What makes invasive plants able to thrive

Help to prevent the spread of invasive plant species.

By Renee Sandelowsky and Helen Varekamp

–  Renee Sandelowsky and Helen Varekamp are volunteers from the Bayfield area. They are writing, each month, about the importance of planting native species of plants and the importance of removing, and reducing the introduction of, invasive plant species.

The Government of Canada classifies introduced plant species, that cause harm or have the potential to cause harm, as Invasive Alien Species. 

The spread of these invasive species poses grave risks to biological diversity, reduces food security, impacts our quality of life and even human health. 

There are more than 500 invasive plants documented in Canada’s natural areas and the numbers of invasive plants in Canada are steadily increasing.

What makes invasive plants so ‘successful’ at our expense? 

• Aggressive Propagation: Invasive plants exhibit high rates of seed production and/or vegetative spread and can form dense monocultures, smothering or outcompeting native species of plants. 
• Early Season Vigor: Invasive plants can display rapid growth early in the growing season, maturing faster than native species of plants.
• Environmental Alteration: Some invasive plants possess the ability to modify their invaded environment, causing changes in soil or water chemistry, adjustments to nutrient cycling processes and impacts on water availability. This often creates conditions more conducive to further invasion, which degrade conditions for native plants.
• Few Natural Predators: Due to their origins in different geographic locations, introduced plants often have few co-occurring herbivores, parasites, and/or pathogens to regulate their populations.
• Adaptability: Invasive plants that can thrive in a wide range of environmental and climatic conditions pose the greatest risks. 

Consumers, and some businesses in the horticultural industry, may play roles in the spread of invasive plants. Consumers may have interest in new plants and some players in horticulture could search the globe for new plants to feed that consumer demand.

Those new plants may be introduced without testing for invasive tendencies. In addition, plant breeders pursuing desirable attributes, like improved hardiness and better flower production (which can mean greater seed production), can inadvertently select plants better equipped to become invasive. 

There is an urgent need for enhanced awareness and more stringent risk assessment protocols to strike a balance between horticultural innovation and environmental protection. You too can learn which plants are considered invasive for your area, and make your gardening choices accordingly.

To learn more, go to the Canadian Coalition for Invasive Plant Regulation website.

Read the document (PDF file), Reducing the Sales of Invasive Plants in Canada: To Safeguard Biodiversity and Human Health.

–  Renee Sandelowsky and Helen Varekamp are volunteers writing for the Canadian Coalition for Invasive Plant Regulation.