Crown thinning does not affect the shape or size of the tree but decreases the density of the foliage. The foliage should be retain evenly throughout the tree whilst being well-shaped and obtaining a balanced branch structure. The percentage of branches removed from the tree should be kept to the minimum requirement to achieve the objective, and in any case should not exceed 30%. Branches should be removed throughout the entire tree, not just the inner canopy, and cutting branches back to the main trunk should be avoided, although structurally weak or hazardous branches should be removed if there is no alternative.
This process is carried out to allow more light to penetrate the canopy of the tree, allowing more light to surrounding plants/trees. It also allows the wind to penetrate through the canopy, making the stem and remaining branches stronger because of the reaction growth being put on to counter-act the increase of wind.