Construction crews have started the streetscaping phase of Oak Park’s Lake Street improvement project by removing the roughly 40 trees that lined the street. Forty-eight new trees of various varieties will replace them later in the process.
“We made a conscious decision to remove those trees in order to provide a much better built environment moving forward, as opposed to just cutting them down for no reason,” said Robert Sproule, Oak Park forestry superintendent and assistant public works director.
The trees, primarily of the honey locust variety, have outgrown their too small pits, which has impeded their overall growth. Over the years, some trees have been hit by cars. When originally planted, streetscape planners did not have as wide an understanding of how trees exist in built environments.
The trees were planted on Lake Street in the late 1980s when a failed pedestrian mall was removed and Lake Street was restored as a vehicular route.
“They’re just kind of stunted in a lot of different ways and a lot of that has to do just with the environment in which they’re growing,” Sproule said. “There were no steps taken to prepare underneath the sidewalk for them. They just cut the hole in the sidewalk, maybe they dug out the soil and they plunked in the tree and left it to survive on its own.”
The limestone subbase in which the trees were planted made the soil highly alkaline – something the trees don’t grow as well in, according to Sproule.
Trees growing in poor conditions may start to suffer structurally; the trees on Lake Street have been constrained by their planted environment, growing over the tree grates surrounding them.
“When they were planted, they started to grow right over those grates,” said Sproule. “And that actually starts to kill the trees.”
While aesthetically attractive, the older style metal tree grates were not designed to be pulled back or removed easily, making them difficult to manage.
Grates, however, are considered walkable surfaces if the openings in them are small enough under the Americans with Disabilities Act (ADA). Soil and mulch are not approved by the ADA.
Due to the narrowness of Lake Street, crews will still install tree grates, but the updated design of the grates make them safer for trees.
The new grates are larger than what was used in the past with wider openings, but not so wide that they are non-compliant with ADA standards. The new grates were designed to open easily, making maintenance simpler. Along with the updated grates, the new trees will sit in larger plots.
Unfortunately, the village can’t replant the old trees in a different location, due to their condition and size.
“They’re too big,” said Sproule. “When you would try to do a large-scale tree transplant, you would need to be able to access a lot of root system which is just really difficult to do in a built environment like that.”
Working around the old trees would cause them further stress and make Lake Street renovations more difficult for construction crews.
The replacement trees are of a variety of different species, as well as being better suited for the area. The new plan encourages roots to grow and allows the space to do so.
According to Sproule, the new plan also uses a planting material developed at the University of Cornell, called CU-Structural Soil, which doesn’t have a limestone base.
“It compacts differently and leaves a lot more for floorspace and water holding capacity,” said Sproule.
A new multi-ring circular irrigation system will promote roots to grow underneath the sidewalk, instead of directly at the root ball.
“We have a much better understanding of how the trees exist within that built environment, and how to maximize their growth and their health,” Sproule said. “The plants are just going to be a lot happier and healthier.”