Distribution of Flodman's Thistle and Its Response to Different Disturbances

The importance of disturbance in prairie has long been recognized. Increasingly interest and research have focused on the action and interaction of multiple disturbances. The distribution of Flodman's thistle [Cirsiumflodmanii (Rydb.) Arthur] on ant mounds, badger mounds, buffalo wallows, and potholes and in a lightly and a moderately grazed pasture was compared at the Nature Conservancy's S. H. Ordway Jr. Memorial Prairie in northcentral South Dakota. In the lightly grazed pasture, Flodman's thistle occurred most frequently on hilltops and ridges, but in the moderately grazed pasture it occurred with equal frequency on hilltops and ridges, and low areas surrounding potholes. Flodman's thistle was common on earthen mammal mounds and was less abundant on thatching ant mounds and buffalo wallows. No thistles were sampled in potholes. Relative availability of light may explain the thistle's distribution. Implications of observed patterns are discussed for the evolution of life history traits and the management of prairie remnants.