PARENT SESSION
Oral Session #39: Invasions: Effects of invaders -- Aquatic, marsh, riparian. Presiding: C. Kolar.
Wednesday, August 8, 2001. 8:00 AM to 11:45 AM. Madison Ballroom C.
Invasion and impact of Phragmites australis in tidal freshwater marsh ecosystems.
Meyerson, Laura1, Chambers, Randolph2, 1 2
ABSTRACT- Phragmites australis is an aggressive reed grass that invades marsh systems in North America. Several mechanisms that Phragmites may be using to achieve dominance were investigated in two freshwater tidal marshes in Connecticut by comparing selected ecosystem-level properties in Phragmites and non-Phragmites habitat. Our results suggest that the primary mechanism for Phragmites dominance is related to its rate of biomass accumulation and associated nutrient sequestration. Several aspects of biomass accumulation are important for Phragmites. We found that the recalcitrant quality of Phragmites stems leads to slow rates of decomposition. The resulting biomass accumulation decreases available growing space and light levels which in turn reduces plant species diversity. Further, marsh geomorphology is altered by the sediments that Phragmites traps during tidal flooding, as well as the high input and slow decomposition of organic matter that leads to marsh accretion. Eventually, flooding becomes less frequent and the diurnal, and seasonal flooding regime is altered by Phragmites invasion. One consequence of this strategy for Phragmites-invaded ecosystems is alteration of nutrient cycles because slower rates of Phragmites decomposition decrease nutrient availabilities. The long-term trophic effects resulting from the decreased export of organic and inorganic material to estuaries should be further investigated. These changes likely result in a legacy effect on the system that determines the direction of ecosystem development and succession for years to come.
KEY WORDS: Phragmites, invasive, biomass, decomposition