Threatened species monitoring: Results of a 17-year survey of Pitcher's Thistle, Cirsium pitcheri, in Pukaskwa National Park, Ontario

Abstract

As part of the ongoing ecological monitoring initiatives at Pukaskwa National Park, Ontario, park staff have been monitoring Pitcher's Thistle (Cirsium pitcheri, Asteraceae) annually since 1981. This species is endemic to the Great Lakes region and is considered 'threatened' by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Over 17 years, the population has fluctuated greatly (mean = 401.7 plants with a standard deviation of 182.9). This fluctuation is attributed to the bursting of an upstream beaver dam in 1986 that wiped out much of the colony along the stream banks. The population remained low (< 300 total plants) for five years before rebounding in 1991, reaching a peak of 497 plants, in 1996. Although natural succession is of concern, there is no reason to believe that the population will not survive under current management practices.