Great Invaders: What Makes a Plant Invasive?

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English ivy climbs up other plants. Photo: Carl Lewis / CC by 2.0

English ivy climbs up other plants. Image by Carl E. Lewis / CC by 2.0

Uh oh, there it is again. It’s that sneaky plant wriggling its way into the garden. While a ‘weed’ is really just a plant that you don’t want in the garden, an invasive species is more than a weed. It’s a persistent plant that’s good at making a nuisance of itself. Invasive plants can come to dominate an ecosystem very quickly, changing the food and habitats that are available in a landscape. In doing so, invasive plants not only take over from indigenous plant species, but they also manage to alter the environment where animals live, causing a cascade of changes in the ecosystem.

How does a plant become a successful invader?

Ecosystem Damage: Introduced Species Have Few Natural Controls

Invasive plant species enter an ecosystem from somewhere outside of that ecosystem. They may arrive by accident in a shipment of other plants, or they may be purposefully introduced by gardeners who don’t realize that the plant will become invasive. In the places where they naturally live, the plants have animals that eat them and diseases that damage their population. In the new area, however, they may not have any natural predators or diseases.

Invasive Plants Thrive On Challenges

Who’s up for a challenge? Invasive plants grow very well in environments that other plants might find too difficult. Look along the side of the road, or in a pond, and you’ll usually find invasive plant species there. These plants are tough, and they may well be pioneer species in their native environment. These fast-growing plants are poised to move into a hard environment: it’s what they do at home.

Invasives Leap Across the Landscape

While not all invaders are vines or groundcovers, being a groundcover makes it easy to move quickly across the soil, covering large areas and running amok over existing vegetation. Some groundcover plants like English Ivy can also climb trees and will do so very quickly.

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