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Impacts of Invasive Plants

The impacts of invasive plants on natural areas and the economy has led the BC (ornamental) horticulture industry to work cooperatively with invasive plant specialists towards increasing awareness by growers and the gardening public of invasive plants. Impacts of invasive plants include:


  • Once established in nature, invasive plants form dense populations which out-compete native vegetation and reduce species diversity, altering natural habitats. Compared to other threats to biodiversity, introduced invasive species rank second only to habitat destruction, and are a greater threat to native biodiversity than pollution, harvest and disease combined.
  • When a plant invades a habitat, it often out-competes native plants for resources such as light, water and soil nutrients (aquatic plants can even deplete oxygen levels in the water). Over time, this can cause dramatic ecological changes that negatively affect native plants, wildlife, and other organisms. Invasive plants with deep taproots can lower the water table and dry up streams. Because the soil composition and natural hydrologic cycles change, waterways become overrun with invasive plants, depriving the infested area of sunlight and dissolving oxygen formerly available to native vegetation and fish. Invasive plants growing in faster moving waterways can also increase flooding.


  • Economic impacts due to plant invasions are considerable. Invasive plants are very difficult to control when widespread in nature. Economic losses occur as direct costs of controlling the spread of established populations and addressing damage to infrastructures. It requires important workforce and specific materials over several years. Indirect costs include loss of ecosystem functions once invaded. For example, invaded areas in forests are less productive for silviculture (growing and maintaining forests, usually for harvesting), and invaded riverbanks or water surfaces lose a part of their esthetic or function, preventing people from fishing or exploring.
  • In Canada, invasive species include at least 27% of all vascular plants. The cost of invasive species to Canada is between $16.6 billion and $34.5 billion per year. Invasive species cause increased maintenance costs to public parks and private property, devaluing real estate. 
  • The Canadian Food Inspection Agency (CFIA) classifies 94 alien species as agricultural or forest pests and estimates that these regulated species cost the Canadian economy $7.5 billion annually (BC Ministry of Environment). 
  • Just six invasive plants caused an estimated combined damage of at least $65 million to BC in 2008. With further spread, impacts will more than double to $139 million by 2020 (ISCBC Report: Economic Impacts of Invasive Plants in British Columbia).
  • Estimated crop losses in BC cost the agriculture industry over $50 million annually (BC Ministry of Agriculture). Species such as knapweed infest rangelands, reduce forage quality and out-compete desired species.


  • Some invasive plants cause public health problems. They can also reduce property values, cause a loss of traditional food and medicinal plants, reduce land and water recreational opportunities, and drive export and import trade restrictions.

The toxic sap of the invasive ornamental plant, Giant hogweed, may cause severe skin burns and blistering. WorkSafe BC has safety guidelines for its removal.

  • Scotch broom causes seasonal allergies and hay fever;
  • Tansy ragwort can be toxic to horses and livestock;
  • Japanese knotweed obstructs sightlines along roadways and highway corridors

How are Invasive Plants introduced to BC?

  • Through intentional introduction as an ornamental or food plant;
  • By natural dispersal from one area to another by birds, wildlife, livestock, vehicles, railway cars and wind; and
  • As an unintentional by-product of disposal, primarily by garden waste dumping.

Prevention is Key

It is far more cost effective to prevent the introduction of new invasive species than to manage those that have already escaped into the wild. Thus, early recognition and interception of invasive plants would reduce the general financial burden of invasive plants on taxpayers and others trying to contain their spread.

A provincial initiative coordinated by ISCBC


Gardeners: Commit to be PlantWise
Help Spread the Word: Become a PlantWise Ambassador
Industry: Become a PlantWise Industry Partner
Report Invasive Plants

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