|Threat||Level of Concern2||Extent||Occurrence||Frequency||Severity3||Causal Certainty4|
|Habitat loss or degradation|
|Invasion by invasive alien herbaceous plants||High||Widespread||Current||Continuous||Medium-high||Medium|
|Grazing by introduced Canada Geese||Low||Localized||Current||Recurrent||Medium||Low|
|Habitat loss or degradation|
|Housing and urban development||Medium||Localized||Historic and anticipated||Unknown||Medium-high||Medium|
|Disturbance or harm|
|Trampling and soil compaction||Medium||Localized||Recurrent||Recurrent||Medium-high||Medium|
|Climate change and natural disasters|
|Change in weather patterns, especially spring and early summer precipitation||Medium||Widespread||Anticipated||Seasonal||Unknown||Low|
|Changes in ecological dynamics or natural processes|
|Encroachment of native and alien woody vegetation||Medium||Localized||Current||Continuous||Medium||Medium-low|
2 Level of Concern: signifies that managing the threat is of (high, medium or low) concern for the recovery of the species, consistent with the population and distribution objectives. This criterion considers the assessment of all the information in the table).
3 Severity: reflects the population-level effect (High: very large population-level effect, Moderate, Low, Unknown).
4 Causal certainty: reflects the degree of evidence that is known for the threat (High: available evidence strongly links the threat to stresses on population viability; Medium: there is a correlation between the threat and population viability e.g., expert opinion; Low: the threat is assumed or plausible).
4.2.1. Alien, Invasive or Introduced Species
The most serious immediate threat to Muhlenberg’s Centaury in Canada is posed by the invasion of alien herbaceous plant species (Table 2). These alien species are abundant in the vernally moist areas where Muhlenberg’s Centaury occurs and dominate similar habitats throughout its range in Canada. Many of the non-woody invasive alien species, including Sweet Vernal Grass (Anthoxanthum odoratum) and Creeping Bentgrass (Agrostis stolonifera), have contributed to the accumulation of thatch which provides difficult germination conditions, especially for small-seeded annual species such as Muhlenberg’s Centaury. While all of the invasive alien species compete for space, tufted or rosette-forming perennials, such as Ribwort Plantain (Plantago lanceolata), Hairy Cat’s-ear (Hypochaeris radicata), and Hairy Hawkbit (Leontodon taraxacoides), are most problematic because they pre-empt large areas of soil for many years. Invasive alien plant species compete strongly for moisture and nutrients, which disadvantages small annuals such as Muhlenberg’s Centaury that possess shallow, small root systems. Accordingly, this threat is considered to be a high level of concern.
At present, grazing by introduced, resident Canada Geese presents a minor threat to populations of Muhlenberg’s Centaury in Uplands Park and at the Chatham Island site. However, Goose populations appear to be increasing rapidly throughout the region and are causing damage to many coastal meadows and vernal depressions through trampling, direct grazing on most herbaceous species, and fouling by guano. This threat is considered a low level of concern at present.
4.2.2. Habitat Loss and Degradation
Habitat conversion caused by housing and urban development is an anticipated threat to Muhlenberg’s Centaury throughout its range in Canada. Loss of suitable habitat and habitat fragmentation can result in population isolation, reducing the ability of extant populations to disperse to new sites. Further, as Muhlenberg’s Centaury relies on vernal pools, hydrologic alterations caused by nearby habitat conversion can disrupt life cycle processes and cause physiological stress. While two of the three populations appear to be secure from housing and urban development over the foreseeable future, the Joan Point population lies within a proposed residential development. Consequently, this threat was considered a medium level of concern.
