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Forest Invasivesbreadcrumb separatorIntro to Invasivesbreadcrumb separatorWhat Makes a Species Invasive?

What Makes a Species Invasive?

Unique forest environments are created and maintained by a perfect balance of many coexisting factors—climate, food webs, a diversity of species at all trophic levels, nutrient cycles, soils, etc.— that interact to form an ecosystem. Thousands of years of co-evolution and adaptation by native species in a competition for resources creates this perfect balance, where each species occupies its own unique niche within the environment. A species is considered ‘exotic’ when it is introduced into an ecosystem outside of its native range. Exotic species can arrive into Canada through a number of pathways, such as hitchhiking on travelers' luggage, movement of infested wood products (firewood, shipping crates), or through natural dispersal. Many exotic species introductions have very little impact on our native environments, and often disappear as soon as they arrive, or establish themselves within the new ecosystem without disturbing the local balance. Imagine planting an exotic palm tree in a Canadian forest; it would not survive the winter, and would be unable to establish itself on our landscape. However, every so often a species is introduced into a new environment where the conditions are favourable for establishment, and the exotic species becomes invasive.

Usually, an invasive species is also exotic; brought from a different location through a pathway of spread. However, in rare cases, a native species can become invasive if the balance of the ecosystem is changed, like in the instance of climate change. This allows the native species to expand its native range, and invade new environments.


Mountain pine beetle damageThe mountain pine beetle invasion is currently devastating the pine forests in British Columbia and Alberta. Mountain pine beetle is a species native to B.C. that has been spreading far outside its native range and becoming invasive in new environments. Usually controlled by cold winter temperatures and natural disturbance, this dramatic invasion is the result of many factors, including climate change and fire suppression.

  Photo: William M. Ciesla, Forest Health
  Management International, bugwood.org 

In order for a species to become invasive, it must possess the ability to outcompete and overwhelm native flora and fauna in its introduced range. There are a number of traits characteristic to invasive species to facilitate this ecological advantage.

If an invasive species in a suitable habitat is undetected and unregulated, it can become established in the environment, and spread uncontrollably across the landscape. Introductions like this can cause immeasurable impacts to our economy, ecology, and social values. In fact, invasive species introductions are commonly regarded as the second greatest threat to global biodiversity, next to habitat loss (Wilcove et al., 1998). To read more about the potential impacts of invasive species, click here