We prune trees for ourselves, not for the health of the tree. The key to tree health is to know that when we prune, a wound is created.  Tree wounds don't heal, but instead the tree compartmentalizes the wound (covers with woundwood).  So always remember, a wound, is a wound, is a wound!  So how do we minimize negative impacts to our trees?  Proper pruning and pruning at a time when all the environmental factors (heat/drought) we can't control are not present. Why and what am I pruning? The illustration below provided by the A&M Texas Forest Service shows some of the reasons to prune.Other reasons may be clearance, such as but not limited to 15 foot vertical clearance over roadways and 8 foot clearance over pedestrian areas.  These heights are set by City Code. Best time to prune?  In Dallas, Texas the  “best time” would be during our winter months as the temperatures are cooler, normally more rainfall and less insect activity.  All of these factors decrease stress on the tree. But this is not always possible….if you have a broken branch that is at risk of causing damage or harm, remove it as soon as possible.  Below is a diagram how you can make the proper cut and give your tree the best chance for the woundwood to cover and compartmentalize the wound. How to prune.  See the location of the branch collar in the illustration below, you cut just beyond. 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. Improper pruning can create lasting damage or even shorten the tree’s life. 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. 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 improve form, and to reduce risk. 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 corrective or preventive measures. 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. There are many outside considerations, however, that make it necessary to prune trees. Safety, clearance, and compatibility with other components of a landscape are all major concerns. 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 and wound closure are maximized if pruning takes place before spring growth. Heavy pruning of live tissue just after the spring growth flush should be avoided, especially on weak trees. 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. A few tree diseases, such as oak wilt, can be spread when pruning wounds provide access to pathogens (disease-causing agents). Susceptible trees should not be pruned during active transmission periods. 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 a large limb is to be removed, its weight should first be reduced to avoid the possibility of tearing the bark. Make an undercut about 12 to 18 inches 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, leaving the 12- to 18-inch stub. Remove the stub by cutting back to the branch collar. Pruning Types Specific types of pruning may help maintain a mature tree in a healthy, safe, and attractive condition. Cleaning is the removal of dead, dying, diseased, weakly attached, and low-vigor branches from the crown of a tree. Thinning is selective branch removal to improve structure and to increase light penetration and air movement through the crown. Proper 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 to provide clearance for buildings, vehicles, pedestrians, and vistas. Reduction reduces the size of a tree, often for utility line clearance. Reducing a tree’s height or spread is best accomplished by pruning back the leaders and branches to secondary branches large enough to assume the terminal roles (at least one-third the diameter of the cut stem). Reduction reduces the size of a tree, often for utility line clearance. Reducing a tree’s height or spread is best accomplished by pruning back the leaders and branches to secondary branches large enough to assume the terminal roles (at least one-third the diameter of the cut stem). Reduction helps maintain the form and structural integrity of the tree, and is a healthy alternative to topping. How Much Should Be Pruned? The amount of live tissue that should be removed depends on the tree’s 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. Generally, no more than 25% of the crown should be removed at once, and less for mature trees. Removing even a single, large-diameter limb can result in significant canopy loss and can create a wound that the tree may not be able to close. Care should be taken to achieve pruning objectives while minimizing live branch loss and wound size. Wound Dressings Research has shown that dressings do not reduce decay or speed wound closure, and rarely prevent insect or disease infestations. Most experts recommend that wound dressings not be used unless you are pruning an oak in an area where oak wilt is present. Hiring an Arborist Pruning large trees can be dangerous. If pruning involves working above the ground or using power equipment, it is best to hire a professional arborist. An arborist can determine the type of pruning necessary to improve the health, appearance, and safety of your trees. A professional arborist can also provide the services of a trained crew with the required safety equipment and liability insurance. The main reasons for pruning ornamental and shade trees include safety, health, and aesthetics. In addition, pruning can be used to stimulate fruit production and increase the value of timber. Pruning for safety involves removing branches that could fall and cause injury or property damage, trimming branches that interfere with lines of sight on streets or driveways, and removing branches that grow into utility lines. Safety pruning can be largely avoided by carefully choosing species that will not grow beyond the space available to them, and have strength and form characteristics that are suited to the site. Pruning for health involves removing diseased or insect-infested wood, thinning the crown to increase airflow and reduce some pest problems, and removing crossing and rubbing branches. Pruning can best be used to encourage trees to develop a strong structure and reduce the likelihood of damage during severe weather. Removing broken or damaged limbs encourage wound closure. Pruning for aesthetics (Fig. 1C) involves enhancing the natural form and character of trees or stimulating flower production. Pruning for form can be especially important on opengrown trees that do very little self-pruning. All woody plants shed branches in response to shading and competition. Branches that do not produce enough carbohydrates from photosynthesis to sustain themselves die and are eventually shed; the resulting wounds are sealed by woundwood (callus). Branches that are poorly attached may be broken off by wind and accumulation of snow and ice. Branches removed by such natural forces often result in large, ragged wounds that rarely seal. Pruning as a cultural practice can be used to supplement or replace these natural processes and increase the strength and longevity of plants. Trees have many forms, but the most common types are pyramidal (excurrent) or spherical (decurrent). Trees with pyramidal crowns, e.g., most conifers, have a strong central stem and lateral branches that are more or less horizontal and do not compete with the central stem for dominance. Trees with spherical crowns, e.g., most hardwoods, have many lateral branches that may compete for dominance. To reduce the need for pruning it is best to consider a tree's natural form. It is very difficult to impose an unnatural form on a tree without a commitment to constant maintenance. Pollarding and topiary are extreme examples of pruning to create a desired, unnatural effect. Pollarding is the practice of pruning trees annually to remove all new growth. The following year, a profusion of new branches is produced at the ends of the branches. Topiary involves pruning trees and shrubs into geometric or animal shapes. Both pollarding and topiary are specialized applications that involve pruning to change the natural form of trees. As topiary demonstrates, given enough care and attention plants can be pruned into nearly any form. Yet just as proper pruning can enhance the form or character of plants, improper pruning can destroy it. Pruning Approaches Producing strong structure should be the emphasis when pruning young trees. As trees mature, the aim of pruning will shift to maintaining tree structure, form, health and appearance. Proper pruning cuts are made at a node, the point at which one branch or twig attaches to another. In the spring of the year growth begins at buds, and twigs grow until a new node is formed. The length of a branch between nodes is called an internode. Crown thinning - branches to be removed are shaded in blue; pruning cuts should be made at the red lines. No more than one-fourth of the living branches should be removed at one time. Figure 3. Types of branch unions. The most common types of pruning are: 1. Crown Thinning  Crown thinning, primarily for hardwoods, is the selective removal of branches to increase light penetration and air movement throughout the crown of a tree. The intent is to maintain or develop a tree's structure and form. To avoid unnecessary stress and prevent excessive production of epicormic sprouts, no more than one-quarter of the living crown should be removed at a time. If it is necessary to remove more, it should be done over successive years. Branches with strong U-shaped angles of attachment should be retained. Branches with narrow, V-shaped angles of attachment often form included bark and should be removed . Included bark forms when two branches grow at sharply acute angles to one another, producing a wedge of inward-rolled bark between them. Included bark prevents strong attachment of branches, often causing a crack at the point below where the branches meet. Codominant stems that are approximately the same size and arise from the same position often form included bark. Removing some of the lateral branches from a codominant stem can reduce its growth enough to allow the other stem to become dominant. Lateral branches should be no more than onehalf to three-quarters of the diameter of the stem at the point of attachment. Avoid producing "lion’s tails," tufts of branches and foliage at the ends of branches, caused by removing all inner lateral branches and foliage. Lion’s tails can result in sunscalding, abundant epicormic sprouts, and weak branch structure and breakage. Branches that rub or cross another branch should be removed. Conifers that have branches in whorls and pyramidal crowns rarely need crown thinning except to restore a dominant leader. Occasionally, the leader of a tree may be damaged and multiple branches may become codominant. Select the strongest leader and remove competing branches to prevent the development of codominant stems. 2. Crown Raising  Crown raising is the practice of removing branches from the bottom of the crown of a tree to provide clearance for pedestrians, vehicles, buildings, lines of site, or to develop a clear stem for timber production. Also, removing lower branches on white pines can prevent blister rust. For street trees the minimum clearance is often specified by municipal ordinance. After pruning, the ratio of the living crown to total tree height should be at least two-thirds (e.g., a 12 m tree should have living branches on at least the upper 8 m). On young trees "temporary" branches may be retained along the stem to encourage taper and protect trees from vandalism and sun scald. Less vigorous shoots should be selected as temporary branches and should be about 10 to 15 cm apart along the stem. They should be pruned annually to slow their growth and should be removed eventually. 3. Crown Reduction Crown reduction pruning is most often used when a tree has grown too large for its permitted space. This method, sometimes called drop crotch pruning, is preferred to topping because it results in a more natural appearance, increases the time before pruning is needed again, and minimizes stress (see drop crotch cuts in the next section). Crown reduction pruning, a method of last resort, often results in large pruning wounds to stems that may lead to decay. This method should never be used on a tree with a pyramidal growth form. A better long term solution is to remove the tree and replace it with a tree that will not grow beyond the available space. Pruning Cuts Pruning cuts should be made so that only branch tissue is removed and stem tissue is not damaged. At the point where the branch attaches to the stem, branch and stem tissues remain separate, but are contiguous. If only branch tissues are cut when pruning, the stem tissues of the tree will probably not become decayed, and the wound will seal more effectively. 1. Pruning living branches. To find the proper place to cut a branch, look for the branch collar that grows from the stem tissue at the underside of the base of the branch. On the upper surface, there is usually a branch bark ridge that runs (more or less) parallel to the branch angle, along the stem of the tree. A proper pruning cut does not damage either the branch bark ridge or the branch collar. A proper cut begins just outside the branch bark ridge and angles down away from the stem of the tree, avoiding injury to the branch collar. Make the cut as close as possible to the stem in the branch axil, but outside the branch bark ridge, so that stem tissue is not injured and the wound can seal in the shortest time possible. If the cut is too far from the stem, leaving a branch stub, the branch tissue usually dies and woundwood forms from the stem tissue. Wound closure is delayed because the woundwood must seal over the stub that was left. The quality of pruning cuts can be evaluated by examining pruning wounds after one growing season. A concentric ring of woundwood will form from proper pruning cuts. Flush cuts made inside the branch bark ridge or branch collar, result in pronounced development of woundwood on the sides of the pruning wounds with very little woundwood forming on the top or bottom. As described above, stub cuts result in the death of the remaining branch and woundwood forms around the base from stem tissues. When pruning small branches with hand pruners, make sure the tools are sharp enough. Crown raising - branches to be removed are shaded in blue; pruning cuts should be made where indicated with red lines. The ratio of live crown to total tree height should be at least two-thirds. Crown reduction - branches to be removed are shaded in blue; pruning cuts should be made where indicated with red lines. To prevent branch dieback, cuts should be made at lateral branches that are at least one-third the diameter of the stem at their union to cut the branches cleanly without tearing. Branches large enough to require saws should be supported with one hand while the cuts are made. If the branch is too large to support, make a three-step pruning cut to prevent bark ripping. 