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Endangered
Species and Spaces
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2.1
Nature Conservancy Ranking System
The British Columbia Conservation
Data Centre (CDC) was established in 1991, to centralize and standardize
data on natural resources in British Columbia, with a particular
focus on rare plants, animals and plant communities. The CDC employs
the U.S. Nature Conservancy’s ranking system, which ranks each
element of biological diversity (species, sub-species, plant community,
special biological feature) at two levels: global (G) and provincial
or subnational (S). Global rank is assigned based on the status
of the element throughout its entire range, and provincial rank
is assigned on its status in British Columbia. The provincial rank
cannot be more common than the global rank, although it could be
the same or more rare. This system assigns a number from one to
five based primarily on the number of extant (still existing) occurrences
of the element. Other factors such as abundance, range, protection,
trends and threats are also considered (Harcombe, 1994). The tables
below provide definitions for the ranks and modifiers used by the
CDC.
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Table1: Conservation
Data Centre Ranks and Definitions
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Rank |
Category |
Definition |
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1 |
Critically imperiled |
Extremely rare (5 or fewer extant
occurrences or very few remaining individuals) or some factor(s)
make it especially vulnerable to extirpation or extinction. |
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2 |
Imperiled |
Rare (typically 6-20 extant occurrences
or few remaining individuals) or some factor(s) make it vulnerable
to extirpation or extinction. |
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3 |
Rare or uncommon |
Typically 21-100 extant occurrences;
may be susceptible to large-scale disturbances, such as loss
of extensive peripheral populations. |
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4 |
Frequent to common |
Greater than 100 occurrences:
apparently secure but may have a restricted distribution or
future threats may be perceived. |
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5 |
Common to very common |
Demonstrably secure and essentially
ineradicable under present conditions. |
Source:
Harcombe, A. 1994. Ch.2. in Biodiversity in British Columbia.
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Table 2: Conservation Data Centre Rank Modifiers
| Rank
Modifier |
Definition |
| H |
Historical
Occurrence; usually not verified in the last 40 years,
but with the expectation that it may be rediscovered. |
| X |
Apparently extinct or extirpated,
without the expectation that it will be rediscovered. |
| U |
Status uncertain, often because
of low search effort or cryptic nature of the element;
uncertainty spans a range of 4 or 5 ranks. |
| R |
Reported from the province,
but without persuasive documentation for either accepting
or rejecting the report. |
| RF |
Reported in error, but this
error has persisted in the literature. |
| ? |
No information is available
or the number of extant occurrences is based on a "best
guess". |
| A |
An element (usually an animal)
that is considered accidental or casual in the province;
a species that does not appear on an annual basis. |
| E |
An exotic or introduced species
to the province. |
| Z |
Occurs in the province but as
a diffuse, usually moving population; difficult or impossible
to map static occurrences. |
| T |
Designates a rank associated
with a subspecies. |
| B |
Breeding; the associated rank
refers to breeding occurrences of mobile animals. |
| N |
Non-breeding; the associated
rank refers to non-breeding occurrences of mobile animals. |
| Q |
Taxonomic validity of the element is
not clear or is in question. |
Source:
Harcombe, A. 1994. Ch.2. in Biodiversity in British Columbia. Harding
L. and McCullum E. Ed’s. |
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