Mature trees are a key part of our urban forest. They provide us with many benefits, including lower energy consumption, improvements in air quality, carbon sequestering, stormwater runoff reduction, as well as many social and economical benefits.
Bigger and older trees are better able to provide these benefits, which is why it’s important to maintain a healthy urban forest and keep large, mature trees in the landscape for as long as it is safe to do so.
To achieve this, the proper pruning of mature trees is necessary.
What is a crown reduction?
A crown reduction is a pruning technique that removes weight from the end of branches back to a healthy, growing lateral branch, which will form a new crown.
The process reduces long, heavy, or overextended branches, as well as removing any branches with significant defects. The result is a smaller crown, without reducing the structural integrity of the tree.
Why would a tree need a crown reduction?
The older and bigger a tree gets, the more likely it will need some kind of pruning maintenance. Over the years, branches and trunks can develop cracks or cankers which may lead to decay. Crown reductions can take the stress off defects and poor attachment points on the tree.
A poor attachment point is the union of a branch to the tree trunk that has bark included in it. Poor attachment points are common causes for failure. In the Spring Ice Storm of 2016, a lot of the damage done to trees was caused by poor attachments.
When a large tree is removed or a nearby building is taken down, other trees are exposed to different wind loads than before. Reducing the crown of a newly exposed tree will also make it less susceptible to failure in high winds.
Crown reductions can:
- Prevent major damage in ice or wind storms.
- Encourage new growth in a declining tree
- Prevent torsional cracks — branches that twist until they form long lateral cracks. In mature trees, torsional cracks are a common reason for failure.
Crown Reduction vs. Tree Topping
As we have said before, not all pruning is equal. It is important to choose a company who understands how to properly reduce a tree’s crown. Some tree services may not be experienced in crown reductions or they may not understand the difference between crown reductions and topping.
Topping is an outdated pruning technique that cuts branches with no regard for proper pruning practices. Topped trees are very likely to suffer from failures as they continue to mature. If a tree company offers topping as a service, look for another company.
Features of a Crown Reduction
Removes a branch back to a healthy, growing lateral branch. This branch will become part of the new crown.
- Leaves smaller cuts so there is less area for decay to enter.
- Removes less of the live crown, so less shock is caused to the tree.
- Balances the crown and leaves two thirds of the crown remaining after a completed reduction.
Features of Topping
- Removes large portions of the live crown, leaving large stubs and lateral branches.
- Leaves large wounds that are a doorway for decay to enter.
- Removes up to half of the crown and causes extreme stress to the tree.
- Leaves the tree frantically trying to make up for the lost food source (the leaf cover that was removed) by sending out sucker growth (called epicormic shoots) along the remaining branches. These suckers are usually poorly attached to the tree.
The Importance of Mature Trees
Mature trees are important green infrastructure in the urban environment. When one is removed, so much is lost. This is why crown reductions are good options for prolonging the life of the tree and avoiding removal as long as it is safe.
At Baum Tree Care, we specialize in crown reductions of mature trees and have performed this pruning technique on hundreds of trees. One such tree we crown reduced is shown in the video below.
This is a mature Silver Maple that was damaged in the 2016 spring ice storm. The base of the tree is four feet from a house. The tree lost some branches because of the weight of the ice, as it covered the branches that were in full bloom. The extra surface area that the blossoms added made each branch even heavier.
One branch fell and hit the neighbor’s roof, damaging their eavestrough as it bounced down to land on the hood of their car. The client called us, as they did not want to risk the tree suffering further damage in future storms. We reduced the crown and the tree is now back to a healthy, balanced crown.