When two tree stems press against each other, as they grow they will increase in diameter, and push against each other. The wood fiber from either side never connects and bark is compressed in between the two trunks. If left unaddressed, this can potentially split the union. This split may begin unnoticed inside of the trunk, or it may begin to form a crack on the outside. Tree forks with cracks can be dangerous. Fortunately if this is identified early on, the two trunks can be "tied" together so that they do not completely break apart. This may be done in the form of bracing rods, and or cabling.
Trees will extend branches for many reasons, put the most important reason is to access sunlight. These limbs and branches tend to be heavy because of all the wood fiber, water and leaf material that it needs to be strong enough to hold up to gravity and winds. The physics principle of leverage applies here when the union where the branch connects to the trunk, is introduced to the force of gravity spread over the length of the limb. This can concentrate a lot of stress on the connection point to the trunk, especially when limbs are overextended, or the union is poorly structured/connected. In some cases wind and storms will apply too much force on the limb and it will fail and break. Sometimes the limbs will hang in the tree, and others they will fall onto whatever is below such as houses, streets, cars or even people. By installing cabling, and potentially pruning to reduce some of the weight, these incidents can be prevented.
Yet another situation that could be appropriate for cabling are trees with some decay. It must be determined that the decay is not advanced or a fast spreading disease, and that there is sufficient structure to build a cabling and or bracing system off of. This can be determined by one of our Arborist Representatives and our guidance and consulting services. In general hollow trees only need a thin stem all in order to be green and look healthy. Measurements and calculations can be done to determine whether there is sufficient strength for a cabling system.
Cracking can form from several different causes. When temperatures drop abnormally low, or very rapidly, there is potential for cracking to occur. Wind and storms can strain a trunk or limbs enough to cause splitting, and even lighting can superheat and expand the water into vapor within trees enough that they will crack, and in some cases completely explode. Old cracks that may have happened years ago may be hidden by response growth over the vertical portion of the crack. It may appear as a rib parallel to the trunk or limb. Bracing may be a solution for these issues as well.
Preventatively
In this instance, there may not be a visible concern or issue with the structure of the tree, but as an extra measure of safety during storms, cables may be installed for peace of mind. Although not a guarantee, when installed properly cables can reduce the chances of damage resulting from failed tree limbs.