Planting a Tree? Choose a Native Species and Save Some Insects
By Jess Hartshorn, Ph.D.
Invasive plants are everywhere: roadsides, forests, urban green spaces, and more. These plants can cause untold economic damage through their impacts on ecosystems, from competition with crops to choking out native trees in managed forests. Plus, when invasive plants, including ornamental trees, compete with natives, their ecological effects ripple out to to invertebrates and other associates that utilize native species.
One of these invasive ornamental trees is Callery pear (Pyrus calleryana); you may recognize it by its showy, white flowers that bloom significantly earlier than other, native flowering plants. Callery pear is the offspring resulting from a cross between the Bradford pear cultivar and any other pear species. They are frequently thorny, and these thorns can damage logging equipment or hurt people and pets. Several states have placed Callery pear on their invasive plant lists, eliminating the sale of P. calleryana at nurseries and other outlets. However, many states still sell Callery pear and other invasive trees, and some unregulated markets, like Facebook Marketplace, still exist where regulated plants can easily be found.
Many invasive plants were brought over unintentionally as hitchhikers in soil or on other plants, but did you know that every invasive tree we have in the U.S. was intentionally introduced as an ornamental? In a new research review published in January in Annals of the Entomological Society of America, my colleagues Sara Lalk and Dave Coyle, Ph.D., and I searched the literature to find information on interactions between invasive trees and shrubs, like Callery pear, and arthropods. What we found was striking: Many trees planted for ornamental purposes have significant negative effects on native arthropods and other groups.
Two examples include tree-of-heaven (Ailanthus altissima) and Norway maple (Acer platanoides), both of which not only crowd out native tree species but have also now become fertile host plants for invasive insect species: the spotted lanternfly (Lycorma delicatula) and the Asian longhorned beetle (Anoplophora glabripennis), respectively.
And although we have extensive evidence of ecological and economic damage that non-native ornamental plants cause, they are still sold across the country in big box stores, local nurseries, and online. Many more non-native ornamental trees and shrubs are virtually unknown in terms of their impacts on arthropods, other plants, wildlife and humans, and the evidence suggests that these impacts could be huge.
Ornamental trees are, however, important in the urban and suburban landscape; they improve air quality, reduce energy costs, increase biodiversity, and filter water, among other services. Urban trees serve an important role in the ecosystem and deserve our attention. So, now that folks are starting to plan their spring landscaping, its important to do a little research before deciding on what plants to buy.
- Plant the right tree for the right site. Each tree needs its own space to thrive, and trees without the correct conditions may succumb to insect and disease issues. Know ahead of time what you can plant based on your site.
- Know your hardiness zone. These are geographic areas defined by their climatic conditions, and knowing yours can help you determine what plants to purchase for your backyard or garden.
- What do you want to get out of your tree? Knowing what benefits you seek is also helpful in choosing the right tree for your site. Are you looking to attract pollinators? Do you want to reduce road noise or increase your property value?
- Check out your local extension resources. Many extension websites have resources for you to select the right tree for your site. Be sure to visit your local extension website for information on native trees you can select for your needs.
- Ensure proper planting and care. Selection is only half the battle; to be sure your tree lasts well into the future, plant it properly and make sure you care for it well.
- Understand that insect and disease problems happen to native trees. Usually these problems do not require control, but, if they do, be sure to contact your local extension agent to discuss management plans.
Finally, no matter what tree you select, be sure that its native and well cared-for!
Annals of the Entomological Society of America
Jess Hartshorn, Ph.D., is an assistant professor of forest health in the Forestry and Environmental Conservation Department at Clemson University in Clemson, South Carolina. Email: firstname.lastname@example.org.