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.
Cuts
Pruning cuts should, wherever possible, be made at a fork or at
the main stem to avoid stumps, which can die back, and dense
regrowth of shoots. Removal of large branches should only be
carried out when it is unavoidable and wounds from such work should
be kept as small as possible.
Cuts into live wood should be avoided when removing dead
branches and stubs. When a branch collar is present the final cut (
figure 1) 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 so as to avoid splitting of the tissues and irreparable
damage to the tree. 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.
Formative Pruning
Formative pruning should aim to produce a tree which in maturity
will be free from major physical weaknesses. Unwanted secondary
leading shoots and potentially weak forks which could fail in
adverse weather conditions, e.g. strong wind or snow, should be
removed.
Note: Failure to remove such shoots may necessitate premature
felling to safeguard people and property.
When growth within a tree crown results in crossing branches
that may rub together causing loss of strength or possible fracture
in adverse weather, 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.
Crown reduction and /or reshaping
Note: Some trees can be reduced in height and /or spread while
preserving a natural tree shape (see figure 2) 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 (see figure 1)
of the retained branch.
Very substantial crown reductions should, ideally not be made
during a single growing season since severe loss of leaf area and
multiple wounding may impair a tree’s defences against diseases and
decay.
Reshaping should be a ‘once only’ operation to make a tree safe
or to bring it to a desirable condition or shape.
With a few species it may be appropriate to reshape a crown by
careful pruning. This technique has a place in urban area
management programmes for existing mature trees which have
previously been pollarded.
Regular crown reduction may be harmful and may make a tree
unsafe, in the same way that regular pollarding can render a tree
unsafe. It is worth considering the removal and replacement of such
a tree with a more appropriate species.
Crown Lifting
Crown lifting, which involves the removal of the lower branches
to a given height above ground level (see figure 3) 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.
Crown Thinning
Crown thinning, which involves the removal of a 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 should usually be confined to broadleaf
species. Crossing, weak, duplicated, dead and damaged branches
should be removed.
The percentage of crown to be removed should be stated, but the
leaf area removed should not normally exceed 30% of the original
coverage.
Note: Crown thinning can stimulate many tree species into
producing epicormic shoots and a dense crown will frequently form
again.
Pollarding
Note: Topping and lopping are Synonyms for pollarding.
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.
Note: Very heavy pruning may kill some species (e.g. beech)
while others will be stimulated to produce a proliferation of very
dense regrowth of shoots from around each wound. Such shoots grow
vigorously and have weak attachments to the tree making trees
potentially dangerous unless recutting is done frequently. This
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 all growing species.
(British Standards Institution (1989), 'British
Standard Recommendations for Tree Work' ).
