Lightning mostly strikes exposed, isolated, or tall trees at higher elevations in eastern and northern California.
Identification
Suspect other, more-common causes that produce similar damage symptoms unless the lightning strike was observed, plants were inspected soon after lightning struck, or plants show the distinctive damage symptoms caused by lightning. Aeration deficit, mechanical injuries and look-alike causes, and root decay pathogens can cause symptoms that resemble lightning damage.
When lightning is the cause, sometimes bark and wood in a long, vertical streak extending from the point of the strike to the ground may be killed. This wound can be visible where bark is loosened or blown from the trunk. The trunk may split and bark sometimes hangs in shreds around wounds. Wood beneath bark may grow abnormally and form galls. Roots may grow from unexpected places on the trunk (adventitious roots).
Damage
Lightning strikes can break off a tree’s upper limbs or trunk, cause plants to burn or explode, and kill treetops or entire trees. Lightning can also seriously damage roots or internal tissues of trunks and limbs even though damage is not visible externally or appears to be minor. After lightning injury, trees often become attacked by bark beetles, wood-boring insects, and decay pathogens and die prematurely.
Solutions
Where lightning is prevalent, lightning rods wired to the ground can be installed at the top of especially valuable, tall, specimen trees. The National Fire Protection Association and Tree Care Industry Association publish standards for lightning protection systems.
Immediately after a lightning strike, have an arborist who is certified by the International Society of Arboriculture or registered with the American Society of Consulting Arborists inspect trees for limb, trunk, or root damage; the trees may be hazardous and fail (drop limbs or fall over). Immediate repairs include pruning to reduce safety hazards and tacking any loosened bark back into place over wounds, then periodically moistening loosened bark to reduce drying.
Provide injured plants with proper cultural care, especially appropriate irrigation. Have trees periodically reinspected to determine whether hazard-reduction pruning, tree removal, or other remedies are appropriate.
Adapted from Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).
