Don’t top your trees

By William Scott, City Forester
Tuesday, July 1, 2008 1:46 PM MDT

Topping is perhaps the most harmful tree pruning practice known. Yet, despite its harmful effects, topping remains a common practice.

Topping is the indiscriminate cutting of tree branches to stubs or lateral branches. Other names for topping include “heading,” “tipping” or “rounding over.”

The most common reason given for topping is to reduce the size of a tree. Homeowners often feel that their trees have become too large for their property. People fear that tall trees may pose a hazard.

Topping, however, is not a viable method of height reduction and certainly does not reduce the hazard. In fact, topping will make a tree more hazardous in the long term.

Topping stresses trees

Topping often removes much of the leaf-bearing crown of a tree. Because leaves are the food factories of a tree, removing them can starve a tree.

The severity of the pruning triggers a sort of survival mechanism. The tree needs to put out a new crop of leaves as soon as possible.

The tree activates dormant buds, forcing the rapid growth of multiple shoots, or “suckers,” below each cut. If a tree does not have the stored energy reserves to do so, it will be seriously weakened and may die.

A stressed tree also is 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 defend itself against invasion, and some insects actually are attracted to the chemical signals that trees release.

In addition, removal of leaf cover also can lead to sun scald and sunburn, further stressing the tree.

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 it is healthy enough and the wound is not too large.

Cuts made along a limb between branches create stubs with wounds that the tree may not be able to close. The exposed wood tissues begin to decay.

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.

Topping creates hazards

The survival mechanism that causes a tree to produce multiple shoots below each topping cut comes at great expense to the tree. These shoots develop from buds near the surface of the old branches.

Unlike normal branches, these new shoots are anchored only in the outermost layers of the tree. The new shoots grow quickly. Unfortunately, the shoots are prone to breaking, especially during windy conditions.

The irony is that while the goal was to reduce the tree’s height to make it safer, it has been made more hazardous than before.

Topping makes trees ugly

The natural branching structure of a tree is a biological wonder.

Trees form a variety of shapes and growth habits, all with the same goal of presenting their leaves to the sun. Topping removes the ends of the branches, often leaving ugly stubs.

Topping destroys the natural form of a tree. Without leaves, a topped tree appears disfigured and mutilated. With leaves, it is a dense ball of foliage, lacking its simple grace. A tree that has been topped never fully can regain its natural form.

Topping is expensive

Topping is a high-maintenance pruning practice, with some hidden costs. One is the reduction in property value.

Healthy, well-maintained trees can add 10 to 20 percent to the value of a property. Disfigured, topped trees are considered an impending expense.

Another possible cost of topped trees is potential liability. Topped trees are prone to breaking and can be hazardous.

Because topping is considered an unacceptable pruning practice, any damage caused by branch failure of a topped tree may lead to a finding of negligence in a court of law.

Alternatives to topping

Sometimes a tree must be reduced in height or spread. Providing clearance for utility lines is an example.

There are recommended techniques for doing so. If practical, branches should be removed back to their point of origin. If a branch must be shortened, it should be cut back to a lateral that is large enough to assume the terminal role.

A rule of thumb is to cut back to a lateral that is at least one-third the diameter of the limb being removed. This method of branch reduction helps to preserve the natural form of the tree.

Hiring an arborist

Pruning large trees can be dangerous. If pruning involves working above the ground or using power equipment, it is best to hire a professional arborist.

An arborist can determine the type of pruning that is necessary to improve the health, appearance and safety of your trees.

A professional arborist can provide knowledgeable service, with all of the required safety equipment and liability insurance.

For questions about your trees, please contact the City of Casper, Urban Forestry Section, at 235-8309 or e-mail wscott@cityofcasperwy.com.

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