Symptoms of a lightning strike can range from no external evidence of damage, to total destruction. Tall trees, lone-standing trees, and trees growing in extremely moist soil, such as a lake or river bank, are extremely susceptible to lightning strikes.
The moisture in a tree acts as a conductor for the high power electrical discharge of a lightning bolt. Electric current follows the path of least electrical resistance. In the case of trees, the parts of the tree with the greatest moisture content will carry the bulk of the current, hence, will receive the greatest damage. As the current passes through the moist tissue, the water vaporizes, causing an explosion. In some cases only the bark is affected. In other cases the heartwood may be split. Lightning strikes can also cause a tree to burst into flames.
A tree which has been struck by lightning may suddenly die, it may go into irreversible decline, it may suffer some type of permanent cosmetic damage, or it may recover completely. It is important to consult with a qualified arborist to assess the viability of the tree, and to determine the actions necessary to rehabilitate a salvagable tree.
Electronic devices can also provide evidence of a nearby lightning strike to a tree. Color television or computer screens (not flat screen or big screen) may show distorted colors, and computer modems may stop working.