The overwhelming majority of tree-caused outages go unnoticed except by those who lose power. However, on rare occasions, a tree-caused outage turns into something more, something that garners the collective attention of the public, utility industry, mainstream media, politicians and regulators. The Aug. 14, 2003, Northeast Blackout was the most recent such example, and rightly so. This blackout is considered to be the largest power failure in North American history, where 50 million people — one in three Canadians and one in seven Americans — languished without power for as long as two weeks. Reports also suggest that eight people lost their lives, and direct financial losses swelled to approximately US$6 billion as a result of this event.

The U.S. and Canadian governments quickly organized a joint task force to examine the causes and determine actions to prevent a recurrence. This effort included the work of many experts in organizations in both the United States and Canada who ran up thousands of hours of analysis. One of the noteworthy topics, and the subject of this article, was the utility vegetation management (UVM) aspect of this blackout. CN Utility Consulting, under the aegis of the Federal Energy Regulatory Commission (FERC), took on the following four tasks:

  1. Perform a field investigation.

  2. Evaluate UVM programs at three utilities in order to assess their strengths and weaknesses.

  3. Provide recommendations regarding mitigating future occurrences.

  4. Develop a list of best management practices (BMPs) for UVM programs.

This article will explore some of the key findings of this effort, examine recommendations and discuss some of the likely changes in store for utility vegetation management programs in North America. It will also present a checklist of BMPs that a utility can use to evaluate its own UVM program attributes.

Key Findings

While it would be unwise to suggest that there was a single specific cause of the blackout, several tree-related outages on Aug. 14, 2003, were directly linked as triggering events. The field investigation of these incidents and the subsequent review of the UVM programs at the utility companies involved led to the following conclusion:

The utilities associated with the blackout had UVM programs in place that were generally consistent with what should have been expected of them, given current industry standard practices. Put another way, this was not an issue of one or more utilities making substandard efforts to prevent tree-related outages; it was more a matter of substandard industrywide requirements and expectations.

This conclusion was based in part on the following considerations:

  1. The legal requirements for keeping trees away from power lines at the time of the incident were ineffective.

  2. The expectations of utilities, the UVM industry and regulators were lower than that needed to prevent tree-related outages.

  3. Utilities face a myriad of limitations that impede them from preventing tree and power line conflicts.

Consequently, we can conclude that unless changes are made in vegetation-management standards, requirements, expectations and practices, the UVM industry cannot prevent other catastrophic grid failures from happening in the future.

One only needs to look at examples of other major blackouts to drive that point home. We know that tree and power line conflicts were at the center of at least three other catastrophic grid failures in the past decade. Two occurred in Western North America in 1996: one affected 2 million people in July, while the other left 6 million people without power in August. The third, and more recent blackout, occurred in Italy, where a tree-related outage contributed to cutting power to 57 million Europeans in September 2003.

In spite of the disastrous consequences of these events, little was done in the industry to prevent these tree-related grid collapses. While it may be true that localized actions were taken, with very few exceptions, they were so limited in scope that they were unable to protect against recurrences.

Unlike the other three events, however, we believe that the August 14th blackout will directly affect every utility in North America. This impact will result from new laws and regulations, increased oversight of UVM programs by regulators and agencies, and the realization that utility companies must do whatever is reasonably necessary to avoid having a tree on their system cause the next massive blackout.

The Recommendations

The final UVM report contained a great many recommendations directed toward the utility companies, the regulators who oversee their work and the UVM industry in general. The following are some of the specific suggestions for each of those groups.

General utility and UVM industry recommendations:

  • Develop measurable and enforceable standards for UVM programs. The current set of industry rules, guidelines and laws are not sufficiently explicit to ensure that utilities will strive toward the elimination of future blackouts. UVM requirements and standards must be better defined and enforced. Furthermore, oversight organizations should perform routine UVM reviews at the utility companies working under their authority.

  • Ensure that UVM programs are adequately funded. UVM programs have always been prime targets for short-term budget reductions. Unfortunately, the real cost of these reductions does not typically manifest itself for months or even years. Certainly the risk of causing a catastrophic grid failure should weigh into any UVM cost-benefit analysis. Moreover, utility companies should have clear regulatory incentives for adequately funding, and disincentives for inadequately funding UVM programs.

  • Provide the right to perform the work. As it stands now, utilities are placed in the untenable position of having the obligation to keep vegetation from conflicting with power lines but not always having the explicit right to do it. If we expect utilities to do all the work required to prevent future outages, we must find a way to provide utilities with the right to perform UVM.

  • Eliminate unnecessary obstacles. Local, state/provincial and federal governments should review existing requirements that serve to unnecessarily stop or hinder timely completion of necessary UVM work.

