Tree Maintenance

Who will be performing the work on my trees?

Only qualified utility line clearance professional arborists who meet OSHA qualifications are legally permitted to work within 10 feet of power lines or work on a tree that has branches within 10 feet of power lines.

Line clearance arborists are trained to:

  • Prune trees according to American National Standards Institute (ANSI) A-300 pruning standards
  • Follow industry best practices, which helps preserve the health of trees


Homeowners should:

  • Never hire a private tree contractor to work within 10 feet of power lines
  • Never attempt to do the work themselves
  • Always contact the utility for information first
How are trees pruned in a remote or wooded area?

In remote/rural locations, utilities:

  • Often utilize mechanical equipment to increase efficiency and worker safety
    • Large saws mounted on high-reaching booms can be used to prune the sides of right-of-way corridors
    • In some cases, saws are suspended from helicopters
  • Chemical application is another method of side pruning
    • Herbicides are applied to the foliage of selected branches growing into the right-of-way corridor
    • The treated branches eventually die and are shed by the tree

When using this equipment it is understood that the quality of the cuts can be less than those made by hand. Nevertheless, efforts are made to avoid unnecessary damage to the tree.

What specific pruning guidelines are followed?

The ANSI A-300 Part 1: Tree, Shrub and Other Woody Plant Maintenance—Standard Practices, Pruning are:

  • Accepted guidelines
  • Endorsed by the International Society of Arboriculture (ISA)

They promote directional pruning methods which:

  • Minimize pruning stress
  • Focuses on tree health while obtaining necessary clearance from power lines
What is directional pruning?

Directional pruning:

  • Removes branches growing toward the power lines while leaving those that are growing away
  • Is the most appropriate pruning method for utility line clearance

How will a tree look after it is directionally pruned?

  • Trees growing directly under power lines may appear U or V-shaped (crown reduction or throughpruning)
  • Trees growing alongside power lines may appear L- shaped, or one side may be completely removed (side pruning)
  • The tree may often appear misshapen but this pruning is being performed to provide for safety and service reliability, not for aesthetic purposes
  • Trees growing near the power lines will never have the potential to grow with a “natural” shape

Do Not Top Trees! Also called ‘roundingover’. It involves cutting branches to stubs or lateral points that are not large enough to grow successfully.

  • This is not directional pruning
  • Not an acceptable pruning practice

It can:

  • Severely weaken the tree
  • Kill some species
How much will be cut from my tree?

Typically, a qualified utility forester or vegetation manager prescribes the amount and type of pruning necessary based on:

  • Tree growth rate and structure
  • Wind direction
  • Tree species: strong or weak wooded
  • Tree health or vigor
  • Environmental factors
  • Water sources
  • Proximity of tree to wires and line configuration— higher voltage lines require greater clearance
Why do electric utilities prune trees?

It’s a matter of safety and providing reliable power for the members we serve.

Safety—Utility vegetation maintenance reduces electric hazard risk to the public by:

  • Providing separation between wires and vegetation to eliminate potential electrical shock
  • Reducing potential wildfire hazards from tree/wire conflicts

Reliability—Trees are among the most common causes of utility service interruptions. Trees that are too close to power lines can interfere with electric service; especially when weather brings lightning, wind, ice, or wet snow.