MINNEAPOLIS - A University of Minnesota study sheds new light on what caused hundreds of trees in Minneapolis to topple during a storm last June. It also provides tips to save trees in the future.
"One storm, one day, one city," recalled University of Minnesota's Gary Johnson, of the Department of Forest Resources.
The storm sparked a city study to inspect and help figure out what happened.
The study examined 122 city blocks and more than 3,000 trees. It also took a closer look at about 400 trees that fell to the ground.
Researchers noticed most of the damaged trees were uprooted, most were near sidewalks and most were top heavy and dense.
The team found that sidewalks installed along tree lines often require the roots of those trees to be cut to help install that sidewalk. That meant it was just a matter of time before a great wind was no match for a tree with a cut or compromised root system.
"Rather than cutting roots, is to kind of swing the sidewalk out further so you replace the sidewalk but you don't have to cut the roots," Johnson explained.
Johnson has come up with alternatives to prevent more sidewalk and stump removals in the future.
He says if the boulevards are wider at least 8 feet, rather than 4 feet, studies show those trees are better able to handle a windy storm.
Moving sidewalks altogether could also help.
"The sidewalk will be moved right to the curb and then you have this uninterrupted space right here, 10, 12, 15 feet," Johnson said. "That's where the trees are planted."
The types of trees planted also matter. Johnson says Linden trees are the worst, especially if it rains before the wind strikes, they're simply to top heavy and uproot easily.
He said the more open trees, honey locusts, etc., had very little damage.
Johnson's study is now in the hands of the Minneapolis Public Works Department and park board.
The two agencies are working on a solution to maintain the city's urban forest.