It is widely recognised that trees, including shrubs and hedges, need to be maintained to achieve a satisfactory juxtaposition between the natural and the built environment.
Reasons for Pruning
No pruning should be undertaken without a good reason and without a sound understanding of proper pruning techniques.
Good reasons for pruning include:
Safety: The removal of dead, dying, diseased or otherwise defective parts of trees in order to avoid the likelihood of harm or injury occurring.
Security: To improve sight lines, clear lamp columns and road signage.
Statute: The Highways Act 1980, for example, requires that tree owners maintain certain minimum clearances over footpaths and roads.
Fruit Production: Pruning can enhance both the quality and the quality of fruit produced.
Aesthetics: The judicious removal of selected branches can enhance the overall appearance of a tree.
Property Maintenance: Trees have the potential to cause both direct and indirect damage to property.
Grounds Maintenance: The removal of low branches can facilitate grounds maintenance.
When to Prune and When not to Prune
A tree utilizes two types of energy, namely; ‘potential’ and ‘kinetic’. In order for a tree to remain healthy the balance of energy must be in favour of ‘potential or stored’ energy.
There are seven stages in the annual cycle of a tree, as indicated below. The stages in green are when the potential energy is greater than the kinetic energy; the stages in red are when the kinetic energy is greater than the potential energy.
Pruning therefore should be carried out during the stages shown in green and not during the stages shown in red, namely bud burst and leaf fall.
1. Onset of growth
2. Bud burst
3. Production and expansion of leaves
4. High photosynthetic period
5. Storage of carbohydrates and production of wood
6. Leaf fall
The following pruning operations are often used to maintain mature trees in a safe, healthy and aesthetically pleasing manner.
Crown Cleaning: This involves the removal of dead, dying, diseased, crossing and poorly formed or attached branches.
Crown Lifting: The removal of lower branches, in order to achieve a clearance above ground level, usually for pedestrian or vehicular access. It is defined in terms of height.
Crown Reduction: This reduces the overall size of the tree but importantly maintains the shape and form. Primary branches are pruned back to lateral branches that are able to assume the terminal role.
Crown Thinning: The removal of selected branches to increase light penetration and the movement of air through the crown of the tree. It leaves the overall shape of the tree unchanged and is defined in terms of a percentage (normally around 10%).
When it is necessary or appropriate to either remove or shorten a limb, proper pruning techniques should be employed.
- To remove a limb: Please see ‘Natural Target Pruning – How and Where to Remove a Branch’.
- To shorten a limb: The ‘how’ is the same as above. The ‘where’ follows the ‘one third rule’. That is, the branch should be reduced in length to a lateral limb that is at least one third of the diameter of the limb removed.