Missouri Invasive Tree Species

Oct 15, 2020

The top invasive trees/shrubs in our area:

• Callery Pear (Pyrus calleryana)
• Golden Rain Tree (Koelreuteria paniculata)
• Amur honeysuckle (Lonicera maacki)
• Japanese honeysuckle (Lonicera japonica)
• Autumn Olive (Elaeagnus umbellata)

What makes a plant invasive?

An invasive species is any species, either introduced or that escapes cultivation to take over and choke out native growing plants. Typically, this occurs because of rapid growth, copious seed or fruit production and hardiness or ability to acclimate to the area of invasion. This is especially true in the case of all plants listed above, almost all of these plants were brought in from overseas as ornamentals and escaped from cultivation.

The Callery pear (better known as Bradford pear) was widely planted as an ornamental tree as early as the 50’s. The Callery pear was initially from China, but in 1917, seeds were brought to the US as part of a breeding program to help breed fire blight resistance into fruiting pears that were going through a steep decline because of the pathogen. The breeding program turned out to be unsuccessful, but the Bradford pear turned out to be a candidate for an ornamental tree. By the 80’s, questions regarding the trees strength to stand up to wind, snow loads and ice storms caused many nurseries to have breeding programs to create a stronger and more vigorous Bradford.

There are several different varieties of Callery pears, including: Aristocrat, Capitol, Cleveland Select, Chanticleer, White House and Redspire. There are at least 26 varieties of Callery pear, and all can produce viable seeds when openly pollinated with another variety. All of which were bred to be sterile, meaning that they did not produce viable seeds to germinate. But when pollinated with another variety, the seeds produced by the small fruits became viable to germinate (YIKES!!!).

Most Callery pear varieties produce a prodigious amount of fruit, as the fruit ages on the tree and becomes a food source for many species of birds and small mammals who then spread the seeds after consumption. Quick to germinate and establish, a Callery pear can start blooming in as little as 3 years and produce fruit. They have quickly spread to open grasslands, fields, stripped land and along highways, their rapid growing nature allows them to out compete slower growing native trees and shrubs. It’s now not an uncommon sight to see whole groves of Callery pear growing where any open land is. While it’s not illegal to sell Callery pears or it’s named cultivars, the Missouri Department of Conservation urges nurseries to discontinue its sale, distribution, and production.

Alternatives trees to plant:

• Red Buckeye (Aesculus pavia)
• Serviceberry (Amelanchier arborea)
• American Hornbeam (Carpinus caroliniana)
• Redbud (Cercis canadensis)
• Fringe Tree (Chionanthus virginicus)

List provided by Missouri Botanical Gardens