When a powerful electrical discharge descends from the sky, a tree often becomes the recipient of this immense energy. Trees are naturally vulnerable targets for lightning strikes because of their height and the large amount of moisture they contain. This internal water content and sap allow the tree to act as a conductor, making it a prominent pathway for the electric current to follow. The interaction between a lightning bolt and a tree is a rapid, violent process that results in immediate physical damage and potential long-term harm.
The Path of the Electric Current
The lightning strike begins when a negatively charged stepped leader descends from the storm cloud, meeting an upward-moving positive streamer that typically rises from the tallest objects on the ground, including trees. When these two paths connect, an electrical circuit is completed, unleashing a massive current. This current seeks the path of least resistance to the ground, which in a tree is usually the moisture-rich layer just beneath the bark.
The current primarily travels through the sapwood and the cambium layer, the living tissues responsible for transporting water and nutrients. Because the dense heartwood contains less moisture, the current tends to avoid this deeper core. If the tree is completely drenched from rain, the lightning may also flow down the outside surface of the trunk, causing less internal damage. The path often leaves a continuous groove or spiral pattern as the current tracks the most conductive route downward.
The Mechanism of Explosive Damage
The instantaneous, massive surge of electricity through the tree’s tissues generates extreme heat, rapidly converting the internal moisture into superheated steam. When water rapidly changes phase into steam, it expands violently, creating enormous internal pressure within the rigid confines of the tree trunk. This explosive expansion causes the characteristic damage, often resulting in the bark being forcefully stripped off or the trunk being split completely apart. The force can be so great that wood fragments and bark shrapnel are ejected outward for hundreds of feet.
Visible and Hidden Injuries
The most obvious sign of a lightning strike is a long, vertical furrow or strip where the bark has been violently blown away from the underlying wood. These lightning scars often trace the path the current took down the trunk to the ground. In severe cases, the trunk may be splintered, shattered, or cracked deeply, compromising the tree’s structural integrity. There may also be charring or scorched areas on the bark or exposed wood, though a lack of fire damage does not mean the tree escaped internal injury.
Beyond the visible damage, the tree can suffer significant hidden injuries, especially to its vascular system and roots. The intense heat can disrupt the function of the water-conducting xylem and the nutrient-transporting phloem, sometimes causing the entire root system to be compromised. Leaves may wilt, turn brown, or appear scorched due to this internal disruption of water flow, and the tree may suffer delayed death months after the strike.
Factors Influencing Tree Survival
A tree’s ability to survive a strike depends on a combination of factors, including the intensity of the current and the location of the damage. A strike that causes a deep, vertical crack extending more than a third of the trunk’s diameter significantly reduces the tree’s chances of recovery. Trees with higher wood density may exhibit greater tolerance to the electrical discharge, while species with rough bark that holds less surface water during a storm may be more susceptible to internal damage.
The most important long-term factor is the tree’s ability to compartmentalize the injury, a process known as CODIT (Compartmentalization of Decay in Trees). The tree must seal off the dead and damaged wood to prevent the entry and spread of decay organisms and pests. If the lightning strike has girdled the trunk by killing a complete ring of cambium tissue, the tree’s transport system is fatally severed, leading to eventual death. Even if a tree appears fine immediately after a strike, internal damage may lead to a slow decline or sudden failure years later.