An evaluation of mechanisms preventing growth and survival of two native species in invasive Bohemian knotweed (Fallopia xbohemica, Polygonaceae).

Restoring native diversity to habitats dominated by invasive plants requires improved understanding of mechanisms that allow introduced plants to retain dominance. We used a factorial transplant experiment to assess whether light limitation, nutrient limitation, or allelopathic interference by Fallopia ×bohemica reduces growth or survival of Eupatorium perfoliatum or Acer saccharinum. Increased light improved A. saccharinum performance but had no effect on E. perfoliatum growth. Increased light had no effect on A. saccharinum survival but improved E. perfoliatum survival. Activated carbon addition had short-term benefits allowing E. perfoliatum plants to grow for 4 wk and increased A. saccharinum leaf width but not biomass. Nutrient addition had no beneficial effect on transplants. These results in combination with the outcome of a cutting experiment suggest that F. ×bohemica achieves competitive superiority primarily by limiting access to light. Species-specific effects and significant interaction effects particularly of light and activated carbon suggest additional mechanisms. Allelopathic interference or interaction with microbial soil organisms may contribute to the lack of native species in populations of F. ×bohemica. Restoration efforts should combine selective F. ×bohemica control with soil amendments (such as activated carbon) to assess their potential to facilitate return of native species to invaded habitats.