January 16, 2014 — “They are beautiful in their peace, they are wise in their silence. They will stand after we are dust. They teach us, and we tend them.”
– Galeain ip Altiem MacDunelmor
Are you tending to your trees? Even if you aren’t a full-fledged tree-hugger, you probably know that lightning is nature’s predator. Lightning damages and kills more trees than we can account for in the U.S. A single bolt of lightning can carry 100 million volts of electricity, so unless a tree is equipped with a lightning protection system, it can be extremely vulnerable to damage by lightning. Lightning can injure the tree from a direct hit or side flash (lightning jumping from a nearby object), and problems can vary from light limb damage, to total annihilation.
Lightning’s electrical charge can boil the liquid sap, causing natural gases in the tree to expand, which in turn cause the bark to split open or the tree to literally explode. Lightning’s current utilizes the high resistance wood as a conductor, causing massive damage as it transverses the non-conductive elements of the tree on its way to ground. In some instances, the only evidence of a lightning strike may be the internal browning of the xylem (water-conducting woody tissue), which causes a gradual decay of the tree.
Here are a few commonly-asked questions about trees, lightning and lightning protection:
Q. Are there risk factors or conditions that apply regarding a tree’s vulnerability to lightning?
A. Geographic location, species/type of tree and height are factors that may apply. According to agricultural specialists, lightning is most likely to strike trees under these conditions:
- lone trees
- tallest trees in a group or tallest tree at the end of a group of trees
- trees growing in moist soil or close to a body of water
- trees closest to a building or structure
Q. Are some trees more vulnerable to lightning than others?
A. Trees most vulnerable to lightning (those with high starch content) include: maple, ash, poplar, pine, oak, hemlock, elm and sycamore. Large oak trees are often vulnerable due to their size or prominence. Trees less vulnerable (those with high oil content) include: birch, beech and chestnut.
Q. Why should property owners consider lightning protection for trees?
A. Any trees that are valued for landscaping, sentimental or historical reasons should be protected, including those trees which add aesthetic value to the property.
Q. How does a lightning protection system protect a tree from damage?
A. A copper cable and grounding system is used to intercept lightning’s harmful electricity and conduct it safely underground and away from the tree, so that no damage occurs to the wood or the roots. The principle employed for tree lightning protection (in accordance with national safety standards of LPI-175, NFPA 780 and UL-96A), is the same used to protect structures, homes and buildings.
Q. Does the tree lightning protection system also provide protection for nearby structures on the property?
A. No. The system provides protection for the tree only. Separate lightning protection systems should be considered to protect structures on the property.
Q. What kind of maintenance is needed for a tree lightning protection system?
A. An annual visual check of the tree should be made by the property owner or maintenance manager to ensure all elements of the system remain connected and in place. Occasionally, additional cable runs, air terminals or grounding components may need to be added to accommodate tree growth. It’s also important to check lightning protection cables at the base of the tree to ensure no system interruption or damage has occurred from weed trimming, lawnmowers, or ground excavation.
Q. Who can install the lightning protection system?
A. Be sure to contact a UL-listed, LPI-certified lightning protection specialist or a qualified arborist to ensure your system is installed in accordance with national safety standards.
In most situations, a tree struck by lightning will continue to decline over time and eventually require removal. A tree usually succumbs to disease or death more quickly if the lightning strike passes completely through the trunk (streaks of splintered bark are typically visible on both sides of the tree when this occurs). Most often, owners will notice signs of decay within two weeks of a lightning strike. Since few trees survive a direct lightning strike, it may be good insurance for property owners to consider lightning protection for vulnerable trees, specimen trees, historic trees or trees over public shelters.
So if your tree is vulnerable to nature’s destructive hazard, a lightning protection system could be the best hug you could give to keep it green and healthy for years to come!