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Making Room at the Top

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Published on: Apr. 2, 2000

Last revision: Nov. 4, 2010

Tree and utility wires have always vied for space in our rural and urban areas. No clear winner has emerged from this competition. We either were faced with electrical outages caused by broken tree branches, or our roads were lined with disfigured, high-maintenance trees. Today, however, most utility companies are using an improved method of pruning that can help protect the health and safety of trees and provide the necessary clearance for electrical distribution wires. Electric utility companies must provide continuous service for our needs. To guard against power outages, they must regularly remove tree branches that threaten wires. Traditionally, utilities have cut the branches back to a point that would allow needed clearance. Called heading or topping, this method efficiently, if temporarily, protects wires, but the trees suffer enormously.

Topped or stubbed-off branches usually produce numerous fast-growing shoots, which are weakly attached and subject to future breakage. These shoots also grow directly back into the space needed for utility wire clearance. The branch stubs holding the sprouts are left vulnerable to decay, which may progress down into the branches and weaken them.

This will happen even if the sprouts growing from these branches produce seemingly luxuriant foliage. Some trees cannot tolerate drastic removal of branches and may quickly decline. The entire process of repeated topping virtually ensures a population of unhealthy trees. Weakly-attached or decayed branches are susceptible to breakage, especially during wind or ice storms.

Some people mistakenly think the heading or topping technique is acceptable or even desirable for all trees. Countless trees throughout Missouri have suffered irreversible damage from topping by people with perfectly good intentions, even when such drastic treatment was not needed.

Today, many utility company's approach to clearance of electrical transmission wires continues to involve regular maintenance pruning, but cuts are made in such a way that whole branches or limbs growing towards wires are removed, leaving no stubbed-off branch ends. Names given to this utility wire clearance technique include natural target pruning or, more specifically, natural directional pruning.

This technique benefits trees because it is more sympathetic with their natural growth habit. Wounds from cuts made at branch collars, or at their point of attachment, grow over more easily, minimizing decay. Excessive sprout growth is avoided because most live branch ends are left on the tree to sustain future growth.

Utility companies benefit from natural directional pruning because over time trees are more sound and less susceptible to breakage. The number of cuts made on each tree tends to be fewer and the remaining branches are growing away from wires. Time between needed prunings tends to be greater. This all adds up to time saved for pruning crews and fewer electrical outages. Property owners and the general public benefit from safer, healthier, nicer looking trees along streets and roadways. This, not heading or topping, is the pruning technique people should emulate.

Natural target pruning doesn't solve all problems with trees growing under utility wires. Some trees may appear lopsided or bisected, or they may be left with gaping holes, even when correct pruning cuts are made. These shortcomings may be especially obvious when a utility company changes from old heading methods to natural directional pruning, or with trees that require removal of large limbs low in the tree.

Some trees will suffer extreme treatment regardless of the pruning approach, simply because they are the wrong tree in the wrong place. Many utility companies will remove problem trees under wires if it proves the best overall solution. Some companies even offer to replace problem trees with new ones that will not interfere with wires.

Natural target pruning or directional pruning is now practiced by many Missouri utility companies--some have used these methods for years. Five utility companies in Missouri have been recognized by the National Arbor Day Foundation as Tree Line USAs for using approved pruning practices, providing regular training for their crews and promoting well managed municipal trees. These companies are City Utilities of Springfield, the Light & Power Company of St. Joseph and the Water and Light Department of Columbia, Ameren UE of St. Louis and Independence Power and Light. In fact, Missouri is now the national leader in companies so honored.

DO YOUR PART

Utility companies continue to make progress in the quality of their line clearance work, but there are also things we all can do to improve the condition of trees along streets, in parks or in our yards.

  • Plant the right tree in the right place. Don't plant tall-growing deciduous species such as oaks, maples, ashes, sycamore, pines or spruces beneath utility wires. Lower-growing trees, such as redbuds or crabapples, may be appropriate for planting under wires, but check with your utility company or city government if planting on the street right-of-way to be sure.
  • Observe pruning work done in your area for utility wire clearance. Know that some pruning cuts must be made to provide needed clearance that would not be needed for other trees. Support efforts of your utility company to prune trees using natural target pruning principles.
  • Consider removing trees under utility wires if they must be harshly pruned to provide clearance or are in poor condition.
  • Encourage tree workers in your community to use natural target pruning and other good tree care methods for all trees. Employ a trained arborist or commercial tree care service for trimming work. Don't top trees.

If you would like more information about managing or planting trees near wires, or about the Tree Line USA program, contact the Urban Forestry Coordinator, Missouri Department of Conservation, P.O. Box 180, Jefferson City, MO 65102.

Pruning Methods Contrasted

Heading Method

  • Branches are shortened, leaving stubbed-off branch ends.
  • Sprouting occurs near the ends of cut branches. Branches grow back, only thicker.
  • Regrowth is weakly attached and breaks easily in storms
  • Can cause dead branch stubs. Maximizes chances for future decay inside branches and trunk.
  • Trees require pruning as soon as regrowth enters area needed for clearance.
  • Especially destructive if applied to entire tree.
  • Produces a whole population of weak, unhealthy trees over time.

Natural Directional Pruning

  • Whole branches growing toward conductors are removed, leaving branch collars intact.
  • Only offending branches are removed. Remaining growth is directed away from wires
  • Future storm damage is minimized
  • Tree can grow over pruning wounds. Chances for decay are minimized.
  • Tends to lengthen time needed between prunings.
  • Works with natural growth habit of tree.
  • Encourages trees to grow safe and sound.

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