Pitcher’s Thistle (Cirsium pitcher): management plan 2023

Official title: Management plan for the Pitcher’s Thistle (Cirsium pitcheri) in Canada

Species at Risk Act
Management Plan Series

Proposed

2023

Preface

The federal, provincial, and territorial government signatories under the Accord for the Protection of Species at Risk (1996)^{Footnote 2} 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 management plans for listed species of special concern and are required to report on progress five years after the publication of the final document on the SAR public registry.

The Minister of Environment and Climate Change, also the Minister responsible for the Parks Canada Agency, is the competent minister under SARA for the Pitcher’s Thistle and has prepared this management plan as per section 65 of SARA. To the extent possible it has been prepared in cooperation with the Province of Ontario, as per section 66(1) of SARA.

Success in the conservation 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 plan and will not be achieved by Environment and Climate Change Canada and the Parks Canada Agency, or any other jurisdiction alone. All Canadians are invited to join in supporting and implementing this plan for the benefit of the Pitcher’s Thistle and Canadian society as a whole.

Implementation of this management plan is subject to appropriations, priorities, and budgetary constraints of the participating jurisdictions and organizations.

Acknowledgments

This management plan was drafted by Karolyne Pickett (Environment and Climate Change Canada, Canadian Wildlife Service – Ontario Region (CWS-ON). The management plan was informed by the Recovery Strategy for Pitcher’s Thistle (Cirsium pitcheri)) in Canada (2011) prepared by the Parks Canada Agency, and the 2010 COSEWIC Assessment and Status Report on the Pitcher’s Thistle (Cirsium pitcheri) in Canada, prepared by Judith Jones. The management plan benefited from input, review, and suggestions from the following individuals and organizations: Krista Holmes (CWS-ON), Angela Barakat (CWS–National Capital Region), Lucy Patterson (Parks Canada Agency), and the Ontario Ministry of the Environment, Conservation and Parks.

The conservation measures outlined in this management plan were developed based on an assessment of threats to the species. This threats assessment was conducted by a multi-jurisdictional group of individuals that included: David Fraser and Judith Jones (consultants); Lucy Patterson (Parks Canada Agency); Jenni Kaija, Alistair Mackenzie and Edward Morris (Ontario Parks); Eric Snyder (Ontario Ministry of the Environment, Conservation and Parks); Bob Barnett (Escarpment Biosphere Conservancy); Esme Batten and Kaitlin Richardson (Nature Conservancy of Canada); Brent St. Denis (Township of Cockburn Island); Ellen Weatherbee (University of Michigan); and Karolyne Pickett (ECCC-CWS). Acknowledgement and thanks are given to the individuals and respective organizations that participated in the threats assessment.

Executive summary

Pitcher's Thistle (Cirsium pitcheri) is a perennial herb of the aster family that only occurs on the shores of Lake Huron, Lake Michigan and Lake Superior in North America. The plant spends several years in the juvenile life-stage as a ring of narrow, whitish-green leaves growing low to the ground (a "rosette"). At maturity, the rosette forms an upright flowering stalk topped with thistle heads consisting of numerous pale, pinkish-white flowers. After flowering and setting seed, the plant dies.

In Canada, Pitcher's Thistle is only found in Ontario, on sand dunes and beaches located on the southern shores of Lake Huron, on the southern shore of Manitoulin Island and smaller neighbouring islands, and on the shores of Lake Superior in Pukaskwa National Park. Optimal habitat consists of dry, loose sand with little other vegetation. The habitat is dynamic in nature, meaning that suitable habitat patches shift locations over time as vegetation cover naturally increases in some areas rendering them unsuitable for the species, while in others the action of wind, longshore currents, lake level fluctuations and ice scour maintains or creates areas of loose, sparsely vegetated sand dunes.

Pitcher's Thistle was listed as Endangered on Schedule 1 of the federal Species at Risk Act (SARA) in 2003 and a recovery strategy for the species was published on the SAR public registry in 2011. During subsequent surveys, some subpopulations were found to have increased in size and several additional subpopulations were discovered: as of 2022, there are 37 known extant subpopulations in Canada. As a result, COSEWIC re-assessed the species as Special Concern in November 2010, and the species status under SARA was changed accordingly in 2017. The species is listed as Threatened on the Species at Risk in Ontario List under the provincial Endangered Species Act, 2007 (ESA).

Due to the specific habitat requirements of Pitcher’s Thistle, the greatest threats to its recovery are those that impact the availability and quality of habitat. These include destruction of dune habitat from residential development and associated shoreline alteration, off-trail ATV use and pedestrian traffic, vegetation encroachment, and competition from non-native plants. Pitcher’s Thistle is also significantly impacted at some sites by browsing by herbivores.

The management objective for Pitcher’s Thistle in Canada is to prevent the population from becoming Threatened or Endangered by maintaining the population’s extent of occurrence, maintaining or increasing the population’s index of area of occupancy, and maintaining or increasing the number of subpopulations of Pitcher’s Thistle.

Broad strategies to achieve this management objective include management of vegetation cover, invasive plant species, herbivory and recreational activities, public outreach, information sharing with land-use planning authorities, population monitoring, and research related to potential threats from non-native insects and climate change.

1. COSEWIC* species assessment information

Date of assessment: November 2010

Common name: Pitcher’s Thistle

Scientific name: Cirsium pitcheri

COSEWIC status: Special concern

Reason for designation: This globally vulnerable endemic thistle of the Great Lakes occupies a small area including a series of sandy shoreline habitats from southeastern Lake Huron to Pukaskwa National Park on the north shore of Lake Superior. The species’ core range in Canada occurs along the southern margin of Manitoulin Island and nearby islands. Increases in population size and number have occurred over the past decade due to increased surveys. This species is at continued but reduced risk because of its specialized life history of flowering and reproducing only once at age 3 to 11 years before dying, its mainly small populations that undergo fluctuation, and ongoing habitat impacts from a variety of causes. Such threats as recreational ATV use in the species’ habitat, presence of exotic grass (Common Reed) and spread of woody plants into its habitat affect various populations.

Canadian occurrence: Ontario

COSEWIC status history: Designated Threatened in April 1988. Status re-examined and designated Endangered in April 1999. Status re-examined and confirmed in May 2000. Status re-examined and designated Special Concern in November 2010.

