/ Effectiveness of Hand-Pulling the Invasive Mossy Stonecrop (Sedum Acre L.) From Alvar Pavements
ï~~44 THE MICHIGAN BOTANIST Vol. 39 44 THE MICHIGAN BOTANIST Vol. 39 FIGURE 1. Mossy stonecrop (Sedum acre L.). raised about the invasiveness of mossy stonecrop on alvar: whether it spreads rapidly, whether it excludes native plants from using a portion of the habitat, and whether the disturbance caused by its removal would increase renewed growth of stone crop or other weed species. Work on common St. John's wort (Hypericum perforatum L.) by Stephenson (1995) in the alvar grassland of Maxton Plains, Drummond Island, Michigan, showed that hand pulling was ineffective for that species since plants from seeds stored in the soil more than replaced pulled plants. There were additional concerns about pulling mossy stonecrop that didn't occur with other weeds in other situations. For instance, mossy stonecrop roots are thread-like, can be >10 cm long, and are difficult to remove in their entirety because they break. In addition, because the plants grow in areas of such shallow soil, it was thought that hand pulling to remove them might do more damage from soil displacement than good. As well, like most members of the Crassulaceae, mossy stonecrop fragments very readily and easily regrows from both leaf and stem fragments (personal observation). Thus, hand pulling might accidentally increase plant dispersal and regrowth. The selective use of herbicide was not considered as a control method because stonecrop occurs in small, shallow pockets of soil sitting on impervious bedrock. This and the small stature of the weed would make it nearly impossible to prevent the herbicide from pooling on the surface of the rock and affecting other plants.
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