Crown-thinning
With this type of pruning, dead or dying branches are removed from the crown in order to allow better air movement and light penetration to the tree.

Crown-raising
This type of pruning is performed to provide clearance.  Most municipalities have bylaws specifying minimum branch height beside roads and sidewalks. The lower branches are removed effectively raising the crown of the tree.

Crown-reduction  
When a tree has outgrown the available space, crown-reduction pruning is often necessary.  Upper limbs are pruned to either reduce the height or width of the crown.

Proper Pruning Techniques