Part of a series on invasive species by guest blogger Ed Pope
Callery pear is native to China and Vietnam. It was introduced into Europe in the 1800s. It first arrived in the United States at Boston’s Arnold Arboretum in 1906. It was imported by the United States Department of Agriculture in 1916, when a disease called fire blight was ravaging commercial pear growers, who were looking to develop a fire blight-resistant pear tree.
Soon it was used as a rootstock for the commercial pear industry. In the middle of the twentieth century, the Department of Agriculture began promoting Callery pears as an ornamental tree, because in the spring they produce bountiful white flowers. They became very popular with landscapers since they were attractive, inexpensive, fast-growing and tolerant of a wide variety of soil conditions.
Unfortunately, the Callery pear has two major drawbacks. One is that it has very weak branches, which usually fall apart in storms when they become about 25 years old. The second is that it has now become invasive and is damaging native forests.
The Bradford pear variety became very popular as a landscape tree. Bradford pears all have identical DNA and they cannot pollinate each other. When only Bradford pears were being planted, Callery pears were not a problem since no fertile seeds were produced even if there were Bradford pears near each other. However, numerous other varieties (Cleveland Select, Whitehouse, Aristocrat and others) were developed in an attempt to come up with a variety that had stronger branches. Since these differed genetically from Bradford pears, it became possible for Callery pears to reproduce any time two different varieties were within 300 feet each other. Birds eat the small fruits that they produce and transport their seeds. This is how Callery pear became an invasive tree.
The Indiana Invasive Species Council submitted a list of plants that they thought should be banned to the Indiana Department of Natural Resources’ Natural Resources Commission. Callery pear was on that list, but when the commission released its proposed rule, it had been removed. There had been major pushback from the horticulture industry since they had large inventories of Callery pears. To get the rule adopted quickly, DNR elected to remove the Callery pear. (See the complete list in the Indiana Terrestrial Plant Rule brochure.)
The Indiana Native Plant Society recommends these trees as alternatives to Callery pears:
- Hop hornbeam
- American hornbeam
- Pagoda dogwood
More on the Callery pear can be found in this Purdue University video.
Callery pear trees pop up on a number of CILTI properties. The closer to suburban development, the heavier the infestation tends to be. The stewardship team usually tackles Callery pear trees by cutting and treating the stumps. Whether that cutting is done by a hand saw or a chainsaw is determined by the size of the tree. At Nonie Werbe Krauss Nature Preserve, they are a major nuisance, taking over an oak-hickory planting done back in 2008. There the majority of the cutting is done with chainsaws. This property is a perfect example of what Callery pears can do when they take over an area.
Want to help CILTI restore natural areas? Check out volunteer opportunities here. You can help us improve the health of forests and other natural habitats.