An unsatisfactory approach to tree maintenance or pruning is “topping” it. Topping is the indiscriminant removal of branches of a tree above an arbitrary height, leaving unnatural, grotesque stubs and misshapen tree forms. In addition, increased risk tree conditions are introduced with development of decay, weak branch attachments and poor health.
Large evergreen trees do not respond well to topping. The removal of the upper main stem through topping opens the tree to internal decay, disease, or damaging insects; it also removes the most productive portion of the tree. The practice of topping to control tree size or growth is not justified. If the tree is too large to fit the space, it should be removed and replaced with a smaller, more suitable species for its growing space.
Be aware that unprofessional tree service crews use this approach because it takes little skill and is easiest for them to perform. Do not let yourself be persuaded that topping serves your best interest; both you and your tree will suffer from such mistreatment.
The topmost part of an evergreen whose shape is pyramidal, such as a spruce tree has a growing point known as the apical meristem. In evergreen trees, the apical meristem contains a hormone that suppresses lateral growth, helping it to keep its excurrent or pyramidal form. The further away from the tip (apical meristem), the less affect this hormone has on the lateral growth of the tree's branches. This is why spruce trees have that pyramidal shape and not more rounded or decurrent. By topping evergreen trees, it will destroy the apical dominance of the plant and result in growing more round than tall, with a misshaped top. It will try to re-establish apical dominance as it matures, but it will most likely look very unusual and not like these species should appear, with multiple, competing growing tips. Remember, this is a natural form for many evergreens to help shed the heavy loads from snow fall. Remove the apical meristem (tip) and you reduce the suppression of lateral growth. This affects the shape of the spruce tree and exposing it to potentially splitting the tree down the trunk as well as exposure to the problems associated with topping.
Trees are Good
What's Wrong with Topping Trees?
Lindsey Purcell, Urban Forestry Specialist
Department of Forestry and Natural Resources, Purdue University