Competive ability of invasive Miscanthus biotypes with aggressive switchgrass

Miscanthus (Miscanthus sinensis Anderss. [Poaceae]) is an ornamental and invasive grass native to Asia that has naturalized in several areas of the Middle Atlantic United States. Predicting how likely miscanthus is to become invasive in other areas of the US is a concern of ecologists and horticulturists. The objective of this study was to measure the competitive ability of miscanthus with an aggressive native grass, switchgrass (Pancium virgatum L. [Poaceae]), in order to show which grass would be more likely to dominate when the two species were grown together. Although switchgrass is a smaller plant than miscanthus, in this greenhouse experiment it was significantly taller and had more vegetative and flowering culms than miscanthus. Miscanthus however, was a stable competitor and did not significantly change in shoot or root dry weight as 2 and 4 switchgrass plants replaced the respective number of miscanthus plants in each treatment. When miscanthus biotypes from four locations were compared, the Pennsylvania biotype was significantly larger and more competitive with switchgrass than was the Washington, DC biotype. As switchgrass plants were replaced with miscanthus, the shoot and root dry weights of the remaining switchgrass plants increased significantly, showing a higher competitive ability of switchgrass. Despite the fact that switchgrass was more competitive with itself than miscanthus, the highest overall dry weight per treatment contained eight switchgrass plants. Miscanthus showed stable, competitive growth when planted together with switchgrass and it is predicted to likely do the same in a field setting.