1. The first cut is a shallow notch made on the underside of the branch, outside the branch collar. This cut will prevent a falling branch from tearing the stem tissue as it pulls away from the tree. 2. The second cut should be outside the first cut, all the way through the branch, leaving a short stub. 3. The stub is then cut just outside the branch bark ridge/branch collar, completing the operation. 2. Pruning dead branches Prune dead branches in much the same way as live branches. Making the correct cut is usually easy because the branch collar and the branch bark ridge, can be distinguished from the dead branch, because they continue to grow. Make the pruning cut just outside of the ring of woundwood tissue that has formed, being careful not to cause unnecessary injury. Large dead branches should be supported with one hand or cut with the threestep method, just as live branches. Cutting large living branches with the three step method is more critical because of the greater likelihood of bark ripping. 3. Drop Crotch Cuts A proper cut begins just above the branch bark ridge and extends through the stem parallel to the branch bark ridge. Usually, the stem being removed is too large to be supported with one hand, so the three cut method should be used. 1. With the first cut, make a notch on the side of the stem away from the branch to be retained, well above the branch crotch. Begin the second cut inside the branch crotch, staying well above the branch bark ridge, and cut through the stem above the notch. 3. Cut the remaining stub just inside the branch bark ridge through the stem parallel to the branch bark ridge. To prevent the abundant growth of epicormic sprouts on the stem below the cut, or dieback of the stem to a lower lateral branch, make the cut at a lateral branch that is at least one-third of the diameter of the stem at their union. Pruning Practices That Harm Trees Topping and tipping  are pruning practices that harm trees and should not be used. Crown reduction pruning is the preferred method to reduce the size or height of the crown of a tree, but is rarely needed and should be used infrequently. Topping, the pruning of large upright branches between nodes, is sometimes done to reduce the height of a tree . Tipping is a practice of cutting lateral branches between nodes to reduce crown width. These practices invariably result in the development of epicormic sprouts, or in the death of the cut branch back to the next lateral branch below. These epicormic sprouts are weakly attached to the stem and eventually will be supported by a decaying branch. Improper pruning cuts cause unnecessary injury and bark ripping. Flush cuts injure stem tissues and can result in decay . Stub cuts delay wound closure and can provide entry to canker fungi that kill the cambium, delaying or preventing woundwood formation. When to Prune? Conifers may be pruned any time of year, but pruning during the dormant season may minimize sap and resin flow from cut branches. Hardwood trees and shrubs without showy flowers: prune in the dormant season to easily visualize the structure of the tree, to maximize wound closure in the growing season after pruning, to reduce the chance of transmitting disease, and to discourage excessive sap flow from wounds. Recent wounds and the chemical scents they emit can actually attract insects that spread tree disease. In particular, wounded elm wood is known to attract bark beetles that harbor spores of the Dutch elm disease fungus, and open wounds on oaks are known to attract beetles that spread the oak wilt fungus. Take care to prune these trees during the correct time of year to prevent spread of these fatal diseases. Contact your local tree disease specialist to find out when to prune these tree species in your area. Usually, the best time is during the late fall and winter. Flowering trees and shrubs: these should also be pruned during the dormant season for the same reasons stated above; however, to preserve the current year's flower crop, prune according to the following schedule: ? Trees and shrubs that flower in early spring (redbud, dogwood, etc.) should be pruned immediately after flowering (flower buds arise the year before they flush, and will form on the new growth). ? Many flowering trees are susceptible to fireblight, a bacterial disease that can be spread by pruning. These trees, including many varieties of crabapple, hawthorn, pear, mountain ash, flowering quince and pyracantha, should be pruned during the dormant season. Check with your county extension agent or a horticulturist for additional information. ? Trees and shrubs that flower in the summer or fall always should be pruned during the dormant season (flower buds will form on new twigs during the next growing season, and the flowers will flush normally). Dead branches: can be removed any time of the year. Pruning Tools Proper tools are essential for satisfactory pruning (Fig.6). The choice of which tool to use depends largely on the size of branches to be pruned and the amount of pruning to be done. If possible, test a tool before you buy it to ensure it suits your specific needs. As with most things, higher quality often equates to higher cost. Generally speaking, the smaller a branch is when pruned, the sooner the wound created will seal. Hand pruners are used to prune small branches (under 2.5 cm diameter) and many different kinds are available. Hand pruners can be grouped into by-pass or anvil styles based on the blade configuration. Anvil style pruners have a straight blade that cuts the branch against a small anvil or block as the handles are squeezed. By-pass pruners use a curved cutting blade that slides past a broader lower blade, much like a scissors. To prevent unnecessary tearing or crushing of tissues, it is best to use a by-pass style pruner. Left- or right-handed types can be purchased. Slightly larger branches that cannot be cut with a hand pruner may be cut with small pruning saws (up to 10 cm) or lopping shears (up to 7 cm diameter) with larger cutting surfaces and greater leverage. Lopping shears are also available in by-pass and anvil styles. For branches too large to be cut with a