While the majority of my work is as a Consulting Arborist, I have been pruning trees professionally since I started working for a tree service in 1992. I enjoy many things about pruning, including being outdoors, the climbing, the workout, and the challenge of achieving my goals for the pruning while maintaining/improving the trees’ beauty. On my best days, it seems as though I am on a retreat in someone’s back yard! When it’s 100 degrees, I’ve grossly underbid the job and nothing seems to be going well; it can be an arduous chore, however.
The most important objective of my pruning is usually structural improvement of the tree (in some cases I may also be trying to remove diseased wood, or the objective may be aesthetic improvement only). Much of what I am attempting to achieve with the pruning is to reduce the likelihood of trunk or limb failure for those parts which I deem to have any or all of the following: a poor attachment, defect and/or excessive length, weight or exposure.
For trunks or limbs I wish to prune for structural improvement, I either use reduction cuts (reducing limb length by removing the terminal portion back to a lateral branch of at least ½ the diameter of the cut stem) or I selectively remove limbs (thinning cuts) near their ends (Figure 1). In this way, I reduce the lever arm, sail and stress on the trunk or limb and its attachment as well as suppress its growth by reducing leaf area and photosynthetic capacity. This suppression is especially effective if limbs above the pruned limb grow over it and shade it out. Unless I have trained the tree from a young age, the process of trunk or limb suppression takes a few to several prunings.
The following images illustrate how I have suppressed a large limb with a defect (Figures 2-4) and one of two codominant (similar sized) trunks over several prunings.