A University of Minnesota study found sidewalks that cut into the roots of Minneapolis boulevard trees made those trees twice as likely to topple in a June 2013 storm.
The roots of boulevard trees often push up and damage sidewalks, so workers will cut into the roots to keep the sidewalks level. The study showed sidewalk construction made those trees more unstable than other trees, said Ralph Sievert, forestry director for the Minneapolis Park and Recreation Board.
The study went beyond speculation, using data to show root cutting "was the cause of a lot of the trees falling over from that storm," he said.
The study recommends sidewalk contractors avoid cutting into root systems by ramping sidewalks over the roots or building around them, said Sievert.
The study's author, Gary Johnson of the University of Minnesota, will present the report to Minneapolis Park Board commissioners on Wednesday.
Minneapolis city officials say the 2013 windstorm damaged more than 3,000 trees, a toll greater than the 2011 tornado which swept through parts of north Minneapolis.