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A lightning striking an oak tree.

It's a myth that lightning never strikes twice in the same place. Trees, because of their height, are natural lightning rods.

When lightning strikes your tree

By Patrick Weicherding

From eNews, August 16, 2007

We have all heard stories of lightning striking people (professional golfer Lee Trevino has been struck twice while on the golf course) or causing forest fires. Less often, but occasionally in the news, are incidents of lightning strikes involving trees.

Lightning injury to trees is difficult to predict, but it appears to be governed by the tree's position in the landscape, the moisture content of the part struck, and the species of tree involved (Birch, for example, is rarely struck, whereas elm, maple, oak and most conifers are commonly hit). Tall trees, those growing alone in open areas, trees with roots in moist soils, or those growing along bodies of water are most likely to be struck.

Since water or sap is a better conductor than wood, lightning damage is often related to the concentration of moisture in and around a tree. For instance, if the moisture is concentrated in the phloem between the bark and the wood, then the lightning strike will follow this channel and create an explosive separation of the bark. If there is more moisture in the center of the tree, the explosion from within may blow the tree apart. Rain soaked bark often shows little damage because the lightning may follow the outside of the bark and flow into the ground.

A lightning strike can be a traumatic experience for both the tree and its caretaker. If your tree is struck by lightning, the immediate concern should be your personal safety. Broken limbs hanging high in the tree or unsupported branches hanging over buildings or sidewalks should be taken care of quickly, preferably by a certified professional arborist. If the tree does not exhibit obvious safety concerns and seems to be generally intact, you could wait until the end of summer or even the following spring to evaluate the tree's ability to recover (by producing leaves). This is not always the answer a homeowner wants to hear, but a valid assessment of the tree's damage and ability to recover is difficult--sometimes impossible--immediately after a lightning strike.

Storm safety facts

* During heavy rain and lightning:

* Stay indoors and away from windows

* Avoid using electrical appliances

* Move away from open fields and get off heavy equipment

* Don't stand under solitary trees or near a lake

Source: U.S. National Weather Service

It's a myth that lightning never strikes twice in the same place. Trees, because of their height, are natural lightning rods. Lightning seeks the path of least resistance to the ground through the best available conductor in the area. If the best conductor happens to be a tall, isolated cottonwood, it can be struck many times during separate storms events. Multiple lightning scars on the trunks of trees are testimony to this phenomenon.

Can I save my tree from lightning?

Historic, rare, and specimen trees, especially when they are the center of the landscape, are valuable and can be protected by a properly installed lightning protection system. These systems are expensive in terms of labor and materials and they need to be installed by a trained arborist. It is best to consult with an arborist or urban forester and a lightning protection system installer before considering a protection system for a tree.

To find a certified arborist in your area, visit the International Society of Arboriculture or call 217-355-9411.

Did you know? If a tree--or any of its limbs--falls on your house, and you have homeowners insurance, then the insurance company would pick up the tree-clearing bill. If the tree falls in your yard, not touching your home or car, the cost falls on you.
Patrick Weicherding is a regional extension educator and associate professor of natural resources management and utilization with the University of Minnesota.