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Phragmites Invasion; Detrimental or Beneficial - February 14, 2016

Maryland’s marshes are under attack; not from an animal or human activity but from a single, aggressive grass species. Phragmites australis is an invasive species of grass in Maryland that has spread across the state; from the bays behind Ocean City and Assateague to the tidal creeks of the Chesapeake Bay.Phragmites has rapidly changed many of our valuable wetlands from areas of high productivity and biodiversity to areas dominated by a single plant species with questionable productivity. With the damage to our marshes from sea level rise, land development, and pollution, the stress added to these ecosystems byPhragmites infestation is an additional problem marshes must contend with.

Phragmites is an extremely aggressive grass species that targets disturbed marshes that have been altered from their original state by natural or anthropogenic causes. After a disturbance event, such as Hurricane Sandy, many marshes are altered significantly by having soil washed away or having trees and plants torn from the marsh itself. This creates an ideal situation for Phragmites to establish itself in the disturbed marsh system. This can happen by seeds landing on the disturbed marsh or even living sections of root washing onto the marsh and creating new plants. Once a small population is established, the plant will reproduce via wind seed dispersal or more commonly, by extending its rhizome which is a horizontally growing root that grows laterally and adventitious roots. These can grow into a new area of the marsh and create new plants off the extended rhizome. A major problem with Phragmites is that it will continue to expand throughout the marsh until the marsh is a monoculture of Phragmites. Monocultures decrease the overall health of marsh by reducing biodiversity, changing marsh hydrology and nutrient cycles, increasing fire risk, and decreasing productivity compared to mixed vegetation marshes.

There are two main strains of Phragmites in Maryland; the invasive strain and native strain. The invasive strain was brought over accidently from Eurasia in the 1800s. Both strains grow to a maximum height of 15 feet and grow in clusters. The invasive strain grows in denser clusters than the native, which can kill surrounding plants by blocking sunlight and access to nutrients. The native strain lives in saturated to occasionally flooded soils; however, the introduced strain can thrive in permanently flooded soils that the native strain cannot. The native is also more inclined to live in a mixed-vegetation marsh while the invasive creates a monoculture, an area in which only one plant species thrives. The invasive strain has a greater photosynthetic rate and a higher nitrogen uptake rate, which combine to make it a better competitor than the native strain. The invasive strain requires almost four times more nitrogen to outcompete the native species; however, due to excess nutrients in our waterways this is not a hindrance.

Due to the invasive nature of Phragmites, there have been numerous efforts to rid ourselves of this plant; however, none of them have been very effective. The most common forms of removal and control are herbicides, mowing, draining, burning, and grazing. Consistent treatment is more effective than single applications.   Plants can readily regrow from their rhizomes or latent seeds in the marsh soil and the population sky rockets again due to disturbance in the marsh caused by the various extermination methods.  Consistent treatment over a number of years has proven effective in some cases, especially in small areas. So perseverance is necessary.

 New research indicates that Phragmites might have a hidden benefit for marshes. The research done by the Smithsonian Environmental Research Center (SERC) has found that the invasive strain has high carbon storage capabilities. In conditions with high nitrogen availability, Phragmites absorbed three times more carbon than native plants. The excess of nitrogen in our waterways, allows the invasive strain to grow for a longer period of time and create more chlorophyll; the green pigment necessary for plants to photosynthesize. This combination allows for the storage of large amounts of carbon in Phragmiteswhich means there is less carbon in the atmosphere. Excess carbon in the atmosphere increases sea level rise and creates more frequent and intense storms. Invasive Phragmites also builds up more soil belowground compared to the native. This will help protect marshes from sea- level rise and erosion.

 As we continue our battle with Phragmites, it is imperative to consider what is more important; a diverse species of wetland plants or a marsh that helps combat sea-level rise. In the future compromises may be possible, where invasive Phragmites are allowed to remain in marshes that are more vulnerable to sea-level rise. Further studies may be necessary to determine whether the benefits of invasive Phragmites outweigh the costs.

 

 

Jackson is the former Education Coordinator for the Maryland Coastal Bays Program and current graduate student at Clemson University.

 

 



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