Directional pruning: why utility-trimmed trees look lopsided

Directional pruning removes the branches growing toward the conductor and leaves the ones growing away, so next season's growth heads somewhere safe. ANSI A300 requires the cut to land at a lateral branch or the parent branch rather than at a clearance line, which is why so much wood comes off.

A three-person crew finishes a coast live oak beside a 12 kV distribution span and is back on the road by 2:40 in the afternoon. From the driveway the tree has a shape six hours old. The half away from the wire is untouched. On the wire side, two limbs are gone at the trunk and a third ends about fourteen feet out, at what used to be a side branch and is now the end of the limb.

The crew did not cut the tree to a line. They cut it to a branch, and the branch was where the tree had put it.

The utility has a word for this, and will use it

PG&E's Trees and Powerlines page answers the question directly, in the FAQ block headed "Trimming and removing trees":

We use directional trimming to help trees grow away from our powerlines. This is a common utility practice. A tree with directional trimming may look unusual, but it does not affect the tree's health. This helps keep the required distance between the tree and powerline when removing it is not an option.

Four sentences, and the last one is the trade being offered. The alternative to the shape is the stump, and which of the two an inspector prescribes was settled before anybody arrived with a saw.

The word comes out of the pruning standard. The Tree Care Industry Association, which is the secretariat for ANSI A300 Part 1, Pruning, lists among the standard's structural objectives the aim to "Promote or discourage growth in a particular direction (directional pruning)." A directional cut is a decision about next year's growth as much as about this year's clearance.

The cut is made at a branch, not at the clearance line

One clause produces the whole appearance. ANSI A300 (Part 1)-2008, clause 9.3.1.5:

Branches should be cut to laterals or the parent branch and not at a pre-established clearing limit. If clearance limits are established, pruning cuts should be made at laterals or parent branches outside the specified clearance zone.

That sentence forbids the crew from measuring the required clearance, marking that distance on the limb and cutting there. The clearance figure sets a boundary the cut must clear, and the tree's own branching decides where beyond it the saw actually goes.

On the oak, PG&E's published minimum for a distribution wire inside a High Fire-Threat District is 4 feet. The limb came off at fourteen. Those ten feet are the oak's own branching. They are the distance between the four-foot boundary and the first place on that limb where a real branch was growing. What the enforceable clearance figure is and where it comes from is a separate question with a separate answer.

The lateral left behind has to be able to take over

A side branch qualifies only above a certain size. Clause 5.3.4 of the same standard says that "When pruning to a lateral, the remaining lateral branch should be large enough to assume the terminal role." The USDA Forest Service puts a number on it in How to Prune Trees, NA-FR-01-95, revised August 2012:

To prevent the abundant growth of epicormic sprouts on the stem below the cut, or dieback of the stem to a lower lateral branch, make the cut at a lateral branch that is at least one-third of the diameter of the stem at their union.

Work that backward on the oak. At the point where the crew would have liked to stop, the limb is about nine inches through, so the side branch they need is three inches or better. Three-inch branches occur where they occur, and on the underside of a mature oak they can be scarce. The next one in was several feet farther back, and that is the cut in the driveway.

A cut made short of that lateral costs the crown anyway. It kills the end of the limb back to the next branch down, which is the shape you would have been looking at regardless, with a dead stub on the front of it.

A limb that will sprout back at the wire comes off whole

Two limbs on the oak are gone at the trunk while a third was only shortened. Clause 9.3.1.4 is where that split is decided:

Trees growing next to, and into or toward, facility/utility spaces should be pruned by reducing branches to laterals (5.3.3) to direct growth away from the utility space or by removing entire branches. Branches that, when cut, will produce sprouts that would grow into facilities and/or utility space should be removed.

The second sentence is the test. If the stub left behind would push a flush of new shoots straight back toward the conductor, shortening it buys one season and then hands the problem back worse. So the limb goes at its origin, and the asymmetry in the crown is the prescription showing. For a tree standing directly under the span, clause 9.3.1.3 reaches the same conclusion from the other side: remove entire branches or leaders, or remove branches whose laterals grow, or once pruned will grow, into the utility space.

