Don't ignore 'zombie' trees

Travis McDonald has been known to cross the street to avoid certain trees when he and his family go for a walk. When you're a tree expert, it's not hard to spot danger on a peaceful afternoon.

Hanging limbs, dead wood, split trunks, trees that dramatically lean — all signal that a tree is a potential hazard. More subtle signs may alert an expert to a "zombie tree" that appears outwardly healthy but has problems that mean it should be removed.

"Trees have to be respected; they can't be ignored," said McDonald, Twin Cities district manager for the Davey Tree Expert company. "A lot of people think trees just take care of themselves. They will in a native setting. But in a residential setting they need care."

Many of us take our trees for granted. We love the shade and fall color they provide but resent the mess that they make on our lawns. We bang into them with lawn mowers and slash them with weed whips. We plant them too deep and forget to water. And we cut roots that are critical to tree health and stability to lay sidewalks and driveways and to build garages.

It all makes for a stressful environment for urban trees. But few people recognize the signs that a tree needs help, or more dramatically that it's time to say goodbye and remove a tree before something bad happens.

McDonald, a certified arborist, said the biggest misconception he sees among the public is that every big tree must be dangerous. Homeowners call the tree company, say they have lots of big trees on their property and ask if someone can come out and tell them if they're dangerous. McDonald said sometimes they aren't happy when the answer is that it depends on what Mother Nature throws at the tree.

Trees often don't show the effects of storm damage or drought for years. "There are trees that look healthy on the outside, but have structural issues inside or beneath the soil that you can't see," he said.

Dieback at the top of a tree signals a problem, as does cracking or splitting of trunks and broken limbs. If you suddenly hear squeaking high in a tree after high winds, McDonald said, it's time to call someone to take a closer look.

Some problems can be prevented by proper pruning when trees are young. Such shaping, done by an arborist who knows how to properly shape trees, will create a tree with good structure. Such preventive work is especially important with fast-growing, brittle trees like maples.

"You don't want to wait and then take a 4-inch limb off because you can't mow the lawn," McDonald said.

Large trees can have major limbs cabled to prevent branches from sagging or splitting. Tree canopies can be thinned to let wind pass through more easily. And trees can be protected from soil compaction and cutting of too many roots during nearby construction by fencing off the ground under the canopy.

Many certified arborists don't charge for a visit to evaluate a possible hazard. More sophisticated evaluation, like use of a machine to determine if a tree is hollow, comes at a price. But it may be worth the cost on very large, old trees like basswood, which McDonald said can appear healthy but have considerable decay inside.

Straight-line winds and severe storms in 2013 and 2014 wiped out a lot of hazard trees in the Twin Cities area. But even a seemingly tree-friendly, moisture-rich year like this can create issues, McDonald said. Trees are thick with growth and filled with water and won't harden off for winter for awhile, and all of that new heavy growth is vulnerable if bad storms hit.

The emerald ash borer's relentless march across the state could create a zombie tree epidemic, he said. But if people pay attention to trees and seek help if they suspect something's wrong, bigger problems can be avoided.

"Trees don't naturally fall over — there's always a correlation as to why it happened," McDonald said. "And often it's something that could be avoided ... Trees are not dangerous if they're taken care of."