The Urban Forestry Administration (UFA) prunes between 14,000 - 17,000 street trees in the District each year. "Street trees" are trees located between the curb and sidewalk. With the District's street tree population estimated at 100,000 trees total, this pruning volume allows the UFA to maintain a five-to-seven year pruning cycle, which is a recommended industry standard. The purpose of pruning guidelines is to maintain the tree's overall health, form, and safety of the area around the tree.
Although tree pruning is sometimes conducted by UFA in-house field crew staff, most of the systematic pruning that occurs along the streetsides is done by our contractors. All contract pruning work of this type is monitored by UFA inspectors to assure quality control and billing accuracy.
The type of pruning that UFA performs is called "Crown Cleaning" and, where required, "Crown Raising" as identified in the latest edition of the ANSI (American National Standards Institute) guidelines. UFA prunes for the following:
Removal of all dead, dying limbs
Removal of all diseased or weak branches
Removal of any watersprouts
UFA also prunes to maintain the following general clearances:
8 - 10 feet clearance over a sidewalk
15 feet clearance over a roadway
6 - 8 feet from homes or buildings
Clear view of traffic control devices
Clearance to allow unobstructed clearance for "cones of light" cast from street lights
In addition to these basic guidelines, UFA only prunes elm trees from September through March. The reason for this seasonal requirement for elms is because the odor produced by pruning cuts on elm trees can attract the elm bark beetle, which spreads the fungus that is responsible for Dutch Elm Disease, or DED. During the winter months, the beetle is dormant, and elms can be pruned safely without fear of spreading DED. The UFA grants some exceptions to this rule for emergency work. UFA prunes all other species throughout the year.
