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Hazard Mitigation in Large Conifers

Two common "defects" in large conifers are codominant structure – multiple competing tops and the development of "overextended" limbs beyond the natural canopy shape. Both of these increase the likelihood of a large failure and resulting consequences. However, there are proven methods to manage these conditions and provide peace of mind for homeowners.

Example of codominant structure

Subordination Pruning

This technique for managing codominant structure “slows down” the growth of one leader and promotes dominance in the other.  By intentionally removing the the top of one leader with a carefully placed pruning cut (3-4 inches diameter). This type of gentle subordination will encourage the tree to naturally direct energy into the taller remaining top.

Please note; this is not the same as "topping" a tree. Topping is simply a term for over pruning with large cuts that cause structural decay and lead to the development of poorly attached branches.

Canopy Reduction

The proven strategy to manage overextended limbs is reduction pruning. With this technique, the length and end-weight of large limbs are reduced by 15-20%. This “shortens the lever arm” and directly reduces the likelihood of failure. Targeted pruning at the end of the limb, using cuts up to 3 inches diameter, promotes rapid wound closure. Retaining interior foliage protects tree health and encourages lateral growth, rather than extension.

Please note; canopy reduction is very different from the antiquated practice of “wind thinning” or "windsailing" of conifers. These detrimental practice remove entire branches with the intention of allowing wind to pass through the tree. There is no scientific basis for this practice. Removing entire limbs actually promotes development of longer, larger limbs that are more likely to fail and more damaging when that happens.

Preparing for reduction pruning over a busy street

Cable Support Systems

In codominant trees, limbs and foliage tend to grow outward on each stem and naturally create leverage. This generates outward force on the point of attachment. Further, narrow "v-shape" unions between codominant stems are significantly weaker compared to more open "u-shaped" unions.

These factors increase the likelihood of failure at codominant unions. Subordination and/or canopy reduction pruning is the first step to mitigate this risk. Installation of a cable support system provides a higher level of protection which is particularly valuable when the tree is located near significant targets (e.g. structures, vehicles, pedestrians, etc.)

If you have questions or concerns about large conifers on your property, contact Tree133.

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