Invasion of Marsh Islands by Phragmites australis

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)