Tree Care Tips & Regulations
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Topping is perhaps the most harmful tree pruning practice known. Yet despite more than 25 years of literature and seminars explaining its harmful effects, topping remains a common practice. Topping is not an acceptable pruning technique, and there are better alternatives.
What is topping? Topping is the indiscriminate cutting back of tree branches to stubs or lateral branches that are not large enough to assume the terminal role. Other names for topping include "heading," "tipping," "hat-racking," and "rounding over."
The most common reason given for topping is to reduce the size of a tree. Often homeowners 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 50-100% of the leaf-bearing crown of a tree. Since the leaves are the "food factories" of a tree, this can temporarily "starve" a tree. The severity of the pruning triggers a sort of survival mechanism. The tree activates latent buds, forcing the rapid growth of multiple shoots below each cut. The tree needs to put out a new crop of leaves as soon as possible. If a tree does not have the stored energy reserves to do this, it will be seriously weakened and may die.
A stressed tree is more vulnerable to insect and disease infestations. Large, open pruning wounds expose the sapwood and heartwood to attack. The tree may lack sufficient energy to chemically "defend" the wounds against invasion. Some insects are actually attracted to stressed trees by chemical signals.
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 along a limb, between lateral branches, create stubs with wounds that the tree may not be able 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.
Topping Can Lead to Sunburn 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 may be sunburn of the tissues beneath the bark. This can lead to cankers, bark splitting and death of some 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 that develop in a "socket" of overlapping wood tissues, these new shoots are only anchored in the outermost layers of the parent branches.
The new shoots grow very quickly, as much as 20 feet in one year, in some species. Unfortunately, the shoots are very 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 the leaves (up to six months of the year in temperate climates) a topped tree appears disfigured and mutilated. With the leaves, it is a dense ball of foliage, lacking its simple grace. A tree that has been topped can never fully regain its natural form.
Topping is Expensive The cost of topping a tree is not limited to what the perpetrator is paid. If the tree survives, it will require pruning again within a few years. It will either need to be reduced again, or storm damage will have to be cleaned up. If the tree dies it will have to be removed. Topping is a high maintenance pruning practice. There are some hidden costs of topping. One is the reduction in property value. Healthy, well maintained trees can add 10-20% to the value of a property. Disfigured, topped trees are considered an impending expense.
Another potential cost of topped trees is the potential liability. Topped trees are prone to breaking and can be hazardous. Since topping is considered to be 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 There are times when a tree must be reduced in height or spread. Providing clearance for utility lines is an example. There are recommended techniques for doing this. 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 for this is to cut back to a lateral that is at least 1/3 the diameter of the limb being removed.
This method of branch reduction helps to preserve the natural form of the tree. However, if large cuts are involved, the tree may not be able to close over and compartmentalize the wounds. Sometimes the best solution is to remove the tree and replace it with a species that is more appropriate for the site.
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 what type of pruning is necessary to improve the health, appearance and safety of your trees. A professional arborist can provide the services of a trained crew, with all of the required safety equipment and liability insurance.
There are a variety of things to consider when selecting an arborist:
- Membership in professional organizations such the International Society of Arboriculture (ISA), the National Arborist Association (NAA) or the American Society of Consulting Arborists (ASCA)
- Certification through the ISA Certified Arborist program Proof of insurance
- A list of references (Don't hesitate to check.)
- Avoid using the services of any tree company that:
- Advertises topping as a service provided. Knowledgeable arborists know that topping is harmful to trees and is not an accepted practice.
- Uses tree climbing spikes to climb trees that are being pruned. Climbing spikescan damage trees, and their use should be limited to trees that are being removed.
For Additional Information More detailed information about pruning is available in Tree-Pruning Guidelines, prepared by the International Society of Arboriculture (ISA).
ISA offers several other brochures in this series that discuss many of the basic principles of tree care. Watch for these brochures in the lobby at City Hall, 1666 North Main Street, Walnut Creek beginning in April 2001.
Determining where to plant a tree is a decision that should not be taken lightly. Many factors should be considered prior to planting. When planning what type of tree to plant, remember to look up and look down to determine where the tree will be located in relation to overhead and underground utility lines.
Often, we take our utility services for granted because they have become a part of our daily lives. For us to enjoy the convenience of reliable, uninterrupted service, distribution systems are required to bring utilities into our homes. These services arrive at our homes through overhead or underground lines. Overhead lines can be either electric, telephone, or cable television. Underground lines include these three plus water, sewer, and natural gas. The location of these lines should have a direct impact on your tree and planting site selection. The ultimate mature height of a tree to be planted must be within the available overhead growing space. Just as important, the soil area must be large enough to accommodate the particular rooting habits and ultimate trunk diameter of the tree. Proper tree and site selection will provide trouble-free beauty and pleasure for years to come.
Overhead utility lines are the easiest to see and probably the ones we take most for granted. Although these lines look harmless enough, they can be extremely dangerous. Planting tall growing trees under and near these lines will ultimately require your utility to prune them to maintain safe clearance from the wires. This pruning may result in the tree having an unnatural appearance. Periodic pruning can also lead to a shortened life span for the tree. Trees which must be pruned away from power lines are under greater stress and more susceptible to insects and disease. Small, immature trees planted today can become problem trees in the future. Tall growing trees near overhead lines can cause service interruptions when trees contact wires. Children or adults climbing in these trees can be severely injured or even killed if they come in contact with the wires. Proper selection and placement of trees in and around overhead utilities can eliminate potential public safety hazards, reduce expenses for utilities and their rate payers and improve the appearance of landscapes.
Trees are much more than just what you see overhead. Many times the root area is larger than the branch spread above ground. Much of the utility service provided today runs below ground. Tree roots and underground lines often co-exist without problems. However, trees planted near underground lines could have their roots damaged if the lines need to be dug up for repairs. Consult your tree care professional or garden center staff for assistance in choosing the tree which will have the right type of root system for the location you have chosen.
The biggest danger to underground lines occurs during planting. Before you plant, make sure that you are aware of the location of any underground utilities. To be certain that you do not accidentally dig into any lines and risk serious injury or a costly service interruption, call your utility company or utility protection service first. Never assume that these utility lines are buried deeper than you plan to dig. In some cases utility lines are very close to the surface.
(The information on this page was developed by the International Society of Arboriculture (ISA), a non-profit organization supporting tree care research around the world and dedicated to the care and preservation of shade and ornamental trees. For further information, contact: ISA, P.O. Box 3129, Champaign, IL 61826-3129, USA.)
© 1997 International Society of Arboriculture. UPDATED FEBRUARY 2000