Over the past five years, California has experienced a sharp uptick in wildfires caused by power lines, raising concerns over utility line clearing and vegetation management practices across the state. Pacific Gas & Electric Co., in particular, has been found responsible for more than 1,500 California wildfires in the last six years, Business Insider reported. In response to the 2018 Camp Fire, the deadliest and most destructive in the state’s history, a court-appointed monitor was asked to perform an independent audit of PG&E’s wildfire prevention work.
The monitor’s full report was released in July 2019 and identified 3,280 high-risk trees that PG&E’s contractors did not properly trim or remove, averaging 61 per mile. Many of the trees had branches that were dangerously close to active power lines and showed signs of scorching. This was particularly true around high-voltage wires, which are not typically covered with insulation. Paired with California’s warming climate, which has dried out the state’s vegetation and lengthened its wildfire season, the need for proactive line clearance, tree trimming and vegetation management strategies has become a top priority.
Wildfire Prevention: The Role of Utility Line Clearing
Vegetation maintenance is crucial for managing electric safety risks to the public and preventing wildfires in residential areas, utility corridors and around power stations. By providing separation between live wires and the surrounding plant life, arborists are able to reduce tree/wire conflicts that could spark a wildfire. According to the Utility Arborist Association, trees are among the most common causes of utility service interruptions and maintenance issues, especially during periods of intense weather, such as wind, snow and lighting storms. The UAA also points out that energy companies like PG&E have a responsibility to uphold best practices in utility line clearing to maximize the safety and reliability of their electric services.
Although vegetation that comes in direct contact with power lines is a chief concern, utility arborists must also remain proactive about their broader line clearance, tree trimming and tree removal practices. In most cases, contractors are engaged to prune trees before they pose a risk to electrical infrastructure, as swaying branches and weak root systems can lead to unexpected accidents. One of the difficulties, however, is that each tree needs to be inspected for potential risk factors, which informs the amount and type of pruning that is necessary. According to the UAA, utility arborists must consider:
- Tree structure and growth rate
- Wind speed and direction
- Tree and shrub species
- Plant health and vigor
- Power line configuration and voltage
Once a tree has been assessed, the next step is to determine which pruning methods are needed to maintain a safe clearance without damaging the plant itself. While cutting down unruly trees may be the most direct approach, it can have a negative impact on the surrounding ecosystem.
Wildfire prevention and vegetation management go hand-in-hand, which is why utility arborists employ directional pruning strategies to better control the growth of at-risk trees. As outlined by the Tree Care Industry Association’s ANSI A300 Standards, directional pruning helps remove branches that pose a risk to power lines without over-trimming. All high-risk branches should be pruned back to a lateral branch that is at least “one-third the diameter of the branch being removed.” All cuts should also be made close to the main limb to avoid leaving a stump or damaging the tree. Some of the utility line clearing practices that are known to negatively impact tree health, per the TCIA, include:
- Topping: Reducing a tree’s size using heading cuts that shorten limbs and branches to a “predetermined crown limit.”
- Lion’s tailing: Removing an excess number of inner, lateral branches from their parent branches.
- Rooster-tailing: Over-thinning palm trees by removing too many lower fronds and leaves.
Rather than simply chopping down invasive branches, directional pruning aims to minimize wildfire risks and future interference with power lines by guiding the growth of plant life. Generally speaking, the amount of clearance needed depends on both state and federal regulations. For example, California law requires a minimum of 18 inches of clearance between vegetation and energized wires that carry more than 750 volts. While this regulatory variability can make it difficult for arborists to uphold best practices in utility line clearing across state lines, the best way to prevent future wildfires is to keep up to date with these and other industry standards.