Pear trees as an invasive species

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).

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...

Last year, the state of Ohio banned the sale or distribution of Callery pears, effective in 2023. The Indiana Natural Resources Commission has suggested it will add Pyrus calleryana to its list of banned invasive species in the future. In South Carolina, state foresters are asking property owners to remove Bradford pears. “We are saying cut them down when possible,’’ a forestry commission spokesperson told The State in March. “It is just generally a nuisance tree.’’

But deep taproots make the trees hard to eradicate, and rising temperatures are only furthering their reach. Previously, the pears’ intolerance of cold stopped them from moving very far north in the United States. Now climate change is causing growing zones to shift.

“The Callery pear never used to be in Wisconsin. In recent years, we’ve seen it spreading within Madison,” Culley said. “It’s been having a little trouble getting outside of Madison—at least that’s what I’ve heard. But we’re expecting it will slowly start to spread out from there.”

You learn something every day.