hand pruner or lopping shears, pruning saws must be used. Pruning saws differ greatly in handle styles, the length and shape of the blade, and the layout and type of teeth. Most have tempered metal blades that retain their sharpness for many pruning cuts. Unlike most other saws, pruning saws are often designed to cut on the "pull-stroke." Chain saws are preferred when pruning branches larger than about 10 cm. Chainsaws should be used only by qualified individuals. To avoid the need to cut branches greater than 10 cm diameter, prune when branches are small. Pole pruners must be used to cut branches beyond reach. Generally, pruning heads can cut branches up to 4.4 cm diameter and are available in the by-pass and anvil styles. Once again, the by-pass type is preferred. For cutting larger branches, saw blades can be fastened directly to the pruning head, or a separate saw head can be purchased. Because of the danger of electrocution, pole pruners should not be used near utility lines except by qualified utility line clearance personnel. To ensure that satisfactory cuts are made and to reduce fatigue, keep your pruning tools sharp and in good working condition. Hand pruners, lopping shears, and pole pruners should be periodically sharpened with a sharpening stone. Replacement blades are available for many styles. Pruning saws should be professionally sharpened or periodically replaced. To reduce cost, many styles have replaceable blades. Tools should be clean and sanitized as well as sharp. Although sanitizing tools may be inconvenient and seldom practiced, doing so may prevent the spread of disease from infected to healthy trees on contaminated tools. Tools become contaminated when they come into contact with fungi, bacteria, viruses and other microorganisms that cause disease in trees. Most pathogens need some way of entering the tree to cause disease, and fresh wounds are perfect places for infections to begin. Microorganisms on tool surfaces are easily introduced into susceptible trees when subsequent cuts are made. The need for sanitizing tools can be greatly reduced by pruning during the dormant season. If sanitizing is necessary it should be practiced as follows: Before each branch is cut, sanitize pruning tools with either 70% denatured alcohol, or with liquid household bleach diluted 1 to 9 with water (1 part bleach, 9 parts water). Tools should be immersed in the solution, preferably for 1-2 minutes, and wood particles should be wiped from all cutting surfaces. Bleach is corrosive to metal surfaces, so tools should be thoroughly cleaned with soap and water after each use. Treating wounds: Tree sap, gums, and resins are the natural means by which trees combat invasion by pathogens. Although unsightly, sap flow from pruning wounds is not generally harmful; however, excessive "bleeding" can weaken trees. When oaks or elms are wounded during a critical time of year (usually spring for oaks, or throughout the growing season for elms) -- either from storms, other unforeseen mechanical wounds, or from necessary branch removals -- some type of wound dressing should be applied to the wound. Do this immediately after the wound is created. In most other instances, wound dressings are unnecessary, and may even be detrimental. Wound dressings will not stop decay or cure infectious diseases. They may actually interfere with the protective benefits of tree gums and resins, and prevent wound surfaces from closing as quickly as they might under natural conditions. The only benefit of wound dressings is to prevent introduction of pathogens in the specific cases of Dutch elm disease and oak wilt. Pruning Guidelines To encourage the development of a strong, healthy tree, consider the following guidelines when pruning. General  Prune first for safety, next for health, and finally for aesthetics. ? Never prune trees that are touching or near utility lines; instead consult your local utility company.  Avoid pruning trees when you might increase susceptibility to important pests (e.g. in areas where oak wilt exists, avoid pruning oaks in the spring and early summer; prune trees susceptible to fireblight only during the dormant season).  Use the following decision guide for size of branches to be removed: 1) under 5 cm diameter - go ahead, 2) between 5 and 10 cm diameter - think twice, and 3) greater than 10 cm diameter - have a good reason. Crown Thinning ? Assess how a tree will be pruned from the top down.  Favor branches with strong, U-shaped angles of attachment. Remove branches with weak, V-shaped angles of attachment and/or included bark. Ideally, lateral branches should be evenly spaced on the main stem of young trees.  Remove any branches that rub or cross another branch.  Make sure that lateral branches are no more than one-half to three-quarters of the diameter of the stem to discourage the development of co-dominant stems.

Foreword
1 ANSI A300 Standards – Scope, purpose, and application
2 Part 1 – Pruning Standards
3 Normative References
4 Definitions
5 Pruning Practices_
Figures
5.3.2 A pruning cut that removes a branch
5.3.3 A pruning cut that reduces the length of a branch or stem
5.3.7 A final cut that removes a branch with a narrow angle of attachment_
Annex
A. Reference publications
Forward
(This foreword is not part of American National Standard A300 Part 1-2001.)
An industry-consensus standard must have the input of the industry that it is
intended to affect. The Accredited Standards Committee A300 was approved
June 28, 1991. The committee includes representatives from the residential and
commercial tree care industry, the utility, municipal, and federal sectors, the
landscape and nursery industries, and other interested organizations.
Representatives from varied geographic areas with broad knowledge and
technical expertise contributed.
The A300 standard can be best placed in proper context if one reads its Scope,
Purpose, and Application. This document presents performance standards for
the care and maintenance of trees, shrubs, and other woody plants. It is intended
as a guide in the drafting of maintenance specifications for federal, state,
municipal, and private authorities including property owners, property managers,
and utilities.
The A300 standard stipulates that specifications for tree work should be written
and administered by a professional possessing the technical competence to
provide for, or supervise, the management of woody landscape plants. Users of
this standard must first interpret its wording, then apply their knowledge of growth
habits of certain plant species in a given environment. In this manner, the user
ultimately develops their own specifications for plant maintenance.
ANSI A300 Part 1 – Pruning, should be used in conjunction with the rest of the
A300 standard when writing specifications for tree care operations.
Suggestions for improvement of this standard should be forwarded to: NAA300 Secretary, c/o
National Arborist Association, 3 Perimeter Rd. - Unit 1, Manchester, NH 03103, USA or Email:
naa@natlarb.com.