4.2.3. Disturbance or Harm
Trampling and soil compaction caused by pedestrian, bicycle, dog, and off-road vehicle traffic can lead to altered hydrological regimes and facilitate the establishment of invasive alien species. The Joan Point population, which occurs in an opening adjacent to a hiking trail, will receive increased pressure as trail use increases along with residential development. The Uplands Park population receives heavy pedestrian, bicycle, and dog use, which can be particularly detrimental as soils dry out during the flowering and fruiting periods. Off-road vehicle traffic is not permitted at either the Joan Point or Uplands Park sites and is not likely to occur on the Chatham Island site where the third population occurs. Despite these prohibitions, trespass use may occur at the Joan Point site, and tire tracks have been repeatedly observed at the Uplands Park. Until off-road vehicle and bicycle traffic can be controlled, it presents a direct trampling threat to Muhlenberg’s Centaury. Overall, this threat is considered a medium level of concern.
4.2.4. Climate Change and Natural Disasters
Climate change may have devastating effects on vernal pool environments. Research predicts warmer conditions and drier summers in south-western British Columbia as part of a broader pattern of global climate change (Rodenhuis et al. 2007). Small, vernally moist depressions such as those which support Muhlenberg’s Centaury are probably at greatest risk, particularly to changes in precipitation and evaporation losses which determine the duration of continuous inundation, the frequency of inundation events suited to the reproduction of vernal pool species, and the seasonal distribution of inundation (Pyke 2005). While the loss of some vernally moist depressions may be offset by the improvement of currently marginal habitats, the latter are unlikely to develop populations of Muhlenberg’s Centaury without human intervention because of the species’ apparently weak powers of dispersal. This threat was considered a medium level of concern.
4.2.5. Changes in Ecological Dynamics or Natural Processes
Encroachment by native and alien woody species is of relatively less significance because woody species tend to occur only along the periphery of the moist areas where Muhlenberg’s Centaury itself grows. Neither native nor alien woody species are able to grow well on microhabitats favoured by Muhlenberg’s Centaury because of the prolonged saturation in winter and the extreme drought in summer. Nevertheless, woody species may encroach on better-drained microsites within the Joan Point population and along the periphery of both the Joan Point and Uplands Park populations. As woody species encroach, they may reduce the viability of Muhlenberg’s Centaury populations by casting shade and altering hydrological conditions. This threat is considered to be a medium level of concern.
In Canada, Muhlenberg's Centaury is found in vernally moist habitats associated with Garry Oak ecosystems and as such had a naturally, highly restricted range. Within this range, significant habitat loss since European settlement (Lea 2006) has likely resulted in population reductions. Encroachment of vegetation, development, and effects resulting from recreational activities continue to exacerbate the situation (COSEWIC 2008). Given the permanent loss of most of the original habitat, it is not possible to recover the species to its natural area of occupancy or to its original probability of persistence. There are currently three known Muhlenberg's Centaury populations in Canada, one of which had two individuals at last count (COSEWIC 2008, Fairbarns 2009, pers. comm.).
In general, it is believed that multiple populations and thousands of individuals are likely required to attain a high probability of long-term persistence for a species (Reed 2005, Brook et al. 2006, and Traill et al. 2009). In an analysis of several published estimates of minimum viable population (MVP) sizes, Traill et al. (2007) found that the median population size required for plants to achieve a 99% probability of persistence over 40 generations was approximately 4,800 individuals (but see Flather et al. 2011, Garnett and Zander 2011, and Jamieson and Allendorf 2012 for critical evaluations of the analyses and the applicability of the results). Such information provides a useful guide, but developing specific quantitative and feasible objectives must consider more than just generalized population viability estimates, including the historic number of populations and individuals, the carrying capacity of extant (and potential) sites, the needs of other species at risk that share the same habitat, and whether it is possible to establish and augment populations of the species (Parks Canada Agency 2006, Flather et al. 2011, Jamieson and Allendorf 2012). Because not enough of this information is available for Muhlenberg's Centaury, it is currently not possible to determine to what extent recovery is feasible and therefore, it is not possible to establish quantitative long-term objectives. Recovery planning approaches (see Section 6) are designed to respond to knowledge gaps so that long-term, feasible, and quantitative recovery objectives regarding size and number of populations can be set in the future. At this time it is possible to set short-term objectives that focus on maintaining known populations and habitat while exploring the feasibility of establishing and/or augmenting populations to increase abundance and distribution:
Objective 1: Maintain the Uplands Park and Chatham Island populations of Muhlenberg's Centaury.
