It's the time of year that we think about pruning trees. Pruning is both necessary and beneficial, when done properly. A good pruning can remove dead limbs and promote vigorous, healthy growth while retaining the natural growth structure of the tree. The key to pruning is to create a wound that can be grown over quickly.
The only parts of a tree that are actually alive are the leaves, this year's twigs and the area just under the bark, called the cambium. The other important point is about branch structure. Trees don't "heal" like you and I do. Instead, they must grow over wounds. At the base of each branch there are special cells, sometimes called "woundwood" that are especially good at this. In nature, they would grow over where a dead branch had been. For this reason, you would not want to "flush cut" because you would be cutting off or damaging these cells. By the same token, cutting too far away from these cells is equally as bad. This can produce dead limbs that the tree will never grow over. The key is to find what is called the "branch collar." Where you make a pruning cut is critical to a tree's response in growth and wound closure.
The preferred location to make a pruning cut is just beyond the branch collar at the branch's point of attachment. The tree is biologically equipped to close such a wound, provided the tree is healthy enough and the wound is not too large. Because the branch collar contains trunk tissues, the tree will be damaged unnecessarily if you remove or damage it. In fact, if the cut is large, the tree may suffer permanent internal decay from an improp er pruning cut. If a permanent branch is to be shortened, cut it back to a lateral branch or bud.
Internodal cuts, or cuts made between buds or branches, may lead to stem decay, sprout production and misdirected growth. These cuts create stubs with wounds that the tree may not be able to close. The exposed wood tissues begin to decay. Normally, a tree will "wall off," or compartmentalize, the decaying tissues, but few trees can defend the multiple severe wounds caused by topping. The decay organisms are given a free path to move down through the branches. Additional pruning information and graphics can be found on the Web site of the International Society of Arboriculture at www.treesaregood.com
Hiring an arborist
Pruning large trees can be dangerous. According to Dave Scamardella, PA DCNR Bureau of Forestry Service Forester, if pruning involves working above the ground or using power equipment, it is best to hire a professional arborist. An arborist can determine the type of pruning that is necessary to improve the health, appearance and safety of your trees. A professional arborist can provide the services of a trained crew, with all of the required safety equipment and liability insurance.
When selecting an arborist, check for membership in professional organizations such as the International Society of Arboriculture (ISA), or the American Society of Consulting Arborists (ASCA). Such membership demonstrates a willingness on the part of the arborist to stay up to date on the latest techniques and information. Check for ISA arborist certification. Certified Arborists are experienced professionals who have passed an extensive examination covering all aspects of tree care. Ask for proof of insurance. Ask for a list of references, and don't hesitate to check them. Avoid using the services of any tree company that advertises topping as a service provided. Knowledgeable arborists know that topping is harmful to trees and is not an accepted practice. Also avoid using the services of any tree company that uses tree climbing spikes to climb trees that are being pruned. Climbing spikes can damage trees, and their use should be limited to trees that are being removed.
Next week: The perils of tree topping. any pruning cut or wound.