THE OPTIMAL BIOGEOMORPHIC ENVIRONMENT FOR A RARE DUNE THISTLE

Cirsium pitcheri, a thistle endemic to Great Lakes dunes, requires a narrow range of sand movement to survive. Because these specific geologic habitats are declining, C. pitcheri is designated a threatened species. This project investigates the micro- and meso- ecosystems of C. pitcheri to identify the optimal biogeomorphic environment for this rare plant. Our objectives were to investigate the biophysical characteristics of two blowouts, measure the abundance and characteristics of C. pitcheri at each site, and analyze the data to identify the optimal conditions for C. pitcheri to thrive. We investigated blowout characteristics using GPS and drone mapping, straight-line surveys, and surface change measurements with erosion pins. We recorded all C. pitcheri plants within the sites and conducted quadrat surveys for plant density and nearest neighbors. The mid-sized blowouts had heights of 2-4 meters and similar low levels of erosion and deposition. The two blowouts had large differences in total number of C. pitcheri plants, but all living age categories occurred in both blowouts. Ammophilia breviligulata, a dune grass abundant in Michigan, frequently grew near C. pitcheri. On average, the nearest neighbor of C. pitcheri grew less than 0.5 meters away. Despite the proximity of the nearest neighbor plants, percent vegetation cover around C. pitcheri was less than 40% on average. We concluded that C. pitcheri grows well in nearly-bare sandy soil among scattered plants. This study may provide dune managers with information needed to recognize and preserve biogeomorphic dune environments suited for C. pitcheri.