Objective 2: Maintain the habitat at the Joan Point site while the feasibility of population restoration is assessed for Muhlenberg's Centaury.
Objective 3: Establish and/or augment populations to increase abundance and distribution5 if determined to be feasible and biologically appropriate for Muhlenberg's Centaury.
5The intent is to increase the area of occupancy and maintain the extent of occurrence.
Broad strategies and approaches to meet the population and distribution objectives for Muhlenberg’s Centaury include:
- Habitat and species protection: protect existing populations and their habitat from destruction (e.g., from land conversion) by developing mechanisms/instruments for protection;
- Stewardship: engage and involve landowners, land managers, and First Nations in recovery activities and decisions for Muhlenberg’s Centaury;
- Population restoration: develop and test population (re)introduction/augmentation techniques to recover the species;
- Public education and outreach: increase public awareness of the species threats and harm reduction measures, needs, and conservation value;
- Population monitoring: inventory existing populations and other suitable sites and address knowledge gaps pertaining to population trends, population viability, population augmentation, and restoration techniques;
- Research: address knowledge gaps pertaining to genetic diversity, threats, and habitat requirements.
Protection of the species and its habitat at the three extant sites is a first priority for the recovery of Muhlenberg’s Centaury (Table 3). Diligence must be exercised to prevent extirpation at extant sites due to preventable causes (including benign neglect). In addition, adequate environmental conditions for plant growth and establishment must be maintained at these sites, this includes control of both invasive alien species and encroaching native woody species and maintenance of hydrological processes. Despite uncertainties regarding the potential for (re)introducing the species into unoccupied areas, identifying alternative sites with the ability to support Muhlenberg’s Centaury populations will be an important component of recovery. Where possible, overgrown, degraded, or otherwise non-functioning vernally moist sites should be identified and restored to a point where they can serve as future recovery habitat for this species, as has been recommended for other vernal pool species at risk (Parks Canada 2006). The choice of poor condition vernal pools will limit or avoid impacts on at-risk vernal pool species and community types.
As the three extant populations occur on a variety of land tenures, stewardship, public education, and outreach are important to ensure recovery of the species and its habitat. At the Joan Point site, the first priority will be to ensure stakeholders are alerted to the presence of Muhlenberg’s Centaury so that the species can be adequately protected from the effects of urban land development or other land use activities. At Uplands Park, municipal park staff must be engaged in recovery activities to ensure the incorporation of the Muhlenberg’s Centaury population into park management and planning processes. For the Chatham Island population, the full engagement of First Nations will be a priority.
Research will be important for recovery as there are key knowledge gaps which currently limit recovery. Techniques for population restoration and/or new population establishment will need to be developed. Further, population biology research will be critical to fill knowledge gaps such as pollination limitations and to determine recovery targets for number and size of populations. Additional beneficial research includes gene conservation and studies that address other aspects of its autecology.
Design of the monitoring program is an important consideration, especially for rare annual plants which are likely to exhibit population fluctuations or rely on seed banks (Bush and Lancaster 2004). Data should be collected regularly over several years to account for population fluctuations. Further, data should be collected in years when plants are absent as well as when they are present to provide information on the species responses to environmental conditions. When seed banks are involved, they are an important part of the lifecycle and must be considered in estimates of population size–the presence of even one individual may indicate a viable seed bank is present (Bush and Lancaster 2004).
An important component of the monitoring program will be to identify criteria with respect to rate of population decline (size/distribution) that would trigger immediate re-evaluation of recovery priorities and activities. These criteria can then be incorporated into management plans. In addition, regular population monitoring is needed to track the current viability of the species, its response to threats and management activities, and the success of restoration and augmentation techniques. There are also significant risks associated with new population establishment which, therefore, must be accompanied by a program to monitor the impacts of new population establishment on non-target species, communities, and ecological processes.
