November 28, 2000
Abstract. Spotted knapweed is an invasive plant species that takes over fields, roadsides, beaches, and disturbed land. The growth of spotted knapweed reduces the forage value of these habitats. Spotted knapweed can outcompete native plants because it can withstand periods without water and it releases a chemical that inhibits the growth of other plants. The goal of the study was to assess competitive interactions between spotted knapweed and native plants in selected habitats in the Eastern Upper Peninsula. The objective of the study was to determine whether total species richness, total density, and species composition was different inside and outside of spotted knapweed patches. Spotted knapweed patches were located along roadsides and beaches. Stem density was counted in two 20 cm by 20 cm quadrats in the patches and in adjacent areas without spotted knapweed growth. A paired t-test indicated no difference in species richness inside or outside the patches. Total stem density was greater inside the patches (p = 0.04). Species composition varied inside versus outside the spotted knapweed patches. These results do not indicate that the spotted knapweed is establishing monocultures on these particular sites, but species removal studies maybe necessary to determine long-term effects of spotted knapweed on native flora.
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