Guggenmoos, S. 1995. New program controls tree management. Electric Light & Power, February 1995, p.15-18.

TREES GROW ON MONEY by Sig Guggenmoos

The expression “money doesn’t grow on trees” has a particular ring of truth to electrical utilities. Even the reverse statement that trees grow on money might seem apropos.

Senior management of TransAlta Utilities Corporation (TAU) Calgary, Alberta was highly dissatisfied with the fact that eventhough the distribution line clearance budget had been increased an average 35% a year between 1978 and 1984 there were few if any discernible positive results.

Tree related power outages kept increasing. Complaints and claims against the company were increasing. Lawsuits both for removing trees and not removing enough trees resulting in personal injury accidents were pending. The budget requests from the field indicated a continuation of this sharply upward trend. Was the field staff right? Would further increases produce results?

This line of questioning ultimately led to the question, what is the right amount of funding? This question was pivotal, because in searching for the answer TransAlta was exposed to the concept that the right level of funding can only be determined through an inventory of tree work. This inventory is comprised of basically two factors, the number of trees in proximity to the power lines and the local growth rates.

The value of a tree work inventory is often questioned. One argument is, why spend money counting trees instead of cutting them? Consider this analogy. If you were asked to resolve a flooding problem on a river what are the chances of doing so, if the budget is set but you do not have the width, seasonal flow rates, geological data nor are you permitted to spend any money gathering this information because it would reduce the amount of concrete you could purchase?

TAU hired a consultant to do the inventory. Based on the inventory the consultant made a 12 year budget projection. The period covered entailed a 6 year 1st cycle or catch up phase and a 6 year 2nd cycle maintenance phase. The 1st cycle budget was a significant increase over the existing budget. TAU chose to extend the 1st cycle over an eight year period to more effectively use experienced contractor staff. For the maintenance phase the budget was forecast to drop back to and be sustained at the 1985 level.

In implementing the new vegetation management program in 1986 TAU decided to contact each landowner directly to obtain consent to undertake the tree work. The intent was to reduce the risk of claims while maximizing tree removals. Complaints and claims were dramatically reduced and currently run at about 1 per 1000 landowners. Upon completion of the field work 5% of the landowners are randomly sampled with a door tag survey. The return rate is over 25% of the tags with 98% rating their experience with the vegetation management work as satisfactory or better (1992 and 1993).

Customers place a high value on reliable service. In a 1993 survey, TAU customers were asked to rate twenty service factors in terms of importance and how they perceived TAU’s performance on each of these. Reliability topped the list in importance at 99% while TAU’s delivery of reliable service was rated at 94%. Other factors ranked included restoration of service, operating efficiency, courteous employees, satisfying customer needs, rates and environmental performance. One would expect little elasticity in the customers’ demand for reliability. After all, courteous employees or low rates cannot compensate for a lack of the basic commodity, electricity, the customer believes to have purchased. In fact, one might speculate that service interruptions may lead customers to feel that they are paying too much for what is perceived to be a poor service.

Public safety is the other side of the coin of reliability. While trees falling on a power line may cause a service interruption, each such contact carries with it the risk that some person may be exposed to an electrical hazard either by contact with the tree or downed power lines. Utilities face a considerable liability given that court rulings appear to indicate that the public cannot be expected to recognize electrical hazards and thus electric utilities being cognizant of, and introducing the hazard must act with due diligence to protect the public.

The risks presented by trees within striking distance of a power line, can be minimized. Success requires a budget based on long term thinking, an accurate assessment of all the work required and the courage to remain committed to the plan. Remaining committed to the plan is important because results will not be immediate. Generally, as in TAU’s case, it would not be practical to do all required vegetation management work in one year. Dealing with vegetation one is faced literally, with a growing not static system. Tree caused outages did not start to decrease until the third year. Since then though, there has been a dramatic 80% drop. TAU’s tree related outages were close to the Canadian average of 15% in 1985. In 1992 tree related outages were only 3% of the total.

Outages were caused predominantly by trees falling on the line. Recognizing this and the higher costs associated with repetitive trimming, TAU focused on getting tree removals. During the 1st cycle 75% of all the trees handled were removed. The high tree removal rate is attributed to the decision to meet each landowner face to face to gain consent. Although, consenting is a substantial cost, the idea to empower the landowner by providing information regarding the vegetation management costs and objectives led to a level of cooperation that far exceeded expectations. The benefit of removing trees which otherwise would have to be trimmed offset the cost of obtaining consent.

Outages resulting from the regrowth of trimmed trees are being minimized by an appropriate trim cycle. TAU trim cycles are based on the clearance obtained when trimming and growth rates. While nature sets the growth rate, it can be heavily influenced by the quality of trimming. Improper pruning practises such as stubbing or removal of large portions of the crown often triple the rate of regrowth. The clearance obtained is affected by customer contact policies, the target clearance and customer desires. TAU has set a target clearance of 4.5 metres (15′) for trimming. After customer input the average clearance actually obtained is 3 metres (10′).

TAU invested money to decrease the tree liability but the budgets have dropped back to the 1985 levels as predicted for the maintenance phase. Nature and landowners keep planting trees near power lines. Trees mature becoming susceptible to disease. While trees have many environmental and aesthetic benefits, financially, tall maturing trees are an expanding liability to electric utilities. Though utilities routinely use long term planning for assets such as generation facilities, it’s a shift to apply the same thinking to a liability such as managing vegetation. Just as utilities can’t rationalize a generation facility based on just one year of operation, they can’t manage vegetation on a one year plan. But by making a long term plan based on an actual tree work inventory TAU’s success can be replicated.


Sig Guggenmoos is the Senior Consulting Forester for TransAlta Utilities Corporation’s Forestry group. He holds a Bachelor of Science in Agriculture degree from the University of Guelph, Guelph, Ontario where he majored in horticulture.