Lightning-Struck Wood Puzzle

Observations and speculation about whether lightning weakens the wood of a tree it strikes. August 29, 2006

Question
I had two trees close together that were struck by lightning. I sawed the elderberry that did not get blown apart for my wife's projects. The wood is beautiful – it's black speckled mid way down to a fine line towards the butt. Does the lightning destroy the structure of the wood and make it unstable in any way? The tree did not crack or completely die.

Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
I have never heard of lightning hurting the structure of the tree. But right at the lightning streak (1/2" wide zone) that runs down the tree, I would expect that the heat may have weakened the wood. So, I really do not know, but my thoughts are "no problem."

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From contributor T:
I agree with the Doctor. I have a piece of lumber that was struck by lightning (verified by the sawyer who gave it to me so I could keep an eye on what happens). It has a black streak running through it. It has split just a little bit on the line (not the pith either) but seems to be holding together. The same sawyer also told me that he did saw a tree struck by lightning and that after it dried, it pretty much just disintegrated (air dried). He said it would just fall apart in your hand as you grabbed it. Who knows.

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From contributor A:
I cut a 150 year old Douglas fir log last month. It was struck by lighting about 80 years ago. I quarter sawed more than 1,000 bf from this 24 foot log. The growth rings between the spring-wood and the summer-wood fell apart where the black strike was. I asked an old sawyer, who comes by to see me every so often, what this is. He did not even hesitate to tell me that the tree had been struck by lighting.

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From contributor K:
The electrical discharge of lightning, like any electric current, is looking for the path of least resistance. Since the sap just under the bark will conduct better than air, trees seem to make good targets.

Each little strand of the multiple flashes is about the size of a pencil, but the flickering that we perceive is actually because these pulses are only a few thousandths of a second, and they dance around a little, which makes it look like it may be as big around as a foot or even more than a yard across.

The temperature is around 30,000* C or six times as hot as the surface of the Sun. When this discharge travels down the side of a tree, the sap instantly turns to steam, which usually blows a strip of bark off of the outside of the tree. A good healthy tree can recover from these scars in a year or two. Some may die from insects and pathogens attacking the injury as an after-effect. But I don't think it kills a tree by destroying the cells.