Pitcher's Thistle (Cirsium pitcheri), a native plant of the sandy shores of the Great Lakes, occupies habitats ranging from active beaches and blowouts, through partially stabilized dunes, to stabilized sandy meadows. Dune environments are spatially heterogeneous at a variety of scales. Classical approaches toward dune ecology, comparing beach and inland dunes, have emphasized large-scale environmental gradients in plant community structure and composition, decreasing levels of sand deposition, and increasing availability of nutrients. However, local patches of vegetation, plant litter, or sand deposition can contribute to fine-scale heterogeneity, creating a mosaic of microhabitats independent of the classical gradient. In this study, we tested the hypothesis that C. pitcheri microenvironments and growth were independent of position in the dune chronosequence. Using plants on the sand dunes at Carter Bay, Manitoulin Island, Ontario, we measured the meteorological (air and soil temperature, wind velocity, light), edaphic (soil texture, organic matter, carbonates, moisture, pH, nitrogen, phosphorous, plant litter, sand accretion), and plant community elements of their immediate microenvironments. Preliminary results indicated that plant meteorological environments were independent of their position in the dune chronosequence (Mantel’s rM = 0.04, p = 0.312) but correlated with the local plant community (rM = 0.31, p = 0.04). As a result, regardless of their position, thistles in shrubby microhabitats shared low wind velocities, and low soil and high air temperatures. In contrast, plant edaphic environments correlated with their position in the chronosequence (rM = 0.38, p < 0.01); consequently, foredune plants shared higher soil carbonates, pH, and moisture. Despite these findings, no significant correlations were found between the growth of C. pitcheri and its dune microenvironments. Our results confirmed that the dune environments can be simultaneously heterogeneous at the local and chronosequence scales and demonstrated significant departures from the classically recognized gradients.

Key words: Cirsium pitcheri, coastal sand dunes, dune environments, environmental heterogeneity