Besides bad odor and weak limbs, Bradford pear trees have become a threat to our environment. It's a problem that began in the United States several decades ago in the mid-1960s when the U.S. Department of Agriculture introduced them into the country as decoration. Chattanooga city forester Gene Hyde says they thought it would be the perfect tree for all situations.

"It has beautiful white blossoms. It didn't have any insect or disease problems. But that was only half the story," says Hyde.

The other half is that the Bradford pear, a cultivated off-shoot of the Callery pear, isn't structurally sound. Over time the two main branches grow closer together, closing the V-shaped area where they meet. This leads to rot and decay, making the trees extremely vulnerable to wind and heavy rain.

"After 15, 20 years it's very common to see them, after summer thunderstorms, just split and break into pieces," says Hyde.

While fragile in some ways, it's been easy for Bradford pears to grow quickly and across large areas with the help of a natural fertilizer.

"As the birds eat the seeds and they fly away, wherever it is they stop and poop or fly and poop, wherever that lands [Bradfords will grow]," explains Hyde.

They've have become so overpopulated through the years they've become invasive, crowding out native trees and plants and threatening local ecosystems.

"Native trees will support insects and wildlife and invertebrate animals and so forth," says Hyde. "The Bradford pear just doesn't do that."

He also says with no enemies to keep its population in check, Bradford pears will continue to cause trouble if people plant them.

"If people buy them, they're just asking for a problem," adds Hyde.

He says most nurseries and garden centers no longer sell Bradford pear trees. As substitutes, Hyde recommends native choices such as dogwood, redbud, and serviceberry.