* COSEWIC – Committee on the Status of Endangered Wildlife in Canada

2. Species status information

Pitcher's Thistle (Cirsium pitcheri) is endemic to the Great Lakes basin of North America and is only found in the province of Ontario, Canada, and in four states in the U.S. (Wisconsin, Illinois, Indiana and Michigan).It has been estimated that the Canadian population comprises 15% of global abundance of the species (COSEWIC 2010). The species status at the global scale was ranked as Vulnerable^{Footnote 3} (G3) (last assessed in 2020, NatureServe (2022)). At the national scale, it is ranked as Imperiled (N2) in Canada and ‘Vulnerable’ (N3) in the U.S. At the sub-national level, it is ranked as ‘Imperiled’ (S2) in Ontario, and its status at the state level varies from ‘Critically Imperiled’ to ‘Vulnerable’ (listed in Appendix B, Table B-1).

Pitcher's Thistle was listed as Endangered on Schedule 1 of the federal Species at Risk Act (SARA) in 2003. Subsequent survey efforts found that some subpopulations were larger than previously reported, and several additional subpopulations were discovered. As a result, COSEWIC re-assessed the species as Special Concern in November 2010, and the species status under SARA was changed accordingly to Special Concern in 2017. The species is currently listed as Threatened on the Species at Risk in Ontario List under the Province of Ontario’s Endangered Species Act, 2007 (ESA).

3. Species information

3.1. Species description

Pitcher's Thistle is a perennial herb of the aster family (NatureServe 2022). The leaves are whitish-green, narrow and deeply divided (summarized from COSEWIC 2010). After its first year as a seedling, the plant grows basal leaves low to the ground, in the form of a 15 to 30 cm wide ring (a "rosette") (see COSEWIC 2010, Fig. 1). After remaining in this growth form for 2 to 11 years, the plant produces an upright flowering stalk topped by several thistle heads, each comprising multiple pale, pinkish-white flowers. After pollination, flowers produce seed-like fruit; after setting seed, the plant dies.

Pitcher’s Thistle can be distinguished from other thistles by the colour of its leaves and flowers, together with the presence of spikes on the flower head and at the tip of the leaves (see key to Cirsium genus in Voss and Reznicek 2012).

3.2. Population and distribution

Globally, Pitcher's Thistle occurs on the shores of Lake Superior, Lake Michigan and Lake Huron. In Canada, the species is found on the southeastern shore of Lake Huron, the southern shore of Manitoulin Island and neighbouring islands, and the north shore of Lake Superior in Pukaskwa National Park (Figure 1).

Number of subpopulations

There are currently 234 known extant subpopulations of Pitcher’s Thistle in the world, 197 of which occur in the U.S.: 170 in Michigan (MNFI 2022), 16 in Indiana and eight in Wisconsin (NatureServe 2022), as well as three in Illinois (Illinois Department of Natural Resources 2022). The number of known extant subpopulations has increased compared to what was reported in COSEWIC (2010) in all jurisdictions except Wisconsin (Table 1).

As of 2022, there are 37 extant subpopulations^{Footnote 4} in Ontario (listed in Appendix C, Table C-1). As reported in the federal recovery strategy (PCA 2011) (hereafter, the “recovery strategy”), two subpopulations are located on the shores of Lake Superior in Pukaskwa National Park, and another three occur on the southeastern shore of Lake Huron (Figure 1). The remaining 32 subpopulations, which include those newly recorded since the publication of the recovery strategy, are found on the southern shore of Manitoulin Island and smaller neighbouring islands (see inset, Figure 1). No new subpopulation extirpations have been recorded since the publication of the recovery strategy (extirpated subpopulations are listed in Appendix C, Table C-2).

Abundance

The highest abundance estimate for the Canadian population of Pitcher’s Thistle reported since the publication of the recovery strategy was for the year 2017, when a total of 90,000 plants (16,500 mature individuals) were recorded across 32 surveyed subpopulations (data source: Jones 2020). In comparison, the abundance of the Canadian population in 2008 was estimated at 55,000 plants (15,000 mature) (PCA 2011). However, some subpopulations experience wide fluctuations in annual growth rates (Nantel et al. 2018), and overall population abundance can vary drastically from one year to the next. For instance, total abundance for the subset of subpopulations surveyed in both 2017 and 2018 fell from 86,000 plants in 2017 to 39,000 plants in 2018 (data source: Jones 2020). The year-to-year variability in abundance at the population-level reflects the high degree of yearly fluctuations in abundance of Pitcher’s Thistle at the subpopulation level (characteristic of a species occurring in a dynamic type of habitat, see section 3.3.1 below); for instance, the abundance of several subpopulations on Manitoulin Island dropped by half from 2017 to 2018, yet others remained stable.

It is therefore particularly relevant for the conservation of Pitcher’s Thistle in Canada to consider the viability of each of its subpopulations. The general rule-of-thumb since the 1980s has been that a subpopulation should consist of at least 500 interbreeding individuals in order to retain evolutionary potential^{Footnote 5} (e.g., Given 1994; see review of the rule’s origin in Steeves et al. 2017). Demographic models developed for a Pitcher’s Thistle subpopulation in Illinois showed that subpopulation abundance should consist of at least 500 individuals for its risk of extirpation to be less than 5% over 100 years (Bell et al. 2002). On the other hand, the authors of later study recommended that an effective population size of at least 1,000 individuals would be required to maintain evolutionary potential, and that this number would translate to a minimum viable population size (MVP) of several thousand individuals to achieve a risk of extirpation of 1% over 40 generations (Frankham et al. 2014).

In the absence of species-specific analyses, the above generalizations provide at least some guidance in terms of minimum viable subpopulation size (Frankham et al. 2014). It is thus noteworthy that in 2017, 66% (n=21) of the 32 Canadian subpopulations surveyed that year had fewer than 500 individuals, and 72% (n=9) had fewer than 1,000 (data source: Jones 2020). In 2018, two of those nine subpopulations (one was not re-surveyed) saw their abundance drop below 1,000 individuals (data source: Jones 2020).

Under an alternative estimation of the probability of extinction, based on rosette abundance rather than the total number of plants at all life stages, Nantel et al. (2018) found that 14 subpopulations, out of 25 subpopulations^{Footnote 6} for which there were sufficient data to conduct analyses, had a greater than 5% probability of extirpation over the next 100 years. Most of these vulnerable subpopulations had a declining or stable annual population growth rate and consisted of fewer than 100 rosettes, whereas fluctuations in annual subpopulation growth rate had a weak effect on probability of extirpation (Nantel et al. 2018).

Figure 1. Distribution of Pitcher’s Thistle subpopulations in Ontario. (Data source: Jones (2020, 2022), NHIC (2022)).

