Explanation of S-Rankings
S-Rank, or subnational rank is a method used to determine the rarity of a given species within subnational boundaries such as a province or state. This ranking method is widely used by Conservation Data Centres across North America.
Listed below are the definitions for the S-Rankings used by the Saskatchewan Conservation Data Centre. I will often refer to a plant's S-Rank in my species description.
S1 - Extremely rare in Saskatchewan. Usually 5 or fewer occurrences in the province, or very few remaining hectares; often especially vulnerable to extirpation.
S2 - Very rare in Saskatchewan. Usually between 5 and 20 occurrences in the province, or few remaining hectares, or with many individuals in fewer occurrences; often susceptible to extirpation.
S3 - Rare to uncommon in Saskatchewan. Usually between 20 and 100 occurrences in the province; may have fewer occurrences, but with a large number of individuals in some populations; may be susceptible to large-scale disturbances. Most species with an S3 rank are assigned to the watch list, unless they have a relatively high global rank.
S4 - Common and apparently secure in Saskatchewan; usually with more than 100 occurrences in the province.
S5 - Common to widespread in Saskatchewan and demonstrably secure.