GLEAM

Great Lakes Environmental Assessment and Mapping Project

Phragmites

Invasive phragmites near Lake Erie
Invasive phragmites near Lake Erie (Photo: Michigan Sea Grant)

Invasive common reed (Phragmites australis), is a perennial grass causing significant ecological and economic impacts in the Great Lakes region. The plant grows rapidly, creating dense stands that choke out all other plant species and provides very poor quality habitat for other wetland organisms.  It has been found in coastal and interior wetlands, streamside corridors, roadside ditches, and other areas with wet soil.

Impacts of invasive Phragmites

Phragmites is a major threat to the biodiversity and function of coastal wetlands. The plant forms dense monocultures which:

  • Crowd out native plants
  • Inhibit animal movement
  • Serve as a poor quality food for animals
  • Slow decomposition
  • Alter water levels
  • Block sunlight to underlying plant communities
  • Reduce habitat diversity

A native form of Phragmites does exist in the Great Lakes region, but it is quite rare. The invasive form of the plant is quickly displacing the native variety, along with many other native plant species. Once established, invasive Phragmites is difficult to eradicate, often requiring a combination of repeated herbicide applications, burning and other control techniques.

                           

Mapping Phragmites as a Great Lakes stressor

  • We mapped location information from remote sensing imagery of monotypic Phragmites stands provided by Michigan Technical University Research Institute1 and georeferenced point locations from the Ontario Natural Heritage Information Centre2 and the Global Biodiversity Information Facility.3
  • We used a 10-km shoreline buffer to eliminate observations further inland.
  • Canadian point locations along roadways were converted to stands using a 500-m buffer on the assumption that these were stands too small to be detected in the remote sensing data.
  • For all other Canadian observations, locations were converted to stands using a 5-km buffer, since Phragmites dispersal distances are frequently this large.4
  • To propagate the effects of the stands (most of which were on land) into the lakes, for every 1-km2 waterside shoreline pixel, we calculated the distance to the nearest invasive Phragmites patch.
  • We normalized these data assuming that closer proximity to Phragmites had stronger negative effects (intensity 0 = no effect of Phragmites since all stands were >10 km away; intensity 1 = Phragmites stand located in that pixel).

 

Spatial distribution of Phragmites as a stressor in the Laurentian Great Lakes (Inset: Western Lake Erie).

Web_26_Phragmites.jpg

Data Sources: 

1. Bourgeau-Chavez, L. L., K.P. Kowalski, M.L. Carlson Mazur, K.A. Scarbrough, R.B. Powell, C.N. Brooks, B. Huberty, L.K. Jenkins, E.C. Banda, and D. Galbraith. In Review. Mapping invasive Phragmites australis in the coastal great lakes with ALOS PALSAR satellite imagery for decision support. Journal of Great Lakes Research.
2. Ontario Natural Heritage Information Centre. 2011. Phragmites: georeferenced point locations. Ontario Ministry of Natural Resources (OMNR), Peterborough, Ontario, Canada.
3. GBIF biodiversity occurrence data provided by: Acadia University, University of Alberta, Canadian Museum of Nature, Agriculture and Agri-Food Canada (C.E.F. Ottawa), Eastern Ontario Biodiversity Museum, Manitoba Museum of Man and Nature, Université de Montréal, McGill University, Nova Scotia Museum, Université Laval, Ministère des Ressources naturelles, University of Saskatchewan, University of Toronto, University of British Columbia, University of New Brunswick, University of Prince Edward Island, University of Western Ontario, Royal British Columbia Museum, University of Waterloo, University of Manitoba. Accessed through GBIF Data Portal, data.gbif.org, 2011-10-18.
4. Fer, T. and Z. Hroudova. 2009. Genetic diversity and dispersal of Phragmites australis in a small river system. Aquatic Botany 90(2):165-171.