It has only been in the last ten years that we have learned about proper pruning. And it should be pointed out that since trees behave as individuals - just as humans do - some so-called standards of pruning do not reflect the new knowledge.
Proper pruning equals preventive medicine. In a nutshell, we must not create conditions which predispose to disease caused by pathogens. A foremost example is the creation of cavities in which pathogens thrive. Cavities result from improper pruning i.e. from cutting flush with the trunk when removing branches. And then the problem is often compounded when people "clean" these cavities and remove wet wood, thus facilitating more infection.
Originally trees were meant to grow in groups. A single urban tree without symbiotic relationship with others will develop large lower limbs and co-dominant branches at a young age, leaving weak ones that can easily break off. This can be avoided by knowing the correct DOSE and LOCATION of the branches to be pruned. Another means to enhance the safety is the use of bolt rod, round washers, amon nuts and cables in the correct way.
Besides pruning for health reasons - removing the dead and decaying branches - it may be done for aesthetical or utilitarian reasons such as fruit production or increasing the value of timber. Legal aspects are e.g. right of way, drive-ways, powerlines, etc.
When calling a professional to work on your trees inquire about credentials, insurance and experience. Remember that wound dressing does not stop rot and may actually increase it. Trees do not heal the way we do. We regenerate, they generate (new limbs) in new places. We have organ systems, in trees they are organized in compartments, a defense (resistance) against the spread of pathogens.
For technical details call JOHN A. KESLICK, JR (610)696-5353. We suggest the books: MODERN ARBORICULTURE, TREE PRUNING a worldwide photo guide and PRUNING TREES NEAR ELECTRIC UTILITY LINES all by DR. ALEX L. SHIGO at Shigo and Trees, Associates.
John A. Keslick Jr.
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