Our Callery Pear tree, scientifically known as Pyrus calleryana ‘Bradford’ is located along the walkway leading through Bayne Park, just up the stairs across from where Citizen Way intersects with North Balph Avenue. Due to the cultivar name ‘Bradford’ it is often simply referred to as a Bradford Pear tree.
In the early springtime you may have gleefully noticed clusters of these trees along highways with their prolific display of white blossoms. Unfortunately, that beauteous sight signifies the unfolding of an ecological calamity.
In 1964, The New York Times printed an article in favor of the new tree stating, “Few trees possess every desired attribute, but the Bradford ornamental pear comes unusually close to the ideal.” The tree was incredibly popular and widely planted.
However, sentiments toward the tree dramatically changed overtime. In 2016, The New York Times printed an opinion article that stated that the Bradford Pear “may be one of the most the most despised trees in this part of the world.” In 2018, an article in The Washington Post described the newsworthy Bradford Pear tree as “an ecological marauder destined to continue its spread for decades.”
How can a tree once so universally beloved, become so reviled? Here is the story…
The species was named after Joseph Callery, a French missionary who first collected the tree in 1858.
A disease caused by the bacterium Erwinia anylovora called fireblight was being spread by pollinators and affecting plants in the Rose family, which includes apples, blackberries, and pears.
The blackened leaves, stems, and bark of the affected plants and trees appear to be scorched as shown in the image above by Emily Hoover. As the twentieth century progressed, concern was mounting that fireblight would devastate the US commercial fruit industry.
Frank N. Meyer, A USDA scientist and agricultural explorer working in China shown in the image above, was focused on locating disease-resistant fruit trees for US agriculture. During a trip to South China from 1916-1918 Meyer collected seeds of the Callery Pear tree, which had shown promise in resistance to fireblight.
The Callery Pear seeds were imported to America where the tree was used in breeding programs and for rootstock to decrease crop losses.
Although Meyers’s life was cut short when he drowned at the young age of forty-two in the Yangtze River, he was responsible for over well over two-thousand plant introductions including the eponymous Meyer Lemon commemorated by the stamp shown below.
Frederick Charles Bradford, a horticulturist working at the USDA Plant Introduction Station in Glen Dale Maryland, noticed the Callery Pear’s ornamental qualities and began working to develop a cultivar, but died in 1950. Horticulturist John Lewis Creech continued his work to establish the cultivar in 1952, which he named in honor of Bradford. Deemed a success, the ornamental tree was released by the US Department of Agriculture to the public in the early 1960’s. Callery Pear ‘Bradford’ quickly became a favored tree lauded for its quick growth and white blossoms. It filled voids in the streetscape left by Elms that fell as casualties of Dutch Elm Disease, and the new tree was readily used in industrial parks, throughout neighborhoods, and in parking lots buffers.
Lacking the foresight of the arboreal events that were about to unfold it was unknowingly touted as a non-fruit bearing tree, but only time would tell…
Cultivars are propagated by cloning, so each resulting tree is genetically identical. Unfortunately all the clones of the the ubiquitous ‘Bradford’ cultivar were found to have an inherent structural weakness. The steepness of the angle where the branch attaches to the trunk makes it particularly susceptible to breakage from snow, ice, and wind. The tree’s branch thickness and foliage density further compounds the issue.
Adept at problem solving, horticulturists were working to develop other cultivars with favorable traits like stronger branching structures that would be less susceptible to breaking. As they achieved desired results, additional cultivars were released and planted.
Now, back to the issue of fruit. Although trees of the cultivar Bradford could not reproduce among themselves, once other cultivars were introduced pandora’s box was blown wide open.
The combination of cultivars created the possibility of pollination, and the seemingly fruitless Bradford Pear cultivar suddenly became fruitful. Thus, invasive Callery Pear trees began their unimpeded march as bounteous fruit tempted voracious birds. On wild wings the birds unwittingly dropped seeds, more akin to bombs, creating imminent destruction across the landscape.
Adding to the horror, the resulting trees often revert back to the form of Callery Pear that produces dense and often impenetrable thickets, with sharp thorn-like spurs protruding from the branches.
The trees grow quickly and aggressively, invading an overtaking native species of plants and trees that are unable to tolerate deep shade and are denied the necessary water, soil and space necessary for survival. As plant and tree diversity decreases, insect and animal diversity plummets too- which means that overtime so much is irretrievably lost to the tidal wave of white springtime blossoms.
Regrettably, the complexity of the issues created by the well-intentioned introduction of the Callery Pear and its subsequent cultivars created ripples of consequences that could have potentially been foreseen, but instead only became glaringly apparent much later.
The botanical specimen shown below from the Herbarium of Muhlenberg College preserves a fruiting Callery Pear collected along a roadway in Pennsylvania in 1962 that escaped from cultivation. Although this was a sign of things to come, hindsight is always clearer than foresight.
While the correspondence by Frank N. Meyer in 1917 contained in a typescript noting the Callery Pear tree’s ability to survive in a wide variety of conditions served as a message on the hardiness of the tree, it could have equally been perceived as a warning about the potential ease with which this tree could dangerously spread and thrive if given the opportunity. “One finds it growing under all sorts of conditions; one time on dry, sterile mountain slopes; then again with its roots in standing water at the edge of a pond; sometime in open pine forest, then among scrub on blue-stone ledges in the burning sun; sometimes in low bamboo-jungle…and then again along the course of a fast flowing mountain stream or on the occasionally burned-over slope of a pebbly hill.”
Stopping the ever-increasing exponential population growth of these invasive trees is like trying to quell the diffusion of glitter in a roomful of children enthusiastically making crafts.
