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Recovery Strategy for the Muhlenberg's Centaury (Centaurium muehlenbergii) in Canada

2013

Table of Contents

Muhlenberg’s Centaury in flower. © Matt Fairbarns
© Matt Fairbarns

Recovery Strategy for the Muhlenberg's Centaury (Centaurium muehlenbergii) in Canada
2013

Recommended Citation:

Parks Canada Agency. 2013. Recovery Strategy for the Muhlenberg’s Centaury (Centaurium muehlenbergii) in Canada. Species at Risk Act Recovery Strategy Series. Parks Canada Agency, Ottawa. vi + 22 pp.

For copies of the recovery strategy, or for additional information on species at risk, including COSEWIC Status Reports, residence descriptions, action plans, and other related recovery documents, please visit the Species at Risk Public Registry.

Cover illustration: Muhlenberg’s Centaury photograph by Matt Fairbarns

Également disponible en français sous le titre
« Programme de rétablissement de la petite centaurée de Muhlenberg (Centaurium muehlenbergii) au Canada »

© Her Majesty the Queen in Right of Canada, represented by the Minister of the Environment, 2013. All rights reserved.
ISBN 978-1-100-22116-8
Catalogue no. En3-4/155-2013E-PDF

Content (excluding the illustrations) may be used without permission, with appropriate credit to the source.

Preface

The federal, provincial, and territorial government signatories under the Accord for the Protection of Species at Risk (1996) agreed to establish complementary legislation and programs that provide for effective protection of species at risk throughout Canada. Under the Species at Risk Act (S.C. 2002, c.29) (SARA), the federal competent ministers are responsible for the preparation of recovery strategies for listed Extirpated, Endangered, and Threatened species and are required to report on progress within five years.

The Minister of the Environment and the Minister responsible for the Parks Canada Agency is the competent minister for the recovery of the Muhlenberg’s Centaury and has prepared this strategy, as per section 37 of SARA. It has been prepared in cooperation with Songhees First Nation and the provincial government of British Columbia.

Success in the recovery of this species depends on the commitment and cooperation of many different constituencies that will be involved in implementing the directions set out in this strategy and will not be achieved by the Parks Canada Agency, or Environment Canada, or any other jurisdiction, alone. All Canadians are invited to join in supporting and implementing this strategy for the benefit of the Muhlenberg’s Centaury and Canadian society as a whole.

This recovery strategy will be followed by one or more action plans that will provide information on recovery measures to be taken by the Parks Canada Agency and/or Environment Canada and other jurisdictions and/or organizations involved in the conservation of the species. Implementation of this strategy is subject to appropriations, priorities, and budgetary constraints of the participating jurisdictions and organizations.

Muhlenberg’s Centaury is a species that inhabits vernal pools associated with Garry Oak ecosystems and recovery of this species will be integrated with the recovery of species in the Recovery Strategy for Multi-Species at Risk in Vernal Pools and Other Ephemeral Wet Areas in Garry Oak and Associated Ecosystems in Canada (Parks Canada Agency 2006).

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Recommendation and Approval Satement

The Parks Canada Agency led the development of this federal recovery strategy, working together with the other competent minister(s) for this species under the Species at Risk Act. The Chief Executive Officer, upon recommendation of the relevant Park Superintendent(s) and Field Unit Superintendent(s), hereby approves this document indicating that Species at Risk Act requirements related to recovery strategy development have been fulfilled in accordance with the Act.

Recommended by:

____________________________________________________
Helen Davies
Field Unit Superintendent, Coastal BC, Parks Canada Agency

Approved by:

____________________________________________________
Alan Latourelle
Chief Executive Officer, Parks Canada Agency

signatures

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Acknowledgments

Thank you to Matt Fairbarns and Michael Miller for writing the draft recovery strategy. The Garry Oak Ecosystems Recovery Team is the recovery team for the Muhlenberg’s Centaury and was involved in the development of this recovery strategy. Further revision was the result of comments and edits provided by a number of organizations: the Province of British Columbia, Parks Canada Agency, and Environment Canada.

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Executive Summary

The Canadian population of the Muhlenberg’s Centaury (Centaurium muehlenbergii) was assessed as Endangered in 2008 by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), and in February 2010 the population was listed as Endangered under Canada’s Species at Risk Act (SARA).

Muhlenberg’s Centaury is a small annual plant that grows 3 to 30 cm in height from a taproot and bears small pink to white tube-shaped flowers. Its range is restricted to North America where it occurs in moisture-receiving areas, such as vernal pools and seeps along the edges of coastal salt marshes. In Canada, Muhlenberg’s Centaury is known from three isolated sites, two sites on southeastern Vancouver Island and one site on an adjacent Gulf Island. The Canadian population of Muhlenberg’s Centaury comprises <1% of its global range.

