size, clear objects, improve fruit/blossom production, raise the crown and reduce liability. The purpose, along with other factors, will determine the type and size of cuts needed. The boundary that separates a tree trunk from a branch is known as the branch collar. The collar seals the pruning cut. If the collar is compromised by an improper cut or other wound, there is an increased chance of decay. Therefore, pruning cuts should be made as close to the collar as possible without harming it. The angle at which a live limb is cut will also affect a tree's ability to seal. An improper cut will leave a dead, angular nub or "dog's ear” protruding from the trunk. Dog's ears may pre- vent sealing, which again increases the chance of harm to the tree. A best practice is to make the finishing cut as close to the branch collar as possible without damaging it. The most common practice in pruning is to remove dead, diseased and dying limbs. Other than removing dead- wood, removing conflicting limbs may be the most bene- ficial to a tree's survival. However, thinning cuts can damage some species of trees in certain environments. Removing too many interior limbs in a mature hardwood may stress the tree and result in a "lion's tailing” effect, where all of the interior foliage is stripped, leaving foliage only at the ends of the limbs. Another variable to consider is exposure to the sun. If a tree loses a large limb on the south side, late-day sun can raise the temperature of the fluids beneath a tree's surface, resulting in "sunscald” with cracking bark. In short, a live limb shouldn't be removed without careful consideration.
For more information on prun- ing techniques, refer to the American National Standards Institute's (ANSI)A300 Pruning Standards. Or contact the International Society of Arboriculture (ISA) at 217-355- 9411 ( www.isa-arbor.com) or Tree Care Industry Association (TCIA) at 603-314-5380 ( www.natlarb.com) for addition- al resources.
Source: Mark Chisholm on behalf of STIHL Inc.