Genetic and Environmental Controls on the Establishment of the Invasive Grass, Phalaris arundinacea

Whether an exotic species becomes integrated into a community or aggressively takes it over depends upon many interacting factors. Using contextual analyses, we combined genetic data about an invasive plant with information about the neighboring species, the community, and the environment to determine what factors enable a genotype or species to invade. We transplanted 50 individuals of each of three clones of the invasive grass Phalaris arundinacea, reed canary grass, into 150 random locations within a Vermont pasture. For each individual, we recorded clonal identity, neighbor identity, community indices (species richness and species diversity), and an environmental variable (soil moisture). The response variables were survivorship, above-ground biomass, below-ground biomass and the ratio of above- to below-ground biomass. Clonal identity affected both survivorship and below-ground biomass. The fastest tillering clone had poor survivorship but survivors produced a large amount of below-ground biomass, making this clone more likely to successfully overwinter. Neighbor species affected above- and below-ground biomass. Reed canary grass produced more above- and below-ground biomass when Anthoxanthum odoratum, a common pasture grass species, was abundant. Community attributes also influenced growth. Although we expected diverse plots to repel the invasion, plants in the more diverse plots had higher amounts of below-ground biomass. Finally, environmental effects also influenced growth. Reed canary grass produced more above-ground biomass in wetter plots, confirming that it does well under wet conditions.