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

Executive Summary

Hill's Thistle (Cirsium hillii) is listed as Threatened under Schedule 1 of the federal Species at Risk Act (SARA). In Ontario, it is listed as Threatened on the Species at Risk in Ontario (SARO) List under the Endangered Species Act, 2007 (ESA). The global rank of Hill's Thistle is vulnerable, and is completely restricted to the Great Lakes Region. The Canadian range of Hill's Thistle may account for as much as 50% or more of the global population.

Hill's Thistle is a perennial with a deep tap root or a cluster of roots with tuberous swellings. The leaf margins and flower heads are spiny. The plants live as sterile rosettes for the first two to several years, until they produce an upright stem with a single, large flower head. After flowering and setting seed, the plants die. In Canada, Hill's Thistle is only found in the Manitoulin Region, on the Bruce Peninsula, and at Wasaga Beach Provincial Park (Simcoe County). There are 93 known sites and upwards of 13,000 individuals.

This species requires dry, open, grassy ground with little canopy cover. The required habitat can be found within several different vegetation types including prairies, sand barrens, oak and jack pine savannas, alvars, openings in woodlands, and behind dunes.

Some habitat for Hill's Thistle probably originates from fire, but there is little evidence to suggest that repeat burning after the initial fire at these sites has occurred. Hill's Thistle often occurs in areas of historic-era disturbance; however, in Canada today Hill's Thistle is never found in recently disturbed areas. In marginally suitable habitat, a trail may provide habitat where there is no other open ground, but in high quality habitat, anthropogenic disturbance may be detrimental and is not recommended as a management tool at this time. Threshold levels at which disturbance becomes harmful have not been determined.

Limited habitat is the primary threat to Hill's Thistle. The limitation may be due to filling in of habitat due to fire suppression or loss of habitat from development (building and road construction). Other threats include heavy machinery use for ornamental stone removal and logging, trampling by pedestrians or mountain bikes, and indiscriminate use of all-terrain vehicles.

Recovery is considered feasible for Hill's Thistle. The goal is to maintain, over the long-term, self-sustaining populations of Hill's Thistle in its current range in Canada, by meeting population and distribution objectives targeted to recover the species to Special Concern or lower. The population and distribution objectives for Hill's Thistle are: 1) No continuing decline in total number of mature individuals, and 2) Populations are maintained in the four core areas the species occupies.

Critical habitat has been identified and mapped for 90 polygons at 17 sites on the Bruce Peninsula, at Wasaga Beach, and in the Manitoulin Region, and will contribute significantly to the recovery objectives. Other recovery tools will be used to meet the objectives, and these will be achieved through implementation of a suite of broad strategies and approaches.

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