3.3. Biological needs

3.3.1 Habitat

In Ontario, Pitcher’s Thistle occurs on sand beaches and sand dunes within the disturbance-prone zone located between open lake water and the landward forest edge. This zone is usually between 25 m to 500 m wide and occurs discontinuously along the shores of Lake Huron and Lake Superior, in stretches ranging from 25 m to more than 1 km in length (COSEWIC 2010). Within this zone, the species will be found in patches of dry, loose sand with sparse vegetation cover (less than 30% in some sites, Havens et al. 2012) comprising grasses such as Marram Grass (Ammophila breviligulata) (e.g., Keddy and Keddy 1984). The species does not seem to be present in several large areas of seemingly suitable habitat (Maun 1997, COSEWIC 2010, PCA 2011).

In a study conducted on the Lake Michigan shoreline, seedling emergence and survivorship has been found to be higher on perched dunes (200 to 300 m above lake level) than on lakeshore linear dunes (1 to 20 m above lake level), which have a lower surface soil moisture (Rand et al. 2015). However dune type did not affect survivorship to the flowering stage, suggesting that once plants have developed a taproot that can access groundwater (which is closer to the surface in lakeshore dunes compared to perched dunes), the initial negative effect of lower surface soil water availability on the species disappears (Rand et al. 2015).

The location, size and configuration of suitable habitat patches for Pitcher’s Thistle shifts over time: as vegetation cover naturally increases in some areas, they become unsuitable for the species; conversely, suitable habitat is maintained or develops in other areas when disturbance from wind, waves, lake level fluctuations and ice scour remove vegetation and create patches of loose, open sand. This pattern of Pitcher’s Thistle disappearing from one area and appearing in a new area is characteristic of a species exhibiting metapopulation^{Footnote 7} dynamics (McEachren et al. 1994, Halsey et al. 2015). Metapopulations cannot persist unless the rate of colonization (establishment of new subpopulations) is equal to or greater than the rate of subpopulation extirpation, which requires a dune system that is large enough to allow dune erosion and dune building events to occur independently (McEachren et al. 1994, Halsey et al. 2015).

3.3.2 Pollination and dispersal

Pitcher's Thistle only reproduces sexually. Although the species is capable of self-pollination (Loveless 1984), fewer seeds are produced when cross-pollination by insects is prevented (Keddy and Keddy 1984). A variety of insects belonging to seventeen different families across six different orders have been recorded visiting Pitcher’s Thistle flowers, including bees, ants, flies, butterflies, beetles and true bugs; more than half of the visits being from bumble bees (Jolls et al. 2019). More specifically, in Pukaskwa National Park the most frequent visitor of flowers at Oiseau Bay was the Half-black Bumblebee (Bombus vagans), followed by the leaf-cutter bee Megachile melanophaea (Keddy and Keddy 1984). Across the species’ entire range, pollination occurs between late May to mid-September (see review in McEachren et al. 1994); the peak flowering period peaks in early July in Wisconsin (Vitt et al. 2020), and in the last week of July further north, in Pukaskwa National Park (Keddy and Keddy 1984).

Seeds are dispersed by wind between July and October (McEachren et al. 1994), and most land within 4 m of the parent plant (Keddy and Keddy 1984, Loveless 1984). The clustering of plants at a scale of about 1 m reported by Girdler and Radtke (2006) is consistent with the observed short seed dispersal distances. Although Pitcher’s Thistle rosettes occur in a clustered spatial pattern (Girdler and Radtke 2006), the species grows at very low densities (e.g., 0.02 plants/m² (Maun 1997), 0.92 plants/m² (Girdler and Radtke 2006). The frequency and mechanism by which long-distance seed/capitula dispersal occurs remains a knowledge gap in the species life history.

The species is monocarpic, meaning that an individual plant produces seed only once, after which it dies; the risk of a plant dying prior to reproduction is inherently increased under this reproductive strategy (Maun 1997). For instance, Rand et al. (2015) have reported an extremely low probability of seeds and seedlings reaching the adult flowering stage (0.3% and 1.7%, respectively). Seed have remained viable for 1 to 2 years in laboratory (Hamzé and Jolls 2000), and up to 2 or 3 years in the field (Rowland and Maun 2001, Nantel et al. 2018).

4. Threats

4.1. Threat assessment

Threats to the Canadian population of Pitcher’s Thistle were described and assessed by a group of species experts during the development of this management plan (ECCC 2019), in order to provide an update to the information published in the species’ status report (COSEWIC 2010). Threats were assessed according to the methodology described in “Guidance for completing the Threats Classification and Assessment Calculator and Determining the number of ‘Locations’” (COSEWIC 2012), which is based on the IUCN-CMP (International Union for Conservation of Nature and Natural Resources-Conservation Measures Partnership) unified threats classification system, version 1.1.

For the purposes of the above assessment, threats are defined as the proximate activities or processes that have caused, are causing, or may cause in the future the destruction, degradation, and/or impairment of the entity being assessed (population, species, community, or ecosystem) in the area of interest (global, national, or subnational). Limiting factors are not considered during this assessment process. For purposes of threat assessment, only present and future threats are considered. Historical threats, indirect or cumulative effects of the threats, or any other relevant information that would help understand the nature of the threats are presented in the Description of Threats section.

The main threats to the Canadian population of Pitcher’s Thistle are residential development and associated shoreline alteration, off-trail ATV use and pedestrian traffic, vegetation encroachment, competition from non-native plants and browsing by herbivores. The threats assessment is summarized in Table 2.

^a Impact – The degree to which a species is observed, inferred, or suspected to be directly or indirectly threatened in the area of interest. The impact of each threat is based on Severity and Scope rating and considers only present and future threats. Threat impact reflects a reduction of a species population or decline/degradation of the area of an ecosystem. The median rate of population reduction or area decline for each combination of scope and severity corresponds to the following classes of threat impact: Very High (75% declines), High (40%), Medium (15%), and Low (3%). Unknown: used when impact cannot be determined (e.g., if values for either scope or severity are unknown); Negligible: when scope or severity is negligible.

^b Scope – Proportion of the species that can reasonably be expected to be affected by the threat within 10 years. Usually measured as a proportion of the species’ population in the area of interest. (Pervasive = 71–100%; Large = 31–70%; Restricted = 11–30%; Small = 1–10%; Negligible < 1%).

^c Severity – Within the scope, the level of damage to the species from the threat that can reasonably be expected to be affected by the threat within a 10-year or three-generation timeframe. Usually measured as the degree of reduction of the species’ population. (Extreme = 71–100%; Serious = 31–70%; Moderate = 11–30%; Slight = 1–10%; Negligible < 1%; Neutral or Potential Benefit ≥ 0%).

