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Invasive trees and plants

Some trees, shrubs, and other plants are not recommended for planting because they are considered invasive.

Invasive plants have a tendency to spread and disrupt ecosystems in natural areas such as state and national parks and forest preserves. They can out-compete native plants, upsetting the balance of the ecosystem. They can make the habitat less suitable for native plants and animals. Invasive plant species are a significant and ongoing land management concern.    

Even if these trees, shrubs, and other plants don't cause problems in a garden or yard, they may still be a serious threat when they spread to nearby natural areas.

In northern Illinois, examples of invasive species include common buckthorn, Callery pear, Amur maple, burning bush, Norway maple, tree of heaven, and barberry. Even some native plants have undesirable invasive tendencies, such as boxelder.

How does a plant become invasive?

These species are often from another continent; most were introduced as ornamental plants for gardens and landscapes. In the distant places where they originated, they evolved as part of a complex ecosystem. They had natural enemies such as insects and diseases to keep their populations in check. Since they left those natural controls behind when they were brought here, these plants can spread more freely and rapidly than our native plants.

Because they did not evolve with our native animals, many of these plants do little to support our local wildlife. When they crowd out native plants, they deprive native animals of food.  

How do invasive plant species spread?

  • Many trees, shrubs, and other plants considered invasive are spread by birds and animals that consume the fruit and then deposit seeds in other locations, spreading these species far from the sites where they were planted.
  • Some invasive trees and shrubs have seeds that are spread by the wind and water, such as Norway maple, tree of heaven, and black alder.
  • Invasive perennials often produce thousands of small seeds that are easily dispersed. Others spread by sending out underground side stems that can sprout into new plants.
  • Some of these trees, shrubs and vines are still being sold as ornamental plants and planted by public and private landowners and managers, landscapers and contractors.


What can you do about invasive plants?

The Morton Arboretum does not recommend purchasing or planting these species and has removed many of them from its own property.