Invasive species are plants, animals and micro-organisms that have been accidentally or deliberately introduced into areas beyond their native range. Invasive plants are alien species whose introduction or spread negatively impact environment, the economy, and/or society including human health.
Degradation of Our Natural Environment
Natural areas such as forests, prairies, wetlands and lakes provide many ecosystem services and benefits. Natural areas provide shelter and food for wildlife, remove pollutants from air and water, produce oxygen and provide valuable recreational and educational opportunities.
Invasive species threaten and can alter our natural environment and habitats and disrupt essential ecosystem functions. Invasive plants specifically displace native vegetation through competition for water, nutrients, and space. Once established, invasive species can:
- reduce soil productivity
- impact water quality and quantity
- degrade range resources and wildlife habitat
- threaten biodiversity
- alter natural fire regimes
- introduce diseases
Invasive species threaten many rare and endangered species and now those species are at risk of extinction. Once established, invasive species become costly and difficult to eradicate. Often, the impacts are irreversible to the local ecosystem.Back to top
Impacts on Agriculture
Invasive plants can have a wide range of impacts on the agricultural industry. Invasive plants can act as new or additional hosts for new or existing crop diseases and crop pests, they can cause reductions in crop yields and may require increased use of pesticides to control them. This increases costs for farmers and reduces crop values. Estimated crop losses in BC agriculture industry of over $50 million annually. Species such as knapweed infest rangelands and reduce forage quality. Many other species out-compete desired species in cultivated fields (Source: BC Ministry of Agriculture, Food and Fisheries. 1998. Integrated weed management—an introductory manual). The estimated annual economic impact of invasive plants on Canadian agriculture is $2.2 billion (Environment Canada, 2010).Back to top
Interference with Forest Productivity
Invasive species, specifically invasive plants, can interfere with forest regeneration and productivity through direct competition with tree seedlings, resulting in reduced density and slowed growth rate of tree saplings. Reduction in forest regeneration and productivity results in the loss of wildlife habitat, and decreases the diversity of a stand, making it more vulnerable to insects and disease.Back to top
Social and Aesthetics Impacts
When established in crops or natural areas, invasive plants and/or species can result in:
- lost income
- reduced water quality and quantity (increased erosion and sedimentation)
- reduced property values
- damage to private property and infrastructure
- loss of traditional food and medicinal plants
- reduced land and water recreational opportunities
- increased control and management costs
- export and import trade restrictions imposed
Some invasive plants, like giant hogweed (Heracleum mantegazzianum) and wild parsnip (Pastinaca sativa), cause human health concerns because their sap is toxic to skin. Other plants can cause physical injuries to the body; common buckthorn (Rhamnus cathartica) branches end in a short, sharp thorn which may inflict injury. Human safety may also be impacted by fast growing invasive plants. For example, Phragmites australis (hereafter referred to as Introduced Phragmites) grows large and rapidly, and may reduce visibility at rights of ways, increasing the risk of car accidents. Dead, dry stalks of Introduced Phragmites are also highly combustible and can become a fire hazard.
Natural areas in municipalities support a wealth of recreational activities including hunting, fishing, swimming, hiking, bird watching, and mountain biking. Invasive plants that invade recreational areas often reduce the area’s attractive and enjoyable qualities. For example, invasive plants may reduce native plant biodiversity, affecting the number of songbirds in the area; walking through dense vegetation can prove difficult; and popular swimming areas may become unusable with the presence of invasive aquatic plants. Seeds and other plant parts can hitch rides on hiking boots, clothing, pets, birds and vehicles, resulting in new infestations, potentially over great distances.Back to top
Invasive plants can have a large economic impact on individual landowners and municipalities. A recent study shows that property values for shoreline residences in Vermont affected with Eurasian water-milfoil (Myriophyllum spicatum) were down as much as 16.4 % (OMNRF, 2012). Due to the explosion of leafy spurge (Euphorbia esula), Manitoba has experienced a $30 million reduction in land values (CFIA, 2008). Leafy spurge infests 340,000 acres of land in Manitoba, costing taxpayers an estimated $19 million per year to protect grazing land, public land, and rights-of-way (CFIA, 2008). In Ontario, the MNRF has been involved with invasive Phragmites control pilot projects since 2007 and to date control costs range between $865 and $1,112 per hectare (OMNRF, 2012). Invasive species have an impact on approximately 20% of Species at Risk in Ontario (OMNRF, 2012).
Invasive plants directly affect municipalities with reforestation projects and recreational trails. They increase management costs (e.g. project planning and monitoring) and they increase operational costs (e.g. mowing, pruning and hand pulling). They also complicate reforestation projects as they need to first be removed, and then the gaps created through removal must be addressed by using large, potted plant stock, or additional site maintenance to prevent the risk of re-invasion.
The economic impact of invasive species in Canada is significant. According to Environment Canada and Climate Change:
- The estimated annual cumulative lost revenue caused by just 16 invasive species is between $13 to $35 billion.
- Invasive species that damage the agricultural and forestry industries results in an estimated $7.5 billion of lost revenue annually.
To find more information about the invasive species in your province or territory, visit their websites hereBack to top
Canada's Unwanted Invasive Plants
This list outlines some of Canada’s unwanted invasive plant species from coast to coast to coast. The goal of the list is to raise awareness of invasive plant species across Canada. It was developed by cross-referencing Invasive plant lists from Invasive species councils across Canada as well as regulated species lists. Not all of the species are currently widespread in the gardening, horticulture or landscaping trade, but are still of high concern across Canada and could be traded among gardeners or the horticulture community. As Canadians, it is our responsibility to not grow, plant, trade or buy these high risk, invasive plants in order to protect the natural diversity of Canada’s landscapes.Back to top