Structural Pruning

A Must-Do for All Trees Near Buildings or Walkways

Picture a tree in a forest, growing straight up through a shady canopy with a single stem, stretching for the sunlight above. Now think of a tree in your landscape. Growing alone, it has full access to the sun with minimal competition from neighboring trees. Outside of its natural habitat, it develops a wide crown with large lower branches and many limbs. These features structurally weaken your landscape tree.

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Growing conditions in a forest encourage development of a strong central stem and reasonable branch size. Conditions in a landscape are inherently different and favor the development of structural defects.

Problematic structural defects develop at an early age and worsen as the plant matures, posing an ever-increasing risk to the property, and the people on it. Maintain the stability of your trees and you reduce this risk. That’s where structural pruning comes in.

Structural pruning aims to develop and maintain stable trees. This type of pruning can benefit all landscape trees, but for those growing near buildings, next to sidewalks or over parking areas, this practice is not a nice-to-do, it is a must-do.

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An unbalanced crown, with branches dominating one side, poses a serious risk to people and property. This issue could have been prevented with structural pruning.

Consequences of Not Pruning for Structure

Poor tree structure often results in breakage of major limbs and contributes to overall tree failure. These trees are usually the first to fall during inclement weather, but are even at risk under normal conditions.

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Structural defects predispose a tree to failure, even under normal weather conditions.

Trees in urban landscapes frequently begin developing undesirable traits at a very young age. They may develop poor crown structure, large branches that dominate the central stem as well as weak branch attachments or codominant stems with inclusions. Though these problems seem minor when trees are young, they become major headaches as trees grow.

Large trees support more weight and are exposed to greater forces from wind so poor architectural traits greatly increase the likelihood of failure. Given the size of mature trees, it is exceedingly more costly to correctively prune later in life. Plus, when matures trees do fail, they have the ability to cause much greater damage. That is why it is so critical to give special attention to those trees that potentially pose a danger to people or property.

Features of a Strong Tree

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A co-dominant stem is a common structural issue in urban landscapes and on commercial properties.

Single Central Stem
Unless the tree is intentionally grown as a multi-stemmed specimen (like some birch and serviceberry trees for example), a single stem should be maintained for approximately half of the eventual mature height of the tree.

Reasonable Branch Size
The size of all branches and leaders should always be less than one-half the diameter of the parent stem at the point of attachment.

Adequate Branch Spacing
Branches should not be clustered closely together. A radial distribution of branches around the stem will distribute weight and minimize stress.

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Included bark weakens a branch attachment, making that branch more likely to fail.

Strong Branch Attachments
Unions where the trunk wood wraps around the base of the branch are preferable. When bark becomes included (squeezed or embedded), that attachment will be weaker. Inclusions on large, long branches pose the greatest risk.

Good Foliage Distribution
Foliage should cover at least the distal of two-thirds of the stem and each permanent branch. Maintaining lower branches encourages diameter growth that leads to desirable trunk taper.

Life and Limb

Starting at a young age, proper pruning techniques can encourage development of all the above features for a strong, stable tree at maturity. This type of pruning decreases maintenance costs over time, reduces tree and limb failures and helps ensure trees live longer.

After planting young trees, the first ten years are a critical time period for guiding correct architecture. On large, maturing species, pruning may need to continue at regular intervals for up to 25 years following planting. While it may seem counter-intuitive, the cost savings of early, consistent structural pruning can be significant. At a young age, a problematic limb can often be removed with a hand pruner. Leave that limb to grow into a co-dominant stem and you’re faced with major pruning, installation of structural supports or even removal.

For trees in an urban landscape, structural pruning will always be a good investment. When it comes to those trees near parking lots, buildings or walkways, it is more than an investment. For these trees, structural pruning is an essential strategy for mitigating risk and maintaining the safety of people and property.


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Posted in Tree Pruning
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