Invasive plants have many strategies that ensure their success and include:

• Releasing toxins that are toxic to native species. For example, diffuse knapweed (Centaurea diffusa) emits a toxin called catechin into the soil that can kill native plants.
• Growing rapidly to shade out native species. For example, The Garry Oak Ecosystem Recovery Team states that Scotch broom (Cytisus scoparius) and gorse (Ulex europaeus) pose some of the most serious threats to Garry oak ecosystems by shading out open understory plants and altering conditions needed by many birds, butterflies, and other species.
• Reproducing both by seed and vegetatively. For example, orange hawkweed (Hieracium aurantiacum) reproduces by seed, stolons, and rhizomes.
• Being unpalatable to livestock and other grazing wildlife or containing alkaloids that can be poisonous when ingested. For example, tansy ragwort (Senecio jacobaea) contains toxic alkaloids that can taint honey produced by bees and cause liver damage when ingested by grazing animals.
• Producing millions of seeds per plant that can lie dormant for decades. For example, purple loosestrife (Lythrum salicaria) can produce 2.5 million seeds per plant per year and gorse seeds have a hard coat and can persist in the soil for up to 40 years.

The key is understanding the impacts associated with invasive plants and collaboratively preventing the introduction of new species in British Columbia or detecting them early and responding quickly and efficiently. Once areas are infested by invasive plants, it is extremely difficult – if not impossible – to restore the area to it's natural state.

"...invasive plants (can cause) a level of destruction to the environment and the economy matched only by damage caused by floods, earthquakes, wildfire, hurricanes, and mudslides." US Secretary of the Interior

Economic Impacts

Invasive plants cause estimated crop losses of over $50 million annually in British Columbia. Species such as knapweed infest rangelands and reduce forage quality. Many other species out-compete desired species in cultivated fields. Invasive plants can also impact forestry operations by competing with seedlings for light, nutrients, and water; and recreation opportunities by puncturing tires, obstructing trails, and reducing aesthetics.

Currently, economic impacts of invasive plants is not well documented in British Columbia; however, in 2007 an Assessment of Models for the Collation and Communication of Information on the Economic Impacts of Invasive Plants (Report #2) was completed to summarize the benefits of improved awareness of economic impact information for invasive plants. Recommendations from this report led to partnerships with the provincial government to undertake Economics Impacts Research, which will quantify the economic impacts of invasive plants and their management in BC and is currently underway.

Ecological Impacts

Ecologically, invasive plants can alter habitats and disrupt essential ecosystem functions as well as displace native vegetation through the competition for water, nutrients, and space. More specifically, once established invasive plants can reduce soil productivity, impact water quality and quantity, degrade range resources and wildlife habitat, threaten biodiversity, and alter natural fire regimes.

Societal Impacts When established in crops or natural areas, invasive plants can result in lost incomes; reduced water quality and quantity (increased erosion and sedimentation); reduced land values; damage to private property and infrastructure; and loss of traditional food and medicinal plants. For example, due to the explosion of leafy spurge (Euphorbia esula), Manitoba has experienced a $30 million reduction in land values. Invasive plants can impact human health and safety by obstructing sightlines and road signs along transportation corridors, causing skin burns and dermatitis, and increasing allergies. For example, the leaves and stems of giant hogweed (Heracleum mantegazzianum), an escaped ornamental, contain a clear, watery, highly toxic sap that, if touched, can cause hypersensitivity to sunlight resulting in burns, blisters, and scarring of the skin. WorkSafe BC has issued a Toxic Plant Warning for this plant.