NatureServe Global 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.
A note about rounded ranks. NatureServe Explorer now allows users the option to view search results as rounded ranks. As the table below shows, one variant in the ranking system is a range rank, which communicates uncertainty associated with conservation status ranks. For example, incomplete survey data may lead to the designation of a species or ecosystem as G1G2. Rounded ranks convert conservation status ranks to a single value that is easier to interpret and summarize. Range ranks that span adjacent ranks (e.g., G1G2 or G4G5) are rounded to the more imperiled rank (e.g., G1G2 is rounded to G1). Range ranks that span three ranks (e.g., G2G4) are rounded to the rank in the middle of the range (e.g., G2G4 is rounded to G3).
| GLOBAL RANK | DEFINITION |
|---|---|
| GX |
Presumed Extinct (species) — Not located despite intensive searches and virtually no likelihood of rediscovery Presumed Collapsed (ecosystem) — Collapsed 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 Collapsed (ecosystem) — 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 in human-dominated landscapes 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 collapsed throughout its range. |
| G1 | Critically Imperiled — At very high risk of extinction or collapse 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 collapse due to restricted range, few populations or occurrences, steep declines, severe threats, or other factors. |
| G3 | Vulnerable — At moderate risk of extinction or collapse 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 collapse 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 collapse due to a very extensive range, abundant populations or occurrences, and little to no concern from declines or threats. |
| RANK | DEFINITION |
|---|---|
| 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). |
| RANK | DEFINITION |
|---|---|
| ? | 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). |
| RANK | DEFINITION |
|---|---|
| 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, territory, province, or tribal-level jurisdictions (e.g., California, Ontario).
Assigning national and subnational conservation status ranks for species and ecosystems (ecological vegetation types, natural communities) 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, territory, provincial, or tribal NatureServe Network programs.
| RANK | DEFINITION |
|---|---|
|
NX SX |
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] |
|
NH SH |
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 in human-dominated landscapes 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. |
|
N1 S1 |
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. |
|
N2 S2 |
Imperiled— At high risk of extirpation in the jurisdiction due to restricted range, few populations or occurrences, steep declines, severe threats, or other factors. |
|
N3 S3 |
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. |
|
N4 S4 |
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. |
|
N5 S5 |
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. |
| RANK | DEFINITION |
|---|---|
|
N# S# |
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). |
|
NU SU |
Unrankable—Currently unrankable due to lack of information or due to substantially conflicting information about status or trends. |
|
NNR SNR |
Unranked—National or subnational conservation status not yet assessed. |
|
NNA SNA |
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 49 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. |
| RANK | DEFINITION |
|---|---|
|
N#? S#? |
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. |
| RANK | DEFINITION |
|---|---|
| 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. |
Relationship to Other Status Designations: NatureServe conservation status ranks are a valuable complement to legal status designations assigned by government agencies such as the U.S. Fish and Wildlife Service and the National Marine Fisheries Service in administering the U.S. Endangered Species Act (ESA), and the Canadian Ministry of Environment and Climate Change in administering the Species at Risk Act (SARA). NatureServe status ranks and accompanying documentation may be used by these agencies in making official determinations, particularly in the identification of candidates for legal protection. Because NatureServe assessment procedures—and subsequent lists of imperiled and vulnerable species—have different criteria, evidence requirements, purposes, and taxonomic coverage than official lists of endangered and threatened species, they do not necessarily coincide. Assessment by NatureServe of any species as being critically imperiled (G1), imperiled (G2), or vulnerable (G3) does not constitute a recommendation by NatureServe for listing under the U.S. ESA or Canadian SARA.
The International Union for Conservation of Nature’s (IUCN’s) Red List of Threatened Species is similar in concept to NatureServe's global conservation status assessments. Due to the independent development of these two systems, however, minor differences exist in their respective criteria and implementation. One study showed that when applied by experienced assessors using comparable information, the outputs from the two systems are generally concordant. NatureServe is a founding member of the IUCN SSC Red List Committee, and in the region covered by NatureServe Explorer, NatureServe status ranks and their underlying documentation often inform Red List assessments. NatureServe also participates in the IUCN Red List of Ecosystems Committee.