This standard was processed and approved for submittal to ANSI by Accredited Standards
Committee on Tree, Shrub, and Other Woody Plant Maintenance Operations – Standard
Practices, A300. Committee approval of the standard does not necessarily imply that all
committee members voted for its approval. At the time it approved this standard, the A300
committee had the following members:
Tim Johnson, Chair (Artistic Arborist, Inc.)
Bob Rouse, Secretary (National Arborist Association, Inc.)
Organizations Represented Name of Representative
American Forests Staff (Observer)
American Nursery and Landscape Association Craig J. Regelbrugge
American Society of Consulting Arborists Andrew Graham
Donald Blair (Adviser)
Beth Palys (Adviser)
American Society of Landscape Architects Ron Leighton
Asplundh Tree Expert Company Geoff Kempter
Associated Landscape Contractors of America Preston Leyshon
Jeff Bourne (Alt.)
The Davey Tree Expert Company Joseph Tommasi
Dick Jones (Alt.)
Richard Rathjens (Adviser)
The F.A. Bartlett Tree Expert Company Peter Becker
Dr. Thomas Smiley (Alt.)
International Society of Arboriculture Ed Brennan
Sharon Lilly (Alt.)
National Arborist Association Ronald Rubin
Tom Mugridge (Alt.) National Park Service Robert DeFeo
Professional Grounds Management Society Kevin O’Donnell
Society of Municipal Arborists Andrew Hillman
U.S. Forest Service Ed
Macie_ Mike Galvin (Alt.)
Philip D. Rodbell (Alt.)
Utility Arborist Association Jeffery Smith
Matt Simons (Alt.)
American National Standard for Tree Care Operations –
Tree, Shrub, and Other Woody Plant
Maintenance – Standard Practices
(Pruning)
1 ANSI A300 standards
1.1 Scope
ANSI A300 standards present performance standards for the care and
maintenance of trees, shrubs, and other woody plants.
1.2 Purpose
ANSI A300 standards are intended as guides for federal, state, municipal and
private authorities including property owners, property managers, and utilities in
the drafting of their maintenance specifications.
1.3 Application
ANSI A300 standards shall apply to any person or entity engaged in the
business, trade, or performance of repairing, maintaining, or preserving trees,
shrubs, or other woody plants.
1.4 Implementation
Specifications for tree maintenance should be written and administered by an
arborist.
2 Part 1 – Pruning standards
2.1 Purpose
The purpose of this document is to provide standards for developing
specifications for tree pruning.
2.2 Reasons for pruning
The reasons for tree pruning may include, but are not limited to, reducing risk,
maintaining or improving tree health and structure, improving aesthetics, or
satisfying a specific need. Pruning practices for agricultural, horticultural
production, or silvicultural purposes are exempt from this standard.
2.3 Safety
2.3.1 Tree maintenance shall be performed only by arborists or arborist trainees
who, through related training or on-the-job experience, or both, are familiar with
the practices and hazards of arboriculture and the equipment used in such
operations.
2.3.2 This standard shall not take precedence over arboricultural safe work
practices.
2.3.3 Operations shall comply with applicable Occupational Safety and Health
Administration (OSHA) standards, ANSI Z133.1, as well as state and local
regulations.
3 Normative references
The following standards contain provisions, which, through reference in the text,
constitute provisions of this American National Standard. All standards are
subject to revision, and parties to agreements based on this American National
Standard shall apply the most recent edition of the standards indicated below.
• ANSI Z60.1, Nursery stock
• ANSI Z133.1, Tree care operations - Pruning, trimming, repairing, maintaining,
and removing trees, and cutting brush - Safety requirements
• 29 CFR 1910, General industry 1)
• 29 CFR 1910.268, Telecommunications 1)
• 29 CFR 1910.269, Electric power generation, transmission, and distribution 1)
• 29 CFR 1910.331 - 335, Electrical safety-related work practices 1)
4 Definitions
4.1 anvil-type pruning tool: A pruning tool that
has a sharp straight blade that cuts against a flat metal cutting surface, in
contrast to a hook-and-bladetype pruning tool (4.21).
4.2 apical dominance: Inhibition of growth of lateral buds by the terminal bud.
4.3 arboriculture: The art, science, technology, and business of commercial,
public, and utility tree care.
4.4 arborist: An individual engaged in the profession of arboriculture who,
through experience, education, and related training, possesses the competence
to provide for or supervise the management of trees and other woody plants.
4.5 arborist trainee: An individual undergoing on-the-job training to obtain the
experience and the competence required to provide for or supervise the
management of trees and other woody plants. Such trainees shall be under the
direct supervision of an arborist.
4.6 branch bark ridge: The raised area of bark in the branch crotch that marks
where the branch and parent meet.
4.7 branch collar: The swollen area at the base of a branch.
4.8 callus: Undifferentiated tissue formed by the cambium around a wound.
4.9 cambium: The dividing layer of cells that forms sapwood (xylem) to the
inside and inner bark (phloem) to the outside.
4.10 cleaning: Selective pruning to remove one or more of the following parts:
dead, diseased, and/ or broken branches (5.6.1).
4.11 climbing spurs: Sharp, pointed devices affixed to a climber’s boot used to
assist in climbing trees. (syn.: gaffs, hooks, spurs, spikes, climbers)
4.12 closure: The process of woundwood covering a cut or other tree injury.
4.13 crown: The leaves and branches of a tree measured from the lowest
branch on the trunk to the top of the tree.
4.14 decay: The degradation of woody tissue caused by microorganisms.
4.15 espalier: The combination of pruning, supporting, and training branches to
orient a plant in one plane (5.7.2).
