Trees take to the streets

Bristlecone pine trees grow in California's White Mountains. They are thousands of years old--and are some of the oldest trees in the world.

Most trees aren't this hardy. In the country, a tree might live 150 years. But in the city, a tree might live for only 10 years--or even less! That's because city trees have to deal with a lot of stress. The sources of that stress include air pollution, bad weather, insects, busy streets, and power lines.

All the things that people don't like about cities--guess what? Trees don't like them, either!

But we need trees in our cities. So scientists have developed special varieties of trees that can handle life on the mean streets.

John Hammond works at the U.S. National Arboretum in Washington, D.C. He and other USNA scientists put together a team with scientists from other local, regional, and national groups to see if they could figure out how to give trees a needed boost.

They wanted attractive trees. They wanted trees that wouldn't grow too big for their neighborhoods. They wanted trees that could stand up to having their roots walked on--over and over again. They wanted trees that could shrug off pests such as insects. One such pest is a metallic-green beetle, called the emerald ash borer, that feeds beneath the bark of green, white, and black ash trees. Since its discovery near Detroit in May 2002, borer infestations have destroyed the ash tree population in parts of Michigan and also threaten parts of Ohio and Ontario.

Hammond and the other scientists looked at trees that had already been developed at USNA. These trees already had their "family tree" on record. So the scientists went looking for the trees that already had the characteristics they wanted in their city trees.

For instance, if all the grownups in your family are over six feet tall, there's a pretty good chance that you'll grow to be six feet tall, too.

The team worked for over four years, and selected several different trees that met their goals--like this robust red maple.

These trees won't grow so tall that they bump into power lines. Their branches are sturdy enough to stand up to strong windstorms. Their foliage protects birds and other urban wildlife.

And in the spring or in the fall, their blossoms and bright leaves add color and contrast that the Public Works Department doesn't have to set up and take down!

12/22/08
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Date: 12/12/08

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