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When trees grow into power lines, they become a major cause of power outages and can create safety hazards. We manage vegetation growing near our power lines and equipment to encourage public safety and service reliability.

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The APS Forestry and Special Programs Department conducts vegetation management on approximately 11,400 miles of distribution lines (lines carrying 4,000 to 21,000 volts) and over 6,000 miles of transmission lines (lines carrying 60,000 to 500,000 volts). 
Vegetation interference with power lines is one of the most common causes of electrical outages on distribution systems, and also has resulted in transmission grid failures subjecting millions of people to lengthy blackouts. Vegetation management is necessary for safety, system reliability, access to facilities, regulatory compliance, security, and fire risk. Vegetation, if unmanaged, can cause electric service interruptions, can ignite wildfires, and become a safety risk to the public. It is the Forestry Department’s responsibility to maintain vegetation to reduce these risks to the public and to the utility resources.
​At APS, vegetation management is conducted following best management practices defined in ANSI A300 Part 7 (ANSI 2012) and the ISA companion publication to the ANSI A300 Standards (ISA 2007). Our approach uses the Integrated Vegetation Management system of managing plant communities in a continually improving process of choosing appropriate control methods to achieve established objectives, justify and implement these methods, and monitor results of the various vegetation management treatments. 

Method selection is based on effectiveness of control at a given location, economic viability of the method, environmental impact, sustainability, and other factors.  Each power line is evaluated using these factors to determine appropriate maintenance cycles and treatment methods at local and landscape scales. (ISA 2013)
The APS approach to vegetation management includes:

  1. annual inspections of transmission and distribution lines to evaluate status in relation to desired outcome
  2. identification of annual and 10-year work plans to schedule vegetation management cyclically according to location specific factors such as plant species, growth rates, environmental concerns, treatment methods, stakeholder concerns, and desired outcome
  3. cycle inspections to select vegetation management control methods for each cycle of work
  4. implementation of vegetation management methods using manual, mechanical, chemical, and biological control methods
  5. post treatment monitoring and quality assurance
  6. documentation of annual work inspections, treatments, and monitoring.

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annual vegetation management summary

In 2016, the APS Forestry and Special Programs Department conducted vegetation management work along its transmission and distribution power line corridors throughout Arizona as part of its ongoing Integrated Vegetation Management Program. Utility vegetation management helps prevent trees from falling into power lines and significantly reduces the change of a catastrophic wildfire.

Some 2,000 miles of transmission line and just over 1,800 miles of distribution line were inspected and treated where necessary through removal of vegetation using manual or mechanical tree and brush removal, pruning of vegetation, and/or herbicide application to targeted incompatible vegetation. 

These ve​getation management activities involved 313 distribution and 73 transmission power line circuits.  This represents 37 percent of the APS overhead transmission and 16 percent of the APS overhead distribution system. 
Vegetation that required treatment posed a potential risk to power lines, structures, or equipment.

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Vegetation maintenance in 2016 was a continuation of ongoing vegetation maintenance practices within the APS power line corridors. The work was carried out across multiple land jurisdictions including: private, Bureau of Land Management, Forest Service, tribal lands, local and state parks, military, National Park Service, State Trust, and Bureau of Reclamation lands. 

Of the total miles of transmission and distribution power line corridors ground inspected and managed in 2016, 1,000 miles of transmission power line were inspected and spot treated where needed with herbicide to control and prevent regrowth of previously cut vegetation and new growth of incompatible vegetation.

Herbicide treatments target specific woody plants through foliar application with the long-term goal of converting tall-growing tree and shrub communities in power line corridors to stable, low-growing, early successional plant communities.
A portion of the herbicide work included touching up previous herbicide applications. 

All herbicide applications follow the Closed Chain of Custody Best Management Practices (UAA 2011). Herbicide application occurred on private, state trust, and Indian Reservation lands. 

All work conducted in 2016 was audited for quality and accuracy of work by qualified utility arborists. 

UAA 2011. Utility Arborist Association (UAA) Best Management Practices: Field Guide to Closed Chain of Custody for Herbicides in the Utility Vegetation Management Industry. International Society of Arboriculture. Champaign, IL USA. 20 pp. ​

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improving system reliability

Our Transmission Vegetation Management program is designed to improve system reliability by minimizing risks of vegetation-caused power outages. Our goal is to complete work in compliance with all applicable regulations, safety standards and science-based best management practices.

