What are Invasive Plants?

Invasive plants are non-native plants which are generally free of the natural predators that help to keep them in check in their native habitats. Without these natural controls, invasive plants have a competitive edge over native vegetation. Their competitive edge is also attributed to an ability to produce thousands of seeds per plant, aggressive absorption of nutrients and moisture, rapid growth, and many others.  The impacts from invasive plant infestations are many: crop yields are reduced, range productivity for livestock is lowered, wildlife suffers from a reduction of their forage base, and recreational land values

The arrival of knapweed...

are diminished.

Most invasive plants were accidentally introduced to North America from Europe and Asian countries. For example, knapweed came here in the late 1800s as a hitch-hiker in alfalfa seed from Europe. Invasive plants, like knapweed, have spread rapidly and now infest many different regions of the continent, including BC. People are the major cause of invasive plant spread, as plants are easily caught up and transported on the undercarriage of trains, cars, RVs, logging trucks and heavy machinery. Spread is common in the movement of hay from infested areas to non-infested areas, and by florists and nurseries who unknowingly use and sell invasive plants. 

What are the Impacts?

Invasion of British Columbia's Southern Interior rangelands by invasive plants is causing considerable environmental deterioration and economic loss to the cattle industry. For example, over 60,000 hectares in BC are currently infested with spotted and diffuse knapweed, but there is a potential for these weeds to infest 1 million hectares of grassland range and undetermined area of fringe forest. The map at right shows the areas of knapweed infestation in the CRD. Note how the infestation tends to follow the transportation corridors.

Economic Loss
Invasion of rangelands by invasive plants impacts the beef production industry by displacing the grasses that cattle forage on. Since most invasive plants are unpalatable to cattle, grassland lost to invasive plant encroachment represents a substantial economic loss in equivalent hay production. In the case of knapweed, It is estimated that the economic impact from lost hay production amounts to over $400,000 annually, but could total over $13 million if knapweed spreads to its ecological limits within BC. If allowed to infest the total susceptible grassland area in Western Canada, the potential economic loss could climb to over $58 million, which would have devastating impacts on the cattle industry.

Environmental Loss

Bighorn Sheep

Displacement of native range vegetation by invasive plants affects wildlife too. Animals like bighorn sheep, deer, and elk rely on grasses and herbs for much of their diet. Although difficult to quantify, it can reasonably be expected that rangeland forage lost to invasive plant encroachment could result in a significant decline in their numbers, as well as changing their distribution patterns.  Invasive plant encroachment can also impact the biodiversity of range environments by changing the habitat characteristics that native mammals, birds, and insects rely upon for their nesting, breeding, dietary, and other needs.  Second only to habitat loss, invasive species are among the biggest threats to biodiversity.