Conservation status (TNC)
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The Nature Conservancy has developed its own conservation status ranking system.
In their system, G codes refer to rankings made at the global level, N codes refer to rankings made at a national level and S codes refer to rankings made at the sub-regional level, such as states within the US:
- X - presumed extinct (not located despite extensive searches)
- H - possibly extinct [or h historical occurrence (still some hope of discovery)]
- 1 - critically imperilled (typically five or fewer occurrences or 1 000 or fewer individuals)
- 2 - imperilled (typically six to twenty occurrences or 1 000 to 3 000 individuals)
- 3 - vulnerable (rare; typically 21 to 100 occurrences or 3 000 to 10 000 individuals)
- R or ? - Recorded within nation or state, but local status not available; when combined with global rank of G1 to G3, local status is 'Indeterminate'
- 4 - Apparently secure (uncommon but not rare; some cause for long-term concern, usually more than 100 occurrences and 10,000 individuals)
- 5 - Secure (common, widespread and abundant)
Thus, for example, a G3 species is "globally vulnerable", and an N2 species is "nationally imperilled" for whatever country the rank is assigned. Species with G, N, or S rankings of 4 or 5 are generally not the basis for major conservation actions.