Co-Dominant Trunk – On maple

Q: I have an ‘October Glory’ Red Maple that I planted in May,1999. It is in good health, about 20 feet tall with a 3 inch diameter trunk. The problem is that the trunk forks 4 feet above the ground and it looks like there is some kind of scarring or debris around a seam at the point of the divide. The branch from the fork is not far off vertical and is nearly as big as the main trunk. Also, the growth it supports is nearly as much as that growing from the main trunk. I’m worried that it may split and wreck the tree in later years. Should I lop off this branch?

A: Technically what you have is called a “co-dominant trunk”. The tree began with one trunk but early in its life a competing bud sprouted and began to head for the sky. Now, both of them are trying to be the main trunk of the tree.

Imagine what will happen in the next ten years as they both grow larger in diameter. A layer of bark (the scarring you noticed) will remain between them at all times. The joint will become weaker and weaker as the two trunks grow heavier and heavier. One morning you will wake up to find the weightier of the two lying on the ground….if not your SUV!

I suppose you could cable the two together according to the technique I described a few weeks ago but that is a dangerous solution. A much better resolution would be to cut off the smaller of the two trunks and wait a few years for the bare side of the tree to sprout branches into the open space that’s left. Thought the tree will look mis-shapen for a few years, it will eventually regain a reasonably attractive form. Make the cut as close as you can to the joint between the two. Do not coat the wound with tree tar. Simply allow the tree to grow larger and it will eventually seal over the scar.