In 2018, Toronto and Region Conservation Authority (TRCA) initiated a multi-year management strategy for the removal of the invasive species Phragmites australis (Common Reed) around the shores surrounding Grenadier Pond in High Park with support from Urban Forestry. This multi-year management strategy will see the control of Phragmites over the next 3 to 5 years.
In fall 2018, TRCA controlled Phragmites growing in the terrestrial areas of shoreline surrounding Grenadier pond. In fall 2019, TRCA will continue management of phragmites around Grenadier Pond. Please see TRCA Handout and Map below for more details.
- TRCA Map
An alien invader is among us in Grenadier Pond. It has taken up residence along sections of the shoreline and in the marshes. Known as Phragmites, or the Common Reed, it is the most widespread plant on earth.
The plant’s scientific name is Phragmites australis, even though it has no connection to Australia. There are three strains of the plant. One is native to North America, and is widespread, but co-exists with other plant communities. This strain was used by aboriginal people to make arrow shafts and was woven into baskets.
A second is found along the southern areas of the U.S. from Florida to California and into Mexico and Central America. The third, much more invasive strain migrated to eastern North America from Europe, and possibly originated in the Middle East. A plant that takes over wetlands and displaces native species, it is believed to have been introduced to the U.S. east coast during the late 1800s, possibly through ships' ballasts. It spread through colonization of railway and road ditches.
It is thought to be this European strain, which moved from the U.S. East Coast to other parts of North America, that has become so widespread. Its appearance at Grenadier Pond is fairly recent: it was not until 1997 that it found itself on the list of the Canadian Botanical Conservation Network. By 2005, it was at the top of the list for invasive plants of natural habitats in Canada. It can now be found in all Canadian provinces.
Phragmites’ dense, dark purple flag-like flowers are produced in late summer. They are about 20 to 50 cm long. Later in the year, the numerous long, narrow, sharp-pointed spikelets appear greyer due to the growth of long silky hairs.
Phragmites colonization commonly occurs in disturbed marsh areas where plant communities, hydrology and topography have been altered through natural events such as floods and erosion, or human interventions such as pedestrian traffic, intentional flooding, dredging and soil disposal.
The germination success of phragmites increases with increasing temperatures while the time required for germination decreases as temperatures rise. For that reason, global warming enhances the plant’s ability to flourish.
The phragmites’ erect stems typically grows to 2 to 6 metres (6 ft 7 in to 19 ft 8 in) tall, with the tallest plants growing in areas with hot summers and fertile growing conditions. It has a hollow stem, stiff wide leaves and large plumy flowers. It commonly forms extensive stands of tightly-matted plants.
The plant is a highly successful colonizer in that it reproduces by spreading its seeds and by horizontal runners (rhizomes) which put down roots at regular intervals. It can grow 3 metres or more per year. It is also versatile, with the ability to grow in damp ground, in standing water (up to a meter or so deep), or even as a floating mat.
Phragmites is an invasive species. Invasive species are plants, animals or microorganisms whose introduction or spread threaten the environment, human health and/or the economy. Invasive species can alter how natural ecosystems function. They also often form clusters of a single species that displace most other native plants, animals and birds within an area. The negative impacts of invasive species are second only to the destruction of natural habitats as the leading cause of biodiversity loss.
In the case of Phragmites, its continuing spread is causing serious problems for many other North American wetland plants. Like many invasive species, it is resilient to disease and pests, hardy (well-adapted to many climatic and soil conditions) and has a high reproductive rate with high viability of offspring. It can tolerate standing water at various levels, low oxygen levels, salt water and acidic sediments, which allow it to thrive in disturbed habitats, such as roadside ditches or disturbed wetlands. In addition, the plant has a chemical weapon: it exudes an acid from its roots so toxic that the substance literally disintegrates the structural protein in the roots of neighboring plants. In this way, it topples the competition.
In Grenadier Pond, it has taken over an area where cattails, other emergent vegetation and open shore previously prevailed. The plant now forms a virtually impenetrable wall between the walking path and the pond, obstructing our view and possibly reducing available nesting areas. Conversely, the same wall provides shy wading birds some privacy from people and domestic pets that pass on the walking path.
Once established, Phragmites stands are difficult to control. The best approach is to monitor their growth through early discovery and to remove them regularly. In non-park areas, application of herbicides can be effective in killing established populations of Phragmites, but may also kill other, more desirable plants in the area. As well, if the site is not monitored thereafter, any surviving plants can quickly reoccupy the area.
The use of pesticides is not a practical option on the Grenadier Pond shoreline. For that reason, expectations are low for restoring wetlands already colonized by large, long-established populations of Phragmites in disturbed landscapes.
City Parks, Forestry and Recreation staff, along with the High Park Stewards, a group of volunteers, spend a substantial amount of time each year removing and controlling invasive plants. If you wish to become involved, see the Volunteer Stewardship Program or contact firstname.lastname@example.org.
Author: Ken Sharratt
Management Plan 2018 - Resources
Dept. of Agriculture and Agri-Food Canada per Ontario MNR website
US Dept. of Agriculture - Natural Resources Service and National Agricultural Library factsheet
Science Daily, Oct. 15 2007 article
Yvon Jodoin et al. Journal of Applied Ecology 2008 vol. 45 article
Michigan Dept. of Water Resources and Environment factsheet
Bernd Blossey - Cornell University website
Great Lakes St. Lawrence Cities Initiative
Ontario Grasses, Lauren Brown – handbook of Ontario plants
J. Swearingen and K. Saltonstall - Phragmites Field Guide, May 2010