Callery Pears: The Rise and Fall of a Popular Tree
The story of the ‘Bradford’ pear, a cultivar of Pyrus calleryana, reflects a classic tale of unintended consequences and the resiliency of plants to proliferate.
Originally introduced to the U.S. in 1908 from China, this tree was celebrated for its early-season white flowers, exceptional fall color, and purported fruitlessness. It was seen as the perfect ornamental tree, hardy across various climates, and resistant to many diseases. However, its weak structure and the introduction of new cultivars have led to unforeseen ecological challenges.
Here, I will refer to Bradford Pear and Callery Pear as the same thing. However, these names extend to all varieties, such as ‘Cleveland,’ ‘Aristocrat,’ and more. So, don’t think you’re off the hook if you have one of these varieties.
History of an Ecological Disaster
Initially, the Bradford Pear served as a rootstock for grafting commercial pear varieties on the United States West Coast. It offered a solution to the fireblight epidemic that was devastating the pear industry from Northern California to Washington. The Callery pear played an essential role in preserving the industry for a period.
In the 1950s, studies identified an exceptionally favorable seedling, later named ‘Bradford.’ Renowned for its wide, oval shape, abundant white blossoms, striking burgundy-red fall foliage, resistance to disease, adaptability across USDA Zones 4-9, and its lack of thorns and fruit, Bradford became a sought-after ornamental tree among retailers and homeowners alike. However, the narrative takes a sad turn from here.
Generally, pears, including fruit-bearing and ornamental varieties, are self-infertile, unable to pollinate and produce fruit independently. Initially, Bradford, being the sole variety available, was promoted as fruitless, even though this was not entirely accurate. While it rarely produced viable fruit without other cultivars for cross-pollination, its fruitlessness was overstated.
By the late 1980s, the downsides of Bradford had started to emerge. Particularly its structural weakness due to the acute angles of its branches, which led to damage from wind or storms.
The quest for sturdier, more resilient varieties led to new cultivars like ‘White House,’ ‘Chanticleer,’ and ‘Aristocrat.’ This diversity enabled cross-pollination with Bradford, unexpectedly leading to prolific fruit production. A single Bradford tree could yield up to a half-million seeds annually, considering the high fruit count and seed production per fruit.
The situation worsened when nurseries began using thousands of Callery pear seedlings as rootstock for grafting desirable cultivars. If the graft failed, the robust Callery pear rootstock would sprout, resulting in the invasive, thorny Callery pear growth.
Concurrently, the Callery pear was widely used in urban beautification projects, unknowingly facilitating its spread into native ecosystems. Pyrus calleryana, being a pioneer species, thrives in disturbed sites, further exacerbating its invasion into native habitats and competing with indigenous species.
This rapid spread underscores the threat to ecosystems, where seed banks and old plantings contribute to the proliferation of this invasive species. The role of controlled burns, homeowners removing the trees, community involvement, buyback programs, and more in managing this threat is critical, emphasizing the delicate balance between human intervention and the preservation of natural landscapes.
This situation serves as a cautionary tale of how well-intentioned horticultural practices can lead to unintended ecological consequences.
The Ecological Impact of Displacing Native Plants
One of the gravest concerns with the spread of invasive species like the Bradford pear is their displacement of native plants. This disruption has a cascading effect on local ecosystems, particularly on pollinators.
Approximately 75% of the world’s flowering plants rely on insects and other animals for pollination. Many insects have evolved to feed primarily or exclusively on specific native plant species—a phenomenon known as host plant specialization. The loss of native plants to invasive species like the Callery pear disrupts these crucial relationships, endangering insect populations that play a vital role in our ecosystems and agriculture.
Without native plants to feed these insects, the foundation of local food webs is weakened, posing a direct threat to human food sources and biodiversity.
The Unwitting Culprits
Interestingly, a significant force behind the spread of invasive Callery pears is birds, and in particular, the European Starling, a bird species not native to North America. These birds, thriving in urban and suburban landscapes, feast on the fruits of Callery pears and other invasive plants, spreading the seeds across large areas. Their foraging habits have facilitated the establishment of Callery pear thickets, which quickly dominate fields, pastures, and other open spaces, outcompeting native vegetation.
On a roadside near my house, there is a large area planted with Eastern White Pines directly across from a neighborhood with homes that use Bradford pear as their sole landscaping tree. In the fall/winter, large flocks of Starlings and some American robins use these pine trees to roost at night.
