservation status ranks.
- NatureServe’s Biotics database provides management for all conservation status information.
Conservation status is summarized as a series of ranks derived at global, national, or subnational (state/provincial) levels on a five-point scale from critically imperiled (G1, N1, S1) to secure (G5/N5/S5).
NatureServe’s methods, which have been evolving since 1978, are used by its network of Natural Heritage Programs and Conservation Data Centers throughout North America. In recent years, NatureServe has worked with IUCN to standardize the ratings for shared information fields, such as Range Extent, Area of Occupancy, Population Size, and Threats. This standardization permits the sharing of information among organizations and countries, and allows the information to be used in both IUCN as well as NatureServe assessments.
NatureServe conservation status assessment methodology contains a number of features, most notably that it (1) considers all of the status factor data collectively in assigning a status; (2) may produce “range-ranks,” (e.g., G1G3 = globally critically imperiled to vulnerable) to transparently reveal the degree of uncertainty in a status when the available information does not permit a single status rank; (3) explicitly considers threats in the assessment; (4) assesses conservation status for both species and ecosystems; and (5) is sufficiently complete for North American species that global, national, and subnational ranks are routinely linked to facilitate conservation priority setting.
NatureServe Conservation Status Ranks
Listed below are definitions for interpreting NatureServe’s global (range-wide) conservation status ranks. Global conservation status ranks are assigned by NatureServe scientists or by a designated lead office in the NatureServe network.
Presumed Extinct (species) — Not located despite intensive searches and virtually no likelihood of rediscovery
Presumed Eliminated (ecosystems, i.e., ecological communities and systems) — Eliminated throughout its range, due to loss of key dominant and characteristic taxa and/or elimination of the sites and ecological processes on which the type depends
|GH||Possibly Extinct (species) or Possibly Eliminated (ecosystems) — Known from only historical occurrences but still some hope of rediscovery. Examples of evidence include (1) that a species has not been documented in approximately 20-40 years despite some searching and/or some evidence of significant habitat loss or degradation; (2) that a species or ecosystem has been searched for unsuccessfully, but not thoroughly enough to presume that it is extinct or eliminated throughout its range.|
|G1||Critically Imperiled — At very high risk of extinction or elimination due to very restricted range, very few populations or occurrences, very steep declines, very severe threats, or other factors.|
|G2||Imperiled — At high risk of extinction or elimination due to restricted range, few populations or occurrences, steep declines, severe threats, or other factors.|
|G3||Vulnerable — At moderate risk of extinction or elimination due to a fairly restricted range, relatively few populations or occurrences, recent and widespread declines, threats, or other factors.|
|G4||Apparently Secure — At fairly low risk of extinction or elimination due to an extensive range and/or many populations or occurrences, but with possible cause for some concern as a result of local recent declines, threats, or other factors.|
|G5||Secure — At very low risk or extinction or elimination due to a very extensive range, abundant populations or occurrences, and little to no concern from declines or threats.|
|G#G#||Range Rank — A numeric range rank (e.g., G2G3, G1G3) is used to indicate uncertainty about the exact status of a taxon or ecosystem type. Ranges cannot skip more than two ranks (e.g., GU should be used rather than G1G4).|
|GU||Unrankable — Currently unrankable due to lack of information or due to substantially conflicting information about status or trends. NOTE: Whenever possible (when the range of uncertainty is three consecutive ranks or less), a range rank (e.g., G2G3) should be used to delineate the limits (range) of uncertainty.|
|GNR||Unranked — Global rank not yet assessed.|
|GNA||Not Applicable — A conservation status rank is not applicable because the species or ecosystem is not a suitable target for conservation activities. A global conservation status rank may be not applicable for several reasons, related to its relevance as a conservation target. For species, typically the species is a hybrid without conservation value, or of domestic origin. For ecosystems, the type is typically non-native (e.g, many ruderal vegetation types), agricultural (e.g. pasture, orchard) or developed (e.g. lawn, garden, golf course).|
|?||Inexact Numeric Rank — Denotes inexact numeric rank; this should not be used with any of the Variant Global Conservation Status Ranks or GX or GH.|
|Q||Questionable taxonomy that may reduce conservation priority— Distinctiveness of this entity as a taxon or ecosystem type at the current level is questionable; resolution of this uncertainty may result in change from a species to a subspecies or hybrid, or inclusion of this taxon or type in another taxon or type, with the resulting taxon having a lower-priority (numerically higher) conservation status rank. The “Q” modifier is only used at a global level and not at a national or subnational level.|
|C||Captive or Cultivated Only — Taxon or ecosystem at present is presumed or possibly extinct or eliminated in the wild across their entire native range but is extant in cultivation, in captivity, as a naturalized population (or populations) outside their native range, or as a reintroduced population or ecosystem restoration, not yet established. The “C” modifier is only used at a global level and not at a national or subnational level. Possible ranks are GXC or GHC. This is equivalent to "Extinct in the Wild (EW) in IUCN's Red List terminology (IUCN 2001).|
|T#||Infraspecific Taxon (trinomial) — The status of infraspecific taxa (subspecies or varieties) are indicated by a "T-rank" following the species' global rank. Rules for assigning T-ranks follow the same principles outlined above. For example, the global rank of a critically imperiled subspecies of an otherwise widespread and common species would be G5T1. A T subrank cannot imply the subspecies or variety is more abundant than the species, for example, a G1T2 subrank should not occur. A vertebrate animal population (e.g., listed under the U.S. Endangered Species Act or assigned candidate status) may be tracked as an infraspecific taxon and given a T rank; in such cases a Q is used after the T-rank to denote the taxon's informal taxonomic status.|
NatureServe National and Subnational Conservation Status Definitions
Listed below are definitions for interpreting NatureServe conservation status ranks at the national (N-rank) and subnational (S-rank) levels. The term "subnational" refers to state or province-level jurisdictions (e.g., California, Ontario).
