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Protecting trees against lightning strikes

Published July 7, 2010
Following the wake of recent storms across the country, you may have had one of your trees struck by lightning.

"Lightning can strike a tree unexpectedly. You may not have been home to hear it and there is not much you can do for the tree afterward," said Jeff Rugg, a University of Illinois Extension horticulture specialist.. "But if a person has a susceptible tree, they can prepare for future lightning strikes."

Lightning tends to strike the tallest object in an area and trees are especially prone to being hit. Areas that were wooded often have homes built on them and many trees removed, leaving the remaining ones more likely to be hit. Lightning's electrical charge can move up from the ground, and jump from tree to tree and even into buildings.

"Installation of lightning and grounding rods not only helps protect the trees, but the houses and electrical equipment near them," he said. "Our electronic appliances run on about 120 volts of electricity, but lightning can be over 100 million volts. A strike can ruin computers, the TV, the microwave, and a lot of other appliances."

Because they are tall and often grow in the open, ash, maples, oaks, palms, pines, and spruce are likely lightning targets. Trees along the edges of fields, streets and lakes are hit more often than trees in the woods. Trees in lakes can also be hit and the electrical chaDrge travels down through the mud and dissipates into the water, killing fish and other wildlife.

"A lightning protection system can be installed by a professional arborist," he said. "Lightning rod tips are installed on the highest-growing branches and on those farthest from the trunk. They must be maintained as the outermost tips of the tree and so they must be moved farther up and out on a regular basis. Conducting wires connect the various tips to larger and larger wires down the trunk. At the base of the tree the cable is buried in the ground all the way out as far as the end of the branches. A grounding rod is then driven down into the ground."

If you have trees overhanging the house, consider the protection offered by the installation of these systems. Trees in parks and on golf courses should also be considered for protection.

Occasionally, when lightning strikes a tree, it just runs down the water on the outside of the bark and into the ground, causing little harm to the tree.

"Sometimes it runs down the sap on the inside of the bark," Rugg explained. "When it does this, it turns the sap into steam and the whole tree explodes like one giant piece of popcorn. What a noise that makes!

"Most trees are in between these extremes. Lightning usually it causes a long, straight crack an inch or two wide and other times it spirals down the side of the tree. Often there are patches of bark blown off. If the tree is still alive and green a few weeks later, that is a good sign, but some trees have too much internal or root damage and slowly die over the next year or two.

"In instances of partial damage, try to keep the tree from experiencing other types of stress," Rugg said. "If your area has a drought, then make sure it gets enough water, without drowning the remaining roots.