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Forests - Invasive Species

Whether they are called invasive, nonnative alien, exotic, or nonindigenous, introduced species are those that evolved elsewhere and have been purposely or accidentally relocated . While some species have invaded habitats on their own (e.g., migrating wildlife, plants and animals rafting on floating debris), human exploration and colonization have dramatically increased the diversity and scale of invasions by exotic species. Introduced species often find no natural enemies in their new habitat and therefore spread easily and quickly.

Invasive species represent a threat to our forests. Plants such as dog-strangling vine, garlic mustard, and common buckthorn spread quickly in the understory and diminish the forests’ resiliency and health.

Common Buckthorn

Garlic Mustard

Dog Strangling Vine

Giant Hogweed

Russian/Autumn Olive


Common Buckthorn (Rhamnus cathartica)
Common Buckthorn
Common Buckthorn
  • Native to Europe
  • Also called European buckthorn
  • Naturalized in much of Southern Ontario
  • First introduced as an ornamental shrub
  • Produces seed at a young age
  • Prolific seed production, dispersed by birds
  • Resprouts from cut stumps
  • Usually successful with repeated control measures

    Common Buckthorn Fact Sheet (PDF - 5MB)

Videos: Invasive Species Hunter (Youtube)

Join Nate the Invasive Species Hunter as he looks for Southern Ontario's highly invasive species. He'll show you how to manage and control common buckthorn on your property.

Youtube Link



Youtube Link


Garlic Mustard (Alliaria petiolata)
  • Native to Europe, introduced to North America in late 1800's for medicinal use and as a green vegetable
  • Hamilton, Toronto and Ottawa are the main areas of abundance for the species
  • Produces a garlic odour when its leaves are crushed
  • Commonly found in woodlots, urban areas, and roadsides
  • Garlic mustard reproduces by seed production only
  • Forms monocultures and displaces native spring flora
  • A biennial plant (flowers every 2nd year)
  • Forms monocultures and displaces native spring flora
  • Success with control measures

    Garlic mustard Fact Sheet (PDF- 5MB)

Garlic Mustard
Garlic Mustard

Dog-strangling vine (Cynanchum rossicum)
Dog-strangling vine
Dog-strangling vine

  • Native to Europe, brought to North America n late 1800's
  • Possibly introduced to Ontario from the Experimental Farm in Ottawa as research plot escapee during testing in WWII as a possible filler for lifejackets
  • Member of the Milkweed family, reproduces by windborne seed and spreading underground rhizomes
  • Forms dense mats
  • Quickly becoming a problematic species in Southern Ontario first noticed by CLOCA in 1997
  • Difficult to control

    Dog Strangling Vine Fact Sheet (PDF - 5MB)
Giant hogweed (Heracleum mantegazzianum)
  • Native to Asia, brought to North America as ornamental plant
  • Often found in floodplains, wet soils, and roadsides
  • Can reach heights of 2.5 - 5 metres tall, each plant can produce 100,000 seeds
  • Due to its large stature it can outcompete native plants by over shading them and spreading aggressively by way of seed dispersal
  • Very similar to the native Cow Parsnip (Heracleum lanatum)
  • Represents a significant public health hazard
  • Sap reacts on skin with exposure to sunlight
  • Contact with sap can cause painful burning blisters within 24 – 48 hours, contact after contact and can cause can lead to scarring. Contact with eyes can cause permanent blindness
  • Not yet a major problem in Durham with few occurrences. Spreading quickly in Southwestern Ontario, Halton Region, recently discovered in Ottawa Valley/ Renfrew County

    If You Become Exposed:

Giant Hogweed

Russian /Autumn Olive (Elaeagnus angustifolia/Elaeagnus umbellate)
Russian Olive (E. angustifolia)

  • Originally from Asia and was introduced in the late 1800’s
  • Grows 5 -7 metres tall as a shrub or tree. It produces small fruit and seeds are spread by bird
  • Autumn olive is from eastern Asia
  • Can fix nitrogen through its roots allowing it to grow in poor soils
Autumn Olive (E. embellate)
Insect species that are threatening our forest health but have not yet been located within this region are the Asian Longhorned Beetle (Anoplophora glabripennis) and the Emerald Ash Borer (Agrilus planipennis) . The Asian Longhorned Beetle has been found in Toronto and Vaughan. Emerald Ash Borer was first observed in 2002 and has since spread throughout Southwestern Ontario. Although it has yet to be found in the region, it has been identified in Toronto and Pickering.

The Canadian Food Inspection Agency (CFIA) is the lead agency when it comes to these two invasive insects. If you think you have discovered either of these insects on your property, please call your local CFIA office.

Asian Longhorned Beetle
Asian Longhorned Beetle
Emerald Ash Borer
Emerald Ash Borer
For additional information on invasive species visit the Streams and Wetlands sections.

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