^d Timing – High = continuing; Moderate = only in the future (could happen in the short term [< 10 years or 3 generations]) or now suspended (could come back in the short term); Low = only in the future (could happen in the long term) or now suspended (could come back in the long term); Insignificant/Negligible = only in the past and unlikely to return, or no direct effect but limiting.

4.2. Threat descriptions

Threat 1.1. Housing and urban areas - impact: low

Construction of residential structures

Undertaking construction projects where Pitcher’s Thistle occurs will kill individual plants and eliminate the species’ habitat located within the project’s direct footprint. For instance, Maun (1997) attributed the extirpation of the Kettle Point subpopulation to coastal development (and recreational activities, see threat 6.1 below). Associated shoreline alteration (e.g., installation of riprap or armour stone) can disrupt longshore currents thus altering patterns of sand transport and deposition, both on and off-site, which may prevent colonization of new areas of suitable habitat by the species (Girdler and Radtke 2006). Reduced habitat connectivity may also lead to lower genetic diversity and higher inbreeding levels (Fant et al. 2013, 2014).

Given that most sandy bays on Manitoulin Island are currently subdivided for residential development, ongoing and planned residential construction is a threat to Pitcher’s Thistle (ECCC 2019). For example Carter Bay, where 50% of the Canadian population occurs, is zoned for development, though there is no plan of subdivision at this time. The scope is nevertheless assessed as ‘Small’ to account for scenarios where the extent of habitat loss is reduced when structures are built landward of the beach zone rather than directly on the sand dunes. Furthermore, the overall impact of the threat may be tempered by the generally large size of lots, such that the proportion of habitat destroyed by the building footprint is small relative to the lot size (ECCC 2019).

Threat 4.1. Roads and railroads - impact: negligible

New road construction

Undertaking a road construction project where Pitcher’s Thistle occurs will kill individual plants and eliminate the species’ habitat within the road’s direct footprint. There would also be negative effects to the species from the use of associated machinery within the project’s direct and indirect footprint. At this time, this threat only applies to the Port Franks subpopulation, where an application for the construction of a new road allowance has been submitted to municipal council by landowners seeking an alternative access to their properties (ECCC 2019). The impact to the species may be mitigated by the fact that a large proportion (60 – 70%) of the subpopulation occurs outside of the proposed road allowance footprint, on provincial park property. Nevertheless, the subpopulation would be impacted by sand erosion stemming from wind action generated by vehicles using the road.

Threat 5.2. Gathering terrestrial plans - impact: negligible

Deliberate removal of plants

Some landowners pull individual plants from their properties for a variety of reasons, such as landscaping, a dislike of thistles, or because the species is mistaken for a noxious weed. This threat does not currently impact the Carter Bay or Great Duck Island subpopulations, which together account for 74% of the Canadian population. Severity may be more serious than assessed in ECCC (2019) given that the species does not have a persistent seed bank (seed viability of 3 years or less, see section 3.3.2).

Threat 6.1. Recreational activities - impact: low

Trampling by pedestrians and all-terrain vehicles (ATVs)

Although habitat disturbance events that are staggered in time and place within a dune system are necessary to maintain the presence of areas of suitable habitat for the species at the landscape scale, they can be detrimental at the local scale and lead to the extirpation of a subpopulation. Trampling by off-trail pedestrian activity and ATV use can accelerate subpopulation extirpation by causing plants to be killed from being crushed, uprooted or buried by sand (Girdler and Radtke 2006). Seedlings are especially vulnerable to complete burial (Maun et al. 1996). In addition, seed germination and seedling emergence decrease with increased burial depth (Chen and Maun 1999).

ATVs can also damage habitat by altering the structure and configuration of dunes and ridges directly, which may subsequently render the habitat unsuitable for Pitcher’s Thistle. Damage to habitat from ATVs occurs on Manitoulin Island, especially where there are municipal road allowances within the beach zone. Subpopulations at Burnt Island Harbour, Belanger Bay West, and Doc Hewson Bay on Cockburn Island are at particular risk of extirpation due to ATV use. The threat from ATV use is more severe when lake levels are high (see Threat 11.1) as they force ATVs onto higher ground where plants beyond the flood line persist (ECCC 2019).

Blowouts (depressions in the sand dune) due to people jumping off the top of dunes result in holes that increase in size over time because loosened sand is vulnerable to wind erosion. This threat is a particular concern for the Pinery Provincial Park subpopulation (ECCC 2019).

Threat 7.3. Other ecosystem modifications – impact: medium

Encroachment by woody vegetation

Vegetation succession is a natural process by which herbaceous plant communities (e.g., fields) gradually transition into forests until, or unless, an environmental disturbance (e.g. wildfire) removes or prevents the establishment of woody vegetation. On the coast of the Great Lakes where Pitcher’s Thistle occurs, encroachment of shoreline habitat by woody vegetation is mainly influenced by daily, seasonal, and long-term fluctuations of lake water levels that occur in response to wind, precipitation and temperature (Fuller et al. 1995), ice scour, and wave and wind action directly.

Site-level disturbances such as wind, wave action and ice scour prevent vegetation encroachment of dunes along the lakeshore and maintain the sparsely vegetated, tree-less habitat that is suitable for Pitcher’s Thistle (see section 3.3.1). (Conversely, during years of lower lake water levels, decreased proximity of Pitcher’s Thistle individuals to disturbance from wave-action facilitates vegetation encroachment (PCA 2011)). Vegetation succession can negatively impact Pitcher’s Thistle, as shown in a study simulating vegetation succession: Pitcher’s Thistle experienced negative population growth and decreased seedling emergence in lower light conditions and higher plant litter depth that would result from greater vegetation cover (Jolls et al. 2015).

Although the succession cycle is a natural process, it is discussed as a threat in this management plan because Pitcher’s Thistle abundance is such that the absence of disturbance in a relatively small subset of subpopulations is likely to have a more severe impact on the Canadian population than it would have had prior to the species being put at risk by human activities.

Currently, the Oiseau Bay subpopulation in Pukaskwa National Park is threatened by woody vegetation encroachment. Within that subpopulation, the species was extirpated from the Crescent Beach site over a span of 20 years largely due to vegetation succession that ensued following a change in the course of a nearby river in 1985 (Patterson pers. comm. 2019). Plants growing at a second site within the subpopulation, Creek Beach, are now at risk of extirpation due to encroachment by vegetation such as the native Silverberry shrub (Elaeagnus commutata). As a result of vegetation encroachment, Pitcher’s Thistle is no longer found in some areas within the subpopulations at Fisher’s Bay, Michael’s Bay and Christina’s Bay, and only one plant remains of the Sand Beach subpopulation on Cockburn Island.