In addition, they feast on the Bradford pear fruits in the neighborhood. You can see thousands of birds during migration, flying at dusk from the neighborhood to the pine trees. In just several years, the entire roadside and much of the field and pine forest are now full of Bradford pears.
Birds on migration predominantly rely on fat for energy, as fats pack more energy per gram than either carbohydrates or proteins, offering birds the high energy they need for their journey. Compared to invasive fruits, native fruits offer superior nutrition, being rich in fats, carbohydrates, and other nutrients essential for birds to endure the winter. While native fruits boast a fat content between 6% and 48%, invasive fruits lag significantly behind, with their fat content never exceeding 1%.
Barriers to Overcome | FAQs
It’s “Bradford Pear Season” here in Ohio. I am disgusted for weeks everywhere I drive because I see these trees planted in so many yards and even more that have invaded every field, forest edge, and roadside.
What amazes me is that most people who have one in their yard have no idea it’s the cause of this invasive infestation. Nor do they seem to understand the problem with it.
I have been talking to more and more people this year and posting on Facebook groups about the ever-increasing problem.
These are some of the comments I hear and the challenges we face in overcoming the hesitancy to remove them.
Comment: “I have an ‘Aristocrat’ (or ‘Cleveland’ etc), not a Bradford Pear, so I don’t think it’s invasive.”
Response: It is! None of them were supposed to be invasive, but they all are now. If your tree produces fruit in the fall then, yes, it is invasive regardless of what variety you have or how sterile you think it is. Each tree can produce tens to hundreds of thousands of berries that birds then spread.
Comment: “They’re so beautiful, though.”
Response: White flowers are beautiful. However, this tree’s fleeting beauty and rancid-smelling flowers, are displacing so many more attractive and functional plants it’s hard to fathom what native flora and fauna it may push out. Beauty should not be the only function considered for a plant. Our beautiful and functional native plants that are being severely affected by Callery pear invasions include Dogwood, Redbud, American Plum, Wild Cherry, Serviceberry, Chokecherry, Viburnum, Buttonbush, Spicebush, every young native tree seedling, Virginia Bluebells, Trillium, Mayapple, and so many more.
In addition, all of the plants I mentioned that are being affected are host plants for bugs, butterflies, and moths, which means their caterpillars are also affected. Birds use those caterpillars to fledge their broods; birds are also severely declining. This food web is directly or indirectly interconnected and severely affected by invasive plant infestations such as the Bradford pear.
That “beautiful” Callery pear tree in your yard has a deleterious effect on the local ecosystem. Without a doubt. No matter why you planted it, or when, or any of the other reasons, you tell yourself to keep it!
Comment: “Birds eat the berries.”
Response: YES! That’s precisely the problem. See the information above about Starlings but there are a lot of birds that spread it. Seed dispersal into natural ecosystems is exacerbated by multiple and abundant birds such as American robins, northern cardinals, northern mockingbirds, and gray catbirds, and a seed bank persists in areas even after mature trees have been removed. Furthermore, some traits of the Callery pear that were explicitly selected during its development as an ornamental tree could also promote invasiveness. These include rapid growth, abundant flowering, and wide environmental tolerance.
It is sad that birds eat them, thinking they are getting the fats and nutrition needed to survive the winter or migrate. They get little to no nutrition.
Comment: “Bees are always on the flowers.”
Response: Bees do visit the flowers. Bees must visit flowers to survive. If native trees and shrubs were available, the bees would visit those. Flies are one of the primary pollinators of Bradford Pears. They’re attracted to the smell. Research by students at the University of Findlay researched this as well. Nearly five years after starting the project, students found that the bees pollinated planted and feral Callery pear trees. They also found that the same bees caught pollinating Callery pear trees were also pollinating other area trees and flowers. The research showed that bees were not reliant upon the Callery pear trees.
Due to the state-wide ban in Ohio on the sale and distribution of invasive Callery pear trees as of 2023, many villages and towns are looking to replace the trees that line their streets. The University of Findlay students and faculty research found that removing the trees won’t affect native pollinators. “The trees are not affecting the pollinators (bees) in a negative way, meaning it wouldn’t be a bad thing to remove the invasive trees entirely,” said Animal Science/Pre-Vet major Madeline Haase.
