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ST. PAUL, Minn. – The intense rain sweeping across the Twin Cities in recent days has endangered a number of trees in the area.

The softened soil can turn greasy around the root systems of taller, older trees leaving them more vulnerable, according to experts.

An old backyard tree toppled into the second floor a duplex in the 1600 block of McAfee Street Sunday night. The tree punched through the window of a boy's bedroom, but fortunately he had not gone to bed yet. The Red Cross is assisting the families involved.

"Soil structure fails when it is too wet," said Val Cervenka, Department of Natural Resources Forest Health Program Coordinator. "The soil is no long able to hold that tree in place. Then, you couple that with strong winds and you are going to have the whole tree falling."

Cervenka said homeowners with large trees should keep an eye on the verticalness of their trees.

"If the tree has developed a lean, if it is a recent lean, you can often see mounding right on the other side of the tree (where the root system is rising through the soil)," said Cervenka. "Where a tree has developed a recent lean, I would get it out of there pretty quickly."

In the case of the McAfee Street tree, Timberline Tree Service's Karl Brogren said the inside of the tree was rotted.

"There was a lot of decay in the root system of this tree, so it let go," said Brogren. "It was not a healthy tree that came down, but a seemingly healthy tree that had some issues."

Brogren pointed out that homeowners should take note if a tree has mushrooms or toadstools growing on the tree.

"That is always a sign that you want to pay attention to. It is going to tell you that there is some decay in there," said Brogren. "Large trees, it does not hurt to have them checked out every few years by a certified arborist to make sure everything seems on the up and up."

"Certain types of trees are more prone to root decay," said Cervenka. "For example, Norway Maples can develop what is called stem girdling roots. The roots, in their attempt to get air, come up to the surface and begin to grow around the base of the tree. In effect, it girdles the tree, constricts the tree at the base and it can topple over."

Cervenka says the contour of the property can also be a factor.

"If your home is typically saturated, the ground around your home, you get basement flooding every spring, for example, that is going to be a really likely area for tree failure. Low lying areas could hold water longer."

University of Minnesota professor Gary Johnson said there are two things homeowners can do to prevent tree failure. One is to refrain from planting trees on the narrow boulevards of city streets. Second is to avoid cutting or confining the tree's roots, since the roots on the windward and leeward sides and deeper are what holds the tree in place.

Cervenka agrees with Johnson to avoid placing a tree close to a driveway or other pavement.

"Plant a tree where it can grow openly, where the roots have a chance to spread because they grow out to where the branches stop. The root system is really extensive."

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