Areas of critical habitat for Muhlenberg’s Centaury are identified in this recovery strategy. Critical habitat is defined in the Species at Risk Act as “...habitat that is necessary for the survival or recovery of a listed wildlife species and that is identified as the species’ critical habitat in the recovery strategy or in an action plan for the species” (Subsection 2(1)). Habitat for a terrestrial wildlife species is defined in the Species at Risk Act as “…the area or type of site where an individual or wildlife species naturally occurs or depends on directly or indirectly in order to carry out its life processes or formerly occurred and has the potential to be reintroduced” (Subsection 2(1)).
Critical habitat for Muhlenberg’s Centaury is identified in this recovery strategy to the extent possible based on best available information. It is recognized that the critical habitat identified below is insufficient to achieve the population and distribution objectives. While habitat can be fully identified for two known occurrences (Uplands Park and Joan Point), additional information is required to identify critical habitat at the one remaining location (Chatham Island). The schedule of studies section (Section 7.2; Table 4) outlines activities required to identify additional critical habitat necessary to support the population and distribution objectives of the species.
The habitat of Muhlenberg’s Centaury in Canada occurs in the Coastal Douglas-fir Biogeoclimatic Zone and is generally characterized as moisture-receiving areas, such as vernal pools and seeps along the edges of coastal salt marshes (Matt Fairbarns pers. obs. 2005; COSEWIC 2008). Field investigations, conducted in 2009 at two (Uplands Park and Joan Point) of the three extant locations, provided additional information required to identify critical habitat at those sites.
Muhlenberg’s Centaury likely depends directly on canopy openings to provide high light levels for germination. These openings must be large enough that Muhlenberg’s Centaury plants and seed bank area are not sheltered by surrounding vegetation. The minimum size of the openings can be determined based on the height of vegetation likely to grow in the area and cast shade on the Muhlenberg’s Centaury (Spittlehouse et al. 2004). An additional consideration with regard to canopy opening is that when tall vegetation falls it covers an area of ground for a distance equal to its height.
In addition to openings, specific hydrological characteristics are critical to the survival of this species. These hydrological characteristics are directly tied to rainfall (Graham 2004). Muhlenberg’s Centaury grows in level or depressional open areas that collect water from the surrounding area, called the catchment area. Surface water flow and subsurface seepage from this catchment area is essential to the survival of the Muhlenberg’s Centaury plants. These catchment areas are generally small and isolated within landscape scale catchments.
Critical habitat required for the survival of each patch6 of Muhlenberg’s Centaury (includes both plants and seed bank area) is composed of two habitat features: the minimum canopy opening and the catchment area. These features are always connected to a plant or patch of plants and in all cases will overlap to some degree (no special status is applied to areas of overlapping critical habitat). The default minimum canopy opening required for light to reach the plants is the area bounded by a 20 m distance surrounding each plant or patch of plants in all directions (20 m is generally the maximum height attained by trees in the soils surrounding Muhlenberg’s Centaury). The catchment is delineated by following the upslope high point of land which divides water flowing towards the plants from water flowing away from the plants; these catchment areas are generally relatively small and isolated within landscape catchments.
Within the geographical boundaries identified in Figure 4 and Figure 5, critical habitat for Joan Point and Uplands Park consists of the minimum canopy openings and any catchment areas associated with the recorded location of each Muhlenberg’s Centaury plant or patch. The critical habitat for these locations was mapped in 2009 (Fairbarns unpublished data 2009).
While the BC Conservation Data Centre has an element occurrence for this species on Chatham Island, neither the occurrence nor habitat has been recently confirmed. No critical habitat is identified for this occurrence, pending further studies.
The critical habitat attributes below cover the range of attributes for some but not all of the known sites, and may not exclude some habitat types that are unsuited to the species. Critical habitat attributes are as follows:
- Shallow depression with slope angles of < 2% that occur between 0.5-90 m above sea level.
- The lowest portion of the depression is sunny with short or sparse vegetation, woody plants may be found on areas less prone to winter flooding.
- Soils at the lowest point are poorly drained, generally shallow (< 10 cm deep) and usually have a negligible component of coarse fragments.
- Soils tend to be moist during the winter and are very dry by mid-summer (June/July).
