Crown thinning is the removal of a portion of internal secondary branches or young shoots within a trees canopy, this procedure will not alter the size of the tree and is generally performed on broad leafed species of trees. An Arborist will climb through the canopy of a tree (shown below a Birch tree)
Systematically removing an even amount of internal foliage throughout the tree. Common reasons why crown thinning should be considered can include allowing more light to pass through the tree, reduce windsale or possibly to reduce weight. This method of pruning is considered less harmful and stressful to a tree as opposed to crown reduction and should always be considered first.