Threat 8.1. Invasive non-native/alien species – impact: low

Non-native plants

There is concern that non-native plants that have the capacity to rapidly spread within newly colonized areas pose a threat to Pitcher’s Thistle given that the species grows in habitat that is sparsely vegetated. For example, quickly growing plants might overtake the substrate, and/or shade out Pitcher’s Thistle. These potential scenarios are inferred from observations such as, for example, that the species is only found in habitat that is sparsely vegetated, or that Pitcher’s Thistle juveniles that are further isolated from conspecifics have been found to grow to larger sizes than those closer together (Girdler and Radtke 2006). Until recently, the non-native European Reed (Phragmites australis subsp. australis) was considered a threat to some Pitcher’s Thistle subpopulations, particularly those on Manitoulin Island (ECCC 2019). However, a program to eradicate European Reed from the shores of Lake Huron has significantly reduced the scope and severity of the threat, though on-going management will likely be necessary to prevent re-colonization (ECCC 2019).

The two non-native plant species discussed below are considered low impact threats given that there is some uncertainty as to how severely they may negatively affect Pitcher’s Thistle.

Baby’s Breath

Baby's Breath (Gypsophila paniculata) is a perennial flowering plant native to Europe and Asia, likely introduced in North America in the late 1800s as an ornamental plant (Lamar and Partridge 2021). It is now found throughout the northern and western U.S. and occurs in several Canadian provinces (EDDMapS 2022), and is considered an invasive species in coastal sand dune habitat of Lake Michigan (Emery et al. 2013, Reid and Emery 2018, Rice et al. 2020, Lamar and Partridge 2021). The first herbarium record of the species for Ontario dates from the time period 1964 to 1983 (Lamar and Partridge 2021), and the plant is currently present where Pitcher’s Thistle occurs on Cockburn Island, Duck Island, and at Horseshoe Bay on Great Duck Island (ECCC 2019). The deep roots of G. paniculata stabilize dunes that would otherwise be subjected to natural disturbance (Emery et al. 2013). Yet although Baby’s Breath can significantly reduce the amount of bare sand (Reid and Emery 2018), studies have not provided conclusive evidence that its presence is detrimental to Pitcher’s Thistle. For example, removal of Baby’s Breath did not increase the absolute number of pollinator visits to Pitcher’s Thistle flowers (Baskett et al. 2011), or the abundance of the species (Emery et al. 2013, Reid and Emery 2018).

Spotted Knapweed

Spotted Knapweed (Centaurea stoebe subsp. micranthos) is another plant native to central Eurasia that is considered a major invader of the Great Lakes’ coastal dune habitat in the U.S. (Girdler et al. 2016). Although Spotted Knapweed has not been reported in the Early Detection and Distribution Mapping System (EDDMapS) where Pitcher’s Thistle occurs in Ontario (EDDMapS 2022), it was found in Pukaskwa National Park in 2021, approximately 25 km from the Oiseau Bay subpopulation (Patterson pers. comm. 2022). The Spotted Knapweed record closest to Pitcher’s Thistle subpopulations on Manitoulin Island is located 45 km to the south on the Bruce Peninsula (EDDMapS 2022). Again, there is also uncertainty as to whether the plant has negative impacts on Pitcher’s Thistle. For example, one study found that the proportion of Pitcher’s Thistle individuals surviving to the flowering stage was lower for individuals growing near Spotted Knapweed compared to those growing in areas of open sand, and seedling emergence was lower, particularly in habitat with lower surface soil water (Rand et al. 2015). On the other hand, Girdler et al. (2016) did not find negative effects of Spotted Knapweed on Pitcher’s Thistle abundance.

Non-native insects

Four introduced, seed-eating weevil species have been found to impact Pitcher’s Thistle in some U.S. subpopulations. They are discussed below as potential threats because they have not been detected in Canadian subpopulations of Pitcher’s Thistle at this time.

Larinus planus, L. minutus and L. obtusus

The Eurasian weevils Larinus planus, L. minutus and L. obtusus were deliberately spread in the U.S. in the early 1990s as biocontrol agents for non-native plant species: L. planus, to target the thistle Cirsium arvense (Louda and O’Brien 2002, Dodge 2005), and the other two weevil species, to control invasive knapweeds (CALS 2022). All three weevil species can feed on Pitcher’s Thistle flowers (Warneke et al. 2020). The prevalence of L. planus on the flowers appears to be influenced by dune elevation and by the presence other vegetation around plants (Hakes and Meunier 2018).

L. planus also uses the flowers for reproduction: the weevil bores holes in the flower heads in which it deposits an egg, and the developing larvae feed on the thistle’s ovules and developing seeds (Dodge 2005). As a result, Havens et al. (2012) found that 45% of flower heads did not disperse any seeds due to damage by the weevil, and according to the authors’ model, weevil infestation could decrease the growth rate of Pitcher’s Thistle by 10 to 12%. Infestation of flower heads by L. planus has also been found to reduce the number and weight of mature seeds produced (Gijsman et al. 2020). Warneke et al. (2020) further suggest that C. arvense may facilitate the movement of L. planus into Pitcher’s Thistle habitat, and that extensive feeding L. minutus and L. obtusus could reduce the reproductive success of Pitcher’s Thistle. The severity of the threat from L. planus may be reduced by applying kaolin clay, an organic insect deterrent (Inkster 2016).

Rhinocyllus conicus

Another European weevil from a different genus, Rhinocyllus conicus, was introduced to North America in 1969 as a biocontrol agent for the non-native thistle Carduus nutans (Havens et al. 2012). Since its introduction, R. conicus has been documented feeding on the seeds of 16 native Cirsium species (Dodge 2005), and was found on Pitcher’s Thistle flower heads in a botanical garden in 2007 (Havens et al. 2012). Based on the rate of oviposition of R. conicus on C. pitcheri observed in an experimental setting, demographic models predict a decrease in population growth rate and a steep decrease in the time to halve a population of Pitcher’s Thistle colonized by R. conicus (Louda et al. 2005).

