Callary Pear invasiveness

[John Paul Sanborn]

I just read an online article on how the once thought sterile trees are hybridizing between var's and seeding out somewhat prolifically. Seems MO is looking at them as potentially invasive.

 

[John Paul Sanborn]

Scientists Look for Clues into How Tree Populations Become Invasive

Media Contact:
Jennifer Martin, CSREES Staff (202) 720-8188

By Stacy Kish, CSREES Staff
January 15, 2008

By studying the Callery Pear tree, scientists have determined how nonthreatening plants have become invasive, as the trees are now dense and thorny and are expanding into urban locations they were never intended to grow in.

Ornamental plants, like the Callery Pear, were originally planted in the United States for their beauty and were not considered an invasive threat because they did not produce fruit. Over the past decade, the Callery Pear has evolved to become a significant invasive tree species. Besides producing fruit, which can be messy and cause the population to expand into inconvenient locations, the newly evolved trees are dense and thorny. Scientists are using the Callery Pear as a model for studying the factors that contribute to the evolution of invasive traits in introduced plants.

Callery Pear trees were first introduced to the United States from China in the early 1900s and became one of the most popular ornamental tree species planted in urban areas. This species, which includes the Bradford, Aristocrat and Cleveland Select varieties, was chosen because it produces an impressive springtime flower display and vibrant fall foliage and is tolerant to drought and pollution.

Within the last decade however, wild type Callery pear trees, Pyrus calleryana , have begun producing fruit, allowing them to multiply in natural areas, especially in disturbed sites along railroads, roads and park boundaries. Urban backyards are not immune to the tree expansion and the fruit is appearing in neighborhoods where it was not invited. The situation is aggravated by bird species, such as starlings, that disperse the tree fruit. In addition, the seedling plants differ from its cultivated parent, growing densely and producing impressive thorns that make controlling the new tree a challenge.

Theresa Culley and Nicole Hardiman at the University of Cincinnati published their findings in the December issue of the journal Bioscience.

The scientists determined that having multiple varieties planted in the same area can lead to the production of a new and invasive variety. This is known as intraspecific hybridization between the widespread 'Bradford' variety and other newer varieties.

Because Callery pear varieties are so well established as landscaping trees in urban settings, there is an urgent need to monitor the impact of the newly evolved P. calleryana on the ecosystem. This study provides the first step to combat this potential problem. By understanding the factors that contribute to the evolution of invasiveness in an introduced species, scientists can provide practical suggestions for how the horticultural industry can monitor plant introductions and implement effective methods of control to prevent introduced plants from becoming invasive and spreading within the United States.

The USDA's Cooperative State Research, Education, and Extension Service (CSREES) funded this research project through the NRI Biology of Weedy and Invasive Species in Agroecosystems program. CSREES advances knowledge for agriculture, the environment, human health and well-being, and communities by supporting research, education and extension programs in the Land-Grant University System and other partner organizations. For more information, visit National Institute of Food and Agriculture (NIFA).

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[ATH]

A couple of years ago I heard a talk from one of the University of Cinncinatti professors mentioned in the article. She was pretty convincing that there was a problem. Since then I have seen it around Columbus along wild road edges quite a bit - but not in the more rural parts of Ohio. But that is expected to see more invasives where there is more seed source.

Based on that, I am sold that there is yet another reason to dislike Callery pear (not that I needed another reason...but I add that in when talking clients out of planting the tree).

 

[John Paul Sanborn]

I see lots of callary pear volunteers in this area of Georgia.

I'm surprised to see the report say that Bradford doesn't produce fruit. I've always known it to and have had hundreds of seedlings sprout from wood chip piles. Very thorny and bright fall color.

I think that this is just confirmation, you have a chanticleer, or aristocrat near by and you have viable fruit production.

 

[PinnaclePete]

Down here in Arkansas, Callery pears have always been considered invasive, we just don't have any laws to support controlling them. They spread by root sprouts, root suckers and by seed. From hillsides, you can see their spread down streams, creeeks and waterways - easy to spot in the spring.

I know if an Aristocrat, Bradford or Chanticleer (Cleveland Select) dies or is cut, the resulting sprouts will be the native Callery pear. Can't really say if I've seen them reproduce from seed though. Best control is a stump or basal spray of 25% Garlon4 in oil.