Invasive Non-native Species
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Sound the alarm!! There are aliens among us, but not the type seen in science fiction movies. These aliens are organisms that come from around the world as well as from other regions of Canada. You may like to eat some of these alien species (e.g., corn and wheat); others may be growing in your garden (e.g., Lily of the valley, periwinkle and even Giant Hogweed); and some may come to your bird feeder (e.g., European starling and house finch).
Most alien or non-native species peacefully co-exist with the plants and animals native to our region. In fact, about 27% of the organisms found in southern Ontario come from outside the region. But when non-native species aggressively spread and take over, they can harm the environment, the economy, and human health. When non-native organisms become invasive, we all need to be concerned!
There are many ways for alien species to find their way into our region. Some are brought here deliberately but the majority are accidentally introduced. For example, early European settlers unintentionally brought the first alien invaders to North America – the Norway rat, influenza and smallpox. Today, most alien species and diseases are transported with goods or people that are moving locally, nationally or internationally. Recreational activities such as boating, fishing and gardening are also significant pathways. Zebra Mussels, for example, first arrived in the Great Lakes in ballast water carried by ships from Asia. Boaters and anglers have since unintentionally helped these tiny creatures spread, carrying them on boats and equipment from contaminated water bodies. The Emerald Ash Borer is another invader that’s been getting a lot of attention lately.
Environmental groups and agencies have long been concerned about the impact of alien invaders on humans, habitats and other organisms. The spread of invasive alien species is a serious matter that affects the human health as well as ecosystem health.
Alien plant species come from other parts of the world such as Europe and Asia. Many non-native plants do not create problems in our environment and are an important part of our agricultural and horticultural industries.
However, some introduced species can disrupt the natural balance of our ecosystems. These invasive plants take over habitats, creating a mono-cultural environment (i.e., one species only) and depleting our native plant populations. They may also cause erosion in woodlots and reduce the beneficial mycorrhiza (fungus) in the soil that native trees and plants depend on to survive. They can hybridize with native species, thus depleting the genetic stock of our native flora. Native wildlife also have limited use for these plants and thus their food, cover and nesting sites are decreased when alien plants take over.
Once these plants are in our natural environment they can be very difficult to control. Many have aggressive root systems, produce an abundance of seeds and/or do not have any natural enemies in this area.
The best way to control these plants is to avoid planting them in your garden or near a natural area. They may be introduced through new topsoil, by wind or wildlife, or with other plants. Many are still sold at nurseries so buyer beware. Know what you are buying and learn the botanical or scientific name of the plant before purchasing. Research any new plant you may want to add to the landscape to make sure that it is not a potential threat to the environment. If the plant is already there, remove it from you property, especially if you are located near a natural area where it could spread.
An effective control method can depend on a number of factors such as location, species and life cycle. Some species may need two or more control methods and persistence to bring under control.
• Pulling – Hand pulling throughout the growing season can weaken the plant’s root reserves. Ensure that all parts of the root are removed or it may re-sprout.
• Cutting – Cutting works well with annual weeds. Remove the flowering parts so that it does not produce seeds and spread.
• Girdling – Remove a strip of bark 3 inches wide around the circumference of the tree or shrub to cut off its supply of food and water. Girdle near the ground to minimize suckering.
• Smothering – This method involves covering the area so that no light or moisture can reach the soil, thus killing the plant (e.g., lay several sheets of newsprint of black plastic over a weedy patch).
• Burning – Regular burning can control some early growing weeds and help encourage the growth of native species. This method is particularly useful for prairie habitats.
• Chemical control – Chemical control should be used as a last resort for hard-to-control or persistent species. Round-up™ can be spot applied to herbaceous plants to kill their roots. Non-toxic products are also available (e.g., Scott’s Eco-clear™ is a vinegar-based product).