Best Trees for the Street
Editor's Note: This article originally included the photo on the left, describing it as "The ‘Natchez’ crapemyrtle (Lagerstroemia)." As many astute readers have noted, the Natchez has white flowers, as shown in the photo on the right. The photo at left shows a crape Myrtle (Lagerstroemia indica)
Scientist John Hammond of the Agricultural Research Service (ARS), the U.S. Department of Agriculture’s chief scientific research agency, has announced the findings of a four-year project to determine the best trees to use in urban spaces.
Hammond, who also heads the ARS Floral and nursery Plants Research Unit in Beltsville, Md., aimed to find “trees that can survive years of service shading city sidewalks or traffic median strips.” Important factors included small to medium size, pest-resistant and low-maintenance trees that do well in environmental extremes. Other benefits included good looks, such as “springtime blossoms, shapely crowns, brilliant fall foliage, etc.” Size was important because if a tree grows too large for the space it occupies, it might have to be severely pruned or even removed entirely to accommodate utility lines or to be safely away from other structures.
Hammond’s team, whose partners included the U.S. Forest Service, the Maryland Department of Natural Resources, the University of Maryland, Washington, D.C.’s Urban Forestry Administration, and local utility companies, found good street tree candidates in the U.S. National Arboretum’s cultivar collection, including three species of red maple (Acer rubrum)—‘Brandywine,’ ‘Somerset’ and “Sun Valley’; red maple (Acer rubrum); ‘Natchez’ crapemyrtle (Lagerstroemia); and the Frontier elm (Ulmus).
The team is also investigating how early cultivation methods affect street tree survival. Initial tests showed that container-started trees outperformed in-ground trees, which do not have to be dug up to be transported and thus undergo less root damage. The team will continue to examine whether any performance related variables hold true as the trees mature.
This “Power Trees Project” (powertrees.com) is important because of the huge amounts of resources required by municipalities to care for trees. One Washington, D.C.-area utility spends about $20 million annually on tree trimming, removal and replacements.
According to USDA’s Economic Research Service data for 2005, woody shrubs, flowers and other ornamentals comprised sales of more than $16 billion.