Hill’s thistle (Cirsium hillii) COSEWIC assessment and status report: chapter 11
Technical Summary
Cirsium hillii
Hill's thistle – Chardon de Hill
Range of Occurrence in Canada:
Ontario
Extent and Area Information
Extent of occurrence (EO) (km²)
3,000 km². (Based on GIS calculation of a polygon in which all points at outer limits of range are included)
Specify trend in EO
Stable currently with decline historically
Are there extreme fluctuations in EO?
No
Area of occupancy (AO) (km²)
30 km². (Estimated as noted in text of report)
Specify trend in AO
Decline
Are there extreme fluctuations in AO?
No
Number of known or inferred current locations
64
Specify trend in #
Decline from 70 to 64 (mainly historical losses)
Are there extreme fluctuations in number of locations?
No
Specify trend in area, extent or quality of habitat
Declining
Population Information
Generation time (average age of parents in the population)
3 years
Number of mature individuals
About 500 flowering plants estimated
Total population trend:
Unknown
% decline over the last/next 10 years or 3 generations.
Unknown
Are there extreme fluctuations in number of mature individuals?
No
Is the total population severely fragmented?
Likely not
Specify trend in number of populations
6 of the 70 populations known have been extirpated but mainly prior to the last several decades
Are there extreme fluctuations in number of populations?
No
List populations with number of mature individuals in
Threats (actual or imminent threats to populations or habitats)
- Main threats: Aggregate demand; Limited habitat (restricted to alvars, savannahs, and open woodlands); Successional change & lack of disturbance; Shoreline development; ATVs and trail bikes; Conversion to agriculture
- Minor or potential threats: Invasive Species (mainly of potential threat); Deer browse
Rescue Effect (immigration from an outside source)
Status of outside population(s)?
USA: Rare (S1 or S3) in all six US states where it occurs
Is immigration known or possible?
Possible
Would immigrants be adapted to survive in Canada?
Likely
Is there sufficient habitat for immigrants in Canada?
Probably
Is rescue from outside populations likely?
Possible but not likely
Quantitative Analysis
Not applicable
Current Status
COSEWIC:Threatened November 2004
Status and Reasons for Designation
Status: Threatened
Alpha-numeric code: Met criterion for Endangered, C2a(i), but designated Threatened, C2a(i); D1, because the species is not at imminent risk of extirpation due to the occurrence of numerous sites, some in protected areas.
Reasons for Designation: This is a perennial herb restricted to the northern midwestern states and adjacent Great Lakes that is found in open habitats on shallow soils over limestone bedrock. In Ontario, it is found at 64 extant sites but in relatively low numbers of mature flowering plants that are estimated to consist of fewer than 500 individuals. Some populations are protected in national and provincial parks, however, the largest population is at risk from aggregate extraction. On-going risks are present from shoreline development, ATV use, and successional processes resulting from fire suppression within its habitat.
Applicability of Criteria
- Criterion A (Declining Total Population): Not met (Insufficient data)
- Criterion B (Small Distribution, and Decline or Fluctuation): Not met (Too many sites and no fragmentation or extreme fluctuation in population size)
- Criterion C (Small total population size and decline): Meets Endangered C2ai with <2500 mature individuals and no population with >250 flowering plants but recommended as Threatened. Imminent extirpation is unlikely because of the occurrence of numerous sites, presence of about 1/3 of the populations in protected areas, few recent losses and not all sites have been completely surveyed. However, significant risks are present to the largest population containing mature plants and there is on-going degradation of habitat through successional changes and shoreline development.
- Criterion D (Very Small Population or Restricted Distribution): Meets Threatened D1 with <1000 mature plants
- Criterion E (Quantitative Analysis): Not met (Insufficient data)
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