August 11, 2005

What property owner doesn't want healthy trees? But is pruning an essential part of tree maintenance and health?

Before going any further, I cannot find any evidence, other than anecdotal, that pruning live branches and limbs from a tree will make the tree healthier. In fact, overpruning a mature tree could significantly shorten its lifespan. Dr. Kim Coder has published a very informative article concerning this very subject. He notes that severe pruning could lead to a correspoding dieback of roots. Many research arborists believe that ANY live wood pruning may equate to some level of dieback in the root system.

Larry Stouse, president of Horticulture Solutions correctly defines pruning as "The removal of plant parts to benefit the remaining parts." So before a saw is taken to a tree, there must be goal in mind first. What are we trying to achieve? Then the most important question must be answered: "is the pruning the correct solution to the problem?" I have not seen supporting studies showing how the removal of healthy limbs and branches actually helps the vigor of a tree. Keep in mind, though, that careful and judicious pruning may not negatively affect the tree either.

How much is enough? Some people say 20% of the canopy is the limit. Others say 15%. Those ARE guesses. There is no standard threshold that is based on empirical evidence. The 20% rule is something that has been widely accepted but never statistically proven. So who can be sure? Is there a significant physiological risk? We don't know. However, that figure is all we have right now, so we should conservatively live with it until credible research can give us a clearer understanding of the relationship between tree vigor and pruning cycles. Tree owners need only to take off what is necessary for people to comfortably coexist with trees.

Be wary of those who claim that live-wood pruning equals health. One of the catch words is "thinning." Sometimes it is used to nudge people into purchasing services. It sure sounds good, doesn't it? Everyone wants to 'slim down' a bit.

Removal of dying or diseased limbs, and safe house and understory clearance is the most pruning that the average property owner will ever need to ever do. Successful tree health programs rely on little pruning and a lot of environmental and soil management. Be protectful when it comes to investing your tree care budget in pruning