Many trees within or near power line rights of way pose some level of risk to the electrical system. Extreme weather, such as wind, flooding and lightning, can add to that risk and cause trees or tree limbs to fail. Some trees are at greater risk of failure due to structural issues, disease, species characteristics, insect damage or other issues.
A great example of how an introduced pest can negatively affect forest health is the dramatic increase of ash tree mortality in North America due to the emerald ash borer (EAB). The EAB has killed millions of ash trees, adversely affecting electric reliability across much of eastern North America.
Utility arboriculture categorizes trees that can impact power lines as either danger trees or hazard trees. A danger tree is any tree that could contact electric lines by growing or falling into the lines, or by the lines swaying or sagging into the tree. The proximity of the tree to power lines and equipment determines a danger tree, regardless of the health or condition of the tree.
A hazard tree, a subset of danger trees, is a structurally unsound tree that could strike a target, such as electric lines, when it fails. Danger trees and hazard trees are often targeted for removal.
Aside from danger trees and hazard trees, other trees may be targeted for removal for other reasons. These include:
- Tree species incompatible with nearby power lines
- Trees that must be severely pruned and have no chance for reasonable natural development
- Trees that will remain unsightly because of excessive pruning
- Trees whose removal will create a more aesthetically pleasant right of way and provide for more cost-effective line maintenance
There are a variety of factors that determine whether or not a tree must be trimmed or cut down. Trees are taken down by either felling the entire tree from the ground or by piecing the tree down sections at a time. Felling trees is when we cut trees down inside or outside of the rights of way that are at risk of falling on or otherwise threatening power lines.
We make reasonable efforts to obtain written permission before any trees are removed. However, in rural or remote situations when efforts to obtain written permission have failed, we may proceed with tree felling operations. Trees may also be felled during emergency operations without prior notification.
Find out more about how we manage debris after removing a hazardous tree. Stump grinding is not part of our hazard tree program, but hazardous trees and vegetation threats to power lines can be reported through a tree trimming request.