ANSI A300 Pruning Standards
A minimum or maximum diameter size of branches to be removed should be specified in all pruning operations. This established how much pruning it to be done.
Hazard Reduction Pruning (HRP)
Is recommended when the primary objective is to reduce the danger to a specific target caused by visibly defined hazards in a tree. For example, HRP may be the primary objective if a tree has many dead limbs over a park bench.
Maintenance Pruning (MP)
Is recommended when the primary objective is to maintain or improve tree health and structure and includes hazard reduction pruning. An example here might be to perform an MP operation on a front yard tree.
Hazard reduction pruning and maintenance pruning should consist of one or more of the pruning types noted below:
The selective removal of one or more of the following items: dead, dying or diseased branches, weak branches, and water sprouts
The selective removal of branches to increase light penetration, air movement and to reduce weight
The removal of the lower branches to provide clearance
The selective removal of terminal branches to decrease end weight on long heavy limbs, or to manage the height and/or spread of a tree
The selective thinning of framework limbs or specific areas of the crown to allow a view of an object from predetermined spot
Should improve the structure, form, and appearance of trees which have been severely headed, vandalized or storm damaged.