2 main types of tree pruning
Crown cleaning is the removal of dead, dying, diseased, crowded, rubbing, and structurally unsound branches. It will reduce the risk of branch failure, improve plant health, and enhance the appearance of trees and shrubs. A high level of skill is required for crown cleaning, yet the cost for this very sound type of pruning is comparable to that for harmful methods of pruning (topping!)
Crown thinning includes the selective removal of branches to ensure light and air penetration. Thinning reduces weight on heavy limbs and helps return the tree to its natural shape. This method requires the highest skill and may initially cost more than less effective pruning techniques, but properly thinned trees require less frequent pruning and are much more resistant to storm damage.