Saltonstall, K., 2003. Recent Research on Phragmites australis in North America: Implications for Management, University of Maryland Center for Environmental Science.

Proceedings of the Aquatic Invaders of the Delaware Estuary Symposium, Malvern, Pennsylvania, May 20, 2003, pp. 12-15.

Recent Research on Phragmites australis in North America: Implications for Management

Abstract: Dr. Saltonstall presented a summary of recent Phragmites research with a focus on issues relevant to the Atlantic coast region. This included a discussion of causes and impacts of the invasion as well as background on native populations which persist.

Historical evidence of Phragmites in the United States:

  • 40,000 years ago: Scientists examined sloth caves from the Pleistocene period in Southwestern United States.  Examination of dung samples illustrated that Phragmites composed 60% of sloth diets.
  • 3,500 - 4,000 years ago: Phragmites was present in New England coastal marshes. Peat core analysis in Connecticut marshes indicated presence of Phragmites rhizomes.
  • 600 – 1,400 AD: Phragmites was integral to Anasazi culture. Archeaological findings in cliff dwellings indicated Phragmites was used for arrowshafts, cigaretts, prayer sticks, mats, flutes, etc.

Although historically present in the United States, Phragmites did not seem to grow as a monoculture. During peat core analysis, it was often found in mixed communities of sedges and forbs. Botanical records indicate that Phragmites was uncommon or rare in the 1800’s, however by 1975, it was recorded across all of the lower 48 states.

How did it arrive in the United States and rapidly spread? Packing material on ships and ballast from Europe containing peat and sediments was frequently dumped in coastal marshes bordering ports. Human–mediated transport, associated with Phragmites genetic traits, facilitated rapid range expansion.

Characteristics of Phragmites

  • Generalist; wide habitat range; brackish and freshwater conditions
  • Reproduces through wind dispersal of seeds, and vegetatively through rhizomes
  • Expands clonally through underground runners at a rate of several meters per year

Anthropogenic sources affecting Phragmites distribution

  • Habitat manipulation and disturbance
  • Tidal restrictions, flood control, and resulting changes in salinity
  • Pollution
  • Introduction of new genetic strain. The aggressive nature of Phragmites is likely the result of cryptogenic invasion, where the introduced species enters a lag phase, then undergoes rapid population expansion.

Several factors may also serve to limit the spread of Phragmites. They include:

  • Salinity (optimal range 0-15ppt)
  • Sulfides – clonal expansion enables Phragmites to escape high sulfide concentrations
  • Wave action
  • Reduced disturbance
  • Chemical and physical controls with repeated applications
  • Competition with other plants?
  • Nutrients?

Phragmites infestations affect whole ecosystems, in addition to individual plant and animal species. However, not all impacts are negative.

Positive impacts of Phragmites:

  • Sediment accretion; Phragmites is highly productive, creating nutrient-rich litter, and high inorganic sediment loading
  • Stabilizes soil, preventing erosion. In the 1940’s-1950’s, Phragmites was widely used in marsh restoration projects.
  • Pollution-tolerant; can concentrate pollutants, such as heavy metals, in roots and rhizomes.
  • Provides habitat

Negative Impacts

  • Alters marsh topography through accretion, filling in channels and tidal creeks
  • Ties up nutrients in biomass, not released as quickly as native vegetation
  • Alters light and temperature dynamics in the marsh; freezing occurs earlier in fall, thaws later in spring
  • Forms monoculture, has secondary impact on nutrient export
  • Changes marsh structure. Plant communities shift from mixed to monoculture in freshwater marshes; short grasses shift to tall grasses in saltwater marshes.
  • Alters animal communities? Impacts to marsh residents are largely anecdotal and are influenced by the stage of the invasion. In the early stages, fish and invertebrate communities are rarely impacted. In a late stage invasion, sediments accrete and fish habitat deteriorates.

Despite the common perception that all Phragmites is bad, recent research by Saltonstall demonstrates that Phragmites is native to the United States. Native populations are found primarily in tidal freshwater oligohaline marshes, along creeks, and near uplands. They occur in mixed communities and typically exhibit lower stem densities than non-native strains. Native populations have been confirmed in Maryland, Delaware, and Virginia, due in part to the vigilance of natural resource managers in conducting field studies. Plant samples can be analyzed through a free diagnostic service at Cornell University (www.invasiveplants.net).

Phragmites exhibits morphological variation. Although several characteristics can be used to differentiate between strains, no single “key” can be used in the field to label a plant native or non-native. A future goal for Saltonstall is to identify morphological characteristics that can be used to identify Phragmites in the field. Finally, as natural resource managers consider Phragmites control strategies, Saltonstall posed several questions that should be addressed when native populations are present:

  • Should we preserve native strains of Phragmites?
  • Are attempts to restore native Phragmites populations worthwhile?
  • Do native strains have similar impacts to the invasive strains on the environment and
    other species?

Discussion Questions:
 
Q - Phragmites populations are declining in Europe. Can any lessons be applied to control in the United States?
A - Not likely, because Phragmites is commercially harvested for thatching and there are multiple native herbivores that feed on Phragmites in Europe.

Q - When you’re restoring an unvegetated site, how do you prevent invasion by Phragmites?
A - The key is vigilance. By removing individual plants early (through digging or Rodeo application) before they send out shoots, you have a chance at preventing an infestation. Once native grasses and perennials become established, Phragmites is much less capable of invading. Ongoing monitoring is required.

Q - Are there ecological differences between the strains that affect competition?
A - This is the focus of Dr. Saltonstall’s future research; to examine competition among populations ranging from Maryland to Southern Canada along nutrient and salinity gradients.

Q - Is Phragmites being used for bioremediation of contaminated sites?
A - It has been used for wastewater treatment by local municipalities.

View Entire Proceedings (9.75 MB)
Contact: Kristin Saltonstall, Horn Point Laboratory, University of Maryland Center for Environmental Science, P.O. Box 775, Cambridge, Maryland 21613-0775, USA
Key Words: Common_Reed, Population_dynamics, Environmental_impacts
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