  • Require proper planting of vegetation near power lines. Simply choosing appropriate tree species to plant near overhead lines would save hundreds of millions of dollars annually for electric ratepayers in North America. It would also result in tangible reduction in the likelihood of future outages, as well as dramatically improve the health of our urban and rural forests.

Recommendations specific to oversight and enforcement of UVM activities:

  • Oversight agencies and organizations need to learn more about UVM activities. While trees may be the single largest cause of electrical outages, few oversight agencies or organizations can claim they have the internal expertise to address and correct UVM issues and problems. Internal staff at regulatory and oversight agencies receive at least rudimentary training on all aspects of UVM.

  • Develop clear UVM expectations for utility companies. Oversight organizations should work with utility companies, the UVM industry and other stakeholders to develop measurable and achievable program objectives. The development of these expectations will require a joint effort to identify what specifically can be done to reduce the likelihood of future tree and power line conflicts. These types of initiatives could include: adoption of specific UVM best practices, required adherence to comprehensive UVM schedules and program improvements, and the development of performance goals related to the mitigation of tree-related outages.

  • Develop incentives/penalties for compliance. Oversight organizations should develop, communicate and enforce clear incentives or penalties related to utility-specific performance.

  • Make enforcement and oversight routine. Oversight organizations should continually monitor utility-specific UVM program activities and progress. This could be accomplished through standard utility reporting requirements, regular meetings between staff and the utility, and verification of progress through routine field audits. Specific attention should be given to the issue of adequate inspections and the scheduling of work.

  • Oversight organizations need to be directly involved in UVM. There are numerous situations where responsible agencies and organizations can actually assist in reducing the likelihood of tree/power line conflicts. For example, a common problem occurs when local governments erroneously restrict or prevent the timely completion of necessary UVM work. Where legal authority for developing and enforcing UVM requirements is held by a specific state or federal oversight organization, that authority should not be superseded by possibly competing local interests. In these cases, the utility regulators should become involved in order to ensure timely resolution of the problem and to ensure the work is completed before there is an outage.

    While all of us have seen report recommendations come and go with very little resulting changes, it appears that many of the preceding suggestions are indeed being acted upon. They are being acted upon by individual utility companies, federal and state agencies, reliability organizations and numerous UVM industry groups, such as the Utility Arborist Association and the Edison Electric Institute's Vegetation Management Task Force.

Here are a few changes that utility companies can expect to encounter in the not-too-distant future:

  • Utilities can expect to be held to higher expectations. UVM is currently a top issue for groups like FERC, the North American Electric Reliability Council (NERC), the Department of Energy (DOE) and the National Association of Regulatory Utility Commissioners (NARUC).

  • New legal and regulatory requirements. Where the NESC Rule 218 dominated the list of requirements in the past, several initiatives are underway that will directly impact all UVM programs. These include new transmission standards being developed by NERC as well as the increased likelihood of Public Utility Commissions implementing new UVM requirements on a state level.

  • Focus toward removing obstacles to performing UVM. One of the positive outcomes of the blackout was a clearer focus by utilities, government agencies and the public in removing obstacles to performing UVM work. The future may hold fewer customer refusals, streamlined permitting processes with agencies, and an enhanced public understanding of what is involved with UVM.

But don't just take our word for it. We recommend that every utility should comprehensively track, review and evaluate all of the initiatives that are currently underway, which will impact their UVM programs. See “Internet Resources” for organizations that do exactly that.

Summary and Conclusion

The Northeast Blackout was not the first catastrophic grid failure in the past decade to be related to tree/power line conflicts. What is different this time is the apparent resolve to shore up inadequacies in current UVM practices and standards across North America. Utilities can expect higher expectations from regulatory agencies, new legal and regulatory requirements, and hopefully a helpful and supportive effort in removing obstacles to keeping trees out of the lines.

Stephen R. Cieslewicz is currently president of CN Utility Consulting and has over 20 years of experience in the utility vegetation management (UVM) industry. He was one of the principal UVM investigators for the Federal Energy Regulatory Commission (in support of the federal investigation of the Aug. 14, 2003, Northeast Blackout) and has co-authored several of the resulting official reports. His firm works with utility companies, regulators and industry service providers on all issues/projects related to UVM.

Randall H. Miller chairs the Edison Electric Institute's Vegetation Management Task Force. He joined PacifiCorp in 1993, and has been system forester with them since March 1999. He has more than 40 arboriculturally related writing credits and speaks widely on arboricultural, urban forestry and utility forestry-related topics. He holds a BS degree in horticulture and an MS degree in urban forestry. He is an International Society of Arboriculture (ISA) certified arborist and certified utility specialist. He has served on ISA's Certification Test Committee, is a past president of the Oregon Urban and Community Forest Council, and currently serves on the editorial board of the Journal of Arboriculture.