4.16 establishment: The point after planting when a tree’s root system has
grown sufficiently into the surrounding soil to support shoot growth and anchor
the tree.
4.17 facility: A structure or equipment used to deliver or provide protection for
the delivery of an essential service, such as electricity or communications.
4.18 final cut: A cut that completes the removal or reduction of a branch or stub.
4.19 frond: A leaf of a palm.
4.20 heading: 1. Cutting a currently growing, or a 1-year-old shoot, back to a
bud. 2. Cutting an older branch or stem back to a stub in order to meet a defined
structural objective. 3. Cutting an older branch or stem back to a lateral branch
not large enough to assume apical dominance in order to meet a defined
structural objective. Heading may or may not be an acceptable pruning practice,
depending on the application.
4.21 hook-and-blade-type pruning tool: A pruning tool that has a sharp curved
blade that overlaps a supporting hook; in contrast to an anvil-type pruning tool
(4.1). (syn.: by-pass pruner)
4.22 interfering branches: Crossing, rubbing, or upright branches that have the
potential to damage tree structure and/or health.
4.23 internodal cut: A cut located between lateral branches or buds.
4.24 lateral branch: A shoot or stem growing from a parent branch or stem.
4.25 leader: A dominant or co-dominant, upright stem.
4.26 limb: A large, prominent branch.
4.27 lion’s tailing: The removal of an excessive number of inner, lateral
branches from parent branches. Lion’s tailing is not an acceptable pruning
practice (5.5.7).
4.28 mechanical pruning: A utility pruning technique where large-scale power
equipment is used to cut back branches (5.9.2.2).
4.29 parent branch or stem: A tree trunk, limb, or prominent branch from which
shoots or stems grow.
4.30 peeling: For palms: The removal of only the dead frond bases at the point
they make contact with the trunk without damaging living trunk tissue. (syn.:
shaving)
4.31 petiole: A stalk of a leaf or frond.
4.32 phloem: Inner bark conducting tissues that transport organic substances,
primarily carbohydrates, from leaves and stems to other parts of the plant.
4.33 pollarding: The maintenance of a tree by making internodal cuts to reduce
the size of a young tree, followed by the annual removal of shoot growth at its
point of origin (5.7.3).
4.34 pruning: The selective removal of plant parts to meet specific goals and
objectives.
4.35 qualified line-clearance arborist: An individual who, through related
training and on-thejob experience, is familiar with the equipment and hazards in
line clearance and has demonstrated the ability to perform the special techniques
involved. This individual may or may not be currently employed by a line-
clearance contractor.
4.36 qualified line-clearance arborist trainee:
An individual undergoing line-clearance training and who, in the course of such
training, is familiar with the hazards and equipment involved in line clearance and
has demonstrated ability in the performance of the special techniques involved.
This individual shall be under the direct supervision of a qualified line-clearance
arborist.
4.37 raising: Selective pruning to provide vertical clearance (5.6.3).
4.38 reduction: Selective pruning to decrease height and/or spread (5.6.4).
4.39 remote/rural areas: Locations associated with very little human activity,
land improvement, or development.
4.40 restoration: Selective pruning to improve the structure, form, and
appearance of trees that have been severely headed, vandalized, or damaged
(5.7.4).
4.41 shall: As used in this standard, denotes a mandatory requirement.
4.42 should: As used in this standard, denotes an advisory recommendation.
4.43 stub: An undesirable short length of a branch remaining after a break or
incorrect pruning cut is made.
4.44 thinning: Selective pruning to reduce density of live branches (5.6.2).
4.45 throwline: A small, lightweight line with a weighted end used to position a
climber’s rope in a tree.
4.46 topping: The reduction of a tree’s size using heading cuts that shorten
limbs or branches back to a predetermined crown limit. Topping is not an
acceptable pruning practice (5.5.7).
4.47 tracing: The removal of loose, damaged tissue from in and around the
wound.
4.48 urban/residential areas: Locations, such as populated areas including
public and private property, that are normally associated with human activity.
4.49 utility: An entity that delivers a public service, such as electricity or
communications.
4.50 utility space: The physical area occupied by a utility’s facilities and the
additional space required to ensure its operation.
4.51 vista pruning: Selective pruning to allow a specific view (5.7.5).
4.52 watersprouts: New stems originating from epicormic buds. (syn.: epicormic
shoots)
4.53 wound: An opening that is created when the bark of a live branch or stem is
penetrated, cut, or removed.
4.54 woundwood: Partially differentiated tissue responsible for closing wounds.
Woundwood develops from callus associated with wounds.
4.55 xylem: Wood tissue. Active xylem is sapwood; inactive xylem is heartwood.
4.56 young tree: A tree young in age or a newly transplanted tree.
5 Pruning practices
5.1 Tree inspection
5.1.1 An arborist or arborist trainee shall visually inspect each tree before
beginning work.
5.1.2 If a condition is observed requiring attention beyond the original scope of
the work, the condition should be reported to an immediate supervisor, the
owner, or the person responsible for authorizing the work.
5.2 Tools and equipment
5.2.1 Equipment and work practices that damage living tissue and bark beyond
the scope of the work should be avoided.
5.2.2 Climbing spurs shall not be used when climbing and pruning trees.
Exceptions:
-when limbs are more than throwline distance apart and there is no other means
of climbing the tree;
-when the bark is thick enough to prevent damage to the cambium;
-in remote or rural utility rights-of-way.
5.3 Pruning cuts
5.3.1 Pruning tools used in making pruning cuts shall be sharp.
5.3.2 A pruning cut that removes a branch at its point of origin shall be made
close to the trunk or parent limb, without cutting into the branch bark ridge or
collar, or leaving a stub (see Figure 5.3.2).
