U of M study: Sidewalk repair weakens trees

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May 19, 2014
By: Ben Johnson
Ben Johnson

The intense storms of last June toppled more than 3,000 trees in Minneapolis, and now a University of Minnesota study has confirmed a popular neighborhood theory: trees planted near sidewalks that had been repaired or replaced were 2.24 times more likely to fall during the storm.

“When no replacement work was done, the average Tilia (Linden tree) had a 10.6 percent chance of root failure; this increased to 21.0 percent when replacement work was done,” the report read.

The study found that tree species and size were also factors determining whether a tree withstood the storm. Linden trees were the most likely to fail, followed by ash, maple and elm, and trees with larger trunk circumferences were more vulnerable to tipping.

The report calls for coordination between city public works and the Park Board forestry department whenever construction takes place near boulevard trees. It advocated for ramping or rerouting sidewalks around existing root systems rather than cutting through them, or using tools like an Air Knife or Air Spade to remove dirt without harming roots.

Other recommendations include making all new boulevards a minimum of eight feet wide, removing trees in poor condition near construction projects and avoiding planting large tree species in narrow boulevards.