Population ecology of Cirsium pitcheri on Lake Huron sand dunes I. Impact of white-tailed deer

Abstract

Cirsium pitcheri is a monocarpic perennial endemic to the shorelines of the Great Lakes, primarily Lakes Huron and Michigan. Its populations are being reduced by anthropogenic impact and deer grazing throughout much of its range. Several of its once abundant populations at some locations have been extirpated. The species is listed as threatened and endangered in Canada and the United States, respectively. Greenhouse studies were conducted to determine the effects of simulated herbivory by white-tailed deer on the survival, growth, and compensatory ability of plants. We found mat Cirsium pitcheri possessed good ability to compensate for tissue loss. However, simulated intensive browsing resulted in significant reductions in root dry weight. Since the flowering ability of monocarpic perennials such as Cirsium pitcheri is dictated by the amount of stored root reserves, such reductions in root biomass may delay the onset of flowering, reduce overwinter survival, and affect the future growth and survival of this threatened species. Keywords: white-tailed deer, browsing, defoliation, compensation, Cirsium pitcheri, Pitcher's thistle.