We believe the best investment to protect our urban forest and mitigate the risks of having trees near our homes and businesses is proactive tree care. By properly caring for our trees, we can prolong their life and avoid premature and unnecessary removals. We introduced this idea beginning with our base, providing nutrients to the soil and roots that are often depleted in an urban environment. Then we moved up to the ground to eliminate environmental stressors like compaction and harmful insect activity. Next we would like to move up the tree and discuss helping potentially high risk trees withstand weather conditions with supplemental systems such as cabling, bracing and lightning protection.
When weather moves in with strong wind and lightning, your trees may appear to be a threat. Occasionally, they do fall over or a portion can break out of the tree. However, healthy structurally sound trees rarely fail in storms. Some conditions commonly occurring in trees that make them have a higher potential for failure can be minimized by supplemental support systems.
The most common hardware that is installed in trees is a support cable. Cables are installed in trees that have weak branch unions or to prevent movement in heavy limbs. Have you ever noticed a tree that appears to have two or more trunks when walking through your neighborhood or even in your own yard? This is a codominant stem and there is often a weak union where the two stems join (see illustration). If this is not corrected through structural pruning when the tree is young, it can be a source of potential risk of failure, particularly during high wind. A cable can be installed to prevent the limbs from moving in opposite directions, which will decrease the risk of a break at the union.
Cables installed high in a canopy to facilitate connected movement.
Having a codominant stem does not necessarily mean that your arborist will recommend a cable. The tree should be free from other structural defects such as excessive decay or root issues. In some cases, removing the tree is a better option to bypass the risks. Almost every time your arborist recommends cabling, it will be combined with pruning. Pruning will help to remove excess weight for the limbs and remove dead and decaying limbs. An arborist should provide a thorough inspection of the tree before recommending cabling.
A less common, but similar approach to enhancing the structural integrity of your tree’s trunk is bracing. While cables are installed high in the canopy (⅔ the distance from the junction of the branches/trunk to the branch tips) and are designed to allow movement within the canopy, brace rods are installed to provide rigid support. Brace rods can be used to reinforce when there is a crack or split in a union or if there is a decayed area. They are often used in conjunction with cables to stabilize the union and provide support.
Even less common support system is a limp prop or support. A great example of the effectiveness of this application can be seen at the Angel Oak near Charleston, SC. Heavy branches that hang low to the ground can stress the union to the tree and occasionally need additional support to prevent breaking. We do not see this commonly in the Piedmont region of Georgia, but there are occasions where this is recommended.
Finally, lightning is more likely to strike trees that are particularly tall, are located at the highest point in an area and those that stand alone. These trees may be good candidates for lightning protection if they are close to a home, provide shelter to people, or if they are deemed significant enough to protect by the owner or community. Should the tree be struck by lightning, the protection system directs currents away from the canopy of the tree and into a grounding rod near the base of the tree. This can prevent lightning from damaging the tree and/or potentially injuring anyone near the tree during a storm.
When deciding if your trees need any of these support systems, it is important to consult with a certified arborist. Incorrectly installed, a support system could provide a false sense of security or cause more damage to the tree you are trying to protect. Once installed, having your arborist inspect any installed cable, brace rod or lightning protection annually will best ensure that it is still functioning correctly.