In Pittsburgh, Callery Pear trees were once heavily planted as street trees along Penn Avenue, Liberty Avenue, and Grant Street. Thankfully, when we know better, we tend to do better. The Pittsburgh Urban Forest Master Plan of 2012 listed Pyrus calleryana (Callery Pear) as one of the tree species restricted from use in public planting projects, including any of its cultivars.
Our Bayne Park tree was planted well before people realized that these trees were creating ecological issues. It is producing fruit, so we know there must be another cultivar nearby. As birds can transport the seeds, we know the Bayne Park tree is actively contributing in furthering the invasive spread. The trees usually only have a maximum life-span of approximately twenty-five years, so when the time comes to replace it (which will likely be soon as many of the leaves have withered) some better options would be Allegheny Serviceberry – Amelanchier laevis or Eastern Redbud – Cercis canadensis.
In the meanwhile, lets learn about the physical features of our Callery Pear ‘Bradford’ tree in Bayne Park.
The flower buds appear in the very early Spring prior to leaf formation. It’s among the first of the trees to blossom and show its leaves. The early leaf formation gives this tree a head start, which is one of the reasons it is so successful at crowding out other plants and trees.
The flowers are strongly malodorous, inspiring people to create clever memes like the one below to humorously indicate the severity of the rotten-fish odor.
The blossoms are highly attractive to insect pollinators including the honeybee, bumblebee, and hoverfly shown below.
If the flowers are pollinated by an insect bringing pollen from another cultivar, hard fruits will develop over several months and remain on the tree dangling from short stems. The first few frosts cause the fruit to soften and become darker in color. In form, they appear to deflate with the outer skin texture resembling a rumpled paper bag. While they are inedible for humans, birds will greedily make a feast of them.
The bark is scaly and brownish/grey in color. The greenish-yellow color is lichen on the bark of our Bayne Park Tree. Lichen is a symbiotic relationship between algae and fungi, and does not damage the tree.
The tree shape is pyramidal and the branches feature numerous short lateral twigs.
The leathery smooth green leaves are glossy, ovate, and have rounded teeth. They easily flutter in the wind on their long petioles revealing slightly paler undersides.
The leaves remain green late into Autumn, and occasionally frost causes the foliage to drop before it even changes color. The Autumn color ranges from rich reddish/purple to bronze/gold.
Leaves can sometimes exhibit interesting patterns of varying color in the Autumn.
While native birds like Robins eat the fruit and spread the seeds, the European Starling, the invasive bird shown above, is also known to assist in spreading the seeds of the invasive tree. In the 1890’s, approximately one-hundred European Starlings were introduced by Shakespeare enthusiasts to Central Park in New York because they wanted to see all the birds mentioned in Shakespeare’s works represented in North America. European Starlings are now one of the most abundant birds in North America. They are easily recognized due to their iridescence, and well known for their extensive vocal mimicry-often imitating the sounds of electronics and machinery. The unique soundscape is particularly noticeable when an entire flock of Starlings gather in a tree.
The wood of the Callery Pear is prized for making woodwind instruments, and is also used in preparing woodcuts for printing.
Making Woodblock Prints by printmakers Merlyn Chesterman and Rod Nelson introduces this ancient art form in this inspirational technical guide featuring a wide range of examples of printed woodcuts.
Mozart’s Starling by naturalist Lyanda Lynn Haupt shares the true story of Wolfgang Amadeus Mozart’s meet-cute with a flirtatious starling who sang an improvised version of the theme from his Piano Concerto no. 17 in G major in a Viennese shop. Delighted, Mozart brought the bird home where it influenced his work and served as a companion, distraction, and muse.
Wicked Plants: The Weed That Killed Lincoln’s Mother & Other Botanical Atrocities by Amy Stewart is an incredibly interesting book of of botanical atrocities. It features botanical illustrations by Briony Morrow-Cribbs created with a copper etching technique and drawings by Jonathon Rosen.
Plant Families: A Guide for Gardeners and Botanists by Ross Bayton and Simon Maughan is an easy-to-use guide with full-color botanical illustrations and diagrams for more then one-hundred plant families. Interestingly, the Callaway Pear tree belongs to the Rose (Rosaceae) family along with the Hawthorn tree, Crab Apple tree, and Sweet Cherry tree. Learning about the plant families will help you notice the unique characteristics of each plant, opening your eyes to the spectacular array of biological diversity.
Landscaping With Native Trees by Guy Sternberg is the perfect resource book if the cautionary tale of the invasive Bradford Callaway Pear has piqued your interest in learning more about native planting. Covering everything from landscaping, transplanting, and planting, it is inspirational to read about the benefits each tree provides to wildlife.
Bringing Nature Home: How You Can Sustain Wildlife With Native Plants by Douglas W. Tallamy is a thought provoking book that will build your understanding of biodiversity, insects, the food web, and how it all ties together. The author studied and counted caterpillar species and overall population on a Callery Pear ‘Bradford’ tree versus a similarly sized White Oak tree in an attempt to quantify how much more native trees contribute to habitat richness. The results were astounding, for just one caterpillar found on the invasive tree, he discovered hundreds on the native tree.
You can help sustain biodiversity simply by choosing native plants and trees. If you are interested in locally purchasing native trees, shrubs, or herbaceous perennials check with the Native Plant Nursery to see what is available. It’s located at Beechwood Farms Nature Reserve which is a property of the Audubon Society of Western Pennsylvania. The National Audubon Society also features a Native Plants Database so you can explore a list of the best native plants for your location by simply entering your zip code.
This post written by Linda, 9/15/20