Arizona Public Service Recently Completed a Comprehensive Survey Of Trees on or Near Its Rights-of-way. In cooperation with the city of Phoenix, the utility surveyed 17,000 trees — 12,000 of which were found to be problem species for their location (such as near electric power lines) and which are now scheduled to be removed over the next three to five years.

In a perfect world, trees wouldn't be planted in the vicinity of electric lines. This, as any utility knows, isn't always possible. When large, maturing trees are planted under lines, the utility needs to prune the trees to ensure a safe and reliable supply of electric power to its customers. To solve this problem, Arizona Public Service (APS; Phoenix, Arizona) encourages the planting of low-growing, compact-form varieties in the vicinity of power lines.


In his book titled Pruning Trees Near Electric Utility Lines, Dr. Alex Shigo said: “Plan before you plant and plant the right tree in the right place.” This is also advice the International Society of Arboriculture (ISA) and other green industry participants have been preaching for the past six decades. Yet tall trees continue to be planted near power lines. The problem is particularly acute in cities and suburbs.

With proper planning, utilities can address historically poor vegetation management performance near electric power lines. With 60-plus years of experience in modern vegetation management, we know what practices stand the test of time.


Utilities must be less reactive and more proactive when it comes to vegetation management. Utility arborists must work more closely with city and community planners who lay out streets, parkways and alleyways.

Poor planning of cities and towns is one of the reasons line-clearance arborists, in the past, have had to stay on the front streets. Historically, many towns and titles have placed utility services along alleyways. Newer housing developments, however, are being laid out without these areas, because indiscreet real estate developers are looking to sell every available foot of land to make their lots look bigger.

There is also a more concerted effort to develop highways and roadsides. Utilities need to perform intelligent long-range planning to make these projects last. Utilities should not be criticized too severely for pruning and repruning trees that have been planted along roadsides. In some cases, there hasn't been any consideration given to existing utility facilities and which trees were not planted or grown in accordance with ANSI A300 guidelines.


APS, Arizona's largest and longest-serving electric utility, serves about 1.1 million customers in 11 of the state's 15 counties. The metropolitan area of Phoenix is one of the fastest-growing areas in the United States. With this growth, it is increasingly difficult to prune trees in the city away from power lines, as APS has done in the past. Now city regulations require APS to have lane, bike and sidewalk closures, which increases pruning costs due to traffic barriers and off-duty policemen who must monitor traffic and pedestrian safety. In addition, line-clearance crews are only allowed to perform pruning activities from mid-morning to early afternoon if city street access is required.

Working closely with the city is paying dividends for APS. APS's arborists have fostered a great relationship with the city forester that dates back to the mid-1990s. For example, the city forester promotes the ANSI A300 pruning standard. At the same time, APS is committed to following applicable standards and correcting any work that doesn't meet the city forester's expectations.

The APS forestry department and the City of Phoenix Parks & Recreation department have worked together to prune trees and remove hazard trees on city property. They have collaborated on many projects, even sharing resources on occasion to tackle tree-related projects.

Back in 2004, in cooperation with the Phoenix forestry supervisor, APS met with city officials to develop a project to remove tall-growing trees from under or adjacent to power lines, and then replace those trees with low-growing tree varieties. The first and most critical part of the project was to perform an inventory of the city trees along APS's power lines. APS agreed to have this survey performed at its expense.


In 2005, APS contracted with Davey Resource Group, a division of The Davey Tree Expert Co. (Kent, Ohio), to perform an inventory of street trees near power lines. It should be pointed out that other companies, including ACRT Inc. (Akron, Ohio) and ECI (Stoughton, Wisconsin), perform this same type of analysis.

The city provided the APS GIS department with GIS map layers that included the rights-of-way and center lines of city streets. Aerial photographs and property parcels also were provided. In turn, APS provided a GPS-based inventory of the existing location of conductors, poles, equipment, substations and easements.

ISA-certified arborists, who had been cross-trained for both utility and municipal projects, then collected field data using ruggedized pen-based tablet PCs. By using work-planning software, they were able to collect data on a unique GIS layer that accepts customized data fields in shapefile format using ESRI's ArcObjects.

The arborists posted the data in a centralized database that is updated daily. APS modified the system security to meet APS security requirements. The data, accessible to both city and APS staff through Internet browser queries, was verified for integrity through an ongoing quality-control/quality-assurance program.

