One of the most destructive tree pruning practices is topping -- which is the removal of a tree's branches above a certain height without giving consideration to its overall structure and health.
Common misconceptions for topping a tree are to reduce its size and the false notion that it will lessen the likelihood of a tree falling on structures during storms. The end results are weak unsightly shoots growing in place of the removed wood. It also leaves large open wounds which will increase the tree's susceptibility to disease and decay.
Topping removes a large part of the leaf bearing crown of the tree thus disrupting the delicate crown to root ratio important to maintaining tree health. The leaves are the food factories of the trees and the loss of a large area of the canopy can cause the tree to "starve." The growth rate of the roots is greatly reduced lessening their ability to transport nutrients and water to the leaves. Severe pruning causes the growth of multiple shoots below each cut. This is the tree's attempt to replace the lost leaf area. These shoots are weak and have a rapid growth rate. Normally branches develop in sockets of overlapping wood tissues, but these new shoots are anchored only to the outermost layers of the branches. They are highly susceptible to breakage during storms.
Topping interferes with the tree's natural ability to protect the pruned areas against insect or disease problems. Cutting a limb between lateral branches creates stubs which can cause the decay of wood tissue. Topping also removes many of the leaves that absorb much of the sunlight hitting the tree. The remaining branches are exposed to higher levels of sunlight. The tissues beneath the bark in the exposed area can suffer sunburn which can result in cankers, bark splitting, and the death of some branches.
Topping destroys the natural shape of a tree. It will never be able to recover its original form. The process can be expensive in the long run. In time, the tree will require pruning again.
In contrast to using topping techniques, an arborist who engages in proper pruning practices will spend time selecting and removing certain tree branches based on the growth pattern of the tree. Correct pruning of a tree's crown will reduce wind resistance, allow for improved light penetration into the canopy, and improve its overall health without destroying its natural shape.
In some situations, the best course of action is to remove the tree and replace it with one that has a mature size more suitable for the site. Match your tree selection with site conditions such as proximity to other trees, buildings, or above ground utilities. The crown of a tree is its primary growing area. Topping robs the tree of its natural form, shape, and beauty. Proper pruning practices enhance the visual aspects of the tree and stimulate good tree health.
Timothy Daly, MS, is and Agricultural and Natural Resource Extension Agent with Gwinnett County Extension. He can be contacted at 678-377-4010 or firstname.lastname@example.org.