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Recovery Strategy for the Hill's Thistle (Cirsium hillii) in Canada

2. Recovery

2.1 Population and Distribution Context

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).

Figure 2: Global Range of Hill's Thistle by Jurisdiction

Figure 2. Global Range of Hill's Thistle by Jurisdiction. Red areas: Critically Imperiled; Yellow areas: Vulnerable (NatureServe 2009).

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)

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.

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.

2.2 Population and Distribution Objectives

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:

  1. No continuing decline in total number of mature individuals.
  2. 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.

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.

2.3 Broad Strategies and Approaches to Recovery

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. These communities should be engaged in action planning for the species.

2.3.1 Protection and Maintenance of Existing Populations

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.

2.3.2 Reduction of Threats to Habitat

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.

2.3.3 Promoting Site Stewardship

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.

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.

2.3.4 Using Monitoring Information and Research to Guide Recovery Activities

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.

2.4 Critical Habitat

Critical habitat is defined in Section 2(1) of the Species at Risk Act (S.C. 2002, c. 29) as "the habitat that is necessary for the survival or recovery of a listed species and that is identified as the species' critical habitat in the recovery strategy or in an action plan for the species". In a recovery strategy, critical habitat is identified to the extent possible, using the best available information. Ultimately, sufficient critical habitat will be identified to completely support the population and distribution objectives.

Critical habitat has been identified for Hill's Thistle and the amount of critical habitat identified in this recovery strategy contributes to a substantial portion of the targets outlined in objectives 1 and 2 (Section 2.2), but does not fully meet the objectives. In total, 90 critical habitat polygons are identified at 17 sites in the Manitoulin Region (38), the Bruce Peninsula (40), and Wasaga Beach Provincial Park (12). This mapped critical habitat captures an IAO of 56 km2, and an Extent of Occurrence of 9,150 km2. Per objective 2, critical habitat is also mapped in each of the four core areas the species occupies. Recent surveys funded by the Species at Risk Program have discovered many additional populations of Hill's Thistle. At this time, we do not have adequate information to determine which of those populations should be identified as critical habitat to achieve the objectives. A schedule of studies, which outlines the work required to complete the identification of critical habitat, is included below. In the meantime, implementation of the broad strategies and approaches, as outlined in Section 2.3, will aid in meeting the population and distribution objectives.

2.4.1 Information Used to Identify Critical Habitat

Critical habitat was identified from current data on habitat occupied by the species. Confirmed records on the Bruce Peninsula, at Wasaga Beach, and in provincial parks, crown lands5, and lands owned by environmental non-governmental organizations (ENGOs) in the Manitoulin Region were all used as the basis of the mapping.

Habitat for Hill's Thistle occurs as patches within several types of open non-forested vegetation, or as openings within successional forest (based on field work by many workers including Reschke et al. 1999; Brownell and Riley 2000; Jalava 2004-2008; Jones 2004-2008; North-South Environmental 2005; vegetation community data from the aforementioned workers is on file at NHIC). In Canada, critical habitat is found within the following vegetation community types, as per the Ecological Land Classification of Ontario (ELC) (Lee et al. 1998):

Bruce Peninsula and Manitoulin Island Region

Dry-Fresh Little Bluestem Open Alvar Meadow
Dry-Fresh Poverty Grass Open Alvar Meadow
Common Juniper Shrub Alvar
Creeping Juniper-Shrubby Cinquefoil Dwarf Shrub Alvar
Scrub Conifer-Dwarf Lake Iris Shrub Alvar
White Cedar-Jack Pine Treed Alvar
Jack Pine-White Cedar-White Spruce Treed Alvar

Wasaga Beach

Dry Black (Red) Oak-White Pine Tallgrass Woodland
Dry Tallgrass Prairie-Open Sand Barren
Dry-Fresh White Pine-Red Pine Coniferous Forest
Dry-Fresh White Pine-Red Oak Mixed Forest
Cultural Meadow/Dry Tallgrass Prairie

These community types often have a distinct boundary where they change from open (suitable) to forest, wetland, or cultural meadow (all unsuitable). Thus, the general areas in which critical habitat patches occur are fairly easy to distinguish in the field and relatively easy to map (methodology below). All known alvar sites on the Bruce Peninsula and at Wasaga Beach have recently been mapped in detail based on a compilation of more than 15 years of field data and observations of satellite imagery (North-South Environmental Inc. 2005; Jalava 2008a).

2.4.2 Critical Habitat Identification

Critical habitat for the Bruce Peninsula and Wasaga Beach Provincial Park was mapped by Parks Canada in October 2009, and for the Manitoulin Region by Parks Canada in cooperation with staff from Ontario Parks, Ontario Ministry of Natural Resources, Ontario Nature, and the Nature Conservancy Canada in April 2010, based on the following methodology:

Inventory gaps identified by the Recovery Team were surveyed in 2004-2009 to support the identification of critical habitat (Jalava 2004-2008; Jones 2004-2008). All occurrence data for Hill's Thistle for the Bruce Peninsula and Wasaga Beach Provincial Park, and for protected areas in the Manitoulin Region were gathered from all available sources (especially NHIC and BPNP data bases, as well as Wasaga Beach monitoring data). All records were scrutinized and updated in October 2009 and April 2010 by Parks Canada. Only records with coordinates taken on the ground with GPS or localities mapped very precisely in the field on aerial photography were used. Records without GPS coordinates, or not field mapped on air or satellite imagery, or records with only vague locations, were not used to identify critical habitat.

