The raising of a trees crown(the main area of foliage & branch mass by removing the lower branches is applied to many different situations. But in most cases it is to create space below the tree whether it is to gain access pedestrian(2.5m) or vehicle(5.2m). Another reason would be to allow light to pass through either on to the ground of into a nearby building. A crown lift can also be used for visual reasons it might improve a view or just the way the tree looks.
The lowering of a trees crown(the main area of foliage & branch mass) by removing the upper branches again is applied to many different situations e.g. to control the height of a tree where if left to its own the tree would become in contact with power lines, block sunlight from solar panels. Lowering of the crown may also be used to improve the aesthetics of a tree.
This process involves the removal of living branches from within the crown were possible leaving the shape of the tree in its original shape.
Pollarding is a method of pruning were the branches are cut back to a selected point and on a regular basis(1 to 2 years)the regrowth is removed. This can create dense fast growing foliage.
Felling or Removal
This process involves the total removal of the tree (excluding the stump). There various methods to achieve the removal of trees dependent on your situation Bark and Branch will use the best method suited to the tree in question.