The condition of co-dominance occurs when two leaders, or main upright branches, of a tree are of the same size. Some trees naturally have a strong central leader. Species like pin oak, sweet gum and white spruce are typical examples. These species can display co-dominance when pruning removes the dominant leader. When this occurs one or more new leaders will take on the role and start to compete. This leads to bark being included in the narrow “V” crotch between the two leaders. Over time this union becomes weaker and weaker as the tree grows apart.
Given the right conditions the two leaders will separate as the bark in the crotch splits and the tree tears itself apart. When the tree has been torn it is unable to form the protective boundaries that prevent decay from entering into the remaining leader. The weakened leader decays at an accelerated rate and can fail in an unpredictable manner.
Timely pruning of young trees prevents this condition from developing and causing major problems later in the trees life. If the condition already exists, cabling and bracing can help to prevent catastrophic failure and extend the life of mature trees. These measures are not complicated but need to be performed by a skilled technician. It can be quite interesting and even Gothic, the measures that people will employ to prevent their trees from splitting. The correct, effective solution of cabling and bracing are so subtle and non-obtrusive, that I have been called out on many occasions to point them out. Not so with the logging chains, mummy cables, steel welded bars, and other assorted paraphernalia I have seen used in less successful attempts.
Recently I was called out to look at a tree that I had on two occasion’s recommended remedial action to stabilize it. The tree, a mature Red Oak, had been covered with 6 inches of snow while in full leaf. The resulting stress pulled the 20 inch oak stems apart like pealing a banana. How unfortunate that the home owner declined to spend the small amount it would have taken to keep this 200 year old tree growing for another 100 years. Now they are faced with the cost of removing this giant tree a prospect many times more expensive than the original preventative action. A case of, “a stitch in time saving nine” if ever there was one. I.S.A. Certified Arborists are trained to identify and recommend corrective action to prevent the destructive forces that can be released in a co-dominant leader failure.