The red oaks and surrounding soil were replaced and the tree pits were also expanded to allow for better air space.
Pedestrians along Columbus Avenue could be enjoying a shady canopy for decades after a recent project replaced the trees on the sidewalks with a more resilient species.
“The average street tree is only going to last 7 1/2 years, but when you have the right tree in the right spot, we try to extend it as long as possible,” says Greg La Plume, associate director of horticulture and grounds at Northeastern University.
“We’re hoping for them to at least last a good 50 to 70 years,” he says.
The eight new trees stretch from in front of Northeastern’s Interdisciplinary Science and Engineering Complex to the Columbus Parking Garage and are maintained by the university.
The area was originally planted with red oaks when ISEC was built and then replanted with the same species when the EXP research complex came online.
But La Plume says that the high water table in the area — from only 18 to 24 inches below the surface — effectively drowned the red oaks.
“They were inundated with water and they just got choked out — they didn’t have enough air porosity in the soil, so they went from aerobic to anaerobic respiration, which eventually leads to the die-off of the tree,” La Plume says.
So, La Plume looked to a wetland species — the native swamp white oak — to fill the gap.
The trees and surrounding soil were replaced in October, and workers also expanded the surrounding tree pits to allow for better air space.
“Instead of replacing it with bricks on top or the concrete pavers that were there, we ended up utilizing Porous Pave, which would allow more porosity to that area so the immediate area around the root of the trees could dry out a bit more instead of just being fully saturated all the time,” La Plume says.
He expects the trees to reach about 60 feet high in the conditions — even with the snow, wind, rain, poor urban soil and swampy conditions that Boston can throw at it.
“It’s found in a variety of landscapes already,” La Plume says. “It’s a great tree species for cityscapes because it has the capacity to have those prolonged periods of anaerobic condition or water inundation for longer periods of time.”