The Proper Pruning of Trees

Alex Shigo conducted research on the proper pruning of trees for over a quarter of a century while working for the United States Forestry Service. Approximately 10 years ago I was privileged to attend a seminar conducted by Mr. Shigo as well as to meet this plantsman at the Royal Botanical Gardens in Hamilton, Ontario. Through his research conducted on over 15,000 trees in order to determine the effect of proper or improper cuts in tree physiology, he came up with a pruning guide for branch removals.

Flush cuts were out... "Target Pruning" was in! While I must admit there was some initial skepticism on my part, this initial apprehension quickly gave way to Shigo's recommendations.

From that initial seminar several years ago to the present day, there is ample evidence to support the fact that improved education and training is still required for some individuals responsible for pruning operations as well as those supervisors responsible for forestry maintenance practices. Specifications for planting appropriate trees under power lines and along municipal roads also need to be carefully reviewed.

Poor selection of trees under power lines.
Improved selection of tree species required under power lines.
Absence of pruning standards.
Need for pruning operational standards.

At the provincial, regional and local levels of government, pruning activities still need considerable improvement. Specifications in many cases need to be upgraded for line clearing practices as well as urban forestry activities.

These kinds of cuts as shown in the accompanying photo will eventually dry out and provide an ideal environment for decay organisms which weaken the tree and ultimately reduces it's life expectancy. The swollen branch collar is not a stub and should not be flush pruned.

Flush cuts that reduce the life expectancy of the tree.
Unacceptable pruning practice...
need for improved standards / supervision.
A tree with branch removed by excavator.
The end result... branch removed by excavator.

In this case, an excavator did some side limbing on a roadside tree. Structurally, the tree has been weakened and its appearance has been ruined forever.

Branch collars vary in size in the same tree and a proper pruning cut is based on the actual angle of the collar.

Branch collar on Quercus (Oak).
Branch collar on Quercus (Oak).
  • A well defined branch collar.
    A well defined branch collar.
  • Branch collar on Fagus (Beech).
    Branch collar on Fagus (Beech).

Cut the living branch as close as possible to the branch collar. This may involve 3 cuts depending on the size of the branch that is being removed.

To avoid tearing the bark, oftentimes a "drop cut" is made. In this case, the initial cut is made on the underside of the branch approximately 12 to 18 inches out from the trunk. This cut should be made with a sharp pruning saw until the saw starts to lightly bind. Depending on the size of the branch, the second cut is made from 2 to 6 inches out from the initial cut on the upper side of the branch. The final cut is made as close as possible to the branch collar.

Callused over cuts on Quercus (Oak).
Callused over cuts on Quercus (Oak).

Painting the wound is not necessary as there is ample evidence to suggest that tree wound dressings provide an ideal environment for microorganisms under the surface which facilitates rot fungi.

Previous practices such as painting wounds or making a flush cut to facilitate proper healing of a cut are old technical facts that need to be set aside and replaced with proven up to date research.

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