by Jewel Pickert

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Gary Johnson, Assistant Extension Specialist of Urban & Community Forestry, has studied trees falling in storms, going back to 1994. He’s referring to thunderstorms, not tornadoes, straight-line winds, or derechos.

He has found three main reasons trees are more prone to toppling in a thunderstorm: decay and wounding, lack of pruning, and burying when planting.

The #1 reason, decay and wounding, can occur from animals, weed-trimmers, or pruning incorrectly. Deer, for example, like to rub their antlers on tree trunks.

Typically, he said multi-stemmed trees with lots of leaders that have weak attachments tend not to fare as well in a storm.

The second reason is a lack of regular pruning when a tree is young. Gary recommends pruning a tree every year for the first 15 years. Make sure you don’t wound the tree trunk.

He said Autumn Blaze maples are a “train wreck” in a windstorm, if not pruned regularly.

The Valley Forge and Princeton elms grow so fast, they have to be pruned once a year. Burr and white oaks, honey locusts, and sugar maples, on the other hand, grow more slowly and are more solidly built. Therefore, pruning once every five years would be fine.

The third reason a tree can topple easily in a storm is becase the tree was planted too deeply. Gary recommends you plant a tree. Don’t bury it.

When it’s buried, the tree will not develop a normal root stem. In fact, the roots will girdle the stem instead. When a tree trunk snaps off, it’s likely due to stem-girdling roots.

Gary said a wind speed of 30 mph or more is considered a windstorm. With 40-50 mph winds, a tree trunk can snap off. At a speed of 60-65 mph, it’s getting close to straight-line winds.

To study why trees fell, Gary said he “looks for areas where trees shouldn’t have failed.”

If you’re concerned about losing a magnificent tree, otherwise known as a heritage tree, you might consider installing a lightning protection system in the tree.

A lightning protection system is a rod or rods in the tree that are grounded, like what you see in a barn. The National Heritage Farms out East all have lightning protection systems for their trees.

Lightning will kill a red oak or a hackberry with no such system.

A burr oak, on the other hand, will probably still survive, even if hit by lightning.

If you pay attention to your trees and prune regularly, you’ll enjoy healthy trees for many years to come.