In a split second a lightning bolt can permanently damage or destroy a perfectly healthy heritage tree that has been growing steadily for decades. Lightning is attracted to tall trees because they are relatively good conductors – especially when they are filled with sap in the summer storm months. A lightning bolt can carry 50,000 amps of direct current and the heat in a lightning strike is 5 times hotter than the surface of the sun. When lightning capriciously chooses a tree as its path to ground, the near instantaneous vaporization of the sap can peel the protective bark right off a tree. Sometimes whole limbs can be blown off trees as in the pictures and videos below.
Trees can be protected from strikes with a lightning protection system similar to lightning rods on a tall building. A heavy copper wire is placed at the top of the tree and affixed to the tree all the way to the ground with special copper standoffs. The copper wire is 60 billion times more conductive than green wood! At ground level the wire is buried 1 foot beneath the earth and clamped to a copper grounding rod driven 8 feet into the earth at the drip line of the canopy. A fuse is placed in parallel with the main conductor so that the homeowner can see if the system has safely intercepted a lightning strike.
|The aftermath of a lightning strike|
The National Fire Protection Association calls for lightning protection in the following types of trees:
- Tall trees with limbs or trunks within 10 feet of a valued structure. The proximity to the structure increases the risk of side flash, which is when the lightning bolt jumps from the tree to the structure. Side flash can cause electrical surges, fires, and personal harm.
- High value or historic trees - especially those that are out in the open or that have emergent crowns (i.e are significantly taller than surrounding trees).
- Tall trees in recreational areas (parks, golf courses, cemeteries) where people may seek shelter during a thunderstorm.
- Tall trees on the edge of a field facing the prevailing approach path of summer storms.
The incredibly destructive force of a direct lightning strike is show by these security camera clips.