At the University of West Virginia, Dr. Alex Shigo swiftly earned his doctorate in pathology by starting on it while still pursuing his master's in biology--"a loophole," he conceded, since "the university quickly closed." Thirty years and some 15,000 dissections later, Shigo was a pathologist, author, lecturer, and known to many as the "Father of Modern Arboriculture."
Shigo was a pathologist with the USDA Forest Service in 1960 when he was asked to investigate the discoloration and decay of timber. At the time, most pathologists and tree service workers had long preferred "cross-cut" or "transverse" dissection, arboricultural reports but Shigo's chainsaw convinced him that cutting should be done longitudinally as well. The process led him to discoveries suggesting that theories of such timber ailments as heart rot and decomposition were, among others, entirely wrong.
"I could either go with the books or go with what I saw," he said. "I chose to go with the trees."
In his lifetime, Shigo published more than 200 papers and wrote a half-dozen books, including "Tree Pruning: A Worldwide Photo Guide." Published in 1989, the book begins with what Shigo considered the seven most important practices about pruning. They are:
1. Planting the wrong species in the wrong place. Trees must grow larger every year, or they will die. Choose a species appropriate for where you want to plant. When in doubt, call your tree service expert.
2. A flush cut can be pruning too close to the trunk. When you flush cut, never cut into the branch collar, the point where the branch joins the trunk. The collar belongs to the trunk, not the branch being removed.
3. A stub can remain after a branch is pruned away. Never leave a stub, whether it's living or dead. Stubs are "sugar sticks," meaning that they have pathways for pathogens to enter the wood. Carefully removing a stub enables the wound to close and to seal itself.
4. Never tip and top. Tipping and topping is the removal of entire tops, high trunks, and branches of timber. It's difficult and dangerous for the workers, and it kills trees. The process does not enhance the safety, health, or dignity of a species. Prune with respect and leave nature in control.
5. When over-pruned, older shade varieties are being prepared to die. Over-pruning strips away precious photosynthetic materials, impeding the production of food necessary for survival.
6. Pollarding is the careful reduction of the crown to precisely the same point each year. Although pollarding is usually performed on old-world timber, U.S. tree service experts do so on a smaller scale. When applied appropriately, pollarding is not mutilation.
7. Do not paint pruning cuts or apply dressing of any kind over rotted or infected wood. Some dressings actually stimulate rot. After a cut is made, discoloration occurs as defense reaction to stall decay from entering the wound site.
Throughout his career, Shigo emphasized that unlike re-generating organisms as human beings, these plants are generating organisms that create their own food from carbon dioxide, sunlight, and water.