Topping significantly depletes the resources of a tree, while creating a very dangerous situation. As new branches grow out of the topped stubs, the exposed wood begins to rot. When the new branches become larger, you will find them attached to a rotten or hollow base. There is not enough strength to hold up the large branches and they will crash down in a few years. For more information on topping, visit the Trees Are Good web site.
Lion’s tailing refers to a practice where all interior branches are removed leaving the outer-most ends with a large “tuft” of leaves and small branches (picture the tail of a lion…). While this does not look as bad as topping, it does look much worse than a well-maintained tree. Lion’s tailing also creates a hazardous condition. All of the weight is concentrated on the ends of the branches. The majority of the new growth will also be added to these bushy ends. A tree’s branching structure is designed to support evenly distributed weight. When a tree has been lion’s tailed, much more stress is placed on the branch, making breakage more likely.

This tree has been lion’s tail-pruned. Too much weight on the ends of the branches will likely lead to breaking.
An arborist with a strong understanding of tree biology and mechanics will be able to offer pruning practices that will improve the long-term health of your trees and accomplish your goals for pruning.