In almost all cases newer georeferenced observations were available and supercede these records.

For the Bruce Peninsula and Wasaga Beach: All occurrence data for Hill's Thistle on the Bruce Peninsula (except those on First Nations lands) and at Wasaga Beach Provincial Park were plotted digitally on 2006 ortho photography with 30 cm resolution (South Western Ontario Orthorectification Project 2006). Suitable alvar community polygons as mapped by Jalava (2008a) were superimposed on this. Field data were available for most records to tell if the plants were spread throughout the vegetation community despite having only a single centroid UTM coordinate.

For the Manitoulin Region: All occurrence data from protected areas were superimposed on Quickbird imagery (6 satellite images at 60 cm resolution with a date range of June 2005 - August 2008). As well, field mapping from hard copies (IACI unpublished field notes 1995 and 1996 on file in NHIC database) was scanned and superimposed on satellite imagery to show field-mapped locations. Again, field data were available to tell if the plants represented a single point or were spread throughout.

For the entire Canadian range: The species occupies edges and openings where substrate and other factors are suitable, and fluctuations of some factors may cause population size to wax and wane. Therefore, some radial distance around the plants (to allow for dispersal and expansion of the population and to provide shelter and edge habitat) must be identified as critical habitat. A radial measure of 30 m around the plants was derived in the field by a core group of the Recovery Team as the distance required to prevent impact to extant populations and habitat. Using GIS software, a 30 m circle was plotted around all single point occurrences. In cases where 30 m circles overlapped, they were joined to form one polygon. In cases where 30 m circles were less than 30 m apart, they were joined if the intervening land contained suitable habitat. In cases where a centroid was provided for a population known to be >50 plants but the locations of individual plants in the habitat were not known, if the suitable habitat patch was larger than a 30 m radius circle, the entire area of suitable habitat was considered critical habitat.

Biophysical attributes of critical habitat for Hill's Thistle in Canada include the following:

  • Dry, open ground with little or no immediate canopy cover;
  • Trees if present are predominantly coniferous species in a savanna or very open woodland situation;
  • Patches of low grasses or sedges, especially Poverty Oat Grass (Danthonia spicata) and Richardson's Sedge (Carex richardsonii), and reindeer lichens (Cladina rangiferina and C. mitis), or Bearberry with scattered shrubs;
  • Habitat patches are often found on edges and in openings, especially the edges of alvars and in trails;
  • Soils are generally shallow and range from sandy near Lake Huron to silty and slightly alkaline on alvars.

In total, 90 polygons of critical habitat, collectively covering 41 hectares at 17 sites, are identified here. Some sites have more than one polygon. The general locations of critical habitat polygons are depicted in Figures 3, 4 and 5 with detailed maps showing the extent of each critical habitat polygon provided in Appendix D. GIS shapefiles of all critical habitat polygons are maintained by the Federal Government.

2.4.3 Activities Likely to Destroy Critical Habitat

Examples of activities that are likely to result in the destruction of Hill's Thistle critical habitat are listed here with the habitat features or properties they are likely to destroy. These activities would be destructive in any part of critical habitat, because they may damage or destroy Hill's Thistle plants, damage or remove the substrate required for growth, introduce competition, or interrupt natural processes that maintain habitat.

Activities that destroy or remove native grassy vegetation:

  • Building cottages, houses, and driveways over critical habitat patches
  • Building roads across critical habitat
  • Limestone/dolostone quarrying or extraction of surface materials such as boulders
  • Clearing of ground
  • Using critical habitat as landing areas or roads during the logging of adjacent forests

Activities that disturb the extremely shallow soil:

  • Driving heavy machinery across critical habitat
  • Off-trail ATV or mountain bike use

Activities that reduce native species presence by introducing exotic or potentially invasive species:

  • Trucking-in fill dirt and gravel
  • Off-trail ATV use as a vector for weeds
  • Seeding lawns or planting non-native species
  • Planting trees of any kind
  • Grazing of livestock
  • Feeding hay to livestock in critical habitat

Activities that trample and damage vegetation and soil:

  • Off-trail use by hikers at a level that tramples or destroys vegetation
  • Camping activities such as placing a tent, fire pit, or latrine on top of critical habitat patches
  • Off-trail use of critical habitat for group events.

There are several instances where trail use is beneficial to Hill's Thistle because the light disturbance keeps the ground clear of other vegetation. Threshold levels at which trail usage could become harmful rather than beneficial have not been determined. Thus, it is intended here that in general the use of existing trails and roads within critical habitat may continue. The determination of the point at which trail usage may potentially become harmful and protective action needed is more appropriately handled by land managers on a site by site basis.