6 Patch is a term used to refer to a group of several plants in close proximity. The exact definition of a patch will vary with the scale of mapping, size of the species being mapped, and landscape features. For the purposes of this recovery strategy the identification of patches is based on survey work performed by a biologist familiar with the species. Lacking any detailed information on seed bank extent, the seed bank is assumed to be included within each patch: the only information pertaining to the spatial extent of the Muhlenberg's Centaury seed bank is derived from the physical characteristics of the seeds, and dispersal distance is probably very limited (COSEWIC 2008).
Figure 4: Area (~ 0.36 ha) within which critical habitat for Muhlenberg's Centaury is found at Joan Point near Nanaimo and is located entirely on private lands.
Figure 5: Area (~ 2.7 ha) within which critical habitat for Muhlenberg's Centaury is found in Uplands Park in Victoria and located on municipal park land. The area of critical habitat within this area is approximately 1.42 ha.
Examples of activities likely to destroy critical habitat are provided below (Table 5). It is important to note that some activities have the potential to destroy critical habitat from outside the critical habitat. Destruction of critical habitat will result if any part of the critical habitat is degraded, either permanently or temporarily, such that it would not serve its function when needed by the species. Destruction may result from single or multiple activities at one point in time or from the cumulative effects of one or more activities over time.
The performance indicators presented below provide a way to define and measure progress toward achieving the population and distribution objectives. Progress towards recovering Muhlenberg’s Centaury in Canada will be assessed using the following measures:
Objective 1:Maintain the Uplands Park and Chatham Island populations of Muhlenberg's Centaury.
- By 2018 best management practices are developed and implemented at one or both sites.
- The populations remain extant.
- By 2023, both populations show a stable or increasing trend in population size3.
Objective 2:Maintain the habitat at the Joan Point site while the feasibility of population restoration is assessed for Muhlenberg's Centaury.
- By 2018 best management practices are developed and implemented.
- Habitat suitable for Muhlenberg’s Centaury remains extant at Joan Point.
Objective 3:Establish and/or augment populations to increase abundance and distribution if determined to be feasible and biologically appropriate for Muhlenberg's Centaury.
- By 2018 additional sites have been identified for establishment or restoration of Muhlenberg's Centaury population(s).
- By 2018 propagation techniques have been developed.
- By 2023 one or more (re)introduction or augmentation experiments are underway at suitable site(s).
3 Note that populations are expected to fluctuate and require long term datasets to estimate (Bush and Lancaster 2004).
One or more action plans will be completed by 2018.
B.C. Conservation Data Centre. 2011. BC Species and Ecosystems Explorer. B.C. Ministry Of Environment, Victoria, B.C. Web site: http://a100.gov.bc.ca/pub/eswp/ [accessed January 4, 2011].
Brook, B.W., L.W. Traill, and J.A. Bradshaw. 2006. Minimum viable population sizes and global extinction risk are unrelated. Ecology Letters 9:375-382.
COSEWIC (Committee on the Status of Endangered Wildlife in Canada). 2008. COSEWIC assessment and status report on the Muhlenberg’s Centaury, Centaurium muehlenbergii in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 32 pp.
Flather, Curtis H., Gregory D. Hayward, Steven R. Beissinger and Philip A. Stephens. 2011. Minimum viable populations: is there a ‘magic number’ for conservation practitioners? Trends in Ecology and Evolution 26: 307-316.
Garnett, S.T. and K.K. Zander. 2011. Minimum viable population limitations ignore evolutionary history. Trends in Ecology and Evolution 26(12): 618-619.
GOERT (Garry Oak Ecosystems Recovery Team). 2002. Recovery strategy for Garry Oak and associated ecosystems and their associated species at risk in Canada: 2001-2006. Draft 20 February 2002. Garry Oak Ecosystems Recovery Team, Victoria, B.C. x + 191 pp.
Government of Canada. 2009. Species at Risk Act Policies: Overarching Policy Framework [Draft]. Pp ii+ 38pp. in Species at Risk Act Policies and Guidelines Series, Environment Canada. Web site: http://www.sararegistry.gc.ca/document/default_e.cfm?documentID=1916 [accessed June 2010].
