The tree in your back yard is starting to become tall. It’s overhanging your house and every time there is a storm you begin to worry. You may think that the solution to drastically cut the tree to a shorter height, however, by doing so you may actually be creating a far bigger hazard.
“Topping” refers to the aggressive and indiscriminate removal of live crown which is typically associated with height reduction. The resulting improper cuts are referred to as ‘stubs’ and are often cut back to bare wood or areas with no viable supporting lateral branches. Topping is an unacceptable arboricultural practise that destroys the crown form and severely jeopardizes tree health and structure.
What happens when a tree is topped?
•Deplete food making ability
•Promotes rapid spread of decay
•Vulnerable to insect attack and spread of disease
•Weakens structure and creates a hazard
•Produces weakly attached water shoots
•Expensive and costly maintenance
•Devalues property and looks ugly
Every leaf on a tree is a food factory that captures light energy from the sun to produce sugars and starches. When a tree is topped the live crown is removed which essentially removes the majority of the leaves. The lack of foliage can starve the tree creating a domino effect of tree decline and tree stress.
When a tree cannot produce enough food it cannot defend itself from fungal and insects attacks. Cut wounds resulting in stubs create decay pockets which can quickly spread into columns of decay. Decay in trees will weaken the structural integrity of the tree whether is at a branch or along the trunk. Without a means to defend itself the tree will also attract insects such as wood borers which can further compromise the structure.
The removal of the shaded canopy will suddenly expose bare trunks and branches to more intense light and heat. Just how people can have a sun burn, trees can have a similar condition referred as sunscald. The burn on branches can destroy tissues under the bark causing canker lesions, bark splits/cracks, and even limb death.
Depending on the tree species, when the tree is starved of food or is stressed, it can trigger a growth response to produce water shoots (a.k.a. suckers). The purpose of these shoots is too over compensate for the lack of food which produces an over-abundance of these shoots all growing at the site of the stub cut. Water shoots are emergency regrowth that are weakly attached to the tree and can grow considerably faster than a normal healthy branch. If the initial objective for home owner was to shorten the height, the effect of topping can in fact over stimulate the production of water shoots resulting a much taller tree over a shorter time span versus leaving the original tree untopped. Topping is not only a waste of money but it is also expensive to do and expensive to maintain as upkeep is more frequent with a faster growing tree.
Many municipalities, including the City of Toronto, prohibit the topping of trees within their Private Tree Protection by-laws. Contravention of these by-laws can result in large fines.
What are the alternatives?
Reduction cuts (aka “drop crotch pruning” and end weight reduction)
If managing for tree height and lateral spread is necessary especially for structural and wire clearances, limbs can be shortened by cutting back to viable live lateral. Reduction cuts can be made from vertical and horizontal stems. A qualified arborist will be able to determine the most appropriate point to shorten a limb without creating new structural hazards in the tree unlike topping.
Proper species selection
Be mindful of planting trees too close to building structures and overhead wires. Trees inevitably grow tall, even so-called dwarf varieties can grow much larger than expected. Planting the proper species in a suitable location will greatly reduce the need to for aggressive pruning.
Hire a reputable qualified arborist
Always consult a professional arborist prior to having any pruning work done and be wary of companies that list “topping” as part of their services.