Wanted: Trees for Urban Landscapes

Imagine this "wanted" ad: Horticulturalists in search of small- to medium-sized, pest-resistant, low-maintenance trees that thrive in the face of environmental extremes. Must be able to tolerate foot traffic, storms, drought, car exhaust, insects and dogs. Good looks—springtime blossoms, shapely crowns, brilliant fall foliage—a plus.

Agricultural Research Service (ARS) scientist John Hammond set out to make a lifelong match: trees that can survive years of service shading city sidewalks or traffic median strips. Hammond, who heads the ARS Floral and Nursery Plants Research Unit in Beltsville, Md., is in charge of the "Power Trees Project."

For four years, Hammond has worked with federal, state and local partners to find trees that can keep their good looks and hold their own against urban stresses. Pick the wrong candidate, and a tree can grow too large for the space it occupies. Then it may have to be severely pruned—or even removed entirely—to accommodate utility lines or other structures. Or it may be vulnerable to pests, diseases and storm damage.

Hammond’s team has found nine good street tree candidates in the U.S. National Arboretum’s cultivar collection, including varieties of red maple, crape myrtle, crab apple, flowering cherry and elm. Most mature at less than 25 feet and thrive in a range of U.S. hardiness plant zones.

Hammond and other ARS scientists are also investigating how a tree’s early cultivation method—either in a nursery container or by in-ground planting—affects its street survival. In initial tests, container-started trees outperformed in-ground trees, in part because container-grown trees don’t undergo root damage from being dug up and bound in burlap for transport. The researchers will now assess whether these early performance indicators are maintained as the trees mature.

With a bit of help, trees will continue to provide the tangible and intangible benefits that people expect—and enjoy—from their green surroundings.

Read more about this research in the October 2007 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.