Recovery Strategy for the Hill's Thistle in Canada [Final Version] 2011: Recovery
NatureServe (2009) reports 141 sites globally, and COSEWIC (2004) listed 64 sites2 in Canada (Figures 2 & 3), but many more have been discovered since then, with a resulting total of 93 Canadian sites for Hill's Thistle now known (Jones 2004-2009; Jalava 2004a, 2005, 2007, 2008a, b; data on file in NHIC database).
2 "Site" refers to the individuals of Hill's Thistle and the physical place where they are found. It is equivalent to an element occurrence (EO), which may include several groups of plants if all are within 1 km of each other. Population is a general term to discuss clusters of plants without specifically discussing the boundaries of the area.
Figure 2. Global Range of Hill's Thistle by Jurisdiction. Red areas: "Critically Imperiled"; Yellow areas: "Vulnerable" (NatureServe 2009).
The Canadian range is restricted to Ontario (Figure 3); populations are located in Simcoe County (1 site), Bruce County (29 sites) and the Manitoulin District (63 sites, of which 20 are on islands other than Manitoulin Island). A complete list of all Canadian Hill's Thistle sites is provided in Appendix B, and a list of sites where Hill's Thistle is considered extirpated is given in Appendix C.
Figure 3. Range of Hill's Thistle in Canada (Environment Canada 2009).
The total number of plants in Canada is estimated to be in excess of 13,000 individuals (Jones 2004-2009; Jalava 2004a, 2005, 2007, 2008a, b; data on file in NHIC database). Several exceptionally large populations and areas of habitat exist (Appendix B), and recently, three populations have been documented that contain >1,000 individuals: Wikwemikong First Nation and Taskerville on Manitoulin Island, and Saugeen First Nation, on the Bruce Peninsula. The size of the Wikwemikong and Saugeen populations were not known at the time of the 2004 COSEWIC report. In addition, four populations are documented as containing >500 individuals.
There are essentially no data showing trends in population size because no long-term monitoring has been done other than at Wasaga Beach Provincial Park. The population there has been stable since 2001; however, it has declined significantly over the entire monitoring period of 1996-2007 (Burke Korol pers. comm. 2007).
The Canadian population as a whole is probably decreasing due to habitat loss from succession (closing-in of forest openings and grasslands), as well as from anthropogenic threats. Loss of habitat is certainly observable. COSEWIC (2004) reports the total area of occupied habitat at 30 km2 (Index of Area of Occupancy3 (IAO)) with a presumed decline to these levels over the past 100 years. Indeed, some populations are known to have become extirpated since the 1970s, but with many additional populations recently discovered, some of which are very large, the overall trend or rate of decline is not yet known.
3 Index of area of occupancy is an estimate of the number of 1X1 km grid squares occupied by extant populations (COSEWIC 2009).
The natural, open grassy areas in which Hill's Thistle is found such as prairies, oak savannas, and alvars, are all vegetation communities deemed to be in decline (ranked "Vulnerable" or less by NHIC 2008). The species can also be found in grassy forest openings, which may be remnants of former larger open habitats.
The goal of this recovery strategy is to maintain over the long-term, self-sustaining populations of Hill's Thistle in its current range in Canada. Specifically, recovery for Hill's Thistle in Canada is interpreted as a change in the species status from its current Threatened designation to Special Concern, or lower, as assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Based on the information presented above, the population and distribution objectives for Hill's Thistle until 2020 are:
- No continuing decline in total number of mature individuals.
- Populations are maintained in the four core areas the species occupies (Bruce Peninsula; Wasaga Beach, Manitoulin Island, and islands surrounding Manitoulin).
In the 2004 COSEWIC assessment, Hill's Thistle was designated as Threatened because of its "Small and Declining Number of Mature Individuals" and its "Very Small Population". In the first category, the species met the Endangered criteria of <2500 mature individuals, a continuing decline in numbers of mature individuals, and no population totaling >250 flowering plants. In the second category the species met the Threatened criteria of <1,000 mature plants. Hill's Thistle was designated Threatened rather than Endangered because imminent extirpation was unlikely given the occurrence of numerous sites, the presence of about one third of the populations in protected areas, few recent losses, and the fact that not all sites had been completely surveyed (COSEWIC 2004).
As noted in the Population and Distribution Context section, 29 additional populations have been discovered since the 2004 COSEWIC status report (a 45% increase), and the sizes of Hill's Thistle populations have been better documented. The total number of mature individuals was estimated in 2004 to be about 500 flowering plants. Recently, three populations have been documented that contain >1,000 individuals, and another four are >500 individuals. The total Canadian population is now estimated to contain more than 13,000 individuals. The proportion of the total number of plants that are mature in any single year remains largely unknown for the species in Canada, and may vary among populations. However, it is prudent to assume that the current number is close to the threshold of 1,000 mature plants.
Therefore, the expectation under the objectives stated above is that in future evaluations Hill's Thistle could remain in the "Very Small or Restricted Total Population", but would no longer be considered under the "Small and Declining Number of Mature Individuals". COSEWIC uses the term "continuing decline" to mean "a recent, current or projected future decline (which may be smooth, irregular or sporadic), that is liable to continue unless remedial measures are taken." Although it is expected that there will be some "naturally occurring" extirpation of very small populations (e.g. <10 individuals), mostly as a result of habitat becoming unsuitable through the filling in of vegetation, these isolated losses could well be offset over the long term by the growth and expansion of some of the larger populations, especially those in protected areas.
