If there is anything Californians have learned in the past five or so years, tall trees and overhead powerlines are not compatible. Therefore, utility agencies have promoted planting smaller trees under power lines, but that campaign does not seem to sink in despite its clear instructions. Designers, public agencies, and homeowners are all susceptible to the problem; planting trees without considering how large they will become under preexisting utility lines. Consequently, utility agencies are spending oodles on monitoring trees close to their lines, and when there’s competition by trees, the overhead power lines will win. That is, so long as the lines are indeed being monitored and arborists are proactively pruning trees away from them. Property owners, too, have this obligation if we want to avoid dangers down the road. All this maintenance for poorly positioned trees means costly maintenance for everyone involved, not to mention ugly trees suffering from hack jobs or odd forms.
When trees are clearance pruned away from power lines, the resulting branch structure is often blunt, as in the above illustration. Over time, the tree will create new limbs extending from the pruned ends. Unfortunately, this is not a good thing. These new limbs are weak and can easily split and break, especially in windy conditions. And Californians have learned what wind and breaking limbs can do to power lines. Rather than repeatedly making the same mistakes, property owners can start by heeding the advice in the link above and "plant the right tree in the right place." Most cities have on staff or on file an arborist that can assist both property owners and designers with tree selections.
• Landscape architects and designers need to include overhead utilities on their plans and specify appropriately scaled trees for their size at maturity. As a plan reviewer, this is a common miss among landscape architects that I see on a regular basis...from residential garden designs to large-scale high-rises.
Costly but often included when properties change hands and undergo remodeling or redevelopment is relocating the overhead utilities underground. This reduces the risk of damage but also allows for larger trees, which will provide greater benefits like reducing heat, comfortable shade, and cleaning the air.
Hopefully, agencies will continue their undergrounding of lines where fire danger is at its highest.
• Homeowners also need to choose wisely and be aware of how tall trees grow if under or near utility lines. They may be cute saplings in the nursery, but if trees grow too tall, the public utility agency may send owners a notice to fix the situation or bill for the necessary work. This can be avoided by PLANTING THE RIGHT TREE IN THE RIGHT PLACE, a mantra many arborists will preach, and I, too, will keep saying it until the cows come home.