Seed germination and seedling growth of invasive Phragmites australis from forested and developed watersheds of the Chesapeake Bay

The rapid expansion of the non-native genotype of Phragmites australis in wetlands in North America has raised questions about what factors control its establishment and whether Phragmites response to these factors varies among populations.  We evaluated Chesapeake Bay populations of Phragmites from developed and forested watersheds, using degree of watershed development as a proxy for nutrient enrichment.  We assessed how seed viability, dormancy, and germination varied within and among populations from different watersheds in a growth chamber experiment using early growing season conditions.  We also evaluated seedling response to nitrogen fertilization in a greenhouse experiment.  We found highly variable seed viability and germination within and among the watersheds, with the highest seed viability and highest and most rapid germination from populations from developed watersheds.  In addition, Phragmites seedling response to nitrogen fertilization varied among populations from different watersheds.  The importance of seeds in Phragmites invasions has been largely discounted in the ecological literature.  Our findings indicate the large potential of some populations of Phragmites to spread readily via seeds and for seedlings to grow vigorously in highly eutrophic watersheds.  These populations clearly will require greater attention when managing Phragmites invasions.