Conifer Topping – It May be Common, But is it Right?

By John Hushagen


Arborists around the world resoundingly condemn tree topping as a harmful practice that ruins tree structure, makes wounds that the tree can't close, and destroys the appraised dollar value that trees add to the landscape. Despite this seemingly universal consensus, there is still confusion within the arboricultural community about the topping of conifers.

In theory, topping a healthy conifer with a small diameter cut (less than six inches) should not do significant harm. I have observed that healthy second-growth Douglas firs (Pseudotsuga menziesii) have effectively closed the topping wound with callus after several seasons. Longitudinal dissections in some of the same trees revealed that discoloration and decay were contained to a fairly small area.

However, we must ask how much benefit (e.g., greater safety from "windsail" is to be gained by cutting the top 15 feet off a 135-foot fir. The answer is little, if any.

The goal of conifer pruning should be to reduce the tree's mass "windsail" without reducing its size. Proper thinning does that.

Hidden problems
In practice, most tree toppers don't stop at a 15-foot reduction and a 4-to-6-inch diameter cut. They prefer to reduce the height of a tree by one-third to one-half. Herein lies the problem. If a 140-foot fir is suddenly turned into a 70-foot fir, this topping cut is probably 12 to 15 inches in diameter. Even the healthiest trees under the best of conditions cannot cover a 12-inch wound. Very often one of the top rot fungi enter the wounded area, rapidly devouring the center of the tree.

As founder and owner of one of the larger tree services in the greater Seattle area, I have had ample opportunity to observe the effects of conifer topping. I once climbed and core sampled in several places an old-growth fir that had been topped many years before by nature or man. The base of the tree was sound, and from the ground it looked healthy. But as I worked my way down from the top, I discovered that there were only two inches of sound wood beneath the bark of a 24-inch diameter trunk, halfway down from the top of the 80-foot tree. The decay column was at least 55 feet long!

Heavy, bushy branches, some covered with fungal fruiting structures, clung to the sides of this grand tree. Halfway down the tree, I stopped coring since it was obvious that the tree was too dangerous to keep. Physiologically the tree's plumbing was working but structurally it was an accident waiting to happen.

It is not uncommon to find handfuls of gooey, rotten wood below large topping cuts. Rot spreads down the trunk, weakening the attachments of large branches and causing them to break and become dangerous hangers. Some toppers cut back to a lateral branch hoping it will "bend" and form a new top. What usually happens is that these previously shielded branches are too weak to endure the winds they soon encounter.

Upsetting the balance
Topping, or any other form of excessive pruning, upsets the delicate balance among leaf area, shoot growth and root growth. Trees need their leaves to feed shoots, developing buds and roots. Topping starves a tree, forcing it to use its stored reserves to rebuild its crown and fight invading micro-organisms. Topped trees become stressed trees that are susceptible to root rots, a major cause of death in Pacific Northwest trees.

Trees do not blow over because they are "too big." Shortening trees to make them safer is unprofessional, at best. In many cases, conifer topping could be considered arboricultural malpractice since the "cure" more often becomes "the cause" of hazardous trees. Topping conifers gives us a somewhat shorter tree that rapidly regrows new, bushy tops that are scabbed onto the outside of a rotting trunk. The tree soon becomes more hazardous than ever.

Maintaining values
As professionals, we must cease providing services of dubious value to the trees and the customers. Instead, we should concentrate on promoting hazard tree evaluations and proper pruning.

I feel the best way to explain the correct method of pruning a conifer is to say that the goal should be to reduce the mass of the tree without reducing its size. Thinning from the top to the bottom and from the inside out will reduce the tree's "windsail," reduce branch weight, remove poorly formed, crowded, broken and dead branches, and allow more light to reach the landscape below.

After this, if the client insists on topping or overthinning, bid the client a good day and walk away with your head held high. You won't get that quick, short-term paycheck, but neither will you have sacrificed your principles or the long-term welfare of the tree.

Recently, a client who owns one of the oldest homes in Beaux Arts told me that eight large conifers that we had pruned lost no branches in Seattle's fierce 100-year storm in December 1990. Getting testimonials like that is what quality tree care is all about.