The inventory included the species as well as the condition and defects of each tree. The location of each tree was determined along with the potential impacts to business bus stops and light-rail facilities. The inventory also included the planting site, which was also referenced with regard to nearby walls, medians, curbs and streets. The condition of the site was also determined. Conditions included any sidewalk damage, any damage to landowner property and any discovered trip hazards.

The inventory was done using the following methodology: obtain GIS base maps, set up field unit, collect tree-site data, upload to database, review data for quality assurance and quality control, and transfer data to APS and city.

After the inventorying, the goal of this project, which is currently under way, is to remove the problem tree and replace it with the “right tree in the right place,” as Shigo said. If it is determined a planting site wouldn't support an appropriate tree, a replacement tree would be planted off-site. As mentioned earlier, of the 17,000 trees inventoried, APS found that 12,000 needed to be removed. That means 70% of the trees were planted in the wrong location. The APS forestry department will be removing the trees and planting the replacmenet trees. The city will then clean up tree debris, grind the stumps and maintain the new trees. This project is scheduled to take place over a three- to five-year time frame.


To justify the additional budget dollars for this project, APS performed an investment analysis. A comparison showed that along rights-of-way, tree replacement was more cost effective than repeated tree pruning. In addition to the economic benefits, eliminating problem-tree replacements drastically reduces and avoids both momentary and sustained outages.

Proper vegetation management allows APS to improve the aesthetics of the communities it serves, while reducing vegetation-caused outages. Tree replacement is often less objectionable to residents than repeated pruning, resulting in improved relationships with the public and with city officials. Tree replacement also provides a safe environment for people living, playing or working near APS power lines.

In comparing tree-pruning and tree-replacement strategies, APS has found that the initial expense of tree replacement can be recovered in as little as five years. APS expends $88,000 to prune 2400 trees each year, based on historical data gathered since 1997. Costs include expenses incurred with two-year pruning cycles.

Replacing 2400 trees will cost $316,000, which includes tree removal and providing the city with replacement trees. A break-even recovery for the one-time cost of $316,000 will occur after the second pruning cycle.

Since there is no longer a pruning requirement, there are no further costs related to pruning the 2400 replaced trees. This project is one of the few APS expenditures to have a positive return on investment in five years or less.


In order to compare costs, the utility used a present-worth economic-analysis program developed by its T&D standards department. The assumptions are an annual escalation rate of 3.5% for pruning costs and an after-tax cost of capital of 8.22%.

The net present-worth value of a two-year pruning cycle per tree for APS over 30 years was $534.20 in 2006. The savings to the utility with the replacement method is $402 per tree over a 30-year period. Under the tree-replacement program, APS will never have to return to that tree; therefore, costs will never increase. Over the life of this project, APS estimates it will save $4.8 million by replacing 12,000 problem trees with low-growing trees.

Clearly, there is a need for utilities to step up and invest in tree-replacement programs. Such programs can be justified with easily tracked dollar savings over time. The concept is catching on. In the APS region, cities including Scottsdale and Glendale are looking to participate in similar programs.

Mike Neal, Arizona Public Service's manager of Forestry & Special Programs, graduated from West Virginia University with a degree in forest resource management. Neal is an ISA-certified arborist, an ISA utility specialist and a qualified party with the Arizona Structural Pest Control Commission. He is a past president of the International Society of Arboriculture, and the immediate past president of the Utility Arborist Association and the Arizona Community Tree Council. Neal also serves on Arizona Gov. Napolitano's Forest Health Oversight Committee and the EEI Vegetation Management Task Force.


When a customer performs work, constructs facilities or allows vegetation to grow adjacent to, or within, an easement or right-of-way of APS-owned equipment, APS can notify the customer in writing. Due to changes in the Arizona Corporation Commission, APS now has the leverage necessary to eliminate the hazard, obstruction, interference or violation at the customer's expense. The utility will take action if the work, construction, vegetation or facility poses a hazard or is in violation of federal, state or local laws, ordinances, statutes, rules or regulations, or significantly interferes with the utility's safe usage, operation or maintenance of, or access to, equipment or facilities.


  • The city of Phoenix will not plant any tree that can normally grow to a height of more than 25 ft (8 m) under or adjacent to the grantee's overhead power lines in the public rights-of-way.

  • Grantee shall have the authority to prune or remove any trees or shrubs located within or hanging over the limits of the public rights-of-way of the city. These trees include those that interfere with the construction, or endanger the operation, of the lines and/or facilities of grantee.

  • All said vegetation management work is to be done at grantee's expense and pursuant to ANSI standard A300.