Muhlenberg's centaury (Centaurium muehlenbergii COSEWIC assessment and status report: chapter 11

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Technical Summary

Centaurium muehlenbergii

Muhlenberg’s centaury - petite-centaurée de Muhlenberg

Range of Occurrence in Canada : SW British Columbia

Demographic Information

Generation time (average age of parents in the population) <1 yrs

Population trend and dynamics

Observed percentage of reduction in total number of mature individuals over the last 10 years. Unknown

Projected percentage of reduction in total number of mature individuals over the next 10 years. Unknown

Observed percentage reduction in total number of mature individuals over any 10-year period, over a time period including both the past and the future. Unknown

Are the causes of the decline clearly reversible? Unknown

Are the causes of the decline clearly understood? Several impacts are known or suspected as limitations : Yes

Are the causes of the decline clearly ceased? No

Observed trend in number of populations . Historical decline; recent unknown. Unknown

Are there extreme fluctuations in number of mature individuals? Unknown but likely being an annual. Unknown

Are there extreme fluctuations in number of populations? No

Extent and Area Information

Estimated extent of occurrence (km²)

Estimate is based on recent survey data and data from B.C. Conservation Data Centre, and represents roughly the area of the triangle formed by Nanaimo, Oak Bay, and nearby Gulf Islands. Historical 1911 Vancouver locality is excluded from EO estimate : 160 km²

Observed trend in extent of occurrence : Unknown

Are there extreme fluctuations in extent of occurrence? No

Estimated area of occupancy (km²) . Actual area occupied, based on authors’ observations at occupied sites and on personal communication with A. Ceska, is about 110 m square. The Area of Occupancy based on a 1x1 km grid is 3 km²; that based on a 2x2 km grid is 12 km² <20 km²

Observed trend in area of occupancy : Stable

Are there extreme fluctuations in area of occupancy? No

Is the total population severely fragmented? Yes

Number of current locations : 3

Trend in number of locations. The most recent collection simply represents a discovery of a previously existing and overlooked population. The trend is unknown, but likely stable since two of the populations have been known for at least 40 years. Unknown

Are there extreme fluctuations in number of locations? No

Observed trend in quality of habitat : Decline

Quantitative Analysis

Threats (actual or imminent, to populations or habitats)

1. Invasive species encroachment –OakBay, Nanaimo
2. Trampling by walkers, dogs, and bicycles; dog scat – Oak Bay, Nanaimo
3. Urbanization/residential development – limited threats from presence of adjacent residential properties at Oak Bay
4. Off-road vehicles – Oak Bay, Nanaimo (some population loss at Oak Bay)
5. Hydrologic alterations – perhaps mainly of historic impact on the populations
6. Fire suppression – ongoing concern
7. Grazing by Canada geese and contamination from guano deposits – potential threat but not yet substantiated

Rescue Effect (immigration from an outside source)

Status of outside population(s)? USA: apparently secure in OR, NEV, CA and ID; presumed extirpated in WA

Is immigration known or possible? No

Would immigrants be adapted to survive in Canada? Unknown

Is there sufficient habitat for immigrants in Canada? Yes

Is rescue from outside populations likely? No

Current Status

COSEWIC: Endangered 2008

Status and Reasons for Designation

Status: Endangered

Alpha-numeric code: B1ab(iii)+2ab(iii)

Reasons for Designation: This small annual plant occurs in only three small areas of mainly wet habitat in southwestern British Columbia. Its total Canadian population consists of fewer than 1000 plants. These are highly disjunct from the main range of the species that extends from Oregon to California and Nevada. The species is at continued risk from such factors as the spread of invasive plants and human activities including trampling in areas used for recreational activities.

Applicability of Criteria

Criterion A: (Decline in Total Number of Mature Individuals): Not applicable. No decline data

Criterion B: (Small Distribution Range and Decline or Fluctuation): Meets Endangered B1ab(iii)+2ab(iii). Extent of occurrence and area of occupancy are below critical values; it is severly fragmented with 3 widely separated locations known, with continuing decline inferred in quality of habitat based on existing threats.

Criterion C: (Small and Declining Number of Mature Individuals): Not applicable. Although the actual number of mature individuals is <2500, and at least 95% of the total population occurs at one site, Endangered C2a(ii) could not be applied because a projected decline in total number of mature individuals could not be inferred with certainty since two of the populations have been known for over 40 years.

Criterion D: (Very Small Population or Restricted Distribution): Meets Threatened D1, D2. Mature individuals are <1000 and the Area of Occupancy is much <20 km² with ongoing threats.

Criterion E: (Quantitative Analysis): None available