The most common tree failure is do to the presence of one or more codominant stems. Codominant stems or “V-crotch” branch unions are structurally weak compared to a single stem or properly spaced branch union. The weakness is due to lack of connective tissue anchoring a stem to the tree trunk and the presence of included bark between the stems.
Cables and brace rods are supplemental structural supports intended to reduce the risk of failure of weak stems, branch unions, and multiple leaders. A cabling system consists of flexible, extra-high-strength steel strand cables attached to bolts installed in the upper crown of a tree by drilling through the wood or a dynamic synthetic system installed in the upper canopy.
Braces are threaded rods that are installed through unions of weak branches and multiple stems by drilling through the tree to provide more rigid support. Brace rods are used when trees have codominant or multiple leaders to reduce the risk of the stems spreading apart or moving sideways in relation to each other. In many instances, bracing can be used to repair a crotch or branch union that has split.
Essentially, cabling and bracing strengthens weak branch unions by transferring the weight from a weak branch union to a stronger one, preventing breakage, and restricting the distance that a branch can move in relation to the rest of the tree. Often a combination of cabling and bracing is implemented to obtain the safest and most stable support for the defective tree parts.