It was the first week of April and everywhere you looked in Northern Kentucky you saw Callery Pear trees festooned with their white blossoms. To many, it is a welcomed harbinger of spring that is celebrated with photos on social media. But to others, myself included, it is anxiety provoking, as the blossoms, and their resultant fruit, are an ongoing attack on our native plant communities. It is truly one of the biggest ecological threats of our time.

The Callery Pear originated in Asia and was introduced to Europe in the mid 1800s by French missionary and botanist Joseph Callery, for whom it is named. It was brought to the U.S. in 1917 by the U.S. Department of Agriculture who was trying to use its genetics to improve disease resistance amongst orchard pear varieties. In the mid-twentieth century, plant nurserymen started to work with Callery Pear, selecting specimens that had attractive features. While these specimens still had the Callery Pear genetics, slight gene mutations gave them sought after qualities. Plant varieties developed through this type of process are called cultivars. The Bradford Pear, the most recognized named variety of the Callery Pear, was developed in the 1950s and introduced to the American public in 1963. It was meant to be a landscape tree, not a pear tree for an orchard.

Because of positive qualities like rapid growth, spring flowering, and fall color, it was popular and widely planted in the developing suburbs.

In addition, it is very tolerant of poor and disturbed soils so it was utilized extensively in commercial development, where clay soils around parking lots were common.

Interestingly, at the time of introduction all the trees were genetically identical, having been developed from grafts of the original parent specimen. These were not self-fertile, meaning that pollen from like specimens could not pollinate flowers to form fruit and seeds, and therefore the tree was classified as infertile. Over the next couple of decades however, other cultivars were developed with names like Aristocrat Pear and Cleveland Select Pear. Gradually these other cultivars were planted more widely and there was enough genetic variation between them and the Bradford Pears to allow for pollination and the development of fruit. This history correlates with my memory of these ornamental trees. In the fall of 1979 I took a college course on trees, saw numerous ornamental pear specimens, and none of them had fruit.

Then in the 1990s and the early 2000s the problem of its invasiveness was recognized as wild Callery Pear trees were noted to be taking over unmanaged fields and forest edges.

They would displace or out compete our native tree and shrub species that formerly thrived in these settings including Sumac, Wild Plum, Redbud, Sassafras, Dogwood, and Persimmon to name a few. In addition, the pears grow tightly, leaf out early, and have a thick canopy, preventing sun from reaching the ground.

In this wintertime photo bare pear trees can be seen clumped together with a tree in every square foot or two.

Therefore, plants that normally grow on the floor of the forest edge, including spring wildflowers, can not survive. Continuing the cascade of impact, insects and other wildlife have less to eat, and larger animals who feed on those insects are then impacted as well. It has far reaching effects.

So the ornamental pears that are now growing so widely in natural areas across the South and Midwest are a mixture (hybrids) of the genetics of the many Callery Pear cultivars and set fruit abundantly.

The small fruit has a somewhat woody quality until it is softened by frost in the fall. By winter it has a raisin consistency. They contain from two to ten seeds and birds eat them whole. The seeds pass through the gastrointestinal tract and are deposited with feces – a little fertilizer packet. Interestingly, the seeds have a high concentration of the toxin cyanide. If the seed is not chewed or crushed the cyanide is not a danger to the ingesting animals. The cyanide acts as a deterrent to the seed being destroyed when eaten, and it also appears to signal tissue transformation and seed germination. The seeds of other stone fruits, like peaches and cherries, contain a cyanide like compound as well.

An interesting development with the hybridization of the multiple pear cultivars is that many of the “wild” specimens now have thorns that can be up to two inches in length. This is the uncovering of a trait that was noted on the trees that originated in China, but was not present on the cultivars here.

Interestingly, the Callery Pear is not considered invasive in Europe. It is felt that this is because they were not as widely planted and they do not have many cultivars, and therefore are not producing significant fruit.

The irony of the Callery Pear story is that they turned out not to be the ideal lawn tree. Due to rapid growth that leads to a weaker wood, tight angle branching patterns, dense branching, and tendency for the leaves to remain on the tree till very late fall, they are easily damaged by early snow and ice storms. So, just when the trees are getting to a nice shade tree size, they will frequently be disfigured by the loss of a major branch.

Some report that the later varieties of the Callery Pear are less prone to the storm damage due to improved branching patterns, but they are certainly still more susceptible than our native trees. In addition, some feel that the blossoms are somewhat malodorous, giving off a scent of death or rotten meat.

Because of the invasiveness, three states, Pennsylvania, South Carolina, and Ohio, have banned the sale of all varieties of Callery Pear. Unfortunately, I’m afraid that we can’t get the genie back in the bottle. Trying to control the spread of the trees is labor intensive and includes pulling out young trees by hand, cutting trunks and applying herbicide to the stump of medium to large trees, applying concentrated herbicide to the bark of larger specimens, and leaf spraying of large groupings. I think that individual battles can be won, but the number of trees on unmanaged land is too great to win the war.

So the paradox is that while the cultivars of Callery Pear offer a welcomed promise of spring early in the season, as well as outstanding fall color, they have a sinister side, aggressively populating our Southern and Midwestern landscapes, displacing the native species of plants, and disrupting entire ecosystems. They can be added to the ever growing list of horticultural mistakes where introduced species, including Bush Honeysuckle, Garlic Mustard, Lesser Celandine, Purple Loosestrife, and Tree of Heaven, lacked a natural control agent and have overrun our native habitats. But unfortunately, this may be the worst of the bunch.

Photos by Peggy Juengling Burns