Assigning national and subnational conservation status ranks for species and ecosystems (ecological communities, vegetation types, and systems) follows the same general principles as used in assigning global status ranks. A subnational rank normally would not imply that a species or ecosystem is more secure at the state/provincial level than it is nationally or globally (e.g., a rank of G1S3 is typically invalid), and similarly, a national rank could not exceed the global rank. However, there are cases where a trend factor (e.g. change in area of an ecosystem, or population size of a species) is relatively stable in a jurisdiction, but is strongly declining across most other parts of the range, resulting in a subnational or national rank being more secure than the global rank. Subnational ranks are assigned and maintained by state or provincial NatureServe network programs.
|Presumed Extirpated—Species or ecosystem is believed to be extirpated from the jurisdiction (i.e., nation, or state/province). Not located despite intensive searches of historical sites and other appropriate habitat, and virtually no likelihood that it will be rediscovered. [equivalent to “Regionally Extinct” in IUCN Red List terminology]|
|Possibly Extirpated – Known from only historical records but still some hope of rediscovery. There is evidence that the species or ecosystem may no longer be present in the jurisdiction, but not enough to state this with certainty. Examples of such evidence include (1) that a species has not been documented in approximately 20-40 years despite some searching and/or some evidence of significant habitat loss or degradation; (2) that a species or ecosystem has been searched for unsuccessfully, but not thoroughly enough to presume that it is no longer present in the jurisdiction.|
|Critically Imperiled— At very high risk of extirpation in the jurisdiction due to very restricted range, very few populations or occurrences, very steep declines, severe threats, or other factors.|
|Imperiled— At high risk of extirpation in the jurisdiction due to restricted range, few populations or occurrences, steep declines, severe threats, or other factors.|
|Vulnerable— At moderate risk of extirpation in the jurisdiction due to a fairly restricted range, relatively few populations or occurrences, recent and widespread declines, threats, or other factors.|
|Apparently Secure— At a fairly low risk of extirpation in the jurisdiction due to an extensive range and/or many populations or occurrences, but with possible cause for some concern as a result of local recent declines, threats, or other factors.|
|Secure— At very low or no risk of extirpation in the jurisdiction due to a very extensive range, abundant populations or occurrences, with little to no concern from declines or threats.|
|Range Rank —A numeric range rank (e.g., S2S3 or S1S3) is used to indicate any range of uncertainty about the status of the species or ecosystem. Ranges cannot skip more than two ranks (e.g., SU is used rather than S1S4).|
|Unrankable—Currently unrankable due to lack of information or due to substantially conflicting information about status or trends.|
|Unranked—National or subnational conservation status not yet assessed.|
|Not Applicable —A conservation status rank is not applicable because the species or ecosystem is not a suitable target for conservation activities (e.g., long distance aerial and aquatic migrants, hybrids without conservation value, and non-native species or ecosystems (see Master et al. 2012, Appendix A, pg 70 for further details).|
|Not Provided||Species or ecosystem is known to occur in this nation or state/province. Contact the appropriate NatureServe network program for assignment of conservation status.|
|Inexact Numeric Rank—Denotes inexact numeric rank; this should not be used with any of the Variant National or Subnational Conservation Status Ranks, or NX, SX, NH, or SH.|
|B||Breeding—Conservation status refers to the breeding population of the species in the nation or state/province.|
|N||Non-breeding—Conservation status refers to the non-breeding population of the species in the nation or state/province.|
|M||Migrant—Migrant species occurring regularly on migration at particular staging areas or concentration spots where the species might warrant conservation attention. Conservation status refers to the aggregating transient population of the species in the nation or state/province.|