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Aspect ratio changes for the better

Aspect ratio is the diameter of the branch relative to the diameter of the trunk, both measured immediately above the union. Branches with a small aspect ratio are very well attached to the trunk; those with a large aspect ratio separate more easily from the trunk. The branch aspect ratio can be made smaller by slowing the growth rate of the branch relative to the trunk. The best way to do this is to remove foliage from the branch by pruning. Here are three examples of changing the aspect ratio with pruning. In each case, the left stem is subordinated with a reduction cut sending more future growth into the retained stem on the right.

Before pruning

After pruning (above).

Five years later, the pruned branch is now barely notable as the small branch in the lower left of the crown. A codominant stem was transformed into a branch with one pruning cut.

Aspect ratio at pruning was about 0.8; the union id weak. (4 photos courtesy Brian Kempf)

Aspect ratio one year later was about 0.5, making the union stronger.

Aspect ratio on this 14-inch diameter tree was about 0.8 when the tree was first pruned (above photo). This means that the branch on the left side of the tree was about eight tenths the diameter of the main stem on the right side. Aspect ratio was much smaller (0.6) 11 years later making the union much stronger (right photo). Photo credits: John Lichter