Population ecology patterns and threats to Cirsium pitcheri

Keywords: population ecology, Cirsium pitcheri, Pitcher's thistle, threatened species, Great Lakes, sand dune, blowout
Abstract Type: Poster Abstract

Abstract

Plant species dependent on a narrow range of environmental conditions are vulnerable to threats at multiple scales – ranging from local impacts due to humans and animals, to global changes in climate. This project investigates how a population of Cirsium pitcheri in a Lake Michigan coastal dune blowout is responding to threats, such as dynamic topography, deer herbivory, and human impacts. The study location is a blowout in Rosy Mound Natural Area, Michigan, where the spatial patterns and plant characteristics of C. pitcheri were mapped using GPS in 2024, as well as 2014, 2016, 2023. Characteristics measured include plant life stage and vitality, evidence of herbivory, sand movement, and surrounding vegetation communities. Results show that seedlings are largely concentrated around dead flowered individuals, in areas with moderate sand deposition, low-density vegetation, and full sun. In this blowout, herbivory by deer or weevils was not a significant threat. Anthropogenic impacts were limited to the boardwalk skirting the blowout. C. pitcheri habitat ranges are altered by major aeolian sand movement events associated with recent lake level changes. Deposition of sand can stimulate the growth of competing species such as Ammophila breviligulata and bury C. pitcheri seedlings. The distribution of C. pitcheri is consistently concentrated on the north half of the blowout, where there is more sun and a lower density of A. breviligulata. The most significant variable in C. pitcheri population patterns is the changing topography and competing species.