Extreme Weather Series: Lightning Strikes

10th June 2021

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When I was a boy we had a giant oak tree at our school. Of course, we were not allowed to climb it, but – boys being boys – that didn’t stop us. Then one day, during a particularly heavy storm, it was struck by lightning. For hundreds of years that tree had grown quietly to become taller than any building in the school, but in an instant that was over and what was left was a mass of blackened, splintered timber. When we got to school the next day it looked like a bomb had gone off in the tree – there were chunks strewn like confetti and a massive hole down the centre where the lightning had literally split the tree in two. But why had that tree been hit when there were others around, and why not the building next to it, or the steeple of the chapel over the road? This article looks at lightning, and how to protect your trees from its devastating effects.

Why does lightning strike trees?
Well, lightning is an electrical charge that is looking for the quickest and most efficient route to the ground, so any tall object will do – it’s just that in rural areas the tallest object is usually a tree. The air is not an ideal medium for the charge to be flowing through so lightning seeks out solid objects because it can travel faster through them.

Trees are ideal because, as we all know, electricity travels well through water, and in trees it’s the sap that conducts the electricity down to the ground.

To understanding the devastating power of a strike, it’s important to know that lightning carries an electrical charge of up to 100 million volts and can produce temperatures of over 50,000 degrees Fahrenheit, around five times the temperature of the surface of the sun.

The damage lightning causes will then depend on a number of factors, but chief among them is whether it’s raining.

If it’s a proper storm with thunder, lightning and torrential rainfall then it’s possible that a lightning strike could leave a tree largely unscathed as the full power of the strike can travel to the ground along the outside of the tree on its wet surface. But in a thunderstorm where there’s lightning without the rain, or with very little rain, the lightning will travel down to the earth through the inside of the tree, using sap as its conduit. When struck the sap will instantly be turned to steam, expanding outwards at such speed that it can often make the tree explode like the oak tree at my school.

Not all lightning strikes are tree killers, but whether it’s bark that’s blown off or the branches set on fire, if the strike doesn’t kill them it could weaken them and allow for a greater risk of infection or infestation, which would compromise the future health or existence of your tree.

So, our advice. If you have a tall tree, especially one that sits on its own, you should consider asking your local tree surgeon about having a lightning protection system fitted. It really is very simple. We’ve already mentioned that lightning is looking for the quickest and easiest way to the ground, and by adding a line of more conductive material from treetop to ground, even a direct strike can be transferred, largely harmlessly, down a tree.

If you have a tree that has been struck by lightning, then you should act fast. Call in a tree expert because damage needs to be dealt with to prevent insects getting in or fungal spores infecting the wound, either of which has the potential to cause long-term harm to your tree.

Lightning can be dramatic, but it does not need to be devastating, so to book a visit from one of our tree surgeons to discuss lightning protection for your trees, call us on 0208 292 8992. We’re always happy to pop round or to help with a little advice.

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