Columbia Parks and Recreation fights back against invasive Callery pear trees

Friday, October 24, 2008 | 1:00 p.m. CDT
Callery pears, originally sterile ornamental trees, have hybridized and are spreading throughout Columbia's open grasslands. Bad branch angles and heavy branches make the species susceptible to splitting, which is dangerous around roads and power lines.

COLUMBIA — Wild Callery pear trees have taken over a field along Scott Boulevard and are sprouting up along Grindstone Parkway, the wetlands in Forum Nature area and an untold number of other locations in and around Columbia.

Callery pear trees — Pyrus calleryana — were first introduced to the United States by the U.S. Department of Agriculture in Glenn Dale, Md., in 1960. These trees, which originated in China, were snapped up as an attractive ornamental tree that could succeed well in urban areas.

Callery pear trees

Appearance: It is a lollipop-shaped tree that can reach 20-30 feet wide and 30-40 feet tall. Leaves are round and glossy, and there are white blossoms in the spring and a maroon coloring in the fall.

History: Native to China, it was first introduced to the United States by the U.S. Department of Agriculture in Glenn Dale, Md., in 1960.

What's the problem?

Heavy branches and bad branch angles can lead to breakage during wind and ice storms.

The domestic tree is sterile, but different varieties of the tree are able to interbreed with each other to produce a fertile offspring.

The non-native species can choke out much of the surrounding flora.


How to stem the spread

Seedlings: burning

For trees around six feet tall: hack-and-spray, or hack-and-squirt, which involves cutting a layer of tissue and applying herbicide

For larger trees: a herbicide injector, or hypo-hatchet, is used


Callery pears are generally selected for their teardrop shape, vibrant white blossoms, manageable size and because they are relatively easy to transplant. This tree, however, is seen by some as more of a headache than a gem. Bad branch angles and heavy branches make the species susceptible to splitting, which is dangerous around roads and power lines. Ornamental pear trees are often the first to come down in heavy storms and snow.

In recent years, the tree has also proven to be environmentally detrimental. Normally a sterile tree, certain cultivars, or plants produced through selective breeding, are now able to interbreed and produce fertile offspring that take hold in the wild.

There are 26 different cultivars, including well-known varieties such as Bradford and Aristocrat. The resulting hybrid tree is difficult to remove. They often have thorns and choke out native tree species, especially in the eastern United States.

In 2002, the problem hit closer to home when the tree was noticed around Grindstone Parkway in Columbia.

"We saw the tree and thought, why would someone put it there?" said Brett O'Brien, park natural resource supervisor for Columbia Parks and Recreation.

At first, O'Brien considered the appearance of these trees "anomalous" and "bizarre," but it was no fluke, and he soon began noticing the hybrids elsewhere.

The appearance of Callery pears along Scott Boulevard in 2004 and 2005 "set off alarm bells," O'Brien said, and the Parks Department began research on how to quell the outbreak.

In a letter to the City Council dated October 2007, Parks and Recreation proposed "Stop the Spread!", a program that aims to educate the public about the "potential economic and ecological consequences of continuing to plant Callery trees."

Funding for the project was approved in November 2007 and came partially from the Missouri Department of Conservation in the form of a Tree Resource Improvement and Maintenance grant, which will provide up to 60 percent of the funding for Missouri community forestry projects. This marks the fourth consecutive grant awarded to Columbia.

The total projected cost of the project is $15,664, with the Conservation Department contributing $9,896 and the city of Columbia providing a match of $5,768. Of the city's contribution, $4,598 will go to force account labor, $300 to TreeKeeper —  Columbia organization that trains volunteers in proper care and maintenance of trees — and $870 to in-kind equipment labor costs.

The "Stop the Spread!" program aims to educate and provide alternatives to potential buyers in order to gradually reduce the trees from the area, rather than strictly removing those that are currently seen. O'Brien said that less than 4 percent of the downtown trees are planted Callery pears, and there are hopes to phase them out completely in three to five years.

O'Brien said that problems arise in taking out invasive plants like honeysuckle and pears.

"You take them out, turn your back, and they're back again," O'Brien said. "You can pay somebody to get rid of them, but who's to say they won't reappear again? There's no bang for your buck."

O'Brien said that Parks and Recreation is not trying to tell people to cut down their ornamental pears, but instead is trying to persuade them to stop looking at the tree as a good investment and look for alternatives when their current tree is gone.

"Homeowners need to grow site-specific trees," O'Brien said. "Long run, it's a better investment."

The project offers alternative solutions through the use of educational brochures and posters. A display and alternative trees are situated along a path at Louisville Park, which is located west of Scott Boulevard. Some of these alternatives include chokecherry, dogwood and redbud.

"In Missouri, the issue is to get people on board," O'Brien said.

O'Brien emphasized not only the ecological damage that these trees cause but also the cost implications that would affect both city and community.

"They're sprouting up under power lines," he said. "Because they have weak limbs, they can be the first trees to break up in an ice or wind storm. The park's removal of all these invasive hybrid pears can become a major maintenance expense. There are a lot of them, many are thorny, and pears get big — more than 30 feet — which is a lot of wood to remove."

Over the summer, part-time employees for Parks and Recreation worked on taking out the trees in the Grindstone and Forum areas.

There are several removal methods. Hack-and-spray, or hack-and-squirt, involves cutting a tree's cambium — a layer of tissue from which the tree's water- and sugar-conducting tissues grow — and applying herbicide to the cuts. This is used predominantly for trees around 6 feet tall. For larger trees, a herbicide injector, or hypo-hatchet, is used.

In the open prairies at Grindstone Park and the Forum Nature area, the city has tried burning, which works on seedlings but not larger trees. O'Brien calls it "nature's way of prairie restoration," but this method hasn't been very effective because of this year's wet summer.

The problem hasn't been noticed as much statewide, but O'Brien thinks it will soon be seen in other places. He speculated that because Columbia is surrounded by open grasslands and has seen a significant population increase in the last few decades, the tree is more prevalent and noticeable.

"The problem can expand," O'Brien said. "That's why people should care."

Parks and Recreation has contacted some nurseries and told them to look ahead into new products, but not all have been informed and of those that have, not all are interested, O'Brien said.

Dave Harr, owner of Lakewood Home & Garden Showplace, offers several pear varieties: Chanticleer, Aristocrat, Bradford and Capital. He said that Parks and Recreation has so far not contacted him.

"Telling people what to plant is not their business," Harr said.

"We don't have the authority to say, 'Don't sell that.' They sell what people want to buy," O'Brien said. "You wouldn't sell tofu if people wanted hamburgers."

Bart Piotter, of E.C. Piotter & Sons Nursery, has been contacted by "Stop the Spread!" The nursery offers both the New Bradford and Cleveland Select pear varieties, as well as other alternative trees.

"If that's what they want, they're going to get it some way or another," Piotter said. "What we really do most is tell people how bad they are. The flower stinks, branches break during ice and only one out of five years do you get an outstanding fall color."

O'Brien again placed emphasis on the importance of educating buyers about the potential hazards of purchasing a Callery pear tree.

"It's not us against the nursery people," O'Brien said. "It's really got to come from homeowners."

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Ray Shapiro October 24, 2008 | 8:14 p.m.
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