Tree Pruning >> |
|
| Pruning Young Trees |
| Proper pruning is essential in developing a tree with a strong structure and desirable form. Trees that receive the appropriate pruning measures while they are young will require little corrective pruning when they mature. |
| |
| Keep these few simple principles in mind before pruning a tree: |
| • Each cut has the potential to change the growth of the tree. Always have a purpose in mind before making a cut. |
| • Proper technique is essential. Poor pruning can cause damage that lasts for the life of the tree. Learn where and how to make the cuts before picking up the pruning shears. |
| • Trees do not heal the way people do. When a tree is wounded, it must grow over and compartmentalize the wound. As a result, the wound is contained within the tree forever. |
| • Small cuts do less damage to the tree than large cuts. For that reason, proper pruning (training) of young trees is critical. Waiting to prune a tree until it is mature can create the need for large cuts that the tree cannot easily close. |
| |
|
| |
| Making the Cut |
 Where you make a pruning cut is critical to a tree’s response in growth and wound closure. Make pruning cuts just outside the branch collar. Because the branch collar contains trunk or parent branch tissues, the tree will be damaged unnecessarily if you remove or damage it. In fact, if the cut is large, the tree may suffer permanent internal decay from an improper pruning cut.
If a permanent branch is to be shortened, cut it back to a lateral branch or bud. Internodal cuts, or cuts made between buds or branches, may lead to stem decay, sprout production, and misdirected growth.
|
| |
|
| |
| Pruning Tools |
| When pruning trees, it is important to have the right tool for the job. |
| |
| For small trees, most of the cuts can be made with hand pruning shears (secateurs). The scissor-type, or bypass blade hand pruners, are preferred over the anvil type as they make cleaner, more accurate cuts. |
| |
| Cuts larger than one-half inch in diameter should be made with lopping shears or a pruning saw. |
| |
| Never use hedge shears to prune a tree. Whatever tool you use, make sure it is kept clean and sharp. |
 |
| |
|
| |
| Establishing a Strong Scaffold Structure |
 A good structure of primary scaffold branches should be established while the tree is young. The scaffold branches provide the framework of the mature tree. Properly trained young trees will develop a strong structure that requires less corrective pruning as they mature.
The goal in training young trees is to establish a strong trunk with sturdy, well-spaced branches. The strength of the branch structure depends on the relative sizes of the branches, the branch angles, and the spacing of the limbs.
Naturally, these factors vary with the growth habit of the tree. Norfolk Island Pine and Liquidambars, for example, have a conical shape with a central leader. Jacarandas and Poinciana’s are often wide-spreading without a central leader. Other trees, such as Weeping Figs, are densely branched.
Good pruning techniques remove structurally weak branches while maintaining the natural form of the tree. |
| |
|
| |
| Trunk Development |
 For most young trees, maintain a single dominant leader growing upward. Do not prune back the tip of this leader. Do not allow secondary branches to outgrow the leader.
Sometimes a tree will develop double leaders known as co-dominant stems. Co-dominant stems may lead to structural weaknesses, so it is best to remove one of the stems while the tree is young.
The lateral branches, growing on the sides, contribute to the development of a sturdy well-tapered trunk. It is important to leave some of these lateral branches in place, even though they may be pruned out later. These branches, known as temporary branches, also help protect the trunk from sun and mechanical injury.
Temporary branches should be kept short enough not to be an obstruction or compete with selected permanent branches. |
| |
|
| |
| Permanent Branch Selection |
 Nursery trees often have low branches that may make the tree appear well-proportioned when young, but low branches are seldom appropriate for large-growing trees in an urban environment.
How a young tree is trained depends on its primary function in the landscape. For example, street trees must be pruned so that they allow at least 4.5m of clearance for traffic. Most landscape trees require only about 2.4m of clearance.
The height of the lowest permanent branch is determined by the tree’s intended function and location in the landscape. Trees that are used to screen an unsightly view or provide a wind break may be allowed to branch low to the ground. Most large-growing trees in the landscape must eventually be pruned to allow head clearance.
The spacing of branches, both vertically and radially, in the tree is very important. Branches selected as permanent scaffold branches must be well-spaced along the trunk. Maintain radial balance with branches growing outward in each direction. Branch spacing is dependant on species and their growth pattern.
Some trees have a tendency to develop branches with narrow angles of attachment and tight crotches. As the tree grows, bark can become enclosed deep within the crotch between the branch and the trunk. Such growth is called included bark. Included bark weakens the attachment of the branch to the trunk and can lead to branch failure when the tree matures. You should prune branches with weak attachments while they are young.
Avoid over thinning the interior of the tree. The leaves of each branch must manufacture enough food to keep that branch alive and growing. In addition, each branch must contribute food to grow and feed the trunk and roots. Removal of too many leaves can “starve” the tree, reduce growth, and make the tree unhealthy. A good rule of thumb is to maintain at least half the foliage on branches arising in the lower two-thirds of the tree. |
| |
|
| |
| Newly Planted Trees |
Pruning of newly planted trees should be limited to corrective pruning. Remove torn or broken branches, and save other pruning measures for the second or third year.
