Invasive Species and Biodiversity

An invasive species is an organism that grows and spreads quickly because it can adapt to a variety of growing conditions. Invasive species are often non-native (introduced from other areas) and lack the usual predators that control their population.  Non-native species can sometimes coexist with native species without becoming a problem. Concerns arise when a non-native species becomes invasive.

Under regular conditions, communities are made up of a variety of species that developed in the area and co-exist in harmony and balance. When a non-native species is introduced, it can grow in an uninhibited manner without the natural controls of its original area. Non-native species can be aggressive or vigorous growers and can overwhelm and out compete the local native species. This upsets the natural balance and results in the loss of the native species and sometimes whole communities, thereby lowering the overall biodiversity and health of an area. Invasive plants can lower biodiversity so greatly that they create a monotypic community (where the invasive species is the only plant growing).

Beyond the ecological losses and issues arising from the negative changes brought on by non-native invasive species, there is a social loss as well. Most of us enjoy the outdoors, especially when surrounded by a beautiful garden or the native species in woodlands. An invasive species can ruin this beauty.

Native Species

The term native can be used on a variety of scales. If a species is native to Canada it is not necessarily native to Ontario, and if a species is native to Ontario it is not necessarily native to your local region. A species can be considered native if it occurred in the region before human settlement introduced non-natives from other areas. Local native species are often called “indigenous.”

Human Impact

Although species introductions and range expansions have occurred throughout history, human activity has accelerated the long-distance transport of non-native organisms. Non-native plants are sometimes brought into a new area intentionally as ornamentals (by individuals or through garden stores) or for medicinal uses. 

Invasive species of plants and animals are also unintentionally transported to new locations in the ballast of ships, in animal fodder and packing materials, or through recreational activities such as fishing, boating, hiking, and camping. 

It is important to be aware of invasive species and to clean all seeds and soil from boots and equipment before moving to a different site. When engaged in water recreation, it is best to let equipment dry in the sun and remain dry for five days before moving to a new location. Be sure to get any firewood from close to where you will burn it; invasive pests can be transported to new areas when people bring wood from other areas. 

Some invasive non-native species that have upset local ecosystems include: Giant Hogweed; Purple Loosestrife in wetlands; Zebra Mussels in the Great Lakes; Garlic Mustard and Dog-Strangling Vine in woodlands; non-native Buckthorn in fields and valleys.

Being Aware

To help raise awareness, Conservation Halton has published their viewpoint on invasive species, and produced a few fact sheets on some major invasive plant species in our watershed

Other invasive species in the watershed include:

  • Gypsy Moth;
  • Emerald Ash Borer.

Preventing the Introduction and Spread of Invasive Plant Species

It is important to understand the differences between native species and invasive species, and to use species native to your local region for any planting or restoration projects. The more local the plant, the better suited the plant will be for your site. The following are tips that you as an individual can learn about and do to help prevent the introduction and spread of non-native invasive species:

  1. Use only locally native species for landscaping in and around natural areas, and use or promote using native species in garden landscaping. Always be aware of invasive species and do not use them. The use of non-invasive non-native plants has its place and they are acceptable in some urban areas and gardens away from natural spaces; it is still recommended however that you use only non-invasive native species. 
  2. Know or research which species are native to your local area and which are problem invasive species. For native woody and herbaceous plants that occur and are appropriate in Halton, you can start by consulting the “Native Herbaceous Vegetation List” and the “Native Woody Vegetation List.”
  3. Beware when you see the term wildflower in seed and plant mixtures! Often, wildflower is used to include non-native species that require low or no maintenance; many of these can be invasive. Read the label to see what species are included.
  4. Wildflower field guides will sometimes state if a species is native to Canada or Ontario. However, local naturalist clubs or conservation authorities will often have more specific knowledge of local native species in your area. It’s a good idea to approach your local gardening club; in many areas, the interest in native species is increasing and there are groups dedicated to promoting the use of native species.
  5. Discuss the issue of non-native invasive plants with your local garden club, garden centres and nurseries, or naturalist clubs. Encourage planting the right plant in the right location.
  6. Approach your local municipality about including native landscape plantings in municipal by-laws and municipal planting projects.
  7. If you see a priority invasive species please complete an invasive species reporting form or please send an e-mail to Brenda Van Ryswyk.

Some of these tips and information come from Conservation Halton’s Landscaping and Tree Preservation Guidelines. While the guidelines were developed to be used by landscape architects and other practitioners who prepare landscaping, restoration, or tree preservation plans for submission to Conservation Halton, they are available to anyone with an interest in learning more about some of the woody and herbaceous (green, leafy) plants that are and are not appropriate in the area.

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