Another key criteria that Hill's Thistle must meet to no longer qualify as Threatened is that the Index of Area of Occupancy be >20km2. The IAO captured by the critical habitat as mapped in the recovery strategy is 56 km2 (39% of the total 145 km2) and the Extent of Occurrence4 captured is 9,150 km2 (48% of the approximated total of 18,990 km2). These factors contribute significantly to the recovery objectives.
4 Extent of occurrence is the area included in a polygon without concave angles that encompasses the geographic distribution of all known populations of a wildlife species (COSEWIC 2009).
Maintenance of Hill's Thistle in the four core areas will prevent major contraction of the species' distribution range and potentially preserve the species' genetic diversity and local adaptations.
Recovery of Hill's Thistle will largely be addressed through ecosystem-based actions for the recovery of alvars or other open habitats, as well as through actions specifically to benefit the species. Broad approaches will primarily be protection and maintenance of existing populations, reduction of threats to habitat, promoting site stewardship through outreach and public education, and using monitoring information and research to guide recovery actions.
Hill's Thistle is one of many species-at-risk (SAR) found in the Bruce Peninsula and Manitoulin Island region. It is crucial that recovery of Hill's Thistle be coordinated with recovery activities being undertaken for other SAR in the same region. This will be the best use of resources and personnel and will be very important in keeping the public engaged and preventing confusion among species. Recovery efforts for Hill's Thistle in the Bruce Peninsula and Manitoulin Island region will be done in coordination with the Pitcher's Thistle - Dune Grasslands Recovery Team, which is also working in the Manitoulin Island - Lake Huron region. There is some overlap in membership between the two teams, as well as in agency staff that are handling both recovery efforts.
Also, a great number of Hill's Thistle populations are found on First Nations lands. First Nation communities have maintained local ecosystems for generations through the use of community Traditional Ecological Knowledge. It is important to gather and share Traditional Ecological Knowledge from Knowledge Holders to others as a means for species and ecosystem protection and recovery. Traditional Ecological Knowledge and Science can, together, better inform assessment, monitoring, and recovery of the ecosystems that support specific species at risk.
Evaluation of site-appropriate conservation tools is a required approach because Hill's Thistle occurs in many different types of ownership and jurisdiction, so a variety of different protection measures are needed. Recovery in protected areas will be based on management actions such as controlling recreational use (or other threats) to prevent impacts to Hill's Thistle and its habitat, constructing barriers to control access, and establishing appropriate zoning for areas where the species is present. Outside protected areas, some examples of site-appropriate conservation tools may include tax incentive programs, conservation easements, funding for habitat protection such as fencing, etc. Acquisition by conservation partners of high priority sites, if they become available, may also be an approach. Encouraging and enforcing compliance is also a necessary approach, where other management measures fail to protect Hill's Thistle.
Threats reduction will largely be done through protection of existing populations and promoting good stewardship. The actual approaches used to address threats will depend on the threats present at individual sites. Some approaches may include working with land managers on site-appropriate activities such as posting signage and constructing barriers to reduce damage by pedestrians and vehicles, and working with municipalities to ensure Hill's Thistle and its habitat are considered during new development. Enforcement may also be required at some sites.
Addressing the threat of habitat loss from filling in of vegetation may be complex. An important approach is to determine whether controlled burning is a useful tool to reduce this threat. Hand removal of shrub material to open up ground is also a potential tool that needs testing.
Recovery on municipal lands will require coordinating and sharing habitat information with planning agencies, facilitating discussion of legal and policy approaches, and helping with site-appropriate management planning. Working with the aggregates industry on protection and restoration of alvars during and after extraction will also be an approach. On private and First Nations lands, actions will require working cooperatively with owners and communities on best management practices. The gathering and transfer of Traditional Ecological Knowledge from Knowledge Holders to others, will be encouraged.
Communications to engage the public in valuing and protecting Hill's Thistle and open habitat is vital. A key to encouraging good stewardship is helping landowners and managers understand what they have on their lands. As well, many populations are on municipal shorelines that have a public right-of-way through them, so educating the public about conscientious use will also be an approach. For populations occurring on First Nations lands, communications and outreach will be needed to gain assistance from the community in protecting Hill's Thistle and its habitat. Cooperating with local partners, such as local stewardship councils, fish and game clubs, etc., to promote awareness and protection of publicly accessible habitat, will also be necessary.
Monitoring information will be essential to recovery because the information gathered will show where recovery efforts are needed most. Monitoring can show if urgent threats need to be addressed, or if protection measures are working. Examples might be tracking visitor foot traffic on trails with Hill's Thistle, or checking for deer browse to see if it is a problem. Monitoring abundance and population trends will also be used to track recovery. Research is one of the primary approaches to recovery of Hill's Thistle, and Section 1.6 Knowledge Gaps, addresses the current important research questions.
Timelines and benchmarks for these strategies are given in Section 2.6 Measuring Progress.