Tree Trimming

Trimming trees to keep overhead utility lines clear is required for two reasons:

• To prevent power outages (depending on the location, an outage can affect thousands of people).
• To prevent damage to the lines from tree branches. Falling tree branches can pull down utility lines with them, and even branches brushing against lines in strong winds can be enough to cause an outage.

The main cause of power line damage is from trees. However, you can’t blame the trees themselves. Trees are naturally flexible and bend in the wind. When a tree is growing into power lines, that flexibility means it can damage those lines as its branches move and sway.

When a tree is growing into power lines, it’s usually because someone chose a tree species without understanding how the tree’s mature size or growth habits might conflict with its surroundings.

We can’t “fix” existing trees that are too big, but we can help homeowners choose trees that are the right size for their planting areas!

Pruning tree branches away from around power lines is usually called line clearing. You may also hear other terms used, such as:

• Right-of-way (ROW) clearing
• Incidental line clearing
• Power-line clearing
• Utility line clearing, and
• Brush and tree clearing.

No matter what name you use, this type of work has standards that are designed to keep utility infrastructure safe from conflicts.

Since overhead utility lines carry our electricity and communication lines, our daily lives rely on them. And, it’s important to remember that pruning to prevent power line accidents or damage is almost always less expensive and disruptive than repairing damage after a tree has caused an outage. So, while many people don’t like to see trees heavily pruned to keep lines clear, major tree pruning is
required around utility lines.

Unfortunately, we can’t let trees grow in their natural form through the transmission lines because of how trees’ branching patterns develop. Instead, a specific type of tree pruning is used for this situation.

“Directional pruning” is the tree trimming technique used on trees growing beneath power lines. Unlike residential or aesthetic pruning that enhances a tree’s natural form, directional pruning removes whole branches back to the main trunk.

This is done to direct the tree’s growth around the overhead lines. Usually, directional pruning results in a V-shaped tree. Where overhead lines and trees intersect, it’s the power line clearance requirements that dictate the tree’s shape.

Each tree that’s pruned around power lines is evaluated individually. This is because there’s usually a mix of tree species planted under utility lines, and each species has its own growth habits.

Individual trees are also evaluated for their general health and their location relative to overhead lines. This helps to determine which branches will be pruned.

Trimming trees for utility line clearance also takes other important factors into consideration, such as:

• Keeping areas clear for emergency-response vehicles.
• Clearing the right-of-way for updating and improving utility line connections.
• Keeping areas clear for fast access is key when power outages from storms disrupt important public and commercial services.

When tree pruning isn’t enough to prevent utility line conflicts, a tree (or other vegetation) may be removed. There are several important criteria used to decide if a tree should be removed. 

• How fast a tree or shrub grows – In addition to its mature height, the rate at which a tree grows is important. Fast-growing trees and shrubs require frequent maintenance. If they grow too much between their scheduled pruning dates and conflict with overhead power lines, an outage can result. 
• Overall tree health – When a tree under powerlines is in poor health from disease or is declining from age, it may be removed before it dies. This is because a tree that may have internal damage or structural problems can be unpredictable. A stressed tree is more likely to drop branches suddenly, and trees with hidden trunk or root damage can fall over even in clear weather. A tree in poor health that is a hazard should be removed before it falls. The positive result of removing a failing tree is the chance to replant with a tree that is the right size for the location. Planting the right size tree reduces the chance of future line conflicts.