Reducing the canopy

View images below as an animation Photo examples of reducing canopy size Printer-friendly page Pollarding

Objectives

There can be several objectives of reduction pruning 1) reduce tree size; 2) reduce a portion of the tree to provide clearance from a structure; 3) reduce a portion of the canopy to minimize risk of failure.

Introduction

Trees sometimes grow larger than desired for aesthetic or safety considerations. These trees may interfere with overhead utility wires, grow into buildings or other trees, or become hazardous because of their size, length, or condition. Reduction pruning is used to reduce the size of a tree by decreasing the length of one or many stems and branches. Although this type of pruning can control tree size to a certain degree, it is no substitute for matching the correct tree species with the site when planting. Big trees planted in small places often require reduction to reduce risk of failure or reduce hardscape damage from roots. Regular pruning will be required to maintain the tree within desired limits.

Reduction pruning performed after the tree has become too large could require the removal of large diameter stems. The resulting wounds can be accompanied by decay, cracks, and sprout development. Therefore, it is preferable to perform reduction before the tree has become too large for its environment. Proper reduction pruning reduces size while more-or-less maintaining a tree's form and minimizes regrowth.

Execution

Sometimes the entire canopy of a tree must be reduced in height or spread, such as for utility line clearance or to minimize risk of failure. In addition to the size of parts to be removed, be sure to specify the clearance required above or along side of the canopy when pruning near a building or for utility line clearance. That way, everyone will have the same understanding of what is to be performed. Portions of the canopy, such as individual limbs, can be reduced in order to balance the canopy or to reduce likelihood of breakage on limbs with defects such as cracks and included bark or those that have grown to become too long.

Reduction is best accomplished by cutting limbs back to their point of origin or back to a lateral branch capable of sustaining the remaining limb and assuming apical dominance of the limb. When a branch is cut back to a lateral, no more than one-fourth of its foliage should be removed. A common rule of thumb is that the remaining lateral branch must be at least one-third the diameter of the removed portion, but this rule can vary with species, age, climate, and the condition of the tree. Consideration must also be given to the ability of the species to sustain this type of pruning. Species that are known to decay quickly from these types of cuts should be reduction pruned more conservatively than more decay resistant species. Never reduce a landscape tree by topping it. Topping causes decay, numerous sprouts, cracks in limbs, root decline, bark defects, and other problems.