How to bring shade to a city

The societal benefits of trees

According to city and environmental officials, the $15 million spent on trees is expected to have social benefits as well. Trees are touted as miracle workers for city problems. Boston officials cite studies claiming that trees reduce energy costs, ease stress, and lower crime rates. Increased vegetation is also credited for decreases in aggressive street behavior, boosts in neighborhood pride, and more people spending more time outside, which serves as increased outdoor surveillance.

Boston is even using the FOS system for a venture into "environmental justice," in other words, equal opportunity trees.

"The question is, does everyone, in terms of race and income, have similar levels of canopy cover in their neighborhoods?" Mr. Hunt says. According to Boston's tree inventory statistics, the crowded and poorer East Boston neighborhood has only 6 percent canopy cover in comparison to the wealthier West Roxbury's 49 percent.

Several Boston environmental organizations are already stepping up their efforts. On this typical Thursday in early July, members of EarthWorks and JP (Jamaica Plain) Trees plant trees in various yards in the Jamaica Plain neighborhood. EarthWorks is a member of Boston's urban forest coalition and reports all tree plantings to the Urban Ecology Institute.

Matt Walter, a certified arborist and JP Trees volunteer, is planting a kousa dogwood in the yard of Jamaica Plain resident David Baron. [Editor's note:The original version misidentified the organization that Mr. Walter volunteers for.]

"They've given me a lot more guidance than I would have gotten just from walking into some nursery," says Mr. Baron as Mr. Walter explains how often he should water the dogwood. "I really wanted to get a tree, and I heard this program was free."

On this same afternoon, Walter examines a black tupelo tree planted two weeks ago. Upon examining the tree and its dried brown leaves, Walter unearths it and pointedly says, "Some trees make it. Some trees don't."

He soon determines the tree grew a double trunk flare, likely caused from repotting in the nursery. The double flare caused a water shortage to the deep roots, he says, and promises the homeowner a new tree will be on its way.

Challenges for city trees

Tom Ward, Dana Greenhouse manager at the Arnold Arboretum, says root damage is a common cause for city tree deaths. Once a tree is unearthed and replanted, as is typical in the greenhouse transferring process, it loses 90 percent of its roots and needs time to recover. Overeager lawn mowers can sometimes disrupt newly planted trees and permanently derail its growth.

But roots are not the only issue for city trees. Biodiversity, including a variety of species and age, increases survival rates and resistance to natural processes, Mr. Ward says. A notorious example is the Dutch elm disease, which decades ago wiped out US populations of the Dutch elm tree. Ward still fields calls from city planners desiring to plant elm trees on their Elm streets.

"They want to know, 'Should we plant it all in elms?'" he says. "I tell them, 'No.' "

Ward praises Boston officials for undertaking a "very ambitious" 100,000 tree project, but cautions that a city tree's life – especially that of an urban sidewalk tree – can be stunted by factors from drought to human interaction.

"These trees take a coalition of people to basically babysit, water, and tend to," says Mr. Ward. "In the end, aftercare makes all the difference."

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