The Trouble With Tree Topping

By John Leaf

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John Leaf is a Forest Ranger with the Maryland Forest Service
and a Certified Arborist with the International Society of Arboriculture.
He may be contacted at 301.791.4010

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We’ve all seen it happen: The fellow down the street gets his big tree trimmed and suddenly there is hardly anything left but the trunk and an ugly looking top, now composed of nothing but blunt, leafless stubs. The owner claims that the tree was getting “too big” or he wanted to “invigorate the tree” and so he got it topped.

For about 30 years now, plant scientists and knowledgeable arborists have considered topping to be an unacceptable tree pruning method -- it is actually the most harmful thing someone can do to a tree short of cutting the whole thing down. Aside from the obvious harm done, the practice simply doesn’t work. Topping will not work to keep a tree small. It will not work to save someone money and it will not work, at least in the long run, to invigorate a tree. Despite all of this, topping continues to be widely practiced and has, in fact, become a major threat to urban forests.

Topping is the drastic removal or cutting back of large branches in mature trees with little or no regard for the location of the pruning cuts. The tree is pruned much as a hedge is sheared and the main branches are cut to stubs. Topping (also known as stubbing, rounding and heading back) harms trees in numerous ways.

The leafy canopy on a tree produces chemical food energy for the tree’s growth and maintenance, which is stored in its branches and twigs. When a large portion of a tree’s crown is removed, its food making capacity is reduced, and the energy that the tree has been storing is suddenly lost. This can lead directly to the decline and eventual death of the tree, as it can essentially starve to death.

After topping, the stubs often simply die back, leaving dead branches on the tree. The large stubs left after topping are unable to receive food energy from other parts of the tree, and as a result don’t have the capacity to seal off the pruning wounds. Decay and rot usually set into the ends of the branch stubs and can go on to spread into the main trunk, creating further problems.

While this is happening, undesirable “water sprouts” are produced and grow rapidly just below the ends of the stubs. Water sprouts are dense, unattractive, upright shoots that are weakly attached to the sides of the stubs. Unlike normal branches that develop in a socket of overlapping wood tissue, water sprouts are anchored only in the outermost layers of the stubbed branch.

The combination of rapidly growing and weakly attached sprouts along with adjacent rot and decay can be disastrous. As the weakly attached sprouts grow and gain weight they become vulnerable to breakage, especially in the wind. Thus, a hazard is created. Water sprout growth is so rapid that the tree will usually return to its original height in a short time -- this time with a far denser canopy. This usually defeats the purpose for which the tree was topped in the first place.

Topping a tree opens up the canopy to increased sun exposure, possibly causing damage to the bark (a condition known as sunscald). The practice also disfigures the tree and ruins its natural form and character. The natural beauty of the tree is replaced with ugly branch stubs, conspicuous pruning wounds and a witch’s broom form of regrowth.

Topping not only hurts the tree -- it can hurt your pocketbook as well, and the price is not limited to what you pay the tree trimmer. Topping is a high maintenance pruning practice; because of the rapid regrowth of water sprouts, the tree must be re-trimmed every few years. If the tree doesn’t survive the topping, there is the cost of removal and replacement. The presence of topped trees may also reduce the appraisal value of your property, as disfigured trees are often considered an impending expense. Healthy, properly maintained trees can add to the value of your property.

Another potential cost of topped trees is the increased risk of liability. Because topped trees are prone to breaking, they can be hazardous to people and property. Since it 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.

So what is the alternative to topping? When the size of a tree’s crown must be reduced, an acceptable practice called crown reduction pruning can be used. Selected branches are thinned out by removing them back to their point of origin, or by pruning back to a side branch of sufficient size to assume dominance. The side branch then becomes the source of new terminal growth and subsequently the tree maintains a natural form. This type of pruning also reduces water sprout growth and the need to re-trim so often. A properly trimmed tree stays “done” longer.

Crown reduction pruning, however, still results in large pruning wounds that may lead to decay in major branches. Therefore, sometimes the best solution is to simply remove the interfering tree and replace it with one that will fit within the given space.

A young tree should be properly pruned to help develop good branch structure as it grows. For health reasons, not more than 25 percent of the foliage of a mature tree should be removed within one growing season. If you need to remove more than this, it is best to do it over a 3- or 4-year period -- never all at once.

Choosing a tree service can be a daunting task and a tree company’s position on topping should be no small part of the decision. Just remember that any company that advertises topping or suggests the practice for one of your trees should get no further consideration.

Over the last few decades, environmental awareness and appreciation for the benefits of trees has generally grown, but many people are still unaware of the detrimental effects of topping. More public education about this misguided practice is needed now.