Threat 8.2. Problematic native species – impact: low

Browsing

Herbivory is another type of local-scale disturbance that can accelerate subpopulation extirpation (Girdler and Radtke 2006). For example, increasing intensity and frequency of herbivory negatively affected Pitcher’s Thistle root biomass (Phillips and Maun 1996). Herbivory may therefore lower the flowering probability of affected plants, by forcing a re-allocation of resources to the regrowth of browsed shoots and leaves while simultaneously decreasing total nutrient and water uptake (Phillips and Maun 1996, Girdler and Radtke 2006). The rate of herbivory, which determines the severity of its impact on individual plants, may be influenced by the spatial distribution and size of Pitcher’s Thistles individuals: for instance, Girdler and Radtke (2006) found that rosettes with only one or two other rosettes within a 1 m radius were more likely to be browsed than those with nine or more neighbours, and that generally, herbivory was more prevalent in larger individuals.

Browsing of the species by the native White-tailed Deer (Odocoileus virginianus) has been observed in the field (e.g., Bell et al. 2003), and is considered a threat to some Pitcher’s Thistle subpopulations –as opposed to a natural component of the species ecology– due to a presumed increase in deer abundance since European settlement. For instance, Maun (1997) reported that in the mid-1990s, deer abundance in Pinery Provincial Park was four times the carrying capacity of the park; concurrently, the author found that 90% of flowering Pitcher’s Thistle individuals were grazed and that 50% of capitula were consumed. Currently, deer browsing is a threat to the Desert Point and Duck Island subpopulations in particular. Deer abundance is low in Pukaskwa National Park and as such deer browse is not currently a threat to the subpopulations that occur within the park (Patterson pers. comm. 2019).

The spotted cucumber beetle, Diabrotica undecimpunctata howardi, is a leaf beetle native to North America that feeds on a wide variety of agricultural crops including gourds, squashes and corn. In one study in Indiana, Marshall (2013) documented the species feeding on Pitcher’s Thistle flower heads. It is not known whether the beetle larvae feed on Pitcher’s Thistle roots, or whether herbivory by D. u. howardi impacts the plant’s reproductive success. The subspecies is present in Ontario (EPPO 2022) but the impact of this insect, if any, on the Canadian population of Pitcher’s Thistle is unknown.

Threat 11. Climate change and severe weather – impact: unknown

In light of a projected increase of 2.85 °C to 3.48 °C by 2050 in mean annual temperature across the species range in Ontario, Pitcher’s Thistle has been assessed as ‘Highly Vulnerable’^{Footnote 8} to climate change under the Climate Change Vulnerability Index (Brinker et al. 2018). This level of vulnerability is in part due to the following intrinsic characteristics of the species: its cool temperature niche (namely, cold-water coastal habitat), its highly restricted dispersal capability (see subsection 3.2.2), its low genetic variation (Loveless and Hamrick 1988; Coleman 2007, Fant et al. 2013, 2014), and its dependence on an uncommon geological feature (sand dunes) (Brinker et al. 2018). The predicted vulnerability is consistent with results of an experimental study that showed depressed growth of C. pitcheri plants under a temperature increase of 6 °C that is projected for Illinois by 2095 (Staehlin and Fant 2015). Seed germination was also found to be lower at 25 °C compared to 20 °C (Gijsman and Vitt 2021), a result that warrants attention given that, under a high-emissions scenario, average summertime air temperature is projected to be above 20 °C in both the Lake Superior and Lake Huron basins by 2066 (ECCC 2022).

Threat 11.1. Habitat shifting and alteration

Increased water levels in the Great Lakes

The threat posed by changes to water levels in the Great Lakes as a result of climate change was not specifically addressed during the species threats assessment (ECCC 2019); however it is discussed in this management plan in light of recently published projections for future water levels in the Great Lakes. This parameter is applicable to Pitcher’s Thistle Ontario subpopulations given their occurrence within 500m of the Lake Superior and Lake Huron shorelines. Model projections show that the greater the increases in global temperatures, the wider the range of future water level values (i.e. both extreme highs and extreme lows compared to pre-2020 measured data are projected); they also show, on average, an increase in total over-lake precipitation and an increase in overall water levels for the Great Lakes (Seglenieks and Temgoua 2022). Under high lake water levels, the amount of Pitcher’s Thistle habitat would likely decrease as water engulfs low elevation beaches and dunes. This was observed in 2019 when water levels were high: habitat availability was reduced and plants were restricted to higher ground at the top of the dunes (ECCC 2019). By the same token, higher lake levels would also decrease habitat connectivity, thereby further isolating extant subpopulations (Fant et al. 2014).

Threat 11.4. Storms and flooding – impact: unknown

Winter storms

Wave action and ice scour stemming from winter storms act as natural beach habitat disturbance events. The recently observed increase in frequency and severity of winter storms is anticipated to affect dune dynamics on the Lake Huron coast, however there is uncertainty as to whether increased wave rush/ice scour is due to natural lake level fluctuations or climate change (ECCC 2019). The scope of this threat is reduced due to the fact that the Carter Bay and Desert Point subpopulations (which together account for 73% of the Canadian population) occur on parabolic (U-shaped) dunes, which are not affected to the same degree by ice scour/ wave rush as other dune forms.

5. Management objective

The management objective for Pitcher’s Thistle in Canada is to prevent the population from becoming Threatened or Endangered by:

• maintaining the population’s extent of occurrence (EOO)^{Footnote 9}
• maintaining or increasing the population’s index of area of occupancy (IAO)^{Footnote 10}; and
• maintaining or increasing the current number of subpopulations of Pitcher’s Thistle

The population’s EOO, currently calculated to be 43,438 km², is above the threshold for Threatened status (20,000 km²) and is not known to have been significantly larger historically^{Footnote 11}. However the IAO, currently estimated to be 136 km², is below the threshold for Endangered status (500 km²)^{Footnote 12}, and its value does decrease when a subpopulation is lost. According to COSEWIC criteria, declines in any of the parameters used to assess a species status, such as the EOO, IAO and number of subpopulations, must be prevented in order to reduce the risk of the species becoming Threatened or Endangered in Canada (COSEWIC 2021b).

To further reduce this risk, the objectives strive to not only maintain, but increase the area of occupancy and the number of subpopulations present in Ontario. The augmentation of extant, and the (re)introduction of new subpopulations could increase the viability of Pitcher’s Thistle metapopulations (Girdler and Radtke 2006, Halsey et al. 2015). Both types of interventions warrant consideration given the extremely small size^{Footnote 13} and/or the elevated risk of extirpation identified for several subpopulations of Pitcher’s Thistle in Canada (Nantel et al. (2018), and the species’ occurrence in dynamic habitat which renders subpopulations highly sensitive to environmental stochasticity^{Footnote 14} (Bell et al. 2003).

