Tree cabling is a technique arborists use to support double-trunk trees or multi-stem trees. Tree cabling systems can also be used to support weak branches or damaged branches as an alternative to removing the weak or damaged tree branch.
Arborists install traditional tree cabling systems using lag hooks and seven-strand cable. In a simple tree cabling system, such as with a double-trunk tree, the arborist will install the tree cable 1/3 of the distance from the top of the tree to where the two tree trunks join. Installing a cable in a tree helps the tree trunks move in unison and can reduce the potential for storm damage. A tree cabling system in a triple-trunk tree is usually installed in a triangular shape and a four-stemmed tree is often supported with a boxed shaped tree cabling system. Another method arborists use to cable multi-stemmed trees is a ring and spoke system. In this type of tree cabling system the arborist runs one cable from each tree trunk to a center ring.
Arborists may use tree cabling on mature trees to give extra support to a main limb. Sometimes a mature tree has a large limb that is growing over a building or the limb may be weakened by decay. If the arborist removed the large limb the resulting wound might never heal or the shape of the tree might be drastically altered. In this situation installing a cable would be an alternative to the arborist removing the entire limb.
Tree bracing may involve using a threaded rod to support a crack in a tree or using a post to support a branch. A crack in a tree trunk or large limb can be held together by using threaded rods. In this circumstance the arborist drills a hole through the tree trunk or large limb. The arborist then installs threaded rods to keep the crack from widening. On rare occasions, and usually on historic or special specimen trees, individual limbs are supported by posts which are anchored to the ground and are attached to the limb.
Installing a tree cabling system or tree bracing does not guarantee that the tree trunk or tree branch will never break, but is does add additional support and may increase the useful life of a mature tree. A qualified arborist should inspect the tree before a support system of any type is installed and the system will need to be inspected periodically to make sure it is still functional.