Branching out
Dave Meadows
Pioneer colominst

Topping is perhaps the most harmful tree pruning practice known. Yet, despite more than 25 years of literature and seminars explaining its harmful effects, topping remains a common practice.

Topping is considered an inappropriate pruning technique as it involves cutting back a tree’s height and/or spread to a predetermined limit without regard to the growth habit or structure. i.e., cutting branches back to stubs or lateral branches not large enough to sustain the remaining branch.

This type of pruning is often used to reduce the size of a tree, usually by homeowners who feel the tree is too large for their property, or the tree’s height and spread poses an unacceptable risk. Topping destroys the natural shape and appearance of a tree. The resulting disfigurement contributes to the loss of landscape appeal and value!

Leaving a large stub maintains an open pathway to decay. By cutting between branches or (internodes), dormant buds are activated, forcing the rapid growth of multiple shoots or waterspouts below each cut. Topping can easily remove 50 to 100 percent of tree’s leaf bearing crown. This situation results in an unbalanced root to crown ratio, disrupting the supply of carbohydrate production and storage. A lack of photosynthetic potential coupled with the rapid depletion of stored energy, inhibits the tree from producing necessary defence mechanisms such as auxins and hormones. Serious tree stress, decline and possibly death can result. 

In response to topping, new vigorous waterspouts or suckers grow rapidly and are weakly attached to the remaining stub. Shoot growth can be as much as 20 feet in one season as the tree tries to recover from the lost branches. These epicormic shoots are now prone to failure, and the risk of branch failure is increased! Excess leaf loss can result in remaining limbs being exposed to heat and sunlight. The result may be sunburn of the tissues beneath the bark, which can lead to cankers, bark splitting, and the death of remaining structural branches. 

So, what alternatives to topping are available? The \American National Standard Institute (ANSI) and the Tree Care Industry Association (TCIA) recognized the need for a standardized, scientific approach that green industry associations, government agencies and tree care companies could agree upon. The A300, industry-developed, national standards of practice for tree care operations, came into effect in 1991.  The A300 currently has ten parts. Part 1 describes pruning operations and Crown Reduction covers reducing a tree’s height and/or spread. 

Briefly described, a Crown Reduction states that larger limbs should be cut back to the main trunk, and limbs to be shortened are pruned back to a lateral branch that is large enough – at least one-third the diameter of the limb being removed – to assume the terminal leader role. This method of branch reduction helps to preserve the natural form of the tree. 

If larger cuts are involved, the tree may not be able to close over and compartmentalize the wounds. Sometimes, the best solution is to remove the tree and replace it with a more appropriate species for the site. 

Dave Meadows has been an ISA, Certified Arborist since 1996. Dave owned and operated Invermere Tree Care until his retirement this year. Dave also works part time for the District of Invermere, Public Works, helping with municipal tree care operations, and planting new trees for the Urban Forest.