An increase in the number of subpopulations (colonization of unoccupied habitat) is likely possible given the existence of numerous areas of seemingly suitable, unoccupied habitat within the Canadian population’s natural range (PCA 2011, COSEWIC 2010). Establishment of new subpopulations will likely require human-facilitated dispersal, given the short dispersal distance of Pitcher’s Thistle seeds and reduced connectivity (greater distances) between extant subpopulations and unoccupied habitat (Halsey et al. 2015, Jolls et al. 2015). Facilitated dispersal has successfully led to the establishment of one introduced subpopulation (Hattie Cove) and two new sites^{Footnote 15} within the Oiseau Bay subpopulation in Pukaskwa National Park (PCA 2017, Patterson pers. comm. 2019), as well as the re-introduction of the species within the Christina’s Bay subpopulation (ECCC 2019). New subpopulations have also been successfully established in Indiana and Illinois (Fant et al. 2013, NatureServe 2022).

6. Broad strategies and conservation measures

6.1. Actions already completed or currently underway

The following conservation measures have been completed since the 2011 publication of the SARA Recovery Strategy for Pitcher’s Thistle (Cirsium pitcheri) in Canada:

• supported by funding from the federal government’s Natural Areas Conservation Program (NACP) and other partners, the Nature Conservancy of Canada (NCC) acquired the following properties where Pitcher’s Thistle occurs:
  • Kenewallyn, June 2011 (Kenewallyn-Murphy Harbour subpopulation)
  • Tasker Wilderness Shore, March 2012 (Taskerville subpopulation)
  • Cockburn Island properties, December 2012 and May 2017 (three subpopulations: Sand Bay - Doc Hewson Bay, Wagosh Bay, and Western Shore; see Appendix C, Table C-1)
• in 2013, Pukaskwa National Park staff initiated a long-term project to facilitate the dispersal of Pitcher’s Thistle seed, which has resulted in the successful establishment of two new sites within the Oiseau Bay subpopulation. Plants at both sites were observed in flower for the first time in 2021 (Patterson pers. comm. 2022)
• in 2013, as part of their project to address the threat of coastal wetland degradation due to recreational activities and invasive species, the Lake Huron Centre for Coastal Conservation developed a guide for the cottager community that provides stewardship recommendations for dune grassland habitat. This project was supported by the federal government’s Habitat Stewardship Program for Species at Risk
• given its status as a Threatened species on the Species at Risk in Ontario List, individuals and habitat of the Pitcher’s Thistle benefit from the protection provisions afforded under the ESA on non-federal lands. In 2014, a regulation prescribing the area as the habitat of the Pitcher’s Thistle came into force under the ESA (see Ontario Regulation 832/21, section 26)
• in 2017, the Parks Canada Agency (PCA) published the Multi-species Action Plan for Pukaskwa National Park of Canada under SARA (PCA 2017). The Action Plan provides details on the measures to undertake towards achieving the population and distribution objectives for the species included in the plan, which includes Pitcher’s Thistle. In 2022, PCA published the Implementation Report: Multi-species Action Plan for Pukaskwa National Park of Canada (2017 to 2022) (PCA 2022), which reports on the progress achieved towards implementing the measures described in the Action Plan
• in 2019, the Lake Huron Centre for Coastal Conservation, a non-government charitable organization, published the Coastal Action Plan for the Southeastern Shores of Lake Huron. The plan identifies management strategies to address threats to natural features and species within the Lake Huron shoreline from Sarnia to Tobermory, and specifically mentions Pitcher’s Thistle
• in 2019, the Ontario Ministry of the Environment, Conservation and Parks published a Review of Progress report for Pitcher’s Thistle under the ESA. The report summarizes recent activities that have taken place in Ontario related to the protection and recovery of the species at risk. 2019 review of progress towards the protection and recovery of Ontario’s species at risk: Pitcher’s Thistle | Ontario.ca
• from 2016 to 2019 and in 2021, a Manitoulin Island-wide project led by Winter Spider Eco-Consulting collected abundance data and controlled or eradicated the invasive European Reed at over two dozen sites where Pitcher’s Thistle subpopulations occur, resulting in the rehabilitation of at least 106.5 ha of Pitcher’s Thistle habitat. Through its outreach activities, the project has also been very successful in raising public awareness of the threat from this invasive species and in engaging landowners in the stewardship and monitoring of Pitcher’s Thistle (Jones 2020, 2021). This project was supported by the federal government’s Habitat Stewardship Program for Species at Risk and by the Province of Ontario’s Species at Risk Stewardship Program

   

  6.2. Broad strategies

  In order to achieve the management objective for Pitcher’s Thistle, conservation measures are organized under the following broad strategies:

  • land management, at both the site and ecosystem scales, to maintain sparsely vegetated sand dune habitat that is appropriate for metapopulation persistence;
  • species management, to decrease herbivory and facilitate Pitcher’s Thistle seed dispersal
  • outreach and communications, to raise public awareness regarding the threat posed by off-trail ATV and pedestrian activity, and to encourage habitat stewardship
  • municipal land-use planning and regulation development/enforcement, to decrease impacts of ATV use and mitigate threats from residential and shoreline development, construction of roads and recreational use in Pitcher’s Thistle habitat
  • research and status monitoring, to effectively address threats, and assess threats and subpopulation abundance trends;
  • alliance and partnership development, to coordinate conservation action implementation and share knowledge with land managers

6.3. Conservation measures

As previously mentioned, the sand dunes where Pitcher’s Thistle occurs is dynamic habitat: over time, sand erosion and deposition patterns, influenced by wind and longshore currents, lead to the creation of suitable habitat in new areas and its disappearance from others. Continued collaboration between the federal and provincial governments in supporting Indigenous communities, municipalities, industry and non-governmental organizations that undertake activities to benefit Pitcher’s Thistle will facilitate a landscape approach to conserving the species.

Measures to conserve the species in Canada are listed in Table 3. They include measures aimed at lowering the risk of extirpation in combination with those that aim to increase colonization of new areas. The conservation measures intend to counter the threats to the species in order to achieve the management objective identified in Section 5 above. The conservation measures have been categorized according to the Conservation Actions Classification system developed by the Conservation Measures Partnership, version 2.0 (CMP 2016).

The first category of conservation measures pertains to direct management of land and of the species itself. The measures focus on the implementation of plans to control vegetation cover and the spread of non-native plants in order to minimize encroachment into Pitcher’s Thistle habitat and maintain sparsely vegetated sand dunes; eliminate trampling from recreational activities in order to avoid direct mortality of individuals and sand erosion; reduce browsing pressure, and improve habitat connectivity at the landscape scale.

