While not universally practiced, many utility companies or their contractors continue the practice of "topping" or "round-over" pruning. This technique describes a method of pruning where cuts are made at arbitrary points on a branch along a uniform plane within the crown.
The resulting crown form is artificially uniform following pruning. Unfortunately, topping causes more problems than it solves. Because the tree sprouts grow rapidly, the tree must be pruned frequently.
There are two commonly accepted pruning alternatives are "lateral drop crotch pruning," also known as "natural pruning," and "side-pruning." Lateral or natural pruning requires the tree trimmer to pick out the branches growing toward the lines and remove them where they attach to the next lateral limb.
Properly placed cuts produce few sprouts and natural growth rates. The next cycle of trimming requires fewer cuts than the topping approach, because the problem branches were removed during the previous cycle and sprout growth has been slower. This method is used both on trees growing beneath or to the side of utility lines
Source of Complications
Problems between trees and utility lines generally occur because the wrong species has been planted directly underneath or adjacent to power lines. Under certain circumstances when this occurs there may be no other alternative short of removal and replanting.
Increasingly, utilities install underground distribution lines that require trenches. These trenches frequently damage tree roots, which slows tree growth, and leads to decline of the crown and root system. Branches may die, increasing the chances of wind damage and invasion of wood decaying fungi or insects. Auguring, tunneling, or boring through the root zone of the tree will cause less damage to the root system.
Safety & Liability
Safety and liability are issues of concern to everyone. Dead or dying trees in a park or along a street will eventually fall, possibly causing injuries or fatalities. If such trees are close to overhead power lines, their failure could tear down lines and poles, causing outages and other damage.
Vehicular and pedestrian traffic is another concern. Street trees must be managed to ensure visibility and clearance for street lights and signs.
The black and white photos are examples of types of utility pruning that may save a tree under or adjacent to a utility right-of-way from being removed.