Invasive species alert!

Callery pear photo by New Invaders Watch List
Callery pear photo by New Invaders Watch List


 Cedar Rapids City Arborist Daniel Gibbons wants residents to be aware of an invasive species that could become a problem soon in Iowa. The ornamental Callery pear is a popular urban landscape tree, valued for its white flowers.  But Gibbons, who served as horticulturist in Columbia, Mo., and has held his Cedar Rapids post since January, warned that as the trees age, hybridizing starts. The wild seedlings, which produce thorns and have weak branches, can grow in the sun, shade, or anywhere and overtake prairies and other native areas. Birds that eat the berries spread the seeds.

    While Gibbons has not heard of the wild version growing in this area yet, he noted that education is important. “In order for it not to happen, the word needs to get out,” he said. “Education may save us.”

      Here is more on this invasive species, from the Cedar Rapids Public Works Department:

 The introduction of exotic plant and tree species for the purpose of aesthetic gardens or utilitarian roles has been practiced within the fields of horticulture and forestry since ancient times.  Our tendency to become dissatisfied with native flora all too often cultivates a desire to expand our landscape pallet to non-native varieties and cultivars.  Such new specimens can produce vivid floral or textural displays, offering an arboretum or landscape renewed appeal. 

 Unfortunately, the cost of promoting newly discovered species that are out of place in our native ecosystem is rarely known until years after introduction.  Much of the time there are minimal impacts to the native ecosystem from well contained non-native landscapes.  Occasionally however, a plant or tree can escape and pose enormous consequences to native plant communities.

 Pyrus calleryana, is one such exotic species that has “escaped”.  Ornamental (Callery) pear trees have been prized for their tidy form and magnificent spring display of snow white flowers.  Although now known to be weak-wooded and prone to storm damage, Callery pear cultivars such as ‘Redspire’, ‘Bradford’, ‘Capital’, ‘Cleveland Select’ and others are foundational to many landscapes because of their sure establishment and nearly pest free acclaim.

 Although earlier thought to be sterile and unable to reproduce, wild hybrids are now sprouting up across the country where landscape pear plantings have matured.  These new pear hybrids are not only thorny, but also have retained the weak branching structure of the parent cultivars.  Hybrids from nursery produced trees are also extremely vigorous, and seem to tolerate numerous site conditions, eventually producing a thorn-filled stand of trees too thick for native regeneration. This spread may prove to be one of the most serious problems to date for land managers and home owners alike.

 Within our neighboring state of Missouri, Columbia Park Natural Resource Supervisor Brett O’Brien successfully partnered with the Missouri Department of Conservation and the Missouri Community Forestry Council to form an educational program called, “Stop the Spread!”  In 2002, the Columbia Parks Department began noticing wild pear trees growing in a natural area.  Within 6 years, thorny hybrid pear trees are now abundant and increasing within Columbia utility right-of-ways, natural areas, and even well-maintained park landscapes.

 According to an article by Theresa Culley and Nicole Hardiman in Bioscience (December 2007 / Vol. 57 No. 11), Callery pear cultivars are now listed by 6 eastern states as invasive, with more to come.  Culley/Hardiman note that pear hybrids spread rapidly within restored prairie wetlands and are capable of producing “impenetrable” thorny thickets.

 As ornamental pear populations increase from landscape plantings within our region, the danger for cross-pollination and the production of wild pear hybrids will increase.  The importance of developing awareness to this problem and reduction of market demand for ornamental pear trees is critical.  Homeowners, developers, nursery growers, and municipal forestry departments share the responsibility to promote the use of alternative species as substitutes for the Callery pear.  Without such cooperation, Central Iowa could soon face the costly and ecologically devastating effects of hybrid pear colonization now being realized elsewhere.

 Pictures are available at under City News.  Click on the Invasive Species Alert link to view the PDF file.








3 Responses so far »

  1. 1

    kyle gassman said,

    Cindy, thanks for this very informative article. I think I might have three of these on the property that I bought. With the coming of spring the leaf structure and blossoms should be what I need to identify these. If they are a Callery Pear I need to remove them. I’m less than 100 yards from river bottom land that is in a natural state and would be perfect habitat for them to proliferate
    Could you possibly make a point of passing this info on to the Linn County Master Gardeners that do the question and answers on WMT radio? They seem to have a large audience of homeowners which is just where this info needs to go.

  2. 2

    mike t said,

    Thank you for your information. I live in the Coburg hills north of Eugene,OR and have many of these trees on our property. They are a nuisance except for being an barrier IMHO. The branches umbrella out and down claiming ground and making an canopy. Much stooping and swerving just to walk thru them. To mow is not possible, I’ve used an walk behind sickle bar mower, tractor with field mower, weed eaters and pruning tools. The branches are so long and intertwined, unbeliveably so. To move cut branches? I wear welding gloves up to my elbows–and still get pricked by the thorns! The fruit is abundant and the deer enjoy them. My wife and I find them puckery and cannot finish even bite. These trees seem to have a personal agenda to claim ground and will seend out very long roots in the ground and send spouts up to grow new trees. I have not tried grafting them to a edible, usable, domesticated variety. Thank you again for bringing an awareness of these trees.

  3. 3

    teresa birch said,

    I am in need of help to get rid of the seedlings from my pear tree. I need to know when and how to manage them as I have a flowerbed under my tree. I did not put these in but inherited them from the previous owner. They are a nightmare to deal with. Thank you for your help.
    Teresa Birch

Comment RSS · TrackBack URI

Leave a Reply to kyle gassman Cancel reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: