Structural Pruning
Structural pruning is the process of pruning trees to promote good structure and reduce the impact of structural defects. This type of pruning can pay dividends for generations, as one of the main ways a tree dies prematurely is structural failure.
Structural pruning should only be performed under the guidance of a certified arborist. Like Dr. Alex Shigo, father of modern arboriculture, once said:
Pruning is one of the best things an arborist can do for a tree, but one of the worst things we can do to a tree.
Structural Pruning 101 with Andrew
Differences from Developmental/Young Tree Pruning
We use the terms “developmental pruning” and “young tree pruning” to refer to structural pruning performed on young and developing trees. Why make the distinction? Pruning young trees for structure is fundamentally different from pruning mature trees for two reasons:
- Young trees are more resilient and can better tolerate aggressive pruning to achieve structural objectives.
- Young trees are much smaller than mature trees, which makes them easier and less expensive to prune than large, established trees.
Although the best results are achieved by pruning early and often, structural pruning is also very beneficial for mature trees and should not be neglected.
Why Perform Structural Pruning?
Structural pruning seeks to imitate the structure that trees develop in their natural environment. Most trees grow in forests and compete with neighboring trees for sunlight. Because of this competition, forest trees typically develop a single dominant trunk (called a “leader”) that is tall and straight.
Without competition from nearby trees, landscape trees are encouraged to grow horizontally rather than vertically. The resulting structure—a short, wide canopy with multiple competing leaders—is weak and prone to failure.
How Do We Perform Structural Pruning?
The specifics of structural pruning vary a lot depending upon the tree to be pruned. In general, these are the strategies we use to promote good structure:
- Promote a single dominant leader (main trunk) by reducing or removing competing leaders.
- Space out branches along the dominant leader to improve airflow and light penetration.
- Suppress branches with included bark.1
- Reduce or remove branches below the bottom of the permanent canopy.2
- Take steps to correct deficiencies introduced by improper pruning practices, such as lions tail pruning.
Footnotes
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Included bark refers to bark that forms inside the “union,” or joining point, of two branches. This weakens the union of the branches and may cause the joint to fail when under stress. ↩
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Identifying the “permanent canopy” helps distinguish between branches worth retaining for long-term structure and others which may need to be pruned back or removed due to site constraints. Branches below the permanent canopy may be removed for various reasons, such as to reduce or remove branches obstructing the sidewalk. Developing trees need low branches for photosynthesis. After the tree has matured enough to tolerate losing them, these low branches may be removed. ↩
