Tree pruning or reductions is needed when a tree becomes too big for its desired space.
A crown reduction is where an overall pruning of the tree is undertaken. All branches will be cut evenly to give the tree a round natural looking shape. Some trees will be reduced by percentage or some trees will be reduced in metres.
A crown thin is another form of pruning, this will not reduce the height or the spread of the tree it will simply reduce the amount of foliage usually around the outer crown.
A crown lift or raising is were the lowest branches are removed from the tree. Epicormic growth or basel growth are both types of growth that are at the base of a tree, this type of pruning is measured in meters. Larger branches should not be removed as a lift/raising.