Issue 7, June 8, 2015

Lightning Damage

Lightning damage to trees may be one of the easiest problems to diagnose, and also potentially one of the most heartbreaking when the big old tree dies.  However, lightning damage doesn't always mean death.  Unfortunately, there's not much to be done once the lightning has struck.

Lightning doesn't always produce the same symptoms.  The easiest to see and diagnose is when the bark is completely blown away from the branches and trunk, leaving jagged edges and the exposed smooth wood beneath.

Sometimes, the bark will remain but be split and puckered or buckled where you can easily slip your hand under the bark.

Other times, you can see a path of damage from upper limbs to the ground, with the bark blown away or raised, or just blackened.

It's easy to diagnose when the bark is immediately blown away.  However, it may take several weeks before the bark actually becomes loose, and the tree could be dead by then.

Lightning can just kill the cambium under the bark, preventing the tree from producing new water-carrying xylem vessels.  This gives the illusion the tree made it through the damage, only to start wilting as the xylem tubes become woody and water isn't moved from the roots.  Depending on the type of tree, this can take days to weeks to months, but the tree usually dies within a year. 

If the lightning strike is significant enough, the xylem vessels can be blown apart, as the water in the vessels is turned to steam by the heat and expand to rupture the xylem tubes.  When this happens, the tree quickly starts wilting as no water is moved.  Leaves start browning in a matter of days.  (If you look closely at the base of the tree, there typically are dead plants surrounding the tree.)

Sometimes the damage may only affect one side of the tree.  When that happens, the tree might be able to re-route water, especially in the early spring or late fall.  However, May through September damage usually kills the branches on that side of the tree.

What can you do?  Not much once the damage occurs.  The cambium can't be regenerated quickly.  Xylem tissue doesn't reproduce, so once it's destroyed, that's it.  Watering may help if the damage is confined to one side of the tree.  Fertilizing doesn't really help.

For high value trees or historic trees, an arborist can install lightning protection devices which funnels the strike to the ground through wires instead of through the tree.  Of course, this is a preventative step.  (David Robson)

David Robson

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