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Our Precarious Relationship With Trees, and The Weather

Our Precarious Relationship With Trees, and The Weather

By Larry A. Sagers | Posted - Oct. 8, 2011 at 7:10 a.m.

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The furious storms that moved through northern Utah last week are a reminder of the sometimes precarious relationships between trees, the weather, and, of course, people.

Trees — like all living organisms — will eventually die off, but when the weather turns fierce, they sometimes meet an untimely end.

During last week's storms, some trees toppled onto homes, cars and fences. In other cases, trees pulled down power lines, leaving thousands without electricity.

A globe willow is uprooted after a severe storm. Willow trees, common in Utah landscapes, are among the most easily damaged.

And if losing a tree wasn't bad enough, some homeowners found removal costs can run into the thousands of dollars. Even if you can do the work yourself, it takes a lot of backbreaking labor.

Yet some problems can be avoided. The most important part in dealing with potential problems is to put the right tree in the right place. If you skip the tree-selection process, you greatly increase the chances of losing trees to severe weather in the future.

Problems fall into three categories, and the trees that fail often have one or more of them:

• They have weak or brittle wood that breaks easily when subjected to stress.

• They have narrow branch angles that do not knit together well so they split apart easily.

• They have shallow root systems that allow the tree to topple over.

Willows are among the most easily damaged because they have all of the above characteristics. These trees are routinely planted in many landscapes because they are inexpensive and grow quickly. Globe willows are among the worst offenders.

Poplar and cottonwoods are closely related trees with weak wood. The lightweight wood breaks easily because the large cells seem more like Styrofoam than solid wood.

Russian olives also have serious drawbacks. They are considered a noxious weed in several counties in Utah because they spread so quickly, and they also break down under stress because the branch angles are weak and narrow.

Siberian elms (often erroneously called Chinese elms) are large trees with brittle, weak and narrow branch angles. Many a power line has been felled by the branches of these trees. Silver maples share the same characteristics.

While flowering pears are beautiful, choosing the right cultivar is essential. Bradford, the original flowering pear, has weak, narrow branch angles. Newer types have better structural characteristics.

Spruce trees are typically shallow-rooted. Large old trees have a tremendous wind resistance but are easily toppled during a microburst. Pines are usually better anchored and less likely to topple.

While the weak wood, shallow root system and growth habits are genetic, we sometimes aggravate the problem by letting problem branches develop. The strongest branches usually come off the trunk at about a 45-degree angle for most species.

When the union between the branch and trunk has a narrow angle, the branch and trunk bark become overgrown. This "included bark" results in a weak union that is likely to split. While some trees naturally develop "included bark," the difficulties are reduced by eliminating the narrow-angled branches when they are small.

A couple of reminders: Homeowners should never try to trim or remove branches near power lines. Always refer these problems to professionals who work for the power company. They are trained to do the job safely.

And homeowners should never climb trees while carrying chain saws. The risk is too great. Look for a certified arborist who can safely remove the offending tree parts without causing additional damage.

Of course, it's best to avoid planting large trees under power lines or too close to your house, fences, sidewalks or driveways. Such restrictions can interfere with root growth, making the tree easier to topple.

Spend a little time learning about quality trees. Avoid those problem trees that are likely to cause risks to life, limb or property. Someday you will appreciate that you made the right decisions.

Written by: Larry Sagers Horticulture Specialist Utah State University Extension Thanksgiving Point.

Larry A. Sagers


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