Topping Causes Decay

The preferred location to make a pruning cut is just beyond the branch collar at the branch’s point of attachment. The tree is biologically equipped to close such a wound, provided the tree is healthy enough and the wound is not too large. Cuts made between lateral branches create stubs with wounds that are difficult or impossible for the tree to close. The exposed wood tissues begin to decay. Normally, a tree will wall off, or compartmentalize, the decaying tissues, but few trees can defend the multiple severe wounds caused by topping. The decay organisms are given a free path to move down through the branches.

Branches within a tree’s crown produce thousands of leaves to absorb sunlight. When the leaves are removed, the remaining branches and trunk are suddenly exposed to high levels of light and heat. The result is often sunburn of the tissues beneath the bark, which can lead to decay, cankers, bark splitting, green branches breaking, and eventual death of the affected branches.

A stressed tree is also more vulnerable to insect and disease infestations. Large, open pruning wounds expose the sapwood and heartwood to attacks. The tree may lack sufficient energy to chemically defend the wounds against invasion, and some insects are actually attracted to the chemical signals trees release.

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