Minneapolis residents are pointing their fingers at recently lain sidewalks as a culprit in their loss of boulevard trees during recent storms that toppled hundreds of trees across the Twin Cities.
They note that many of the fallen boulevard trees have a lighter-colored slab or two of replacement sidewalk next to them, meaning that crews likely severed tree roots before pouring concrete, making the trees less stable and more vulnerable to being uprooted.
“They cut these big roots off that were holding the trees up,” said Darna Peterson, who lives in the Standish-Ericsson neighborhood. And urban forest advocate Donald Willeke, who lives in the Cedar Isles Dean neighborhood, is urging the city to elevate the sidewalks to make room for the roots.
City officials acknowledge cutting the roots but say it’s a compromise between building sidewalks and preserving trees. But Mayor R.T. Rybak said Tuesday that he has asked public works officials to re-examine the sidewalk-tree balance to see whether the city can do more to favor the survivability of the trees.
“It was very sad yesterday to see that a lot of trees came down next to new sidewalks,” he said.
Mike Kennedy, the city’s street maintenance supervisor, said that keeping the roots when new sidewalks are built would mean that the replacement sidewalks in question will soon heave again.
Kennedy rejected Willeke’s suggestion that sidewalks be raised where tree roots have heaved them.
“You can’t have roller-coaster sidewalks,” he said. Sidewalk crews are told to cut roots before pouring concrete so that the top of any remaining root is more than 6 inches below the top of the new slab.
Kennedy has been working with the Park and Recreation Board forestry staff for years trying to help boulevard trees coexist with construction.
Careful tree selection
Gary Johnson, an urban forestry specialist at the University of Minnesota, has studied boulevard tree viability since 1995. He’s concluded that the best solution is to adapt the size of the tree to the width of the boulevard. With a boulevard of 4 feet or even narrower, a 50-foot tree is more likely to topple. A recent root cut for sidewalk or curb repair just exacerbates the issue.
Narrow boulevards are better suited to crabapples or tree lilacs, both of which the Park Board now plants, or buckeyes, Johnson said. They won’t provide as much shade, but they can be planted closer together, he said. Then cities can subsidize the planting of large shade trees in front yards, where their roots can better take hold.
Willeke comes to the issue as a founder and longtime chair of the Minnesota Urban Forest Council, as well as service with its national group. “This is one of the bigger tree disasters we’ve had,” he said of Friday’s storm. He overlooks Dean Parkway, where massive trees went down, including a 110-foot hackberry.
The tree loss was exacerbated by a combination of weather factors, Willeke said. First, the long, cool spring encouraged trees to leaf more fully than normal. The ground was also saturated. The straight-line winds hit as trees were engulfed in moisture, making them top-heavy.
One bright spot is that toppled boulevard trees often raised the sidewalk slab intact, especially where crews left a semicircular cutout for future growth. The city hasn’t announced whether property owners will have to pay anew to replace the walks that some are still being assessed for.
Johnson and Willeke agree that it’s a myth that most trees root as deeply as their crowns, except in unusual conditions. Most roots are in the upper 3 feet, Johnson said. Trees such as spruce also toppled in yards in many places because their thick branches act like a sail, catching the wind.