Study examines causes of tree failure after epic windstorm

A new University of Minnesota tree failure study commissioned after a severe storm uprooted thousands of trees in the city June 21, 2013 has determined that trees located near sidewalks recently repaired had a higher chance of toppling.

Cutting roots during repair projects jeopardizes the trees’ stability. The average Tilia tree had about a 10 percent chance of root failure when it was next to a sidewalk that hadn’t recently been worked on compared to a 21 percent chance of uprooting when a sidewalk had been repaired, according to the study. Other types of trees had double the chance of uprooting as well if located near sidewalks with recent repairs.

Gary Johnson, principal investigator for the University of Minnesota Department of Forest Resources Study, briefed the City Council’s Transportation & Public Works Committee on the study’s findings Tuesday. The study focused on boulevard trees felled during the solstice windstorm.

Johnson said wider boulevards are recommended to protect trees, especially larger trees, to accommodate the roots systems.

Mike Kennedy, director of transportation maintenance and repair for the city’s Public Works Department, said the department will continue collaborating with the Minneapolis Park and Recreation Board’s Forestry Division to minimize the impact of construction and maintenance work on the city’s trees.

The Council committed directed city staff to work with the Park Board, Minneapolis Tree Advisory Commission and the Minneapolis Pedestrian Advisory Committee on recommendations for changes to city policies and practices that will help preserve trees. A report is due to the committee by July 31.