It is unlawful as a normal practice for any person or City department to top any street tree on public property. “Topping” is defined as the severe cutting back of limbs to stubs within the tree’s crown to such a degree so as to remove the normal canopy and disfigure the tree. Trees severely damaged by storms, diseases, or other causes, or certain trees under utility wires or other obstructions where other pruning practices are impractical may be exempted from this chapter at the determination of the City.