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When trees are undergoing chain-saw pruning, I am relieved if they are not being topped. However, closer inspection often reveals a type of pruning almost as bad as topping. Instead of topping, the pruners are "tipping" the trees.
Tipping occurs when people cut the tips of large branches near a bud or small lateral branch. Several weakly attached sprouts then develop near the pruning cut.
Tipping also creates stub cuts that are susceptible to decay. Once the decay starts in a stub-cut branch, it can spread into the trunk, weakening the structural integrity of the tree and ultimately leading to its death. How much rot develops depends on many factors -- species of tree, weather, general age and health of the tree. The process is insidious because it's slow. Few people make the connection between topping or tipping done 5, 10, or 15 years ago and a rotten branch breaking off a tree today.
In most cases, the proper pruning cut is a thinning cut. A thinning cut removes a lateral branch back to its point of origin. You can shorten a branch by cutting back to a lateral branch large enough to take over as the "leader." The diameter of the lateral branch should be at least one- third the diameter of the main branch at the point of the cut. Proper thinning leaves no stubs.
Arborists learn more about trees all the time. We used to tell you to make pruning cuts flush with the trunk. Now we recommend making the cut just beyond the branch collar -- the wrinkled or somewhat swollen area at the base of a branch. Sometimes this area is obvious; at other times you have to estimate its location. Cuts made outside the branch collar result in less decay than flush cuts.
I am encouraged by the attempts of tree pruners to avoid drastic topping. We just need to make sure the alternatives involve "good" cuts, not more "bad" cuts. When we overcome that obstacle, all our trees will be safer.
For further information contact your local WSU Extension Office.
From The Gardener, Vol. 6, No. 4, Winter 1995-96
