Trees and lightning

Lightning is created by the buildup of electrical charge within a cloud. The static electricity is created by the particles of ice and water droplets rubbing against each other. Positive charge is created at the top of the clouds and negative charge at the bottom.

Credit: Bureau of Meteorology

A large voltage difference is created as the charges build within or between clouds, or between the clouds and the ground. Eventually, a rapid discharge occurs – a massive electrical spark. The lightning bolt heats the air around it – to something hotter than the surface of the sun – which causes it to expand rapidly creating a shock wave which we hear as thunder.

When the discharge occurs to the earth, it usually seeks a tall structure such as a building or tall tree for conduction to the ground. Some trees, especially those of high moisture content, are ideal electrical conductors. As the current passes down the tree, enormous temperatures cause any moisture, sap, etc., to vapourize and expand rapidly – the tree can ‘explode’. When the charge reaches the ground, the surrounding root systems may be compromised and the tree may take several months to eventually die.

Depending on the species, moisture content, location, etc., the effect on the tree can vary considerably. The tree may be destroyed, ultimately die over time or the strike may have no effect at all. Most eucalypts seem to survive lightning strikes rather well, even multiple strikes.

Climate scientists tell us we can expect more thunderstorms as the climate heats up. Around the world, there is an estimated 8 million lightning strikes each day. Lake Maracaibo in Venezuela is the most thunderstorm-prone place in the world with about 300 storms a year. Darwin has about 80 thunderstorms each year.