Invasion of Marsh Islands by Phragmites australis
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Invasion of Marsh Islands by Phragmites australis
Morphology• Perennial Rhizomatous Grass• 1-4 m tall (North America)• 50-100 stem m-2
Reproduction• Seeds• Rhizome fragments• Vegetative expansion
Invasive Species• Phragmites
– Large biomass production, restricts water movement
– Reduces light levels
Invasive Species• Phragmites
– Expanding into native Scirpus and Spartina marshin LA
– Impedes nekton movement– Alteration of
nutrient cycling
Hypotheses• Invasion depends
on: – island perimeter– Island area
• Invasion components– Establishment– expansion
Predictions• Large Perimeter
– Entry points
Predictions• Large Area
– Available space– Expansion
Methods• 18 islands• Rockefeller State Wildlife Refuge• Range of areas, perimeters
Methods• Perimeter Hypothesis
– Island Perimeter versus Rate of New Stand Formation
Island 1998 2005 2009
Methods• Area Hypothesis
– Island Area versus Rate of Increase in Proportion Phragmites
Island 1998 2005 2009
Methods• Perimeter and Area Hypothesis
– Island Perimeter/Area versus Proportion Island Area Phragmites
Island 1998 2005 2009
Problems• Invasion rate decreased 2005-2009
Hurricanes
• No decrease in stand formation
• Stand Formation 1998-2009• Stand Expansion 1998-2005• Only concerned with, “If Phragmites is
increasing…”
Limitations• Sample Size
– Expand to more islands, refuges• Time Range
– More years• Semester
– Lack of statistics
Conclusions• Perimeter effect?
– Yes• Area effect?
– No (maybe)
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