Invasive Phragmites
(Phragmites australis)
Overview
Invasive Phragmites, a large perennial reed grass native to Europe and Asia, is quickly spreading throughout North America. This towering plant is capable of reaching heights greater than 5 metres and in densitites of over 200 plants per square meter, forming extensive monocultures that obscure sightlines at intersections, block drainage ditches and agricultural tile outlets, and destroys important habitat for wildlife. Once introduced into an area, the plant’s roots spread far and wide below the surface in a vast network of rhizomes. Its seeds are easily dispersed by wind, allowing phragmites to further invade other habitats.
While it can grow in terrestrial habitats, Phragmites prefers semi-aquatic to aquatic habitats such as wetlands, lakeshores, and wet fields. It also thrives in disturbed habitats, such as roadside ditches.
In 2005, Invasive Phragmites was recognized as Canada’s worst invasive plant by scientists at Agriculture and Agri-food Canada
Main Threats
Economic and Social Impacts
Phragmites has many negative social and economic impacts. It can impede drainage leading to reduced crop production. It can block sight lines at intersections creating driving hazards. Along infested shorelines it may reduce property values, recreational opportunities and aesthetic enjoyment
Loss of Biodiversity and Species Richness
Phragmites significantly reduces biodiversity of native plants and animals once it develops into monoculture cells. Only t he edges of these areas are used by native species while the interior is effectively a dead zone.
Loss of Habitat
Monoculture stands replace natural habitat and food supplies for various wildlife species, including Species at Risk. Phragmites stalks are rigid and touch, and do not allow for wildlife or humans to easily navigate.
Changes in Hydrology
Phragmites lowers water levels through high evapotranspiration rates resulting in the dewatering of shallow isolated pools. The dead plant stalks are resistant to decay and over time a thick layer of dead plant material can build up and fill in open ponds.
Changes in Nutrient Cycling
Phragmites does not break down as easily as native plant species and therefore significantly alters nutrient cycling, levels and availability in a system. This species effectively outcompetes native plants for available nutrients and is capable of sending roots downward several metres to obtain required nutrients and water.
Identification
Phragmites australis can be hard to distinguish from its native counterpart, as they share similar features and habitat. However, there are several trails that tend to differ between native and invasive phragmites and can be used for identification. Features that can be used for identification are listed below.
Photo: Great Lakes Phragmites Collaborative
Stem & Leaf Colour
Invasive phragmites usually has tan or beige stems and blue-green leaves, while native phragmites has more reddish-brown stems and yellow-green leaves.
Photo: Michael McTavish
Seed Heads
The seedhead of native phragmites is smaller and sparser when compared to invasive phragmites seedheads. In the above picture, the far left seedhead is from native phragmites, while the others are from invasive phragmites.
Photo: Nature Conservancy of Canada
Stand Density
Invasive phragmites typically forms very dense stands, forming a monoculture whereas native phragmites usually occurs in lower density stands mixed with other native plants.
Additional Resources
The following resources provide more information on invasive phragmites, including negative impacts, identification tips, and control methods:
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