An aggressively spreading invasive species is completely taking over a Toronto park
An aggressive invasive plant species that has been destroying native vegetation in wetlands across southern Ontario is threatening a Toronto park’s biodiversity and wildlife habitat.
Riverdale Park East is currently undergoing extensive environmental restoration to undo the damaging effects of several invasive plant species, including phragmites, a perennial grass that spreads quickly and outcompetes other native plants for water and nutrients.
It’s not exactly clear how the aggressive plant was transported to North America from its native home in Eurasia, but since its introduction, the species has completely infested coastal wetlands and sheltered bay coastlines across the province.
Phragmites release toxins from their roots in the soil to hinder the growth of and kill surrounding plants, resulting in decreased plant biodiversity.
According to Ontario’s Invading Species Awareness Program, the plant can also increase fire hazards as stands are composed of a high percentage of dead stalks and impact recreational activities such as swimming, boating, and angling.
One factor that makes the identification of invasive phragmites difficult is the existence of a closely related native subspecies. The invasive species can be distinguished by its ability to grow in extremely dense stands, with as many as 200 stems per square metre.
Invasive phragmites can also reach heights of up to five metres, with stems that are tan or beige in colour with blue-green leaves and large, dense seedheads.
In 2017, city staff, volunteers, and researchers began studying and removing phragmites, and other invasive species from the park, including garlic mustard, Canada thistle, common burdock, and stinging nettle.
This spring, more than 500 plants like arrowwood (Viburnum dentatum), purple-flowering raspberry (Rubus odoratus), and red-osier dogwood (Cornus sericea), are being added to the park with the help of volunteers.
Many of the plants are locally sourced trees and shrubs grown from seeds collected through the Tree Seed Diversity Program.
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