The key factors limiting the recovery and survival of the Muhlenberg’s Centaury populations in Canada are its specificity to rare vernal depression habitats, limited dispersal abilities, weak competitive ability, predisposition to demographic failure, small area of physical occupancy, and small, highly fragmented populations that constrain genetic diversity. The Muhlenberg’s Centaury populations are threatened by land conversion caused by urban development, encroachment of native and alien plants, trampling and soil compaction caused by recreational activities, grazing by introduced geese, and climate change as it relates to changes in precipitation.

In the short term, recovery activities for the Muhlenberg’s Centaury will focus on the maintenance of known populations and habitat while exploring the feasibility of establishing and/or augmenting populations to increase abundance and distribution. Broad strategies to address the threats to the survival and recovery of the Muhlenberg’s Centaury are presented in section 6 Broad Strategies and General Approaches to Meet Objectives.

Critical habitat for the recovery of Muhlenberg’s Centaury is identified in this recovery strategy. The best available information has been used to identify critical habitat; however, there are significant knowledge gaps and additional critical habitat will need to be identified in upcoming planning documents to meet the population and distribution objectives.

Further recovery action for Muhlenberg’s Centaury will be incorporated into one or more action plans by 2018.

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Recovery Feasibility Summary

Recovery of this species is considered feasible based on the criteria outlined by the Government of Canada (2009):

  1. Individuals of the wildlife species that are capable of reproduction are available now or in the foreseeable future to sustain the population or improve its abundance.

    Yes. All three extant populations support at least one reproductive individual, while one population supports several thousand reproductive individuals in favourable years. The species appears to be globally secure (G5) so in the event of local extirpation, seed could be collected from populations in the United States and used to restore the Canadian population.

  2. Sufficient suitable habitat is available to support the species or could be made available through habitat management or restoration.

    Yes. Existing habitats have supported self-sustaining populations of the Muhlenberg’s Centaury for at least 40 years. It is likely that additional suitable habitat could be made available through active habitat stewardship or restoration, if needed.

  3. The primary threats to the species or its habitat (including threats outside Canada) can be avoided or mitigated.

    Yes. Some threats, such as competition from invasive species, can be reduced by a regular program to maintain the sites. Other threats, such as urbanization, will be more difficult to avoid or mitigate. There may be other important threats that have not yet been identified. However, at present there is no evidence of unavoidable threats to the species or its habitat that would preclude recovery.

  4. Recovery techniques exist to achieve the population and distribution objectives or can be expected to be developed within a reasonable timeframe.

    Yes. Recovery success will be tied primarily to threat reduction through habitat stewardship in combination with long-term population monitoring and inventory. While the feasibility of introducing/re-introducing populations at the northern edge of the range is still unknown, over the long term, recovery techniques for population establishment and augmentation are likely to be developed.

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1. COSEWIC Species Assessment Information

Date of Assessment: April 2008

Common Name (population): Muhlenberg’s Centaury

Scientific Name:Centaurium muehlenbergii

COSEWIC Status: Endangered

Reason 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.

Canadian Occurrence:British Columbia

COSEWIC Status History:Designated Endangered in April 2008. Assessment based on a new status report.

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2. Species Status Information

The Canadian population of Muhlenberg’s Centaury (Centaurium muehlenbergii) was assessed as Endangered in 2008 by the Committee on Status of Endangered Wildlife in Canada (COSEWIC). In February, 2010, the population was listed as Endangered under Canada’s Species at Risk Act (SARA) affording it legal protection. Conservation ranks are provided in Table 1. The Muhlenberg’s Centaury population in Canada comprises <1% of its global range.

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Table 1. Conservation ranks for Muhlenberg's Centaury. Sources: B.C. Conservation Data Centre 2011, NatureServe 2010.
LocationRank1Rank Description
GlobalG5?Secure
CanadaN1Critically imperiled
  British ColumbiaS1Critically imperilled
United StatesN5?Secure
  CaliforniaSNRUnranked
  IdahoSNRUnranked
  NevadaSNRUnranked
  OregonSNRUnranked
  MontanaSNRUnranked
  WashingtonSHPossibly extirpated (historical)

1 NatureServe Conservation ranks are based on a one to five scale, ranging from critically imperilled (1) to demonstrably secure (5). Status is assessed and documented at three distinct geographic scales global (G), national (N), and state/province (S).

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3. Species Information

3.1. Species Description

Muhlenberg’s Centaury is a small annual vascular plant which grows 3 to 30 cm in height from a taproot. The basal leaves form a conspicuous rosette of egg-shaped leaves (which often wither by flowering time). The upper stem leaves are oppositely arranged, narrower than the basal leaves, and pointed. The few, pink to white flowers are small and tube-shaped. A detailed description of the species is provided in the status report (COSEWIC 2008).

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3.2. Population and Distribution

Muhlenberg’s Centaury occurs from southwestern British Columbia south to California and Nevada (Figure 1). It is currently reported to be extirpated from Washington in spite of a 1992 report from San Juan Island (COSEWIC 2008).

