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Lightning - Lightning may cause all gradations of injury from a slight burn on the outer bark to the complete explosion of a tree. Usually, lightning causes long streaks of injury down (or up?) the trunk. It is always difficult to know the extent of the injury. A tree may look as if it received only a slight burn, yet the tree dies. On the other hand, limbs and portions of a trunk may be blown apart, but the remainder of the tree keeps growing. The point here is that you often must wait to really know the extent of the injury. Always remove branches and trunks that pose a high-risk hazard. Trees out in open places seem to get hit more often than trees in groups. Or, it could be that we recognize those open grown trees easier. Large, old trees with central columns of decay seem to be prime targets. There are all kinds of stories about what sites are hit more often. Beech trees on rocky sites seem to be prime targets. I (SHIGO, 1986B) have seen oaks, pines, and many other trees that were hit. I have always wondered if the large decay columns may be a factor because as wood decays it becomes more ionized. I also wonder about root decay for the same reason. Lightning rods do decrease the chances of a strike. The lightning rod systems should be checked periodically. Make certain that the screws that hold the cable on the trunk are not in vertical alignment. Lightning may cause all gradations of injury from a slight burn on the outer bark to the complete explosion of the tree. Large old trees with central columns of decay seem to be prime targets. (SHIGO, 1986B, pg 65)
About 80% of what has been shown as lightning injury was caused by Joe Lightning tree service! Topping and multiple flush cuts in vertical alignment commonly start long vertical cracks and dead spots that are often called lightning injury. Lightning does strike trees! It may kill the tree instantly, blow it apart, or cause only minor injury. It is very difficult to assess the amount of injury when trees are struck and little mechanical disruption is evident. The only answer is to remove obviously injured branches and to wait and watch the tree. If a long strip of bark has been killed, remove the dead bark, but do not cut into the wood. Follow normal scribing techniques of shallow cuts and do not enlarge the wound. Some people say lightning rods help and others say they do not. I know of no experimental data on this subject. It depends on who you talk to.