The Objective of Structural Pruning.
The main objective in structural pruning is in most trees, to develop and maintain a strong central leader with strong scaffold limbs and branches. Young trees should be pruned to guide growth in ways to develop good form, this will pay off in the long run. When trees are a little older they may require trimming so their crowns clear traffic, signs, and buildings. Established trees in urban landscapes should be pruned primarily to reduce the risk of failures throughout the canopy and maintain the structure. Achieving these customer expectations requires different pruning strategies for trees of different species, life stages, and size at maturity.
Pruning Dose: How much is enough?
The answer is that it depends on the pruning objectives and the severity of the defects. The pruning dose is the estimated percentage of foliage of bud removed during pruning compared with the total amount on the tree prior to pruning. The ANSI A300 Part I. Pruning standards, 6.1.4 state that “Not” more than 25 percent of the foliage should be removed within an annual growing season. The percentage and distribution of foliage to be removed shall be adjusted according to the plant’s species, age, health, and site.