5.3.3 A pruning cut that reduces the length of a branch or parent stem should
bisect the angle between its branch bark ridge and an imaginary line
perpendicular to the branch or stem (see Figure 5.3.3).
5.3.4 The final cut shall result in a flat surface with adjacent bark firmly attached.
5.3.5 When removing a dead branch, the final cut shall be made just outside the
collar of living tissue.
5.3.6 Tree branches shall be removed in such a manner so as not to cause
damage to other parts of the tree or to other plants or property. Branches too
large to support with one hand shall be precut to avoid splitting of the wood or
tearing of the bark (see Figure 5.3.2). Where necessary, ropes or other
equipment shall be used to lower large branches or portions of branches to the
ground.
5.3.7 A final cut that removes a branch with a narrow angle of attachment should
be made from the outside of the branch to prevent damage to the parent limb
(see Figure 5.3.7).
5.3.8 Severed limbs shall be removed from the crown upon completion of the
pruning, at times when the tree would be left unattended, or at the end of the
workday.
Figure 5.3.2. – A pruning cut that removes a branch at its point of origin shall be
made close to the trunk or parent limb, without cutting into the branch bark ridge
or collar, or leaving a stub. Branches too large to support with one hand shall be
precut to avoid splitting of the wood or tearing of the bark.
Figure 5.3.3. – A pruning cut that reduces the length of a branch or parent stem
should bisect the angle between its branch bark ridge and an imaginary line
perpendicular to the branch or stem .
Figure 5.3.7. – A final cut that removes a branch with a narrow angle of
attachment should be made from the outside of the branch to prevent damage to
the parent limb.
5.4 Wound treatment
5.4.1 Wound treatments should not be used to cover wounds or pruning cuts,
except when recommended for disease, insect, mistletoe, or sprout con trol, or
for cosmetic reasons.
5.4.2 Wound treatments that are damaging to tree tissues shall not be used.
5.4.3 When tracing wounds, only loose, damaged tissue should be removed.
5.5 Pruning objectives
5.5.1 Pruning objectives shall be established prior to beginning any pruning
operation.
To obtain the defined objective, the growth cycles and structure of individual
species and the type
of pruning to be performed should be considered.
5.5.3 Not more than 25 percent of the foliage should be removed within an
annual growing season. The percentage and distribution of foliage to be removed
shall be adjusted according to the plant’s species, age, health, and site.
5.5.4 Not more than 25 percent of the foliage of a branch or limb should be
removed when it is cut back to a lateral. That lateral should be large enough to
assume apical dominance.
5.5.5 Pruning cuts should be made in accordance with 5.3 Pruning cuts.
5.5.6 Heading should be considered an acceptable practice for shrub or specialty
pruning when needed to reach a defined objective.
5.5.7 Topping and lion’s tailing shall be considered unacceptable pruning
practices for trees.
5.6 Pruning types
Specifications for pruning should consist of, but are not limited to, one or more of
the following types:
5.6.1 Clean: Cleaning shall consist of selective pruning to remove one or more of
the following parts: dead, diseased, and/or broken branches.
5.6.1.1 Location of parts to be removed shall be specified.
5.6.1.2 Size range of parts to be removed shall be specified.
5.6.2 Thin: Thinning shall consist of selective pruning to reduce density of live
branches.
5.6.2.1 Thinning should result in an even distribution of branches on individual
limbs and throughout the crown.
5.6.2.2 Not more than 25 percent of the crown should be removed within an
annual growing season.
5.6.2.3 Location of parts to be removed shall be specified.
5.6.2.4 Percentage of foliage and size range of parts to be removed shall be
specified.
5.6.3 Raise: Raising shall consist of selective pruning to provide vertical
clearance.
5.6.3.1 Vertical clearance should be specified.
5.6.3.2 Location and size range of parts to be removed should be specified.
5.6.4 Reduce: Reduction shall consist of selective pruning to decrease height
and/or spread.
5.6.4.1 Consideration shall be given to the ability of a species to tolerate this type
of pruning.
5.6.4.2 Location of parts to be removed and clearance should be specified.
5.6.4.3 Size range of parts should be specified.
5.7 Specialty pruning
Consideration shall be given to the ability of a species to tolerate specialty
pruning, using one or more pruning types (5.6).
5.7.1 Young trees
5.7.1.1 The reasons for young tree pruning may include, but are not limited to,
reducing risk, maintaining or improving tree health and structure, improving
aesthetics, or satisfying a specific need.
5.7.1.2 Young trees that will not tolerate repetitive
pruning and have the potential to outgrow their space should be considered for
relocation or removal.
5.7.1.3 At planting
5.7.1.3.1 Pruning should be limited to cleaning (5.6.1).
5.7.1.3.2 Branches should be retained on the lower trunk.
5.7.1.4 Once established
5.7.1.4.1 Cleaning should be performed (5.6.1).
5.7.1.4.2 Rubbing and poorly attached branches should be removed.
5.7.1.4.3 A central leader or leader(s) as appropriate should be developed.
5.7.1.4.4 A strong, properly spaced scaffold branch structure should be selected
and maintained.
5.7.1.4.5 Interfering branches should be reduced or removed.
5.7.2 Espalier
5.7.2.1 Branches that extend outside the desired plane of growth shall be pruned
or tied back.
5.7.2.2 Ties should be replaced as needed to prevent girdling the branches at the
attachment site.
