By Bob Polomski, Ph.D./Clemson University
Once upon a time the Bradford pear (Pyrus calleryana ‘Bradford’) was the darling of the nursery industry. Since its debut on the cover of American Nurseryman magazine on April 15, 1963, Bradford pear’s popularity soared as a street-tough tree that offered beauty and durability.
In early spring Bradford pear trees erupted into bloom, these giant ovate snowballs of bright white flowers that were best admired from a distance because of their rotting fish aroma. The flowers, favored by honeybees, bumblebees and other pollinators oblivious to the stench, gave rise to leathery, dark glossy green leaves that “present[ed] a pleasing picture, particularly as they stir in the breeze and their wavy edges catch and reflect the sun’s rays,” according to the authors of the 1963 American Nurseryman article “Bradford ornamental pear—a promising shade tree.” In the fall the longlasting leaves exploded into shades of orange, red, and purple. The beauty of Bradford pear was matched by its unparalleled toughness: tolerance to drought, pollution, and pests, notably to fire blight, a devastating bacterial disease that injures and kills edible pears.
Bradford pear appeared to be the perfect ornamental street tree, but like kryptonite and Superman, Bradford pear’s Achille’s heel was its production of closely spaced upright branches. As these poorly attached branches grew and expanded in girth, the crown to split apart, often during snow-, ice-, and windstorms. It often happened to unpruned or poorly pruned trees when they reached 15 to 20 years of age.
In the past I counseled anyone who purchased a Bradford pear to buy a pruning saw as well. As described in the 1963 American Nurseryman article, the limbs of young trees must be selectively removed to produce branches with wider angles and stronger unions to develop a strong canopy.
To overcome this structural flaw, cultivars were developed that offered improved branching habits, such as ‘Aristocrat’ and ‘Chanticleer’, a 2005 Urban Tree of the Year by the Society of Municipal Arborists. Other cultivars were developed with narrower forms, such as 'Capital', a U. S. National Arboretum release, that embodied the aesthetic and urban-tolerant traits of Bradford but offered applications in tight, confined locations.
This profusion of callery pear cultivars eventually led to another problem that had ecological consequences. In the past, Bradford pear rarely produced viable fruit because it’s self-infertile and cannot pollinate itself. With the widespread planting of cultivars that were differed slightly genetically, the barrier to fertility and subequent fruit production was overcome. In some cases the callery pear understock of a Bradford pear would sprout, flower, and provide pollen. The fruits were consumed and dispersed by starlings, robins, and other animals to open, disturbed habitats where the progeny formed dense thickets.
Callery pears mature early—flowering at 3 years of age--and is one of the first trees to bloom in early spring. It’s also one of the last trees to lose its leaves. Callery pears are resistant to insects and diseases and their thorny stems and branches discourage deer-browsing. Interestingly, the "Survivor Tree” at the 9/11 Memorial is a callery pear that survived the September 11, 2001 terror attacks at the World Trade Center. In the context of the Memorial, it serves as a symbol of survival, recovery, and resilience.
Some states in the mid-Atlantic, southeast and midwest regions have declared callery pear an invasive, self-sustaining species that dominates and disrupts native flora. In South Carolina callery pear is on the “watch list.”
In the past I encouraged Bradford pear owners in our state to selectively prune the branches. Now that I witnessed large tracts of land throughout our state covered like a white fog in early spring, I encourage them to prune their trees at soil level.
The glorification and eventual demonization of Bradford pear is the result of our unwillingness to foster biodiversity in our urban environments. While we make our communities more livable for people, we don’t do the same for trees. We disregard decades of arboricultural research and practices and continue to shoe-horn trees into unsustainable 4 square ft. tree pits that are better suited for traffic lights, signs, and streetlights than trees. It’s the survival of the fittest, and only a handful of tree species can exist in these inhospitable conditions. Bradford pear is one of them.
This monocultural approach that relies on a single or limited number of species or cultivars had already led to catastrophic losses in our urban forests as witnessed by the demise of American elms to Dutch elm disease and ashes to emerald ash borer. However, we continue to rely on a handful of nearly indestructible species and cultivars that thrive in wretched conditions. Crapemyrtle, Chinese elm, sawtooth oak, and Chinese pistache have supplanted Bradford pear as street-smart urban warriors.
Because cities are responsible for 70% of the world’s greenhouse-gas emissions but comprise only 2% of the world’s land mass (Time; Dec. 26, 2016/Jan. 2, 2017), we rely on trees to assume a greater role as ecological engineers in our urban communities. It’s important that communities create growing conditions that support a diverse population of native and noninvasive adapted tree species that provide environmental services and not ecological messes.
Bob Polomski, Ph.D. is a Clemson Extension Specialist--Horticulture/Adjunct Asst. Prof. • Dept. of Plant & Environmental Sciences