The USDA guide describes what the rejected alternative produces:

These practices invariably result in the development of epicormic sprouts, or in the death of the cut branch back to the next lateral branch below. These epicormic sprouts are weakly attached to the stem and eventually will be supported by a decaying branch.

Those are water sprouts. They grow fast, they grow straight up, and on a tree under a conductor they grow at the conductor. Clause 6.1.7 of the same standard puts topping among the practices it calls unacceptable for trees. How an auditor grades a crew against A300, and which edition the contract named, is its own subject.

The clearance was sized for the next visit, not for today

The crew is cutting for a date in the future. SDG&E's Tree Pruning Guidelines state the target plainly:

Our contractors trim with the goal of having the pruned trees meet clearance requirements for at least one annual pruning cycle.

The same page lists what goes into that calculation:

• Species

• Growth potential

• Tree position relative to the power lines

• Pruning history

• Local site conditions

• Potential for tree and wind sway

• Potential for line sag

Five of the seven are about growth. Two are about movement, and those are the two that surprise landowners. The conductor sags on a hot afternoon and swings in wind, and the limb swings too. The clearance has to survive both at the same time, a year from now, which is why the distance taken on the day is so much larger than the number on the utility's web page.

Why the two figures differ and which one is enforceable is a question for the rule. The growth rate that sets the cycle length is an assumption somebody recorded before the work was scheduled.

What the utilities claim the shape costs the tree

PG&E's position is that directional trimming "does not affect the tree's health." SDG&E's page lists four benefits it attributes to directional pruning techniques:

• Trees maintain a natural shape

• Reduction of weak branch re-growth

• Allows for proper healing of injured trees

• Reduces frequency of pruning

Read those as what they are. Both are a utility's own statement on its own customer page, and both leave out the study and the author. The checkable part sits one level down, in the standards both utilities say they work to. The cut lands at a branch collar or at a lateral. The wound closes from a ring of living tissue. The regrowth is a branch extending itself, in a direction somebody chose.

What those claims leave open is whether this particular tree is now structurally sound, and whether taking two scaffold limbs off one side has loaded it over your roof. The crew was engaged to clear a conductor. The person who can answer the other question is a consulting arborist you hire, standing under the tree, whose opinion is about this tree rather than about the method.

The six feet you are barred from working in

California Penal Code section 385 is the statute SDG&E's page points customers to. Subdivision (b) reads:

Any person who either personally or through an employee or agent, or as an employee or agent of another, operates, places, erects or moves any tools, machinery, equipment, material, building or structure within six feet of a high voltage overhead conductor is guilty of a misdemeanor.

Subdivision (a) defines high voltage as anything exceeding 750 volts, which takes in every distribution primary in the state. The statute is written about tools and equipment rather than about pruning, and a pole saw is a tool.

SDG&E reads it the short way and tells customers "it's against the law (per California Penal Code 385 ) to attempt pruning trees near power lines yourself." The USDA guide arrives at the same instruction without the statute: "Never prune trees that are touching or near utility lines; instead consult your local utility company."

The arborist you hire is caught by a different set of rules. A300 clause 9.2.1 assigns line clearance work to "a qualified line-clearance arborist or line-clearance arborist trainee" only, and in California the approach distances a non-qualified worker owes and the difference between the two tree-work credentials are Cal/OSHA's, not the utility's. A residential tree service typically holds neither credential.

Everything outside six feet of the conductor is still yours. A good arborist can reduce the far side to take weight off it and make the crown read as less one-sided, and will tell you that doing so takes more live wood off a tree that has already lost some.

The prescribed trimming is at the utility's expense. Cosmetic work you commission is yours to pay for, and so is the wire from the pole to your house, which PG&E's page assigns squarely: "Property owners are responsible for keeping service drop wires clear of vegetation and dead or hazardous trees."

