Reasons for pruning
The first consideration when pruning a protected tree, is whether cutting off and removing living branches will actually benefit the tree. It is important that the arborist undertaking the pruning has an understanding of the biology of trees, how they respond to pruning wounds, and an appreciation of the effects of the reduction in stored energy reserves and photosynthetic ability that pruning of the tree canopy will entail.
Care should be taken to avoid excessive pruning. At least one half of the foliage distribution in younger trees should be on branches that arise in the lower two-thirds of the trunk. In general, pruning should employ thinning cuts. Care should be taken not to expose the inner canopy, (shade leaves) to intense sunlight by over-thinning or excessive cleaning out of the entire inner canopy (lions-tailing).
Pruning techniques
All pruning work should employ natural target pruning in accordance with the principles of Modern Arboriculture. Pruning should endeavour to maintain the natural form, structure and visual appearance of the tree using work procedures defined in the Code of Practice for Safety and Health in Treework Part I: Arboriculture.
Pruning should be in accordance with currently accepted arboricultural practices, specifically the target pruning techniques promoted by the International Society of Arboriculture and the New Zealand Arboricultural Association as the industry standard. Contractors unfamiliar with these pruning standards should not be employed to prune protected trees.
Natural target pruning
Pruning cuts should be at branch unions or branch nodal junctions [arrows].
Do not make inter-nodal cuts or “top” trees. To avoid splitting or tearing, branches should be pre-cut or undercut.
The remaining stub is then removed with a final cut made as close as possible without cutting into the branch collar.
Branch bark ridge pruning
If living branches do not have a definite collar, the branch bark ridge can be used as a guide for the final cut.
Line A-X is a line parallel to the stem or trunk occurring just outside the branch bark ridge.
Line A-C opposite indicates the angle of the branch bark ridge and line A-B represents the angle and location of the final cut. Angle 'a' should be equal to angle 'b'.
Proper pruning technique
Pruning of protected trees should always be carried out by an insured professional arborist with the appropriate qualifications and experience, and be in accordance with International and New Zealand Arboricultural Association Amenity Tree Pruning Standards.
Tree topping - Why trees shouldn’t be topped
Topping is the senseless practice of indiscriminate inter-nodal branch and stem truncation, removing the majority of a tree's canopy. Topping violates most commonly accepted methods of proper pruning and is an assault on the health and beauty of your trees.
Important facts to remember about tree topping and indiscriminate pruning practices:
- Topping will not make trees safe; it actually creates hazardous trees, promotes decay in trees, drastically reducing their health, structural stability, and lifespan.
- Topping makes a tree more susceptible to storm damage and can lead to weak re-growth that is poorly attached to a decaying limb and highly susceptible to breakage.
- Topping makes a tree more prone to insect and disease problems.
- Topped trees rapidly try to replace lost foliage and are subject to enormous stress, often exhausting energy reserves in an attempt to balance the proportion of (what once was) canopy to root system.
- Arboricultural standards consider topping an unacceptable pruning practice because it destroys the structural integrity of the tree. This creates hazards that can lead to tree or branch failure.
- Healthy, properly pruned trees can add 10 to 20% to the value of your property. Topped trees are considered a liability and impending expense, reducing the value of your property.
