PARENT SESSION
Poster Session 20: Invasive Species
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Habitat-dependent response to simulated grazing by Canada Thistle (Cirsium arvense).

Dinkins, Meghan ¹, Louda, Svata ¹, ¹ University of Nebraska-Lincoln, School of Biological Sciences, Lincoln, NE, USA

ABSTRACT- Canada thistle (Cirsium arvense) remains one of the most problematic weeds in North America. In this study, we examined two questions. First, will clipping to simulate grazing reduce growth and ramet density of Canada thistle? Second, is the interaction outcome affected by light regime, soil moisture, or the timing and level of clipping? Overall, clipping significantly reduced subsequent ramet height, but it did not affect the number of flower heads per ramet or the change in number of ramets per plot. Moisture and light levels appeared to individually influence Canada thistle response to clipping. Marginally significant interaction accrued between clipping and canopy type (open vs. partial canopy) in explaining ramet height response. Furthermore, the effects of clipping on the number of ramets, flower heads per ramet and ramet height appeared to decrease with increasing soil moisture levels. These results suggest that plant response in relation to habitat conditions will determine when clipping, mowing or grazing on Canada thistle affects plant performance. To predict the effect of grazing, as simulated by clipping, it is clear that the intensity and timing of foliage removal as well as the environmental conditions need to be specified.

Key words: Canada thistle, Cirsium arvense , invasive species, thistle