Thinning:
This involves the reduction
in the density of the crown. This operation would not normally be
carried out on conifers, so it is generally
confined to deciduous broadleaf trees.
Trees may be crown thinned to reduce damage that could result from crown
resistance to strong winds. Crown thinning may be carried out to admit
more air and light into, and through the canopy.

Before Thinning After Thinning
Cleaning Out:
This includes the removal of dead, diseased,
damaged, weak and crossing branches. Cleaning out also entails the
removal of foreign objects and climbing plants, such as Ivy.
Dead Wooding:
This involves the removal of dead wood from the tree
and is normally carried out for safety reasons.