ENVIRONMENTAL CONSTRAINTS ON EARLY ESTABLISHMENT OF PHRAGMITES AUSTRALIS IN SALT MARSHES

Finding environmental constraints on the establishment in salt marshes of Phragmites australis may help elucidate human activities that facilitated its invasion. We tested the effects of rhizome burial, salinity, anoxia, and sulfides on emergence, survival, growth, biomass production, and spread. In greenhouse and field experiments, rhizome burial facilitated initial emergence in well-drained soils. Rhizome emergence was prohibited in poorly drained treatments, regardless of salinity or sulfide concentrations. Emergence in well-drained treatments was not affected by salinity or sulfides, but survival, growth, and biomass storage of the culms and rhizomes were diminished in salt treatments. Combined with other studies, these results indicate that Phragmites invasion is a multi-stage process, with emergence constrained by poor drainage and survival constrained by lack of burial opportunities and salinity. These conditions constrain early stages of the invasion only, as later stages of the invasion can spread into anoxic and high salinity areas. These results also suggest that the process of invasion is facilitated by different human activities at different stages. Emergence is facilitated by soil disturbance, rhizome burial, and altered drainage. Survival through the first season can be facilitated through activities that lower porewater salinity.