Phragmites australis – Phrend or Phoe?
Phragmites australis, also known as common reed, is an exotic grass, which comes from the Greek word “phragma” which means “fence” – a good descriptor of how it can grow – reaching heights of 15 to 20 feet.
Recently named invasive species of the month by the Maryland Invasive Species Council, some environmental specialists feel that it may be unnecessarily getting a bad reputation. Although it competes with native plants by blocking light and occupying underground growing space, “phrag” may help preserve coastal marshes by building up the substrate in pace with rising sea levels, and providing natural shoreline erosion control. The other viewpoint is that it negatively impacts a marsh by lowering plant species diversity, creating undesirable wildlife habitats, and elevating sediment levels to change hydrologic flow. Several species actually thrive in its habitat, including invertebrates, redwinged blackbirds, and muskrats which feed on its robust root system.
“When studied, Phragmites clearly has double the rate of accretion (gradual buildup) of other species, and the advantage is that it keeps in time with sea level rise,” said Dr. J. Court Stevenson, professor at the University of Maryland’s Center for Environmental Sciences-Horn Point Laboratory. “It’s a trade off – sea level rise and breakwater coming in – will inundate marshes if we let things go. Phrag keeps up with sea level rise at double the rate of other species. It also pumps oxygen into the sediments, and that includes denitrification. There are positive values with Phrag, but most wildlife biologists like to see more prevalent species in a marsh habitat, such as – salt marsh wrens and rails, which are not well supported by phrag marshes.” Blackwater Marsh near Cambridge for example – the biggest marsh in Chesapeake Bay – is being saved by Phragmites.
Phragmites is a very aggressive and opportunistic plant that reproduces by seeds and by a spreading root system. As such it has the ability to aggressively colonize large areas. This aggressive behavior gives Phragmites the ability to change a diverse wetland system to a vegetative monoculture. As Phragmites changes the floral composition of marshes, in turn the faunal composition is also changed. “Invasions” of Phragmites are usually associated with physical changes to the wetlands system including filling, dredging, and tidal inundation. Invasions of Phragmites reduces aquatic habitat and beneficial exchange of nutrients to estuaries surrounding wetlands. While these invasions are often considered to be problematic, recent studies show that Phragmites has many associated benefits. For example it provides natural shoreline erosion control, sediment filtration, water quality enhancement, and flood storage, as well as a minor food supply for some mammals, foraging fish, and invertebrates. Consequently, before attempting to control this species it is recommended that its attendant values be taken into account.
MDE frequently becomes involved in the creation and restoration of marshes for mitigation or Bay enhancement projects. In such situations it is critical to manage the site for Phragmites prior to the new marsh being established. A good example is the multi-agency environmental restoration project on Hart Miller Island. Located in Baltimore County waters of the Chesapeake Bay, this state park is accessible only by boat. The project is a commitment to citizens to create a mudflat habitat for foraging migratory shorebirds in the south cell of the Island. The key was to maintain adequate water over the site for the majority of the year. Ponds of carefully controlled depth were created to prevent phragmites from growing in the otherwise semi-moist conditions of the facility. This project will serve as an example on how to manage a constructed wetland to minimize Phragmites invasion. MDE is working with the Department of Natural Resources (DNR) and MD Environmental Service – for the Port Administration on this project.
Controlling the Invaders
Phragmites can be controlled by managing hydrology and herbicide application – the most effective. Small stands can be controlled by regular mowing, particularly before seeds are produced. Systemic herbicides such as Rodeo and Habitat are the preferred treatments. They are best applied during the fall months when nutrients are transported from leaves to root systems in plants.
Remember to Get a Permit
Before applying a herbicide to control Phragmites a Toxic Material Permit must be obtained from MDE by contacting Ed Gertler at [email protected]. Toxic materials use permits are required for any homeowner, farmer, local government or other person who wants to control aquatic life in ponds, ditches or waterways by the deliberate use of chemicals. The Department will also include a schedule for applying the product.
Maryland law requires the Departments of Environment, Natural Resources, and Agriculture to provide cost sharing to land owners to assist in the management of Phragmites australis. DNR is the lead agency for the cost share program. MDE provides technical and financial support. For more information on the cost share program contact Rick Ayella at [email protected] or Donald Webster at [email protected].
Bob Daniel, of the Customer Service Department contributed to the content of this article.