Tree Pruning

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An arborist can determine the type of pruning necessary to maintain or improve the health, appearance and safety of trees.  These techniques include:

• Eliminating branches that rub against each other
• Removing limbs that interfere with wires, building facades, gutters, roofs, chimneys, windows, or that obstruct streets or sidewalks
• Removing dead or weak limbs that pose a hazard or may lead to decay
• Removing diseased or insect-infested limbs
• Creating better structure to lessen wind resistance and reduce the potential for storm damage
• Training young trees
• Removing limbs damaged by adverse weather conditions
• Removing branches, or thinning, to increase light penetration
• Improving the shape or silhouette of the tree

Four basic pruning techniques are used to maintain trees

Depending on tree requirements, client expectations and budget, one or more of the techniques will be used to maintain the plant. Crown thinning is the removal of live, healthy branches on trees with dense crowns. This improves light penetration and air movement, and decreases wind resistance, thus reducing pest infestations and decreasing the risk of storm damage. Crown thinning can also be used to reduce weight of individual limbs and to slow the growth rate on overly vigorous limbs. This pruning technique is most commonly needed on young, rapidly growing trees. On slower growing mature trees, thinning is mainly used when weight reduction is needed on individual limbs to compensate for structural defects. Usually, thinning is performed in conjunction with crown cleaning. Virtually all-urban trees benefit from periodic crown cleaning. This is the removal of defective limbs including those that are dead, dying, diseased, rubbing, and structurally unsound. Cleaning reduces the risk of branch failures, improves plant health and enhances tree appearance by removing limbs that are unsightly, unhealthy and unsound. Although removal of healthy branches is technically “thinning”, selective removal of watersprouts is included in the cleaning specification. Before selecting this option, arborists must judge whether sprout removal will benefit the tree. Stripping sprouts is rarely beneficial and may eventually create many more problems for the tree. The Standard also states that one-half of the foliage should be evenly distributed in the lower two-thirds of the crown and individual limbs. Crown cleaning Unnecessary sprout removal and removal of all lower branches would certainly violate this rule. The concept of not removing sprouts must be clearly conveyed to consumers since many homeowners equate proper pruning with removal of interior limbs. There are a few exceptions where removal of watersprouts is beneficial. Removing sprouts on dogwoods in areas where Discula anthracnose is present is recommended to reduce risk of cankers in larger branches, for example. Leaving interior and lower branches on a tree is equally important when thinning the crown. In order not to violate the one-half the foliage on the lower two-thirds rule, the majority of thinning cuts are on the outer portion of the crown, not the inside. This means working with pole tools or from an aerial lift. After large deadwood and structural problems have been corrected using a chainsaw, hand or pneumatic tools are used for thinning. Crown reduction is needed on trees or individual limbs that are growing close to buildings, other trees, or utility wires. Reduction may also be necessary to prevent or correct storm damage and to shorten errant branches to provide a more desirable shape. This type of pruning involves reducing the height or spread of the crown or individual limbs. Certain species such as beech and sugar maple respond poorly to reductions so consideration must be given to the ability of the species to tolerate this procedure. When reducing a leader or branch cut back to a lateral branch that is large enough to assume dominance. The size of the remaining lateral is not specified in the Standard since it varies with tree species and tree condition. Typically, a lateral one third the diameter of the parent limb is selected. If the lateral is smaller, the limb will either dieback or sprout profusely. If the lateral is considerably larger than the one-third guideline, then thinning the remaining lateral should be considered due to the risk of storm damage. The remaining lateral should be growing in a direction that will maintain a desirable shape and not interfere with objects within the pruning cycle. When lower limbs interfere with mowing, traffic, people or utilities, pruning is needed to provide clearance. While removal of lower limbs goes under many names, the one that has been selected is crown raising. Limbs can either be removed at Crowing raising the trunk or downward growing branches can be removed at the parent limb. Thinning the ends of a heavy limb may accomplish the same goal if the limb raises when weight is removed. When raising is performed, limb levels generally are left at a uniform height around the tree to provide symmetry. These are the four primary types of maintenance pruning - thinning, cleaning, reduction and raising. Other pruning techniques and systems are discussed in the Standard, including crown restoration, vista pruning, young tree pruning, espalier, pollarding and palm pruning. These techniques are generally performed to achieve specific goals that are separate from maintenance considerations or are oriented to a specific type of tree. Consult the Standard for descriptions of these pruning types. The majority of established trees can benefit from one or more maintenance pruning types. How can you prune a tree in more than one way? Easy! If a tree is Before pruning growing next to a house and has deadwood and limbs rubbing against the roof, it needs crown cleaning throughout and reduction or raising of the limbs over the residence. You may use any of the techniques, or combination of techniques, to provide exactly what the tree needs and the customer wants. Choosing the correct pruning technique(s) is relatively easy, even for an inexperienced arborist,  because the tree guides the decision making process. If the tree has deadwood - clean it; if overly thick - thin it; if to tall - reduce it; if too low - raise it. Once the technique(s) have been decided, and then the size of the smallest limb to prune is the next consideration. Typically, the sizes that have been used are 1/2”, 1”, 2” or 4”. However, no numbers are specified in the Standard so you can select any size that meets the needs of the specific tree and customer objectives. If 1” minimum is selected, then limbs 1” in diameter at the point of attachment and larger would be removed when the branches meet the requirements of the technique. The size of the smallest limb to be pruned should be adjusted for the tree and the client
s budget. When crown cleaning a small tree such as a Japanese maple, the smallest branch to remove might be specified at 1/2 inch in diameter. This means that dead, dying, diseased or weak branches greater than 1/2 inch are removed. If 1/4” diameter is chosen instead, the time required to complete the task is easily doubled or tripled. Arborists and consumers must realize that more is not always better when it comes to pruning. The amount of foliage that should be pruned from mature trees is now less than before. The Standard specifies that not more than one quarter of the leaf surface be removed during a single pruning operation. This will benefit the tree by maintaining a greater leaf surface area for producing photosynthates (energy). When work is sold, whether to a municipality, commercial account or residential client, the pruning technique and minimum branch size must be specified, explained and discussed. This will foster fair competition and help ensure that both client and arborist understand what is to be accomplished by pruning. There should be no surprises for the client when purchasing tree work. To ensure this, tree workers as well as the arborist must understand the Standard. If a client selects crown cleaning but budget constraints require pruning 2” and larger limbs, then the crew cannot take the time to remove 1/2-inch limbs. In summary, the new Standard encourages arborists to prune trees based on the tree
s need. This is a significant improvement from the days when we tried to “fit” the tree to a predetermined, artificial classification. Basing pruning on the tree
s needs make the principles described hold true for hardwoods and conifers, small ornamentals and large shade trees, young trees and mature trees. The terminology in the Standard is a change for most arborists, but it is user friendly and descriptive. Industry professionals as well as consumers should readily adopt the terminology.