Crown thinning is employed to increase light and reduce wind resistance by selective removal of branches throughout the canopy of the tree. This improves the tree’s strength against adverse weather conditions as the wind can pass through the tree resulting in less “load” being placed on the tree.
Crown lifting is done for access; these being pedestrian, vehicle or space for buildings and street furniture. Lifting the crown will allow traffic and pedestrians to pass underneath safely. This pruning technique is usually used in the urban environment as it is for public safety and aesthetics rather than tree form and timber value.
Crown lifting introduces light to the lower part of the trunk; this, in some species can encourage epicormic growth from dormant buds. To reduce this sometimes smaller branches are left on the lower part of the trunk. Excessive removal of the lower branches can displace the canopy weight, which could make the tree top heavy adding stress to the structure.
When a branch is removed from the trunk, it creates a large wound. This wound is susceptible to disease and decay, and could lead to reduced trunk stability. Therefore much time and consideration must be taken when choosing the height the crown is to be lifted to.