Study: Trees falling in B'more, most US cities

Nowak said about half the land where trees were lost wound up in grass, but about half was developed.

"Trees are an important part of the urban landscape," Michael T. Rains, director of the Northern Research Station, said in a news release about the study. "They play a role in improving air and water quality and provide so many environmental and social benefits

Only one city saw an increase in tree cover - Syracuse, NY.  But the increase in canopy there was largely from the rampant spread of an invasive shrub, Nowak said, which wasn't exactly good news.

The study examined satellite photos through 2005 - which is why New Orleans fared so poorly, having lost many trees from Hurricane Katrina.

It's not clear whether Baltimore has continued to lose trees the past seven years. Older, larger trees have died and been felled by storms such as Hurricane Irene and Tropical Storm Lee, as well as from development - including, at least temporarily, the trees cut in the Inner Harbor last year for the Baltimore Grand Prix.

Baltimore's sustainability plan adopted in 2010 calls for doubling the city's tree canopy by 2037.  The TreeBaltimore program is planting and giving away about 6,700 trees this budget year, according to city forester Erik Dihle, and plans are to boost that to 8,800 trees for the next year starting in July.

"We're aggressively planting new trees throughout the city," Dihle wrote in an email, "in part based on surveys and a prioritization map developed with the USDA Forest Service last summer."

It's hard to know whether the tree planting has reversed the losses, though.  Dihle said that tight funding has prevented the city from completing a total inventory of Baltimore's trees.

Still, he said, the study should help motivate officials and residents to redouble reforestation efforts in Baltimore.

To help those who want to keep track of urban trees, the Forest Service has developed a Web tool, i-Tree Canopy, with which users can assess their city's canopy using Google images.