Growth stunted along Greenway
Soil depths too shallow for some tree plantings
The Big Dig's roadways are complete, but the mega-project has hit another snag: Some of the 636 trees designed to transform the land atop the tunnels from brownway to greenway will have to be scrapped or moved because the soil is not deep enough.
Several groups involved in the tree plantings for the new Central Artery surface said this week that there will be significant gaps along the 1 1/2-mile Rose Fitzgerald Kennedy Greenway from Causeway Street to Kneeland Street because there is not enough space to plant trees above underground conduits carrying electric, gas, steam, phone, and cable lines. In some spots, the soil is just 9 inches deep, less than half the 20 inches needed for most trees.
In addition, some trees planned or already planted may have to be uprooted or moved to make room for future development.
''People are going to be really surprised by how much less green they're going to see compared to these . . . wonderful, artist renderings of a tree-lined boulevard and a string of parks," said Valerie Burns, president of Boston Natural Areas Network, which promotes greenspace citywide but is not directly involved in the Greenway.
A Big Dig spokeswoman said the problems are isolated, but acknowledged that inadequate soil depth is an issue for nine linden trees planned for Purchase Street between 99
''In essence, we knock out an entire block of trees," said Robert Tuchmann, co-chairman of Mayor Thomas M. Menino's Central Artery Completion Task Force and chairman of the Central Artery Environmental Oversight Committee.
''We're all surprised," said Tuchmann, who is monitoring the tree planting. ''We're all concerned because that block is really bleak. All the buildings have uninteresting fronts, and they're all right up against street. It's an area that would really benefit from trees."
Spokeswoman Mariellen Burns said the Massachusetts Turnpike Authority, which took over management of the Big Dig this month, is working on solutions, including possibly putting the lindens in planters.
But, in planters the roots could be exposed to deadly cold, Tuchmann said. The planters would take up valuable sidewalk space and are difficult to maintain. They also prevent the trees from growing to full height, he said.
In other parts of the Greenway, several trees have been relocated because they would have been too close to underground steam lines that could kill their root systems, Burns said. In other problem areas, trees or underground utility lines could be moved, she said.
Burns declined to provide details on how many trees can't be planted, or on the costs of alternative tree plans. ''It's a complicated problem," she said.
The Greenway covers 30 acres along a 1 1/2-mile corridor from the North End to Chinatown, on land the elevated Central Artery once shadowed. The trees are supposed to line the new parkland and the surface streets atop the tunnels.
The project's sidewalks are built to include ''treeways" -- openings 3 feet by 8 feet in the concrete exposing the ground and filled with planting soil that allow tree roots to spread naturally. Plans also call for underground drainage and irrigation for each tree, adding to the space demands. The average tree's root ball is 18 inches high and 36 to 48 inches in diameter.
Tuchmann and other Greenway supporters are also worried that after trees are planted this spring, future development along the Greenway -- with its requisite curb cuts, and architectural and parking requirements -- could require their removal. For instance, a compromise last month to preserve a sidewalk in front of 500 Atlantic Avenue resulted in the loss of two trees planned in front of the InterContinental Boston Hotel, Tuchmann said.
Toni Pollak, the city's parks commissioner, who is also monitoring the tree planting, said she was unaware of any stretches of shallow soil similar to the one along Purchase Street. The parks department, she said, was committed to keeping as many of the 636 planned trees as possible.
''We are going to try to keep the continuity and the intent of the design, and take care of these trees," she said. ''That is our role and we are working with the Artery to make sure that happens."
Thomas Nally, director of planning for the Artery Business Committee -- a business group formed to support and manage the impact of the Big Dig -- said he has heard of other areas where trees could be relocated or eliminated, including above an underground foundation near 470 Atlantic Avenue and the Moakley Bridge.
''If you focused on having a continuous line of trees, that was never going to happen," Nally said. ''That was the vision, but that's never going to happen . . . In certain locations there are going to be some gaps and that's been well known for a long time."
When construction began on the Big Dig in 1991, one of the first projects was to excavate and relocate utilities along the proposed Greenway, prompting some tree advocates to criticize planners for not properly preparing for the future planting of trees.
Steve Puopolo, project manager with ValleyCrest Landscape Development, the firm that will be planting the Greenway trees under contracts worth $6.5 million, said such conflicts are common with planting urban trees. ''With the trees being the last items to go into the ground, a lot of times they have to go wherever there's a spot," he said.
Landscape architect Horace Aikman, whose firm, Carol R. Johnson Associates in Boston, created the initial park designs for former Big Dig manager Bechtel/Parsons Brinckerhoff, said he would not be surprised by changes in the locations and numbers of trees. For instance, he said, in the final phase of designs for the Greenway, he learned that the underground tunnel was too close to allow plantings near the New England Aquarium.
''We're dealing with highway engineers and electrical engineers, and they're not going to relocate ducts or the tunnel to accommodate a tree," Aikman said.
Lynn Wolff, principal and president of Copley Wolff Design Group, which is designing the streetscape from Causeway to Congress, said a huge effort went into understanding the cross sections of tunnels and utilities underground as well as negotiating and moving utilities to make areas for trees. In that process, she said, one tree was sacrificed because of a nearby steam line.
Pat Bigelow, president of Bigelow Nurseries in Northborough, where nearly 2,000 trees are being grown to be transplanted in Big Dig parklands, said that despite years of planning and mapping the utilities, underground conflicts for urban trees are typical.
''Adjustments are made so that the tree can be planted and the city . . . can have heat, light, and water," she said. ''There's bound to be changes. This isn't a brand new shiny site. This is the city of Boston."
Megan Woolhouse of the Globe staff contributed to this report. Mac Daniel can be reached at mdaniel@globe.com. 