Topping is the removal of main tree branches to stubs in either a straight across hedge type fashion or a complete de-limbing of the tree leaving only the main trunk of the tree. Topping or heading is generally intended to reduce the size of the tree. Some of the reasons trees are topped include the theory that the trees will grow better, growth of foliage into utility lines, interference with solar collectors or blocking a scenic view.
You can always tell after a tree has been topped. The tree looks like an ugly stub, a hat rack some would say, and just a remnant of a once lovely tree.
The over pruning is then followed by a rapid growth of tree limb sprouts, if the tree re-sprouts at all. This will eventually lead to a tree that is bushier and just as tall as when it was topped. However, unlike the original tree prior to topping, the new growth of the topped tree is dangerous because the new branches are not attached as strongly to the tree as were the original limbs and branches. You will end up with a tree more susceptible to disease and insect problems. It is important to understand that every tree variety has within its genes, growth instructions, a fixed plan for tree height and crown spread. All trees will attempt to grow to their mature form pattern. When trees are topped, they will attempt to regain their natural form pattern of height and crown spread.