This is a very common tree-surgery practice. Usually specified in metres, although sometimes as a percentage.
Crown reduction is a very common tree-surgery practice. Usually specified in metres, although sometimes as a percentage. It is typically done for one of three reasons.
To increase light through and around the tree
To reduce the encroachment of tree branches over certain areas (such as roads/car parks) and buildings.
To reduce the “sail effect” of wind on the trees canopy. By reducing the canopy area, and in turn the mass of leaves, the wind force against the tree is reduced. Sometimes a crown reduction is recommended as there is a risk of a tree being pushed over in high winds. Other times a crown reduction is used as a pro-active method to remove areas of the tree that are looking likely to fail in high winds
It is important not to think of a crown reduction as a method to just cut the top of a tree off. I am often asked to cut the top third of a tree off to make it smaller in a garden. It is quite rare that skelping off the top third of a tree is the best course of action.
Myself and my colleagues will always consider the end-goal for the client and then discuss the best and most practical solutions.
How much can I “reduce” my tree by?
There is no one fixed answer as certain species of trees can tolerate different levels of pruning. As a rule of thumb, when calculating the area to be reduced you should only measure the canopy. Not the entire tree including trunk. This area should be reduced by a maximum of 30%, although from the perspective of a trees health the less that is removed the better. It will always be a compromise between best practice for the tree versus the objective of the client and the surrounding area.
Trees such as Cherry, Oak and Beech are less tolerant to hard pruning. Whereas willow, lime and sycamore are more tolerant of harder reductions.
Correct technique for crown reductions involves cutting branches back to growth points. A growth point is a secondary branch that is growing off of a main branch.