Ask An Arborist: September 17, 2009

Trees Struck by Lightning

Moments After a Lightning Strike Bark Blown Off

A Reader Emails...

I have a large oak tree, 3-4 feet in diameter and approximately 70 feet in height. It was struck by lightning over the weekend and has two burn/scar strips from the top of the tree winding around the tree and eventually to the base where the charge followed a huge lateral root for approximately 15-20 feet and blew the soil/dirt away from the root. What should/can I do to try to keep this tree?

And The Answer Is...

This is an extremely common occurrence in Georgia with our strong thunderstorms that produce copious amounts of lightning. I've had four trees struck by lightning in my own landscape during the last decade.

Whether a tree will survive a lightning strike depends upon several factors: the health of the tree, the extent of the damage it received and if any "opportunistic" pathogens will enter the wounds leading to a decline in the tree's health. To date, all four of my trees have survived without serious long term problems.

Unless a tree that's been struck by lightning has severe structural damage such as a significant number of major limbs broken away or has sustained a major split in the trunk, don't be persuaded by a "tree guy" that it should automatically be taken down. I have seen trees with their entire crown blown out that have gone on to survive decades after the injury. In the tree pictured above, the lightning skipped down the outside blowing off vertical stips of bark about two inches wide. The damage is confined to the external parts of the tree and is fairly minimal.

After the storm has passed, make sure that no fire has been caused either in the tree or on the surrounding ground. Usually the heavy downpours that accompany most thunderstorms take care of this problem. Within the first 24 hours after a lightning strike, prune away any torn bark or broken branches leaving clean edges to the wounds. This includes any jagged edges that may be on roots that have been exposed by the blast. On damage that occurs high in the tree, hire a professional that can reach the damage by climbing or by the use of a cherry picker. Do not apply any sealants to the wounds. Cover the exposed roots with the soil that had been disturbed.

While taking care of the tree's wounds this is a good time to do a quick assessment. If it's during the growing season, does the tree appear healthy with a full canopy of green leaves? Are there dead branches or trunk problems that were present prior to the lightning strike? If you see problems, consult a Certified Arborist. Make sure that the root zone of the tree is properly mulched with 2-3 inches of organic mulch (pine straw, shredded bark, leaves, etc.). Once you have addressed the tree's immediate injuries and evaluated its current condition and environment, you will need to be thinking about problems that may occur in the future.

Even minor wounds on a healthy tree can be an open door to pests and diseases that may lead to future problems. Of these, the most severe is an attack by Asian Ambrosia Beetles. These foreign beetles are attracted to wounds. The female beetle will bore into the trunk or large limbs to lay her eggs. When she does, she intentionally introduces a fungus into the egg chamber to feed her developing young. The fungus then proceeds to clog the tree's vascular system which can lead to death rather quickly. Preventative sprays can be applied to help thwart attacks from Asian Ambrosia Beetles, but they must be applied by licensed professionals. Various pine beetles, including southern pine and turpentine beetles may also be attracted to tree wounds on pines. Once again, consult with a professional tree care company for assistance.

Opportunistic diseases that can attack trees injured by lightning include a number of fungal diseases which can lead to various forms of decay and the bacterial disease slime flux which can lead to oozing cankers. Keeping trees healthy after a lightning injury will provide the tree with the best defense. Monitor the wounds on the tree to see that they are sealing over and being walled-off. If these wounds are slow to close, seek professional help.

Trees struck by lightning need time. With a little bit of care, proper maintenance and time many trees recover and live long healthy lives after being struck by lightning. If you have a high-value tree in your landscape that you wish to protect, there are lightning protection devices that can be attached to trees by professional tree companies.

Lightning Protection on a Ponderosa Pine

If you want to find a Certified Arborist or a professional tree company in your area, consult the web site of the Georgia Arborist Association.

If you have comments or questions about this article or want to submit a question that may be used in a future article, please email me.

Images & Drawings Copyrighted © 2009 by Theresa Schrum - All rights reserved