Species Specific Session Abstract

Phragmites australis: An Overview of Introduction, Distribution and Management in Chesapeake Bay Wetlands

Curtis Hutto
Virginia Department of Conservation
and Recreation

Phragmites australis (common reed) is an aggressive coarse rhizomatous perennial grass that can grow up to 15 feet tall; it tends to inhabit brackish or freshwater wetlands, growing at or above mean high water. Recent peat core evidence suggests that Phragmites has been a component of native Northeast marsh mixed tidal wetland communities for the last 3,000 years. Much information has been written recently about the spread of P. australis into coastal communities, often accelerated by anthropogenic disturbances such as dredging and excessive nutrient inputs to fresh water systems. By the late 20th century, P. australis was well established in fresh and brackish wetlands in North America and began to expand its range and abundance exponentially. Although common reed does have some positive attributes (erosion control potential on some sites, nutrient removal and water quality improvement, wildlife habitat for some organisms), the near monospecific stands often replace diverse native wetland plant communities, resulting in altered ecosystem processes and associated detrimental impacts on native birds and other wildlife. Concerns are also being recognized in relation to the colonization of constructed wetland sites by common reed. In a recent study in Virginia, 80% of the 15 largest constructed wetland sites were colonized by the invasive P. australis. Recent work has also emerged to distinguish two separate haplotypes of common reed in North America. Distinctive morphological characteristics can be used to identify the non-aggressive native P. australis. These native stands may also have a higher diversity of plant and animal species, although very little work has been completed to confirm this hypothesis.

Using aerial photographs and GIS image analysis, the distribution of common reed in Chesapeake Bay coastal marshes was documented in the late 1990s by the U.S. Fish and Wildlife Service; over 10,000 acres of Phragmites were found in Maryland and Virginia, with the majority of the infestations along the Maryland shores. While ground mapping is often impossible due to the inaccessible nature of many Phragmites stands, image analysis is also difficult because of the similar signatures of patches of wild rice (Zizania aquatica) and big cordgrass (Spartina cynosuroides).

Successful control measures are targeted toward reduction of abundance on a landscape scale, rather than eradication. The on-the-ground methodology usually centers around a combination of chemical treatment with glyphosate and prescribed fire, although other measures such as the use of black plastic, mowing or water level management have also been used with success on a smaller scale. Timing of application is critically important for chemical control, and is usually scheduled for late summer or early fall after inflorescence development is complete and the plants are actively moving stored energy from the leaves to the rhizomes. Although prescribed fire can be tricky in dense Phragmites patches, this treatment can be used in conjunction with chemical application and serves to remove layers of necromass and accelerate the colonization by desirable native wetland species.

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