Next to habitat destruction, non-native plants are the biggest threat to natural diversity and the other services which forests and other natural areas provide. Certain plants can grow in a wide range of conditions, including low light, and have few natural enemies.

These characteristics make them extremely invasive and they tend to form dense patches of monoculture. As a result, seedlings of many native plants (including some tree species) do not survive. The net result could be a transformation of forest ecology throughout southwestern British Columbia, courtesy of spread from our urban area.

Impacts of Non-native Plants

Impacts on Wildlife

Non-native plants usually have a negative impact on native species resulting in less use by native animals and birds. This leads to decreased pollination, and less seed dispersal.

Interference with Forest Regeneration

Species which are shade intolerant e.g red alder (Alnus rubra) and bigleaf maple (Acer macrophyllum) might fail to become established due to shading by dense invasive plant coverage. Therefore there might be fewer trees over large areas leading to a reduction in biomass and carbon capture.

Reduction in Surface Litter

Reduction in the surface litter layer due to effects on forest regeneration and also to faster recycling of surface nutrients. This in turn leads to:

• Increased water leaching or surface run-off due to removal of water absorption capability at the soil surface.
• Increased temperature fluctuations due to removal of surface insulation.

Nutrient Recycling

Impacts on nutrient recycling due to a reduction of plants associated with nitrogen fixing bacteria e.g. red alder.

Stream Productivity

Reduced stream productivity due to less temperature regulation and food sources for aquatic organisms caused by having fewer riparian trees and shrubs.

Erosion

Increased erosion, and sedimentation in water bodies, due to loss of trees and shrubs with deeper roots, and increased surface run-off.
The net effect is a significant loss of ecological, financial and aesthetic values. (references provided on request)

For more information on invasive plants:

Invasive Species Council of Metro Vancouver
Sea to Sky Invasive Species Council

Threats to Forests & Natural Areas