Trees that have two or more stems that are equal in diameter (codominant) or have weak unions that are less than 60° are at a higher risk of failure. This risk can be mitigated through the installation of supplemental support systems such as a static or dynamic cable and brace rods coupled with systematic pruning.

A crown reduction prune can alleviate the stress put on the weakened unions, making it easier to install the support systems. Reduction pruning is the systematic removal of select branches to reduce the forces on the stems and branches, in turn balancing the crown and reducing forces on the unions. This method of pruning is recommended before supplemental support systems are installed.

Following a reduction prune, trees are encouraged to have a support system installed to limit movement of codominant stems or weakened unions for support; this can mitigate the risk of failure but does not guarantee the safety of the tree.  Static, galvanized steel cables have been used for decades, showing little to no signs of degradation or problems. These cables attached to the tree by installing eye bolts into the sound wood of the crown, perpendicularly, two-thirds the distance from the compromised union to the top of the crown, depending on the tree’s integrity, and should be monitored regularly. These static cables are installed taught to limit the movement of the stems or branches throughout the year. When the cables are installed properly, the tree can fuse compromised unions back together with the aid of a brace rod, extending the life of your tree!

In some instances, a dynamic COBRA cable may be warranted. A COBRA cable can be used to support two or more unions or work as a guy wire to prop up neighboring trees. This style of cabling is not invasive to the tree as the system is wrapped around the stems, eliminating any wounding of the tree. As a result, however, these required regular monitoring and upkeep every two or three years to ensure the system does not girdle to stems. Tree Savvy commonly uses this support system to reduce the likelihood of clump or multi-stem trees succumbing to the snow loads experienced in our winters. COBRA cables have a lower breaking strength and should not be used to support large trees with the intent of mitigating the risk of failure from defective unions.

When unions and compromised stems begin to split or crack, a static cable is recommended to be paired with a brace rod, installed one to two times the stem diameter above the union through each stem.