5.7.3 Pollarding
5.7.3.1 Consideration shall be given to the ability of the individual tree to respond
to pollarding.
5.7.3.2 Management plans shall be made prior to the start of the pollarding
process for routine removal of watersprouts.
5.7.3.3 Internodal cuts shall be made at specific locations to start the pollarding
process. After the initial cuts are made, no additional internodal cut shall be
made.
5.7.3.4 Watersprouts growing from the cut ends of branches (knuckles) should be
removed annually during the dormant season.
5.7.4 Restoration
5.7.4.1 Restoration shall consist of selective pruning to improve the structure,
form, and appearance of trees that have been severely headed, vandalized, or
damaged.
5.7.4.2 Location in tree, size range of parts, and percentage of watersprouts to
be removed should be specified.
5.7.5 Vista pruning
5.7.5.1 Vista pruning shall consist of selective pruning to allow a specific view.
5.7.5.2 Size range of parts, location in tree, and percentage of foliage to be
removed should be specified.
5.8 Palm pruning
5.8.1 Palm pruning should be performed when fronds, fruit, or loose petioles may
create a dangerous condition.
5.8.2 Live healthy fronds, initiating at an angle of 45 degrees or greater from
horizontal, with frond tips at or below horizontal, should not be removed.
5.8.3 Fronds removed should be severed close to the petiole base without
damaging living trunk tissue.
5.8.4 Palm peeling (shaving) should consist of the removal of only the dead frond
bases at the point they make contact with the trunk without damaging living trunk
tissue.
5.9 Utility pruning
5.9.1 General
5.9.1.1 The purpose of utility pruning is to prevent the loss of service, comply with
mandated clearance laws, prevent damage to equipment, avoid access
impairment, and uphold the intended usage of the facility/utility space.
5.9.1.2 Only a qualified line clearance arborist or line clearance arborist trainee
shall be assigned to line clearance work in accordance with ANSI Z133.1, 29
CFR 1910.331 – 335, 29 CFR 1910.268 or 29 CFR 1910.269.
5.9.1.3 Utility pruning operations are exempt from requirements in 5.1 Tree
Inspection:
5.1.1 An arborist or arborist trainee shall visually inspect each tree before
beginning work.
5.1.2 If a condition is observed requiring attention beyond the original scope of
the work, the condition should be reported to an immediate supervisor, the
owner, or the person responsible for authorizing the work.
5.9.1.4 Safety inspections of the work area are required as outlined in ANSI
Z133.1 4.1.3, job briefing.
5.9.2 Utility crown reduction pruning
5.9.2.1 Urban/residential environment
5.9.2.1.1 Pruning cuts should be made in accordance with 5.3, Pruning cuts. The
following requirements and recommendations of 5.9.2.1.1 are repeated from 5.3
Pruning cuts.
5.9.2.1.1.1 A pruning cut that removes a branch at its point of origin shall be
made close to the trunk or parent limb, without cutting into the branch bark ridge
or collar, or leaving a stub (see Figure 5.3.2).
5.9.2.1.1.2 A pruning cut that reduces the length of a branch or parent stem
should bisect the angle between its branch bark ridge and an imaginary line
perpendicular to the branch or stem (see Figure 5.3.3).
5.9.2.1.1.3 The final cut shall result in a flat surface with adjacent bark firmly
attached.
5.9.2.1.1.4 When removing a dead branch, the final cut shall be made just
outside the collar of living tissue.
5.9.2.1.1.5 Tree branches shall be removed in such a manner so as not to cause
damage to other parts of the tree or to other plants or property. Branches too
large to support with one hand shall be precut to avoid splitting of the wood or
tearing of the bark (see Figure 5.3.2). Where necessary, ropes or other
equipment shall be used to lower large branches or portions of branches to the
ground.
5.9.2.1.1.6 A final cut that removes a branch
with a narrow angle of attachment should be made from the bottom of the branch
to prevent damage to the parent limb (see Figure 5.3.7).
5.9.2.1.2 A minimum number of pruning cuts should be made to accomplish the
purpose of facility/utility pruning. The natural structure of the tree should be
considered.
5.9.2.1.3 Trees directly under and growing into facility/utility spaces should be
removed or pruned. Such pruning should be done by removing entire branches
or by removing branches that have laterals growing into (or once pruned, will
grow into) the facility/utility space.
5.9.2.1.4 Trees growing next to, and into or toward facility/utility spaces should be
pruned by reducing branches to laterals (5.3.3) to direct growth away from the
utility space or by removing entire branches. Branches that, when cut, will
produce watersprouts that would grow into facilities and/or utility space should be
removed.
5.9.2.1.5 Branches should be cut to laterals or the parent branch and not at a
pre-established clearing limit. If clearance limits are established, pruning cuts
should be made at laterals or parent branches outside the specified clearance
zone.
5.9.2.2 Rural/remote locations – mechanical pruning
Cuts should be made close to the main stem, outside of the branch bark ridge
and branch collar. Precautions should be taken to avoid stripping or tearing of
bark or excessive wounding.
5.9.3 Emergency service restoration
During a utility-declared emergency, service must be restored as quickly as
possible in accordance with ANSI Z133.1, 29 CFR 1910.331 – 335, 29 CFR
1910.268, or 29 CFR 1910.269. At such times it may be necessary, because of
safety and the urgency of service restoration, to deviate from the use of proper
pruning techniques as defined in this standard. Following the emergency,
corrective pruning should be done as necessary.
Annex A (informative)
Reference publications
International Society of Arboriculture (ISA). 1995. Tree Pruning Guidelines .
Savoy, IL: International Society of Arboriculture (ISA).