The second category of measures relates to human behavioural change. It includes outreach measures targeting private landowners and municipal governments in order to promote and implement beneficial habitat stewardship and management practices, as well as raising community awareness and improving and/or increasing enforcement of recreational trail use regulations.

The third category of conservation measures relates to planning and research activities that will enable the successful implementation of the management and outreach activities described above, the prevention of further negative impacts to the species, and the monitoring of emerging and potential threats. The measures include developing the site management plans described above, using municipal land-use planning processes to avoid impacts on subpopulations, conducting research on the pollination biology of the species, gaining a better understanding of potential impacts of climate change on the population, and conducting abundance surveys to evaluate the effectiveness of management action implementation.

Table 3. Conservation measures

A. Target restoration/ stress reduction actions

B. Behavioural change/ threat reduction

C. Enabling conditions

^a “Priority” reflects the degree to which the measure contributes directly to the conservation of the species or is an essential precursor to a measure that contributes to the conservation of the species. High priority measures are considered those most likely to have an immediate and/or direct influence on attaining the management objective for the species. Medium priority measures may have a less immediate or less direct influence on reaching the management objective, but are still important for the management of the population. Low priority conservation measures will likely have an indirect or gradual influence on reaching the management objective, but are considered important contributions to the knowledge base and/or public involvement and acceptance of the species.

^b See recommendations in McEachren et al. 1994, Stanforth et al. 1997, Bell et al. 2003, Girdler and Radtke 2006, Fant et al. 2013, Rand et al. 2015, Staehlin and Fant 2015, Godefroid et al. 2016.

7. Measuring progress

Every ten years, progress towards achieving the management objectives and monitoring the implementation of this management plan for the Canadian population of Pitcher’s Thistle will be measured against the following performance indicators:

• the EOO has been maintained (most recent estimate: 43,438 km²)
• IAO has been maintained or increased (most recent estimate: 136 km²)
• the number of extant subpopulations (currently 37) has been maintained or increased

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PCA (Parks Canada Agency). 2017. Multi-species Action Plan for Pukaskwa National Park of Canada. Species at Risk Act Action Plan Series. Parks Canada Agency, Ottawa. iv + 16 pp. https://wildlife-species.canada.ca/species-risk-registry/virtual_sara/files/plans/Ap-PukaskwaFinale-v00-Apr2017_Eng.pdf

PCA (Parks Canada Agency). 2022. Implementation Report: Multi-species Action Plan for Pukaskwa National Park of Canada (2017 –2022). Species at Risk Act Action Plan Series. Parks Canada Agency, Ottawa. vi+ 16 pp. https://species-registry.canada.ca/index-en.html#/documents/1620

Patterson, L., pers. comm. 2019. Email correspondence to K. Pickett. Ecologist Team Leader, Pukaskwa National Park, Parks Canada Agency, Heron Bay, Ontario.

Phillips, T. and M. A. Maun. 1996. Population ecology of Cirsium pitcheri on Lake Huron sand dunes I. Impact of white-tailed deer. Canadian Journal of Botany 74(9):1439-1444. https://doi.org/10.1139/b96-173

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Appendix A: Effects on the environment and other species

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^{Footnote 16}. 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 and to evaluate whether the outcomes of a recovery planning document could affect any component of the environment or achievement of any of the Federal Sustainable Development Strategy’s^{Footnote 17} (FSDS) goals and targets.

Management planning is intended to benefit species at risk and biodiversity in general. However, it is recognized that implementation of management plans may 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 management plan itself, but are also summarized below.

Pitcher’s Thistle is associated with the most open parts of dune habitats, both on the foredunes and in natural blowouts in backdunes. At least 46 rare or at-risk species are known from dunes on Lake Huron or Lake Superior in Ontario (Jalava et al. 2003), and some of these species share beach ridge, foredune, interdunal meadow, and blowout habitat with Pitcher’s Thistle and are likely to benefit from similar management activities. However, managing solely for early-successional dune stages could reduce the habitat for some species that require more stabilized backdunes, dune savannahs, or woodlands. The backdune shrubland and savannah communities associated with Great Lakes Dune Grasslands are also globally and provincially rare and support a high number of imperiled species.

The results of ecological modeling and site conservation planning suggest that maintaining a mosaic of dune stages is best for ensuring the long-term survival of the ecosystem (McEachern et al.1994). Management and land use planning for dune sites should therefore allow the dynamic dune-building and breakdown processes to occur, yet also incorporate enough landscape to allow natural succession in the inland parts of the dunes, thus maintaining the mosaic of microhabitats.

This management plan seeks to maintain a balance of microhabitats by simply allowing natural processes to occur unimpeded by threats to habitat, such as inappropriate ATV use and trampling from foot traffic. Reducing threats to habitat should benefit all dune species.

Managing deer and geese populations to limit browse will benefit dune vegetation, but depending on the approach taken, may have direct negative effects on the herbivore population. Currently, deer and geese have high population numbers, so presumably negative impacts from a slight reduction in numbers would be minimal. Discussion with wildlife management staff about how to mitigate the threat of browsing is a recommended approach.

Removal of invasive species, such as European Reed, will benefit surrounding native vegetation and associated native animal and insect species. However, methods to curtail the spread of European Reed have included the use of herbicide and mechanical cutting with machinery, both of which could have potential impacts to dune vegetation. Therefore, assessment will be needed prior to implementing removal to ensure the expected positive outcomes of the removal outweigh the expected negative impacts of not undertaking removal.

Other actions to mitigate threats involve the use of policy or public education and outreach, which are not expected to have any negative impacts to the natural environment or other species. Some examples of species at risk that will benefit from these conservation measures are listed below in Table A-1.

Appendix B: NatureServe subnational conservation ranks for Cirsium pitcheri in Canada and the United States

Rank definitions

S1: Critically Imperiled

At very high risk of extirpation in the jurisdiction due to very restricted range, very few populations or occurrences, very steep declines, severe threats, or other factors

S2: Imperiled

At high risk of extirpation in the jurisdiction due to restricted range, few populations or occurrences, steep declines, severe threats, or other factors

S3: Vulnerable

At moderate risk of extirpation in the jurisdiction due to a fairly restricted range, relatively few populations or occurrences, recent and widespread declines, threats or other factors

Appendix C: Pitcher’s Thistle subpopulations in Canada

* Subpopulations for which there were sufficient data to estimate extinction probabilities by Nantel et al. (2018). Of these, subpopulations assessed has having a greater than 5% probability of extirpation over the next 100 years are identified by double stars (**).