Internet Resources





PSERC (Power Systems Engineering Research Center)

Transmission UVM Best Management Practices: How Does Your Program Measure Up?

As part of the UVM work commissioned by FERC, a panel of industry experts convened to develop the following list of best management practices for transmission UVM programs. It is a useful exercise for any utility to see how its respective program stacks up to these minimum-suggested requirements.

Understanding the Workload

Workload projections, planning, budgeting and scheduling should be based on an accurate understanding of the existing and likely future vegetation under and adjacent to existing transmission lines.


Consistent funding should be based on a clear understanding of the required work and not be solely based on historic budgets. Funding should be based on an accurate understanding of workload and local knowledge of the type, cost and frequency of required work. This also should include the ability to increase or reduce expenses (in a timely manner) in response to unpredictable events. For example, this would include the ability to adjust funding based on the unexpected impacts of drought and above-normal precipitation, or widespread outbreaks of tree pathogens or pests.

Scheduling UVM Work

Scheduling should be based on an updated and ongoing analysis of the workload and current conditions. For example, both excessive precipitation and drought can significantly influence vegetative growth and resulting workloads. Schedules should be flexible enough to address these and other variables, such as customer requests and line patrol initiated work. The intent of scheduling is to manage the vegetation prior to it becoming a threat to service reliability.

Wire Zone — Border Zone Concepts and Integrated Vegetation Management

All transmission UVM work should be identified, scheduled, completed and maintained consistent with Wire Zone — Border Zone objectives and industry accepted protocols. Integrated Vegetation Management (IVM) is the most commonly referred to, and used, protocol for managing transmission rights-of-way. IVM is generally defined as the practice of promoting desirable, stable, low-growing plant communities that will resist invasion by tall-growing tree species through the use of appropriate and environmentally sound control methods. These methods can include a combination of chemical, biological, cultural and mechanical treatments.

Transmission Line Sag and Sway

Conductor sag and sway must be considered whenever managing transmission rights-of-way. Utility and contract employees shall be familiar with how conductor sag and sway can influence clearances on specific ROWs under normal and short-term emergency load conditions. Such elements as training, work assignments, contract specifications and UVM manuals should include instructions for determining potential sag and sway at specific locations.

Reclaiming Rights-of-Way

Transmission UVM programs should identify all sections of line that are not currently managed to the full extent of easement rights, the Wire Zone — Border Zone method or with other compatible land use. A plan should be developed that methodically works toward the goal of putting all rights-of-way under this or other compatible methods of routine management.

Vegetation Conditions Inspections

Field inspections of vegetation conditions should occur on a frequent basis, and the schedule should be based on anticipated growth. Aerial patrols should be complemented and calibrated by routinely scheduled ground patrols.

Organizational Structure

Transmission UVM programs should be centralized within the utility and under the authority of a qualified, experienced and knowledgeable vegetation manager.

Management Support

Utility management throughout the organization should support and be familiar with the necessity of and practices involved with UVM activities.


Utility and contract employees at all levels in a UVM program should have appropriate qualifications, ongoing training and applicable certifications to perform the required work.

Research and Development

Utilities should have ongoing R&D efforts to evaluate current and potential tools and practices related to UVM work. The company should continuously evaluate new technology, products and work methods that are aimed at program improvement.

Clearly Defined, Communicated and Measured Objectives and Milestones

Utilities should have a formal management plan outlining UVM practices, objectives and approved procedures. The plan also should include workload-related references and projections. The utility shall have a documented schedule and appropriate measures to ensure completion of required work. The management plan will require periodic revisions.

Quality-Assurance Procedures

Utilities should have a quality-assurance program and a documented procedure for ensuring that work is completed per specifications and industry standards. In addition, there should be ongoing efforts and protocols to identify and correct quality problems and issues.

External Education

Utilities should have a comprehensive public education program that provides the public, individual landowners, and other agencies and groups with accurate information regarding transmission UVM activities and practices.

Internal Education

Utilities and contractors should have internal training programs that provide ongoing training to UVM employees. Utilities also should provide training to other utility departments regarding UVM activities and objectives.

Work Management Measurement

Utilities should have a system(s) and procedures capable of managing work identification, assignments and the job status for required UVM work. This should include the ability to document and track historic work at any given location.

Pruning and Clearances

Pruning shall be done in accordance with ANSI A300 guidelines. Clearances, obtained at time of pruning, shall be achieved with specific consideration given to line sag and sway, expected weather conditions, and the anticipated pruning response of the specific tree.