Invasive alien species are the second greatest threat to global biodiversity after habitat loss. Non native plants and animals can disrupt native ecosystems to such an extent that the native species can no longer compete. They can become endangered or even extinct, leaving behind a monoculture of weeds.

Some introduced plants and animals are well known for their destructive behavior. For example, cane toads, rabbits, and pigs were introduced into Australia to solve agricultural problems or to provide familiar species for settlers to hunt or raise for food. However, these introduced species have escaped, invaded, and increased in population. The cane toads take up the habitat of native toads and frogs. Rabbits and pigs have no natural predators in Australia, and have become serious agricultural pests. In the southern United States, kudzu was imported from Asia and planted along roadsides as an erosion control measure. But this fast-growing plant soon spread, and now covers trees and bushes, smothering native plants, depriving them of sunlight. When crossing the border from British Columbia to Alberta, there are signs that say, 'Keep Alberta Knapweed Free.' Knapweed, Eurasian millfoil, and purple loosestrife are examples of introduced plants that have invaded ponds, lakes and rivers. They are choking out many of North America's wetland ecosystems.

These are just of few of the thousands of examples of alien species that have become problematic when introduced into an area where there are no biological checks and balances. All over the world, countries are beginning to recognize the magnitude of the environmental and economic threats of introduced invasive species.

Some introduced species are not yet acknowledged as problems because of their short-term economic value. An example is Bromus inermis, or smooth brome. This grass was introduced to North America from Asia with early European settlers. Smooth brome grows quickly, is hardy, and provides good forage for grazing animals. It is also used for erosion control along roadsides. Unfortunately, smooth brome is spreading rapidly and taking over native rough fescue grasslands. Prairie conservationists are not only concerned with the loss and fragmentation of prairie habitats, but they are very concerned about smooth brome's negative impact on native biodiversity.

Nearby to where I live is a small patch of native prairie and aspen parkland, called Whispering Woods. I played in this park as a child, and do not remember there being much thistle or brome there at that time. However, during my 13 years as a steward in this park I have noticed the increasing extent of both. In particular, after an early spring fire in 1999, the entire burned area became infested with brome and creeping thistle [some people call this Canada thistle, but it is also from Eurasia]. In 2003 I began mapping the extent of the brome and thistle and submitted a website on this topic to the Canada Wide Virtual Science Fair. Since that time I have mapped the park two more times, and now have data from three growing seasons. The successive maps show how the brome is creeping in from the edges of the park, and that the small patches have become bigger. This information demonstrates the urgent need for a restoration and management plan for the park.

If smooth brome were formally declared an invasive species, there would be a more focused provincial effort to control it. Environmental management must balance the benefits and costs to both the economy and the environment. Monocultures often precede ecosystem collapse. Thus, managing for biodiversity must take priority in ensuring we all live in a healthy, shared habitat.