Comment: “Why would they sell a bad tree?”
Response: Great question. At one point, it wasn’t a “bad tree.” It was never a native tree, of course, so it wasn’t necessarily a “good” tree either. But homeowners and nurseries sell and buy plenty of exotic, non-native plants daily. The answer is different today based on what we know now. It IS a bad tree. Nasty, stinky, weak, invasive, and an ecologically limited tree.
Comment: “Oh no, why would you cut down a perfectly good tree?”
Response: This one is easy. It is not a perfectly good tree. See the rest of the blog post. 😊
A Call to Action
The case of the Bradford and the other Callery pear trees reminds us of the complex interplay between plants, animals, and human activities in shaping our environment. While the Bradford pear’s ornamental appeal was the driver to its use, its ecological impacts highlight the need for careful consideration in plant selection for landscaping and urban planning from nurseries and responsible homeowners.
As communities and individuals, we are responsible for protecting our native landscapes. Supporting bans on the sale of invasive plants like Callery pear, participating in replacement programs for invasive trees, and advocating for the preservation of native species are steps we can all take. Together, we can combat the spread of invasive species and work towards a more sustainable and biodiverse future.
Several states have it listed as an invasive species, but this doesn’t keep people from purchasing it, especially if they don’t know. They see it at the nursery and buy it. Some states like Ohio, Pennsylvania, and South Carolina have taken the most responsible approach and have banned all sales and distribution. Other states (Kansas, Virginia, and Tennessee) are currently considering the same ban.
Callery Pear Removal
Removing Bradford pears helps minimize the spread of seeds. They seed every year, so you are preventing thousands of seeds per year from being spread. If you have large trees, local tree services can help remove the trees from your yard. But once the tree is cut down, treating the stump is essential, which might mean grinding it down, digging it up, or treating it with an herbicide.
Managing the spread of Callery pear requires attention to land use practices. Regular mowing of fields and pastures at least once a year, especially during the dormant season, can prevent the establishment of woody plants like Callery pear. In areas where native prairies are established, prescribed burns can serve as an effective management tool, replacing or supplementing annual mowing. These practices are crucial for controlling the spread of invasive species and preserving native ecosystems.
For homeowners, you have some removal options as well.
Remove Small Trees
In areas with light infestation, remove small trees by hand when the soil is moist, with care taken to remove the entire root. When too numerous, foliar spraying with a 2 to 5 percent systemic herbicide solution of glyphosate or triclopyr can be used mid to late summer.
Large areas can be mowed yearly, but it takes a very long time if ever, to stress the tree enough for it to die. These trees are highly persistent. With this method, the tree at least gets no larger than a year old and doesn’t set fruit. However, the young trees now develop thorns that can puncture mower tires, so be cautious!
Cut Medium to Large Trees
Medium to large trees should be cut down and stumps treated immediately with herbicide to prevent re-sprouting. Effective herbicides include glyphosate and triclopyr at a 25 to 50 percent solution.
Less labor-intensive control options include basal bark treatment and girdling.
- Use basal bark treatment for trees up to 6 inches in diameter by applying a 1:5 ratio of the ester formulation of triclopyr and basal oil in a 12-inch wide band around the entire circumference of the tree base.
- Mature trees can be girdled during the spring and summer, by cutting through the bark around the entire trunk, 6 inches above the ground.
- Herbicide uptake is most successful in late winter/early spring or during the summer.
More information can be found here from the OSU Extension on girdling and other methods: Controlling Undesirable Trees, Shrubs, and Vines in Your Woodland (pdf). Also from the OSU Extension is a factsheet on Herbicides Commonly Used for Controlling Undesirable Trees, Shrubs, and Vines in Your Woodland (pdf).
Even after I had a significant Bradford pear stump ground, it still sprouts from distant roots two years later. I mow them and spray them with glyphosate as soon as I notice them.
Final Thoughts
The Bradford pear’s story is a cautionary tale of beauty becoming an ecological challenge. By understanding the history, acknowledging the role of wildlife in spreading invasive species, implementing effective land management practices, and recognizing the vital connections between native plants, insects, and our survival, we can address this and other environmental issues.
Let’s commit to making informed choices that support our native ecosystems and ensure their health and vitality for future generations.
I’m Patrick, let’s stay native!
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