Pruning trees when young (formative pruning) may reduce the need for major pruning in middle age and in maturity.
The need to prune middle aged and mature trees is frequently determined by their position in the landscape. There are occasions when changing land use (e.g. building or highway development) may make extensive pruning necessary.
It is worth considering the removal of trees that need frequent major pruning and their replacement with a more appropriate species.
Pruning cuts should, wherever possible, be made at a fork or at the main stem to avoid stubs, which can die back, or stimulate the dense re-growth of shoots. Removal of large branches should only be carried out when it is unavoidable, and wounds from such work kept as small as possible, i.e. cutting perpendicular to the line of the branch. Refer to CODIT.
Cuts into live wood should be avoided when removing dead branches and stubs. When a branch collar is present the final cut should be just outside it. When there is no collar the angle of cut should be the mirror image of the branch bark ridge.
Pruning with either a handsaw or a chainsaw should be done in stages as to avoid splitting of the tissues and irreparable damage to the tree.
NOTE The construction of a chainsaw may make accurate positioning of the cut difficult, especially on small diameter branches, and the use of a handsaw is frequently preferable. This is for both the quality and accuracy of the finished cut and the reduced hazard exposure to the arborist.
Formative pruning should aim to produce a tree which, in maturity, will be free from major physical weakness. Unwanted secondary leading shoots and potential weak forks, which could fail in adverse weather conditions, e.g. strong wind or snow, should be removed.
When growth within a tree crown results in crossing branches that may rub together causing loss of strength or possible fracture in adverse weather, at least one of the branches should be removed.
Removal of heavy branches
Heavy branches should be removed in sections, and when necessary should be lowered with ropes to avoid damage to the tree or its surroundings.
Removing Trees in confined spaces
Trees that are to be removed in confined spaces, or near to other trees or shrubs which are to be retained, should be dismantled in sections by a team using ropes, a crane or a hydraulic platform.
Tree Crown reduction and/or reshaping
Some trees can be reduced in height and/or spread while preserving a natural tree shape by crown reduction and/or reshaping.
Crown reduction and/or reshaping should be carried out by cutting back to a side bud or branch to retain a flowing branch line without leaving stumps. All cuts should be made just outside the line of the branch bark ridge and branch collar of the retained branch. Refer to CODIT and the revised BS3998.
Crown lifting or crown raising
Crown lifting, which involves the removal of lower branches to a given height above ground level should be achieved either by the removal of whole branches, or by the removal of only those parts which extend below the desired clear height. Statutory clearances are 5.2m above a road and 2.5 above a footpath. Generally 6m and 3m are good guidance figures.
Crown thinning involves the removal of a specified proportion of secondary and small, live branch growth from throughout the crown to produce an even density of foliage around a well spaced and balanced branch structure. Crossing, weak, duplicated, dead and damaged branches should be removed.
Pollarding, which in some circumstances has been a traditional form of management, should not be used on trees that have not previously been pollarded, as the large wounds created initiate serious decay in mature and maturing trees.
Very heavy pruning may kill some species (e.g. beech) while others will be stimulated to produce a proliferation of very dense re-growth of shoots from around each wound. Such shoots grow vigorously and have weak attachments to the tree making trees potentially dangerous unless re-cutting is done frequently. The risk is smaller for very young trees but it is better to plant an appropriate species for the site rather than to restrict the size of an unsuitably wide spreading or tall growing species.
NOTE: Topping and lopping are sometimes used as synonyms for pollarding.