2.4.4 Schedule of Studies to Identify Critical Habitat

This document includes a partial identification of critical habitat for Hill's Thistle. Future identification of critical habitat elsewhere in the range of Hill's Thistle will be undertaken as needed to ensure population and distribution objectives are met, or if the degree of risk affecting the species increases. Table 3 outlines and explains the work required to enable further critical habitat identification and mapping.

Table 3: Schedule of Studies

Description of ActivityOutcome/RationaleTimeline
Update occurrence data & mapping for all remaining sites to current CH standards.Complete and current occurrence data set & mapping permits creation of accurate CH polygons for remaining Bruce Peninsula & Manitoulin Region populations.2013. Could piggyback on fieldwork for COSEWIC Status Report Update due in 2014
Identify CH parcels to meet the population & distribution objectives.The amount & distribution of critical habitat required to meet recovery objectives is mapped.As required

Figure 4: General Locations of Critical Habitat Polygons on the Bruce Peninsula

Figure 4. General Locations of Critical Habitat Polygons on the Bruce Peninsula.

Figure 5: General Locations of Critical Habitat Polygons in the Manitoulin Region

Figure 5. General Locations of Critical Habitat Polygons in the Manitoulin Region.

Figure 6: General Locations of Critical Habitat Polygons at Wasaga Beach

Figure 6. General Locations of Critical Habitat Polygons at Wasaga Beach.

2.5 Habitat Conservation

Critical habitat is identified for a total of 17 Hill's Thistle sites found wholly or partly within protected areas (national park, provincial park, or property owned by ENGOs or other federal or provincial lands). There are 9 sites on the Bruce Peninsula, 7 sites in the Manitoulin Region, and 1 site at Wasaga Beach in Simcoe County. Some sites contain several critical habitat polygons. The total amount of Hill's Thistle critical habitat identified in the 90 polygons contained within protected areas is 41 hectares (18 ha for the Bruce Peninsula, 15 ha for the Manitoulin Region, and 8 ha for Wasaga Beach). The sites are listed below, with ownership, according to the four core areas.

Bruce Peninsula:
Brinkman's Corner (Public Works Canada)
Bruce Peninsula National Park
Clarke Property-Baptist Harbour (Ontario Heritage Foundation; Ontario Heritage Trust)
Dorcas Bay Road (Crown Land)
Johnston Harbour - Pine Tree Point ANSI (Crown Land)
Johnston Harbour - Pine Tree Point Provincial Park (Bruce Peninsula National Park)
Lyal Island (Ontario Nature)
Rover Property (Nature Conservancy of Canada)
Williams Property-Baptist Harbour (Escarpment Biosphere Conservancy)

Manitoulin Island:
Macs Bay Conservation Reserve
Misery Bay Provincial Nature Reserve
Quarry Bay Nature Reserve (Ontario Nature)
Queen Elizabeth-Queen Mother M'nidoo M'nissing Provincial Park

Islands surrounding Manitoulin:
Greene Island (Crown Land)
Cockburn Island, Wagosh Bay (Nature Conservancy Canada)
Western Duck Island (Crown Land)

Wasaga Beach:
Wasaga Beach Provincial Park

2.6 Measuring Progress

Evaluation of the progress toward achieving Hill's Thistle recovery will be reported five years following final posting of this recovery strategy on the Species at Risk Public Registry, and every five years following, as per SARA (s. 46). The success of Hill's Thistle recovery will be evaluated by comparing information from monitoring and inventory with the population and distribution objectives as per Table 4.

Table 4: Performance Measures for Progress of Hill's Thistle Recovery

CriterionLinks to Objective #Evaluation Timeframe (years after final posting of recovery strategy)
Monitoring program implemented for all priority sites.1, 23
Some forms of habitat protection begun to be put in place (protective park management, etc.).1, 25
Threats assessment completed and an evaluation of how to address current threats.1, 23
Threats to habitat begin to be addressed e.g. barriers to prevent ATV use or visitor trampling.1, 22
A multi-species communications strategy developed for the Bruce Peninsula and Manitoulin Region, with information distributed to private landowners about stewardship practices.1, 25 (CS)
5+ (outreach info.)
A dialogue begun with First Nations, municipalities, and corporate quarry owners, about stewardship possibilities.1, 23
No continuing decline in total number of mature individuals1Measured over 10 years or 3 generations*
Populations are maintained in each of the 4 core areas2Measured over 10 years or 3 generations

* This time frame is adopted from the COSEWIC assessment criteria, to account for anomalies within a shorter time frame.

2.7 Statement on Action Plans

One or more action plans will be completed by December 2015.

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.
3 Index of area of occupancy is an estimate of the number of 1X1 km grid squares occupied by extant populations (COSEWIC 2009).
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).
5 Crown land is land that is held by the Province of Ontario. Acceptable uses of crown land vary depending on the area but may included recreation, hunting, foresty, mining, or other uses, and may require permits or licences in some cases.