Invasive Species

The increase in global movement of goods and people during recent times has matched the increased transportation of species from their native habitat into foreign ecosystems. When an introduced species can quickly flourish and impact native plants, landscapes or aquatic habitat, it is called an invasive species.

Biologists believe that invasive species are a major cause of global species extinction. When invasive species thrive in a new ecosystem, they often outcompete native species by occupying habitats and competing for food.

Some invasive species are brought intentionally as ornamental plants and pets. For example, English Ivy, still used extensively in gardens, now thrives in many forests across North America. It crowds out native ground-cover and can damage trees either by sheer weight, or by harbouring bacteria.

Many invasive species, such as the Zebra mussel, arrive by accident. The zebra mussel is just one of an estimated 130 alien species introduced into the Great Lakes since the St. Lawrence Seaway opened in 1959. In Lake Erie, this highly invasive mussel has severely impacted the lake's food web by reducing phytoplankton abundance, and has almost eliminated some native clam species. It is an extreme nuisance, causing millions of dollars in damage, mostly by plugging water intake pipes. The mussel continues to spread into freshwater ecosystems in North America.

In British Columbia, non-native Atlantic salmon farms threaten native Pacific salmon stocks by carrying disease and competing for habitat. Atlantic salmon are now found in B.C.’s creeks and rivers, and compete with Pacific salmon for spawning habitat. For more information read the David Suzuki Foundation's "Super un-Natural: Atlantic Salmon in BC Waters" report (PDF). In Manitoba and Saskatchewan, Dutch elm disease has eliminated almost all mature elm trees. Invasive plant species tend to do especially well in disturbed environments, which further clarifies the need to preserve our remaining natural ecosystems.

Keep in mind, however, that many species that are considered pests are actually native species that have important ecological functions. For example, the mountain pine beetle is a naturally occurring species of British Columbia, and contributes to the landscape level dominance of Lodgepole Pine. And mosquitoes, although annoying, have been here a long, long time, and are here to stay.

The seemingly benign rhododendron, which was brought into England as an ornamental plant, covers huge areas in environmentally important national parks in Great Britain. With it’s dense branches and leaves, the rhododendron allows little light to reach the ground, while a symbiotic relationship with a fungus toxifies the soil. Recent efforts to remove this invasive plant has cost tens of millions of dollars, leaving behind soils will not de-toxify for another 5 to 10 years.

For more information about invasive species see www.invasive.org