A Crown reduction is the uniform shortening of branches to reduce the overall size of the canopy.
A trees appearance or form can be enhanced by a crown reduction and the amenity value of the tree increased.
If there are concerns about the structural integrity or root system of a tree then a crown reduction can be employed to reduce the sail effect of the wind on a tree and therefore reduce biomechanical stress, improving safety and the long term viability.
Crown reduction is often the method used to allow a large tree to be retained in limited space; the crown structure is maintained as is a high percentage of the foliage bearing structure this allows the tree to maintain good vitality.
As a general rule we would specify a reduction as either 10%, 20% or 30%, the percentage refers to the amount of foliage removed and not a percentage of the height. As a result a 30% crown reduction is approximately equivalent to a 12% reduction in overall branch length (BS3998 Tree Work Recommendations). If a tree is reduced too much it will often reshoot vigorously which can result in increased maintenance costs and less light filtering through the canopy.
Not all tree species or specimens are suitable for crown reduction, as not all trees or species are able to withstand this treatment; therefore each tree is assessed in regards to its suitability for this type of work. Both the species characteristics and condition of the individual specimen is taken into account before we make recommendations for a crown reduction.
From this assessment the amount of reduction is determined in order to adequately meet the objectives of the management plan. The intention is that after the reduction the tree still has a framework of young branches in good health and able to produce good leaf cover in the following year.
The original crown shape is normally mirrored to maintain the form and balance of the tree unless there is a need to change this for structural integrity of the tree.