LIGHTNING AND TREES
Every spring, just after the magnolias bloom, we are beset with electrical storms that threaten to damage our urban forest. The National Weather Service states that thunderstorm season runs from April to September in the Chicago area. Many people have special specimen trees or especially old trees in their yards that would be a great loss if struck by lightning. It is possible to protect such an asset.
This spring, the media gave much attention to a massive Swamp White Oak in Lake Forest. It was located on city property and the city had it fitted with lightning protection equipment. This oak was fiftyfive feet tall showed no evidence that it had ever been struck by lightning; but, it seemed to be in danger because two nearby trees had been struck, and also because oaks are especially vulnerable to lightning. It is an icon, perhaps the oldest tree in the area, and one that the city felt should be preserved.
Trees that stand alone, trees that stand up above other trees, and trees that are near water are the most frequently hit. Also, deeply rotted, decayed, or dying trees are vulnerable. Because oak trees contain a large amount of water, they are good conductors of electricity and prone to lightning. Oak, elm, pine, spruce, poplar, maple and ash are most likely to be hit. Beech, birch and horse chestnut receive the fewest strikes.
Lightning will do one of three things when it strikes a tree. First, it can scar a tree. When the bolt travels down the trunk in the moist layer of sap and water just under the bark, the heat generated by the lightning blows off a strip of bark. This leaves a very visible slash, open to the attack of insects and fungi. Second, lightning can completely destroy a tree or seriously injure it. If the lightning strikes a tree with a pocket of water in it, the tree will explode. Third, if the tree is wet, and especially if it is a smooth bark tree, the charge may travel down to the ground without damaging the tree.
The best way to protect trees from destruction by lightning is to have lightning rods installed. The protection system intercepts the lightning bolt from the cloud and conducts it harmlessly to the earth. A lightning protection system provides a direct path for lightning to follow, and prevents damage as it travels that path. Lightning protection systems are heavy metal cables which are strung throughout the tree, and connect to many bullet shaped terminals which are strategically placed to protect the tree. These cables are grounded ten feet into the earth.
Few would consider lightning protection for a tree, unless the tree is a beautiful asset worth protecting. Most home buyers want to buy property that has established landscaping. An old tree adds dollar value, and more. It adds the class of an established neighborhood. The cost of protection will vary, depending on the size of the tree. For example, the Lake Forest tree protection cost was $1,500.00. This is substantially less than cutting down a dead tree, and removing the stump.
One should discuss protection with his local arborist or tree expert firm. To be sure you deal with an experienced lightning protection professional; you can confirm their competency by contacting “Underwriters Laboratories” at (847) 272-8800 and/or the “Lightning Protection Institute” at (800) 488-6864.