By Amanda Kolson Hurley
In the 1960s, America fell in love with a new tree: the Bradford pear. Cultivated from Asian stock by scientists at the U.S. Department of Agriculture, Bradford pears display clouds of pretty blossoms in the spring and garnet leaves in the fall, and are hardy enough to grow just about anywhere. Thinking they had found the perfect ornamental tree, homeowners and public-works departments planted Bradford pears up and down the nation’s streets for decades, especially in the East, South, and Midwest.
Then the relationship soured. Bradfords are apt to split and break during storms, and they have a short life span, only 15 or 20 years. Although they are technically sterile, the trees cross-pollinate with other cultivars of the Callery pear species (Pyrus calleryana), producing fruit that splats all over sidewalks. And despite their delicate appearance, the blossoms emit a foul odor that’s been compared to rotting fish (among other things).Cities and states are trying to remove Bradford pears‚ but the “weed trees” have already intruded deep into some forests, a biologist warns.
Once admired for its hardiness, the Bradford pear is now considered an invasive species, which grows even in poor conditions, proliferates fast—thanks to birds that dine on its fruit and spread the seeds—and crowds out native species.
Cities are trying to put an end to the tree’s mischief. Pittsburgh’s Urban Forest Master Plan prohibits planting Bradford pears. This March, Fayetteville, Arkansas, started offering a bounty to anyone who cuts one down. (They can get a free native tree to replace it.)
The bad news is it’s not only in developed areas where the trees threaten to choke biodiversity. Theresa Culley, head of the Department of Biological Sciences at the University of Cincinnati, warns that wild Bradfords and other kinds of Callery pears are making inroads into Eastern forests.
By Adrian Higgins
A pear seedling selection named Bradford was cloned by the gazillion to become the ubiquitous street tree of America’s postwar suburban expansion. Then it turned invasive.
Carole Bergmann pulls her small parks department SUV into an aging 1980s subdivision in Germantown, Md., and takes me to the edge of an expansive meadow. A dense screen of charcoal-gray trees stands between the open ground and the backyards of several houses. The trees are callery pears, the escaped offspring of landscape specimens and street trees from the neighborhood. With no gardener to guide them, the spindly wildlings form an impenetrable thicket of dark twigs with three-inch thorns.
Bergmann, a field botanist for the Montgomery County Parks Department, extricates herself from the thicket and in the meadow shows me that what I take to be blades of grass are actually shoots of trees, mowed to a few inches high. There are countless thousands, hiding in plain sight in Great Seneca Stream Valley Park. If it were not cut back once a year, the meadow would become like the adjacent screen, wall upon wall, acre upon acre of black-limbed, armored trees worthy of Sleeping Beauty’s castle.
“You can’t mow this once and walk away,” said Bergmann, who began her 25-year career in the department as a forest ecologist but has been consumed by an ever-pressing need to address the escape of the Bradford pear and other variants of callery pear, a species that originated in China, along with other invasive exotics.