The belief that trees should be pruned when planted to compensate for root loss is misguided. Trees need their leaves and shoot tips to provide food and the substances that stimulate new root production. Unpruned trees establish faster with a stronger root system than trees pruned at the time of planting. |
| |
| Wound Dressings |
| Wound dressings were once thought to accelerate wound closure, protect against insects and diseases, and reduce decay. However, research has shown that dressings do not reduce decay or speed closure and rarely prevent insect or disease infestations. |
| |
| Most experts recommend that wound dressing should not be used. If a dressing must be used for cosmetic purposes, use a thin coating of a material that is not toxic to the plant |
| |
|
| |
Pruning Mature Trees |
| Pruning is the most common tree maintenance procedure. Although forest trees grow quite well with only nature's pruning, landscape trees require a higher level of care to maintain their safety and aesthetics. Pruning should be done with an understanding of how the tree responds to each cut. Improper pruning can cause damage that will last for the life of the tree, or worse, shorten the tree's life. Australia has a standard that is a guide for pruning. AS 4373 2007 is now our current bench mark for good pruning practice. |
| |
| Reasons for Pruning |
| Because each cut has the potential to change the growth of the tree, no branch should be removed without a reason. Common reasons for pruning are to remove dead branches, to remove crowded or rubbing limbs, and to eliminate hazards. Trees may also be pruned to increase light and air penetration to the inside of the tree’s crown or to the landscape below. In most cases, mature trees are pruned as a corrective or preventive measure. |
| |
| Routine thinning does not necessarily improve the health of a tree. Trees produce a dense crown of leaves to manufacture the sugar used as energy for growth and development. Removal of foliage through pruning can reduce growth and stored energy reserves. Heavy pruning can be a significant health stress for the tree. |
| |
| Yet if people and trees are to coexist in an urban or suburban environment, then sometimes we have to modify the trees. City environments do not mimic natural forest conditions. Safety is a major concern. Also, we want trees to complement other landscape plantings and lawns. Proper pruning, with an understanding of tree biology, can maintain good tree health and structure while enhancing the aesthetic and economic values of our landscapes. |
| |
|
| |
| When to Prune |
| Most routine pruning to remove weak, diseased, or dead limbs can be accomplished at any time during the year with little effect on the tree. As a rule, growth is maximized and wound closure is fastest if pruning takes place before the spring growth flush. Some trees, such as Spotted Gums and Blood Woods, tend to “bleed” if pruned early in the spring. It may be unsightly, but it is of little consequence to the tree. |
| |
| A few tree diseases, such as Oak Wilt, can be spread when pruning wounds allow spores access into the tree. Susceptible trees should not be pruned during active transmission periods. |
| |
| Heavy pruning just after the spring growth flush should be avoided. At that time, trees have just expended a great deal of energy to produce foliage and early shoot growth. Removal of a large percentage of foliage at that time can stress the tree. |
| |
|
| |
| Making Proper Pruning Cuts |
 Pruning cuts should be made just outside the branch collar. The branch collar contains trunk or parent branch tissue and should not be damaged or removed.
If the trunk collar has grown out on a dead limb to be removed, make the cut just beyond the collar. Do not cut the collar.
If a large limb is to be removed, its weight should first be reduced
 This is done by making an undercut about 30-45cm from the limb’s point of attachment.
Make a second cut from the top, directly above or a few inches farther out on the limb. Doing so removes the limb, leaving the 30-45cm stub. Remove the stub by cutting back to the branch collar.
This technique reduces the possibility of tearing the bark. |
| |
|
| |
| Pruning Techniques |
| Specific types of pruning may be necessary to maintain a mature tree in a healthy, safe, and attractive condition. |
| |
| Cleaning is the removal of dead, dying, diseased, crowded, weakly attached and low-vigour branches from the crown of a tree. |
| |
| Thinning is the selective removal of branches to increase light penetration and air movement through the crown. Thinning opens the foliage of a tree, reduces weight on heavy limbs, and helps retain the tree’s natural shape. |
| |
| Raising removes the lower branches from a tree in order to provide clearance for buildings, vehicles, pedestrians, and vistas. |
| |
| Reduction reduces the size of a tree, often for clearance for utility lines. Reducing the height or spread of a tree is best accomplished by pruning back the leaders and branch terminals to lateral branches that are large enough to assume the terminal roles (at least one-third the diameter of the cut stem). Compared to topping, reduction helps maintain the form and structural integrity of the tree. The success of reduction pruning is dependant on the species and the form and structure of the individual tree. |
 |
| |
|
| |
| How Much Should Be Pruned? |
| The amount of live tissue that should be removed depends on the tree size, species, and age, as well as the pruning objectives. Younger trees tolerate the removal of a higher percentage of living tissue better than mature trees do. An important principle to remember is that a tree can recover from several small pruning wounds faster than from one large wound. |
| |
| A common mistake is to remove too much inner foliage and small branches. It is important to maintain an even distribution of foliage along large limbs and in the lower portion of the crown. Over thinning reduces the tree’s sugar production capacity and can create tip-heavy limbs that are prone to failure. |
| |
| Mature trees should require little routine pruning. A widely accepted rule of thumb is never to remove more than one-quarter of a tree’s leaf-bearing crown. In a mature tree, pruning even this much could have negative effects. Removing even a single, large-diameter limb can create a wound that the tree may not be able to close. |
| |
| The older and larger a tree becomes, the less energy it has in reserve to close wounds and defend against decay or insect attack. The pruning of large mature trees is usually limited to removal of dead or potentially hazardous limbs. |
| |
| Wound Dressings |
| Wound dressings were once thought to accelerate wound closure, protect against insects and diseases, and reduce decay. However, research has shown that dressings do not reduce decay or speed closure and rarely prevent insect or disease infestations. Most experts recommend that wound dressings should not be used. If a dressing must be used for cosmetic purposes, then only a thin coating of a non-toxic material should be applied. |
| |
