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You Can Protect Your Trees from the Effects of Lightning Strikes by Jeff Shimonski © Biscayne Times. Reprinted with permission. First appeared in November 2011. We had a very stormy weekend this past October 8 and 9. At Jungle Island we recorded 12 inches of rain in a 24-hour period. The wind was not too bad, so there wasn't a big mess of branches and leaves to clean up, but we did have a couple of lightning strikes to some of our taller palm trees. This reminded me of a site visit I did a couple of years ago to a large homeowners association to review some horticultural issues. While working out some of their problems, I was approached by a homeowner who asked if I could look at a large, dead Dade County pine tree. Apparently the demise of the tree had led to the firing of the property's landscape maintenance company, which was accused of over-fertilizing the tree. The homeowner wanted to know what I thought had happened to his tree. The pine was about 50 feet tall with a canopy that was probably 40 feet wide. It had been a beautiful tree. Now all the foliage was gone. When I got closer, I noticed a thin strip of bark missing down the entire side of the tree. The tree had been struck by lightning and, from the looks of it, had been killed instantly. Because of their height, trees are natural lightning rods. It's a myth that lightning only strikes good conductors like metal. What I've noticed over the years is that trees may not be killed instantly when they're struck; sometimes they continue to live for many years before succumbing to a secondary cause of death, such as insects or disease. Lightning damage will also look different from tree to tree. Damage can be minimal or quite dramatic. This difference is owing to the fact that water and sap are better conductors of electricity than wood. If the tree's moisture is concentrated in the phloem between the bark and the wood, then the lightning will be channeled through this area and cause an explosive separation of the bark. (The phloem is the vascular system that carries sugar and organic nutrients made in the foliage throughout the plant.) This is likely what happened to the Dade County pine I examined. If there is more moisture in the center of the tree, the explosion from within may blow the tree apart. This is similar to what happened to the palms at Jungle Island. The middle of the trunk just below the crown shaft (the green part below the foliage and above the wood) was split open and the crown shaft fell over from its own weight. If the bark is soaked from rain, the lightning may follow the outside of the bark and flow into the ground, causing little damage to the tree. The photo that accompanies this article shows lightning damage on a satin leaf tree that was growing underneath a tall Veitchia palm that had been struck by lightning. The palm died instantly, but only half of the satin leaf tree was affected. 8 Satinleaf tree (Chrysolphyllum oliviforme) damaged by lightning. Photo by Jeff Shimonski This damage showed up a couple of days after the palm was struck. It will be interesting to see if there is further damage on this tree. As I've said, often these damaged trees die years later of secondary causes. When the protective cover of a tree, the bark, is loosened or taken off, insects will be attracted to the exposed areas. Many types of boring insects will lay their eggs in these trees. When the eggs hatch, the larvae will cause damage by tunneling (and eating) throughout the inside of the trunk, eventually killing the tree by destroying the vascular system or giving a pathogenic fungus a nice place to live. A great quote I once read says, "A tree to a fungus is just food with lots of holes around it." This means any damage to a tree will eventually be exploited by fungi. If a tree is considered to be a valuable specimen, a tree lightning protection system can be installed. Tree science and care is becoming quite sophisticated. There are actual industry standards (ANSI A300) and best-management practices from the International Society of Arboriculture and Tree Care Industry Association that will explain the basic principles of lightning physics and provide information on the installation and continued maintenance of lightning protection systems. While driving through my neighborhood the day after that October storm, I saw the occasional damaged tree. At three separate locations, I stopped to look at fallen branches or trees and, in each case, found the cause of the damage to be poorly structured branches or a weak trunk that had decayed because of previous damage and was unable to support the tree during this brief storm. —Jeff Shimonski is an ISA-certified municipal arborist, director of horticulture at Jungle Island, and principal of Tropical Designs of Florida. Contact him at jeff@tropicaldesigns.com. City Trees