Reasons for Pruning
Because each cut has the potential to change the growth of the tree, no branch should be removed without a reason. Common reasons for pruning are to remove dead branches, to improve form, and to reduce risk. Trees may also be pruned to increase light and air penetration to the inside of the tree’s crown or to the landscape below. In most cases, mature trees are pruned as corrective or preventive measures. Routine thinning does not necessarily improve the health of a tree. Trees produce a dense crown of leaves to manufacture the sugar used as energy for growth and development. Removal of foliage through pruning can reduce growth and stored energy reserves. Heavy pruning can be a significant health stress for the tree. There are many outside considerations, however, that make it necessary to prune trees. Safety, clearance, and compatibility with other components of a landscape are all major concerns. Proper pruning, with an understanding of tree biology, can maintain good tree health and structure while enhancing the aesthetic and economic values of our landscapes.
Specific types of pruning may be necessary to maintain a mature tree in a healthy, safe, and attractive condition. Cleaning is the removal of dead, dying, diseased, weakly attached, and low-vigor branches from the crown of a tree. Thinning is selective branch removal to improve structure and to increase light penetration and air movement through the crown. Proper thinning opens the foliage of a tree, reduces weight on heavy limbs, and helps retain the tree’s natural shape. Raising removes the lower branches from a tree to provide clearance for buildings, vehicles, pedestrians, and vistas. Reduction reduces the size of a tree, often for utility line clearance. Reducing a tree’s height or spread is best accomplished by pruning back the leaders and branch terminals to secondary branches that are large enough to assume the terminal roles (at least one-third the diameter of the cut stem). Compared to topping, reduction helps maintain the form and structural integrity of the tree.