Why can't my tree be topped?

Topping is considered unprofessional work. In fact, standards for tree care published by the American National Standards Institute (ANSI), specifically prohibit topping. Topping promotes decay and produces rapid growth of "watersprouts" (limbs that are weakly attached). It decreases the tree's ability to produce energy (photosynthesis) due to leaf reduction, weakening its vigor and starving the tree.