​using integrated vegetation management
Integrated vegetation management (IVM) is a system of managing plant communities to achieve established objectives. IVM is used to systematically choose, justify, selectively implement, and monitor different types of vegetation management treatments.
The methods are used to promote sustainable plant communities that are compatible with the intended use of the site, and to control, discourage or prevent establishment of incompatible plants that may pose concerns, including safety, security, access, fire hazard, utility service reliability, emergency restoration, visibility, line-of-sight requirements, regulatory compliance, environmental, or other specific concerns. (ISA 2013).
At APS, our general desired outcome is to create lush, stable shrubs and grasses that don’t interfere with overhead power lines, pose a fire hazard, or hamper access, and create a dense layer of low-growing cover that will resist the invasion of tall-growing trees. Vegetation management is also designed as much as possible to reduce erosion, enhance plant diversity, establish sustainable cover and forage for wildlife, establish corridors for wildlife movement and viewing, and avoid impacts to and enhance environmental factors. 
Our vegetation management program is consistent with the key steps of IVM as follows:
  1. We have participated in multiple studies, trainings, and education to gain scientific understanding of vegetation and ecosystems in Arizona. We use the best available scientific information to guide vegetation management decisions.
  2. We manage vegetation on a local level such that treatment methods and protocol are designed to best suit each location, vegetation types, and environmental concerns to achieve the desired outcome as closely as possible. These methods are designed to consider environmental and regulatory laws and requirements and involve stakeholder input.
  3. We monitor effectiveness of treatment prescriptions and methods immediately following treatment and annually to evaluate effectiveness of treatments and modify approaches if necessary.

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establishing a long-term management plan

Creating a long-term environmentally responsible land management plan helps us achieve effective clearances between vegetation and conductors with minimal environmental impact.

By effectively managing right-of-way corridors, we provide an asset for forest ecology and forest management. These corridors can aid fire fighters, providing an area to implement burn-outs.

​landscaping substations
We’ve converted several of our 379 substation locations from high-water use vegetation to low-water xeriscapes. These sites require little maintenance, fit in with surrounding desert areas and preserve water.
We also salvage desert plants from our transmission rights-of-way whenever possible. These plants provide excellent additions to our xeriscapes because they’ve already adapted to low water use.
ANSI. 2012. ANSI A300: American National Standard for Tree Care Operations - Integrated Vegetation Management a. Electric Utility Rights-of-way. Part 7 (Integrated Vegetation Management). Tree Care Industry Association. Manchester, NH.
ISA 2007. Best Management Practices: Integrated Vegetation Management on Electric Utility Rights-of-way. Companion publication to ANSI A300 Part 7 - Tree, Shrub, and Other Woody Plant Maintenance - a Integrated Vegetation Management. Electric Utility Rights-of-way. International Society of Arboriculture. Champaign, IL.
ISA 2013. Best Management Practices: Integrated Vegetation Management on Electric Utility Rights-of-way. Companion publication to ANSI A300 Part 7 - Tree, Shrub, and Other Woody Plant Maintenance - a Integrated Vegetation Management. In Electric Utility Rights-of-way. International Society of Arboriculture. Champaign, IL. Unpublished and in Review.
​tree pruning practices
We use directional pruning to maintain most trees along our power lines and remove others that pose hazards because of ill health, rapid growth or location.

Directional pruning involves pruning trees to direct branch growth away from power lines. Although trees may be pruned to an unnatural shape, proper pruning practices allow their natural defense systems to protect them from decay. To determine the proper pruning requirements, we consider the species, location, environmental conditions, line voltage and length of the pruning cycle.

Our pruning practices follow industry best management practices from the International Society of Arboriculture, and are endorsed by the Tree Care Industry Association, Utility Arborist Association and the National Arbor Day Foundation.

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​pruning near energized lines
Only specially-trained line clearing professionals should prune vegetation growing on or near overhead power lines.
Call us if you notice a tree too close to our power lines. We’ll send a forestry representative to assess the situation within 10 business days. We prune or remove trees that are growing into high-voltage electrical distribution and transmission lines along streets, alleys or easements.

​pruning near service wires

Pruning is your responsibility when tree branches become tangled in the service wire – the power line connecting to your house. We’ll disconnect the power while your hired professional prunes the tree if you notify us 24 hours in advance.


​storm damage debris

After a storm hits, our immediate priority is to restore power. We don’t clean up brush, trees or limbs that are cut or on the ground. We’ll knock on your door if we need to work on your property. 

​notification of work
If we need to work on your property, we’ll notify you in advance. As an added bonus, we’ll collect and chip any debris from our work.
If you’d rather have a tree removed than pruned, let us know. Our arborist will review your request during the site visit.





choosing power line friendly trees

We can recommend trees that coexist with overhead power lines

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