In Canada, Muhlenberg’s Centaury is known from three isolated sites: two on southeastern Vancouver Island and one on an adjacent Gulf Island (Figure 2). The Joan Point population near Nanaimo was first recorded in 2003, the Uplands Park population in Oak Bay in 1961, and the Gulf Islands population on the east side of Chatham Island in 1933 (COSEWIC 2008).

In 2009, the population at Joan Point consisted of only two small plants, while there were between 6,000 and 7,000 plants in the largest population at Uplands Park (Matt Fairbarns pers. obs. 2009). The Chatham Island population was not examined in 2009, but probably consists of fewer than 100 individuals since there were only 30 plants in 2003 (COSEWIC 2008) and conditions on the site do not appear to have changed significantly since then.

It is likely that Muhlenberg’s Centaury was more widespread historically. Presently the species' distribution is highly disjunct over a relatively large region of southeastern Vancouver Island and the Gulf Islands (Figure 2). Further, it occupies a variety of moisture-receiving habitat types across its distribution in Canada. The preceding two points imply that the species was not historically restricted to its present small area of occupancy.

Both the Uplands Park and Chatham Island populations have persisted in small areas for at least 40 and 70 years, respectively, suggesting that population dynamics at these locations have remained relatively stable over time (COSEWIC 2008).

 

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Map of the North American distribution
© From COSEWIC

Figure 1 . Distribution of Muhlenberg's Centaury in North America (from COSEWIC 2008). Possibly extirpated in Washington State and hatched circles are reported occurrences that are presumed to be incorrectly identified (COSEWIC 2008).

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Map of British Columbian distribution
© Her Majesty the Queen in Right of Canada.

Figure 2: Range of Muhlenberg's Centaury in Canada (adapted from COSEWIC 2008). Circles indicate extant sites (1 = Joan Point, 2 = Uplands Park, 3 = Chatham Island).

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3.3. Needs of the Muhlenberg's Centaury

Across its range in North America, Muhlenberg’s Centaury is found within various community types where it grows in moisture-receiving areas on poorly drained Gleysol or Sombric Brunisol soils or on materials too thin to be defined as soil. The rooting zone is usually composed of silt and/or clay and drainage is impeded by a lower layer of marine clay and/or bedrock. In the U.S., where it is federally classified as a facultative wetland species (USDA-NRCS 2011), it has been reported from coastal bluffs, wet openings in woods, moist upland prairies, valley grassland, northern juniper woodland, and serpentine grassland (COSEWIC 2008).

In Canada, Muhlenberg’s Centaury is found in the Coastal Douglas-fir biogeoclimatic zone where it known from three rather distinct habitat types: vernal seep, vernal swale, and saltgrass marsh. The Coastal Douglas-fir Biogeoclimatic Zone features a Mediterranean-like climate with warm, dry summers and mild, wet winters--summer drought is an important climatic feature which influences vegetation in this biogeoclimatic zone. The Joan Point population occurs on a sloping, vernal seep at the edge of a Douglas-fir (Pseudotsuga menziesii) and Arbutus (Arbutus menziesii) forest (COSEWIC 2008). The Uplands Park population is located in a vernal swale, in a seasonally flooded meadow, within a Garry Oak (Quercus garryana) woodland at an elevation of 10 m (Figure 3). The Chatham Island plants grow just above the high tide mark on bare, sandy ground at the edge of a saltgrass (Distichlis spicata) marsh.

Given the broad ecological amplitude displayed by Muhlenberg’s Centaury across its range and our currently limited understanding of its physiological needs, few generalizations can be made as to specific habitat requirements. In Canada, the species appears to thrive best in moisture-receiving sites that become wetted in the winter and dry out in summer. It appears to be intolerant of shade and may depend on periodic fire to maintain open habitat and limit competition.

Habitat of Muhlenberg&#8217;s Centaury at Uplands Park.
© Matt Fairbarns

Figure 3. Habitat of Muhlenberg's Centaury at Uplands Park. Photos by Matt Fairbarns.

A number of factors may limit the survival and recovery of Muhlenberg’s Centaury in Canada including the following:

  1. Dependence on vernally moist depressions in Garry Oak and associated ecosystems (at least in Canada), most of which have been lost or damaged by habitat conversion, forest encroachment, and/or a shift to ecosystem dominance by invasive alien plants (COSEWIC 2008).
  2. Lack of special structures to aid in the long distance dispersal of seeds or fruits (COSEWIC 2008).
  3. Apparently weak competitive ability, especially with respect to invasive alien species (COSEWIC 2008).
  4. Potential demographic failure if there are extended dry periods in the late winter and early spring, before plants can reproduce and replenish the seed bank.
  5. Very small area of physical occupancy which leaves it susceptible to chance events including those which operate at a small scale.
  6. Small, highly fragmented populations which may constrain the species’ genetic diversity and limit the potential for local rescue effects (COSEWIC 2008).

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Introduction / Species Information