What happens when lightning strikes a tree?

When lightning strikes a tree, the damage inflicted can be determined by a range of factors; some are structural, the trunks density and dryness, others include the tree’s general wellbeing, whether there is decay or not. The biology of an individual species can also affect the conductivity in the presence of lightning as well as the likelihood of being struck. The strike often causes the tree’s cellular structures to explode from the heat when steam forms. Burns, charring, and sap boil form leading to the barks and branches peeling and falling from the tree. Lightning is more of a risk to taller trees as well as the ones that are further above ground level and closer to the sky.

The lightning damage done to trees often happens instantaneously, the inside of the tree heats up and the aqueous qualities of the tree are vaporized, releasing steam – the transition from liquid to gas. The steam formations often cause the tree to fracture causing splits or branches and bark to fall. Trees can also catch on fire during a lightning strike, completely burning down the tree or starting a bushfire. In the more fortunate cases, only small flames form and burn out rapidly leaving behind only minor burns/charring and the tree lives on.

Trees that have only had one side of the trunk visibly damaged often still recover and have new layers that grow over the damage/wound. Unfortunately, when lightning strikes right through the trunk and there is splintered bark and exploded wood on both sides, the tree often dies.

Trees that have already been decaying are more fragile, and lightning strikes can send large portions of the tree into the air after exploding and sometimes landing dozens of feet away.

People sometimes report having the tree in their backyard struck while simultaneously feeling the electric shock through their feet coming from underneath them from the floor in their home. The adage of lightning not striking the same place twice is believed to be during a single storm, certain trees or buildings are attractors for lightning strikes. In some situations, the removal of a tree that is too close to a home might be necessary given the risk of it collapsing on the house due to wind or lightning.  

If it has been raining and there is a layer of water surrounding the trunk of the tree, sometimes the water conducts the electricity and prevents it from damaging the inner parts of the trunk, instead, the lightning travels around the outer layer of the water and is absorbed by the dirt closer to the ground instead of passing through the roots.

Because lightning can pose a higher risk to trees in certain places, heritage trees are often fitted with lightning protection systems. Lightning protection systems don’t work by absorbing the shock, instead, they release electrical charge potential creating a repelling/non-attractive effect in the presence of lightning.

Lightning is a mysterious phenomenon in nature, not all scientists agree on the causes of it, the most accepted interpretation of its cause is related to large flows of air that converge with opposite charges. Recall magnets where the positive (+) charge is attracted to the negative (-) charge. As pressure reaches a threshold and the plus and negatively charged reaction progresses, a current is formed and light and heat energy are released – once the pressure is resolved a semblance of stability is achieved in that part of the system and that is why it is said: “lightning never strikes the same place twice”.

It is estimated that the Earth is struck by lightning 100 times every second.Many parts of the US have lightning detection systems in place. On average they detect 25 million lightning strikes each year. A strike of lightning can be over five miles long, producing temperatures in excess of 50,000 degrees (F) which is roughly 6 times hotter than the surface of the Sun. A bolt of lightning can provide enough current to power about 10,000 toasters at the same time – 100 million volts is a common estimate for a single bolt.

Lightning can cause death, however, approximately 4 out of 5 people struck by lightning, fortunately, survive. Trees that have been struck by lightning are estimated to have only a 50% chance of survival. After trees are struck by lightning, they often become weaker and more susceptible to disease. When lightning strikes a tree, it often absorbs a lot of the strike, when someone is struck, it can be from being too close to the tree, so the shock has already been somewhat spread out and absorbed. If you are caught in a thunderstorm DO NOT hide under a tree as the water around the tree can create a path of conduction for the electricity to travel through where it can reach you if you are in contact with the water around the surface of the tree.

Some tree species are more likely to be struck than others. Species that are commonly hit by lightning include Maple, Pine, Gum, Poplar and, Oak. Whereas Beech and Birch species are rarely hit and are therefore are less susceptible to damage from lightning strikes.

Often trees are severely damaged by lightning, but the damage is not obvious or visible. The lightening/current passes through the trunk and makes its way through the roots before dissipating as it reaches the bottom. Significant root damage from lightning can cause a tree to slowly die even though on the surface it looks fine after the shock.

Corrective pruning is needed if the lightning damage has caused branches to become hazardous. It is worth having an Arborist or expert look at your tree after some damage to assess the health of the tree and determine the necessary steps to take.  There are actions to take to aid the recovery of a tree that has been affected by lightning if you are able to confirm with an Arborist that the tree is indeed still alive. Plenty of water and fertilizer can help facilitate the growth of the tree along with additional nutrients – all of which can aid the healing process.