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Maslovat, C. 2009. Guidelines for translocation of plant species at risk in British Columbia. B.C. Ministry of Environment, Victoria, B.C.
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Pyke, C.R. 2005. Assessing Climate Change Impacts on Vernal Pool Ecosystems and Endemic Branchiopods. Ecosystems 8: 95–105.
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Spittlehouse, D. L., R.S. Adams, and R.D. Winkler. 2004. Forest, edge and opening microclimate at Sicamous Creek: Research Report 24. British Columbia Ministry of Forests, Research Branch, Victoria, B.C. vii+ 43 pp. Web site: http://www.for.gov.bc.ca/hfd/pubs/Docs/Rr/Rr24.htm [accessed November 2011].
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A strategic environmental assessment (SEA) is conducted on all SARA recovery planning documents, in accordance with the Cabinet Directive on the Environmental Assessment of Policy, Plan and Program Proposals. The purpose of a SEA is to incorporate environmental considerations into the development of public policies, plans, and program proposals to support environmentally sound decision-making.
Recovery planning is intended to benefit species at risk and biodiversity in general. However, it is recognized that strategies may also inadvertently lead to environmental effects beyond the intended benefits. The planning process, based on national guidelines, directly incorporates consideration of all environmental effects, with a particular focus on possible impacts upon non-target species or habitats. The results of the SEA are incorporated directly into the strategy itself, but are also summarized below in this statement.
The range of Muhlenberg’s Centaury overlaps with a suite of other plants and invertebrates at risk, the totality of which comprise one of the most unique species assemblages known in Canada (GOERT 2002). Because locations for potential introductions of Muhlenberg’s Centaury have not yet been determined, and because of the high concentrations of co-occurring species at risk in some locations, it is not possible to anticipate all of the possible positive and negative impacts stemming from recovery activities. However, many of these species are threatened by the same primary factors (i.e., development activities and introduced species) that threaten Muhlenberg’s Centaury. Thus, most of the recovery activities proposed (e.g., protection and habitat restoration) are expected to have a net positive effect on non-target native species, communities, and their habitats.
Nevertheless, if not planned and implemented carefully, large-scale management actions, such as invasive species removal or the use of herbicides, may have a negative effect on other plants at risk (e.g., through trampling, poisoning, increased herbivory, and inadvertent dispersal of alien species). Trampling due to on-site recovery activities (e.g., surveys, research, restoration, and management) poses a threat to co-occurring at-risk species that occur in or near sites with Muhlenberg’s Centaury or that are proposed for Muhlenberg’s Centaury establishment. Further, augmenting populations with non-local genotypes may harm existing populations (McKay et al. 2005).
The potentially negative effects of recovery can be mitigated or eliminated at the project implementation phase through proper field procedures and/or strong involvement of Parks Canada Agency and the Garry Oak Ecosystems Recovery Team. Further, all population augmentation/establishment must take a precautionary approach, and research should involve experimental establishment trials (Maslovat 2006). One approach to ensure that potential negative impacts of augmentation/establishment are minimized would be to select restoration/establishment sites that are already degraded to the point that they no longer support viable populations of other species at risk. Some recovery strategy activities may require project-level environmental assessment as required under the Canadian Environmental Assessment Act. Any activities found to require project-level environmental assessments will be assessed at that time pursuant to the provisions of the Act.
Actions taken to aid in the recovery of this species should, if conducted in an open, informative manner, provide benefits for all species at risk and their habitats by increasing public awareness of the negative environmental consequences associated with invasive alien species, the need to maintain natural ecological processes, and the need to protect natural habitats from the effects of development. This recovery strategy benefits the environment by promoting the conservation and recovery of the Muhlenberg’s Centaury, a natural component of biodiversity. In addition, it is likely that habitat restoration for Muhlenberg’s Centaury will benefit other co-occurring native species which occupy the same habitat. The SEA process has concluded that this recovery strategy will likely have several positive effects on the environment and other species. There are no obvious adverse environmental effects anticipated with the implementation of this recovery strategy.
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