Wanted: Trees for Urban Landscapes
By Ann Perry
October 11, 2007
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 looksspringtime blossoms, shapely crowns, brilliant fall
Agricultural Research Service (ARS)
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
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 prunedor even removed
entirelyto accommodate utility lines or other structures. Or it may be
vulnerable to pests, diseases and storm damage.
Hammonds team has found nine good street tree candidates in the
National Arboretums 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 trees
early cultivation methodeither in a nursery container or by in-ground
plantingaffects its street survival. In initial tests, container-started
trees outperformed in-ground trees, in part because container-grown trees
dont 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 expectand enjoyfrom their green
more about this research in the October 2007 issue of Agricultural
ARS is the U.S. Department of
Agriculture's chief scientific research agency.