Purdue News

June 26, 1998 Don't top trees, Purdue expert says WEST LAFAYETTE, Ind. -- Topping trees, which looks like someone has given the tree a drastic flattop haircut, is a common practice for some homeowners. It's a bad idea, according to Purdue University urban forester Rita McKenzie. "Many homeowners have their trees topped, often by so-called professionals, when their trees reach heights they consider unsafe," McKenzie said. "Some people worry that a strong wind might blow these large trees over. This is an unjustified fear, because the extensive root system of a healthy tree, left undisturbed, provides adequate support for the tree." When a tree is topped, it is sheared like a hedge and the main branches are cut to stubs. Topping is also referred to as heading, stubbing or dehorning. "To someone with a chainsaw, topping a tree is much easier that applying the skill and judgment needed for good pruning," McKenzie said. "But it takes more than a chainsaw and a truck to properly prune a tree." Topping a tree may cost less than pruning it in the short run, but McKenzie said that over time homeowners may experience increased costs brought on by reduced property values, the cost of tree removal if the tree dies, and increased future pruning costs. Besides increased long-term costs, McKenzie offered other reasons why trees should not be topped: Starvation: Trees use their leaves to manufacture nutrients during photosynthesis. The tree's transport system then moves the nutrients from the leaves to the roots. Topping the tree removes so much of the leafy crown that a tree may be unable to provide the roots with the nutrients. This in turn prevents the roots from growing and transporting soil nutrients and water to the leaves, causing the tree to starve. "That's why good pruning practices never remove more than one third of the leafy crown," McKenzie said. Shock: The tree crown acts like an umbrella, shading the bark from the direct sunlight of summer. Sudden removal of the leafy protective layer exposes the bark to sun scald. Neighboring trees that have become used to shady conditions also may be adversely affected. Poor health and death often occur. Insects and disease: Large wounds in the tree caused by tree topping have difficulty sealing, McKenzie said. "The location of the cuts, as well as their size, prevents the tree's natural defense system from functioning," she said. "The stubs are open wounds that invite insect invasions and the spread of decay fungi. If decay is already present in the limb, cutting will only speed the spread of decay." Weak limbs: Many new limbs sprouting from the cut of the larger branch are weakly attached. When limbs develop normally, they attach to the larger branch with layers of wood overlapping year after year. These normal limbs gradually enlarge with the parent stem. On the other hand, small limbs growing from large cut areas develop only from that point, and not as an extension of the entire parent branch. Increased growth: Most homeowners top trees to control the height and spread of the branches. According to McKenzie, the opposite usually happens. "Trees respond to the injury by producing many long sprouts, resulting in a tree that is not only as tall as it was, but also bushier," she said. Tree death: According to McKenzie, some species of trees do not tolerate topping. Beeches, for instance, sprout little after a severe pruning. The resulting lack of foliage will likely lead to the death of the tree. Ugliness: "A topped tree is a disfigured tree," McKenzie said. "Even with regrowth it never regains the grace and beauty of its species. The landscape and the community are robbed of a valuable asset." Instead of topping trees, McKenzie suggested pruning properly and regularly. "On large, mature trees, a light pruning every three years keeps your tree in healthy condition, is less costly, is visually less drastic, and helps to maintain the tree at the desired size," she said. To reduce the size of a large tree, McKenzie suggested using a technique called "crown reduction pruning." "To do this you prune large branches back to the lateral branch that is approximately three times the size of the branch being removed." For small, young trees, McKenzie suggests planting a tree with the mature height in mind. "Plant short-stature trees under utility wires, and begin proper pruning early," she said. Source: Rita McKenzie, (765) 494-3625; e-mail, ritam@fnr.purdue.edu Writer: Steve Tally, (765) 494-9809; tally@purdue.edu; http://www.agcom.purdue.edu/AgCom/homepages/tally/ Purdue News Service: (765) 494-2096; e-mail, purduenews@purdue.edu To the Purdue News and Photos Page