A decade ago, Mayor Thomas M. Menino stood with other local officials in the Geneva Cliffs Urban Wild in Dorchester and vowed that Boston would plant 100,000 new trees by 2020, expanding the city’s tree canopy by 20 percent.
With climate change a growing concern, cities across the country made similar pledges, a simple way to soak up carbon emissions and curb energy use, among many other benefits. That same year, New York City set an even loftier goal to plant 1 million trees by 2017.
New York met its goal — two years early. Boston, however, has fallen woefully short. Not only has the city abandoned its goal for this decade, but it has barely kept up with tree mortality.
Between fiscal years 2008 and 2017, the city planted 9,809 street trees and removed 5,815 — a net gain of fewer than 4,000, city records show. While many more trees were planted on private property, which makes up about half of all land in Boston, the city’s canopy — the amount of leaves and branches from Allston to Mattapan — may have actually decreased.
“Trees need to be a priority, and they haven’t been,” said David Meshoulam, founder of a new city group called Speak for the Trees, a reference to Dr. Seuss’s classic cautionary tale “The Lorax.” “That has to change.”
When Menino announced his plan in 2007, city officials said a “comprehensive assessment” found that 29 percent of city land had trees.
Last year, in the most recent assessment of the city’s canopy, which used more sophisticated, high-resolution aerial imagery and lasers, analysts from the University of Vermont determined that just 27 percent of Boston’s land had trees. A 2014 study by a Boston University professor placed the figure around 25 percent.
While Boston has challenges that some other cities lack, such as densely populated neighborhoods and limited amounts of open space, its tree canopy lags behind most other cities. Overall, urban areas in Massachusetts have about 65 percent of their land covered by trees; nationally, the figure is 35 percent, according to a 2012 study by the US Forest Service.
City officials, while citing the difficulty in growing and maintaining trees in urban areas, acknowledged that progress has been inadequate.
“I would say not only can we do better, but we should do better and will do better,” said Chris Cook, commissioner of the Boston Parks and Recreation Department. “We’re going to have to take a different approach.”
Austin Blackmon, Boston’s environmental chief, said the city has shifted its focus to maintaining its stock of older trees, which absorb more carbon dioxide, provide more shade, and do more to reduce flooding.
“We know that mature trees contribute far more to our canopy than new trees,” he said. “Since coming into office in 2014, Mayor Walsh has made a significant investment in maintaining and protecting that canopy.”
But with the city’s breakneck pace of development, mature trees have often become casualties to new buildings, byways, and other municipal projects.
For example, when the US Army Corps of Engineers began the major project of unearthing the Muddy River in the Fenway in 2012, restoring a broken watery link in the Emerald Necklace, they cut down about 200 mature trees, some more than a century old.
In Jamaica Plain, the city’s leafiest neighborhood, a state project that razed an aging overpass by the Forest Hills MBTA station, making way for an array of new streets and bike paths, took down more than 150 mature oak and maple trees.
While the state has replanted hundreds of additional trees there, some are already dead or are dying. Those that thrive will take decades to reach the stature of the oaks and maples that were removed, while many of the wispy new trees were planted so close to each other that they won’t be able to grow tall.
Surveying the changes to the area on a recent afternoon, Lucy Hutyra, an associate professor of earth and environment at Boston University who studies the urban canopy, said the decision to remove so many mature trees reflects the shortsightedness of city and state officials.
“The city has failed in its efforts to grow the canopy, but the question is whether they were actually trying,” said Hutyra, who conducted the 2014 study of city trees. “It’s easy to make a goal; it’s a lot harder to have the sustained investment to see it through over several years, especially when the political cycle gets in the way.”
Over the past decade, the city has spent about $9 million on planting and pruning trees, a sum that has proven insufficient, Hutyra and others said.
“I think the city should be doing a lot more,” said Peter Del Tredici, a senior research scientist at the Arnold Arboretum.
To cast light on the problem, City Councilors Ayanna Pressley and Matt O’Malley have scheduled a hearing this month, where they plan to urge officials to do more to improve the city’s canopy and to distribute trees more equitably.
“There’s a greater density of trees in some neighborhoods than others,” Pressley said. “In some of the neighborhoods most vulnerable to climate change, where we need them, we don’t have them.”
She pointed to East Boston, where only 7 percent of the neighborhood has trees planted, according to the city’s most recent report on the tree canopy.
That report found that 41 percent of the city’s land could be suitable for planting trees, O’Malley noted.
“We’re not nearly where we ought to be,” he said.
City officials said they’re using the data from the new report to come up with a better plan for how to increase the city’s canopy to 35 percent by 2030. They also said they plan to conduct similar aerial surveys every five years, as the report recommends.
City officials say they are also pressing private developers to preserve and add trees, although there’s only so much they can do.
“When a development project is reviewed by the Parks Commission, we advocate for protection of existing trees and integration of new trees, particularly in parking areas,” said Liza Meyer, the chief landscape architect of Boston Parks and Recreation Department.
Environmental advocates urged the city to work more closely with conservation groups that will help the city care for the new trees, many of which die shortly after being planted. They also called on the city to invest in longer insurance plans for trees, which would allow them to be replaced if they die after several years.
That will be even more important as tree pests, such as the emerald ash borer, move ever closer to Boston. In 2015, the tree-killing insects were found on the city’s border in Brookline. Other threats include Dutch elm disease, which has ravaged some of the city’s oldest trees, and natural gas leaks, which can suffocate trees.
Advocates said the city could also be giving saplings away to private landowners, planting far more trees in public parks, mapping neighborhoods for areas where trees are lacking, and doing more to ensure that existing trees remain healthy, as New York City has done.
“Every acre of Boston needs to be looked at,” said Liz Vizza, executive director of the Friends of the Public Garden, which works with the city to tend to the needs of 1,700 trees in the Back Bay. “Everyone has to be a tree advocate.”