Three questions, and the visit to ask them on

The shape is decided at the pre-inspection, not on the day of the cut. By the time a crew is in the driveway the prescription is written, the work is issued against it, and the person holding the saw did not write it.

1. Which limbs are prescribed, and back to what point? The mark on the trunk says prune or remove. It stops short of where the cut lands, and the inspector can tell you. 2. Are removal and a replanting on the table instead? A tree that will need this every cycle is a different conversation from one that needed it once. 3. What happens to the limbs once they are down? The wood decision is made at the same visit and by the same person.

Where the work is already done and the result departs from what you were told, PG&E's published route is its Report It program. It takes photographs of potential safety issues on the electric system, and returns a notice once the issue is under review or addressed. SDG&E gives 800-411-7343 for questions about trees near its facilities. Photographs taken from the driveway, dated, with the pole visible, are worth more than a description.

Three growing seasons from now the oak will have filled in on the side it was allowed to keep, and the cut ends will have closed over. Symmetry is gone for good. The two scaffold limbs are gone at their origins, and new growth comes from buds the tree still has, which are on the other side. The shape you are looking at in the driveway is close to the shape you are keeping.

Further reading

• Why did the utility mark or tag my tree: The dot on the trunk that committed this tree to pruning rather than removal.

• What to expect during a utility line-clearance visit: Three trips by three people, and which one can still change the shape.

• Tree removal vs. pruning: how the utility decides: The other outcome, and the grounds an inspector writes it on.

Frequently asked questions

Why is my tree cut back so much further than the clearance the utility publishes?

Because the crew is not allowed to cut at the clearance figure. Clause 9.3.1.5 of ANSI A300 (Part 1)-2008 says branches "should be cut to laterals or the parent branch and not at a pre-established clearing limit," and that where clearance limits are established, "pruning cuts should be made at laterals or parent branches outside the specified clearance zone." PG&E publishes a minimum of 4 feet around distribution wires in a High Fire-Threat District. The cut lands at the first lateral branch beyond that 4 feet which is big enough to take over the end of the limb, and on a mature tree that branch is often ten feet farther in.

Will the tree grow back even?

It will grow, and it will grow away from the wire, which is the point of the method. It will not grow back symmetrical, because the limbs on the conductor side are gone at their origins and nothing regrows from there. PG&E's own answer is that "A tree with directional trimming may look unusual, but it does not affect the tree's health." That is the utility's assertion on its customer page, not a finding from a study, and the person who can actually answer it for your tree is an arborist who has looked at it.

Can I hire my own arborist to balance the tree out?

For the side away from the conductor, yes. Near the wire, no. California Penal Code 385(b) makes it a misdemeanor to operate, place, erect or move "any tools, machinery, equipment, material, building or structure within six feet of a high voltage overhead conductor," and 385(a) defines high voltage as exceeding 750 volts. The USDA Forest Service pruning guide is blunter: "Never prune trees that are touching or near utility lines; instead consult your local utility company." A contractor who takes the job anyway is working under Cal/OSHA's line clearance rules, and most residential tree services are not qualified for it.

Why did the crew take one limb off completely and only shorten the one next to it?

Clause 9.3.1.4 of ANSI A300 (Part 1)-2008 draws that line: "Branches that, when cut, will produce sprouts that would grow into facilities and/or utility space should be removed." A limb whose shortened stub would push a cluster of fast new shoots straight back at the conductor gets removed at its origin instead. The limb beside it, whose regrowth will head somewhere harmless, only needs reducing.

Who pays for this?

The utility, for the work it prescribed. Southern California Edison states that "All tree trimming is done as part of SCE's annual vegetation management work at no additional cost to the customer." Work you commission yourself, including any cosmetic pruning on the side away from the wire, is yours to pay for. So is the service drop: PG&E's Trees and Powerlines page states that "Property owners are responsible for keeping service drop wires clear of vegetation and dead or hazardous trees."