Q: I was in a shopping center yesterday and watched a landscape crew trimming the trees, if trimming is the word for what they were doing. I know little about the subject, but why would they cut so far back? There must be some good reason. We don’t get hurricanes, so that isn’t it.
A: There is no good reason for what was done to those trees. The pruning style is called tree topping and it is simply bad for the trees. Trees require a large leaf surface area to provide food for maintenance and growth.
Topping cuts off a major portion of the food making potential and depletes the stored reserves. While removing most of the buds that would form a normal branch system, topping often stimulates the regrowth of dense, unattractive, upright branches (water sprouts) just below the pruning cut. Water sprout regrowth is vigorous. A topped tree will rapidly return to its original height, but will lack its original form.
The branch wounds left from topping are slow to close, therefore more vulnerable to insect attacks and fungal decay. An invasion by either pest can spread into the trunk, killing the tree. Weakened stubs are more prone to wind and storm breakage because they generally begin to die back or decay.
Increased sun exposure on trunk and branches can lead to severe bark damage. Ugly branch stubs, conspicuous pruning cuts, and a broom-like branch growth replace natural beauty and form.
Topping reduces the real estate value of trees by 20 to 100 percent. A correctly trimmed tree increases in value at each pruning. If tree workers suggest topping, I would hire somebody else. I recommend using ISA Certified Arborists whenever possible to assure that your tree workers have received the proper training and passed an exam on the topics most critical to good tree care.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to firstname.lastname@example.org