Pruning Specifications
Douglas L. Airhart & Guy Zimmerman III

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    Pruning Trees- Pruning Specifications:  

Preparing specifications for pruning municipal trees is important because they become the basis for contract obligations. Both parties should be familiar with the basic terminology to eliminate any misunderstandings and to ensure that trees receive the correct treatments. A few basic considerations for any bid requests are:

bulletA Certified Arborist should review the bids for contract before they are made public to contractors.
bulletAll legal, liability and EEO documentation is current, appropriate and provided.
bulletOnly contractors with a Certified Arborist on staff or retainer should be allowed to submit bids for any municipal work. That Certified Arborist should be expected to make regular appearances (at least weekly) at the job site (s) for supervision.
bulletONLY rope and saddle climbing gear without climbing spurs or spikes will be allowed for pruning live trees (spurs and spikes wound trunks and allow decay organisms to enter the trunk, or they may transfer diseases from tree to tree).
bulletAll crewmembers should be wearing the appropriate safety gear: hard hats, eye protection, approved boots, hearing protection, chain saw chaps for groundwork.

Basic Terminology:

    Coarse pruning: (see diagram) removal of deadwood greater than two inches diameter and any hazardous branches.

    Medium pruning: (see diagram) includes Coarse pruning, plus removal of deadwood greater than one inch diameter and specialty treatments (raising branch height, site clearance, crossing or broken branches, thinning canopy).

    Fine pruning: (see diagram) includes Medium pruning, plus removal of all deadwood and any water sprouts, suckers and crossing branches; inspection for health conditions. Climber should inspect to the tip of every branch. Up to 15% of canopy may be removed for light and air penetration.

    Raising branches: removal of lowest branches to a prescribed height for appropriate clearance needs. Generally 8 feet over sidewalks, 14 feet over streets, and a variety of heights for mower clearance (only if needed).

    Natural Target Pruning: removal of branches using a 3-cut process and protecting the branch collar.

Sample Set of Specifications: (From Matheny & Clark, 1998

bulletAll trees (protecting the branch collar): Crown cleaning limbs to a minimum of 1.5 inches;  Vertical clearance of 14 feet over streets and 8 feet over sidewalks; Reduce end weight by removal of limbs less than 2 to 3 inches at end of scaffolds.
bulletTie back branches to provide temporary clearance.
bulletDo not prune if boring insects are flying (they are attracted to fresh wounds).
bulletAll pruning shall be performed by qualified arborist (ISA Certified Arborist or Tree Worker).
bulletAll pruning shall follow ISA’s Tree Pruning Guidelines or most recent ANSI A300 Pruning Standards, and ANSI Z133.1 Safety Standards.
bulletSome interior branches shall remain.
bulletNo live wood greater than 4 inches in diameter shall be cut.
bulletHeartwood shall not be exposed if possible.
bulletA maximum of 20% of live wood shall be removed.
bulletThe arborist shall identify defects by performing aerial inspection, and report to supervisor.
bulletChipped brush shall be spread on the root zone to a maximum of 6 inches, but the trunk shall be clear of mulch.

Pruning Standards

With the American National Standard for pruning, ANSI A300, specifications can be written in a virtual number of combinations.

The following information is designed to help you understand exactly what will be accomplished in a pruning operation.

Branch Size

                A minimum or maximum diameter size of branches to be removed should be specified in all pruning operations.

 Pruning Objectives

            Pruning objectives should be established prior to beginning any pruning operation. A300 provides two basic objectives.

Hazard Reduction Pruning (HRP) is recommended when the primary objective is to reduce the danger to a specific target caused by visibly defined hazards in a tree. For example, HRP may be the primary objective if a tree had many dead limbs over a park bench.

Maintenance Pruning (MP) is recommended when the primary objective is to maintain or improve tree health and structure, and includes hazard reduction pruning. An example here might be to perform a MP operation on a front yard tree.

Pruning Types

                HRP and MP should consist of one or more of the pruning types noted below.

                Crown Cleaning shall consist of the selective removal of one or more of the following items: dead, dying or diseased branches, weak branches and watersprouts.

                Crown Thinning shall consist of the selective removal of branches of increase light penetration, air movement and reduce weight.

                Crown Raising shall consist of the removal of the lower branches of a tree to provide clearance.

                Crown Reduction, or Crown Shaping decreases the height and/or spread of a tree. Consideration should be given to the ability

                Vista Pruning is selective thinning of framework limbs or specific areas of the crown to allow a view of an object from a

                Crown Restoration should improve the structure, form and appearance of trees that have been severely headed, vandalized,

Example Specifications

Tree: 24 inch dbh oak in back yard of residence. Maintenance Prune – crown clean 2 inches or greater, crown thin branch in east side over pool.

Trees: Nine, 20 to 25 inch silver maples on street. Hazard Reduction Prune – crown clean 3 inches or greater, crown raise to 15 feet. 

Figure 7-21a. Tree before pruning.
Figure 7-21b. Tree after Hazard Reduction Pruning – crown clean 3 inches or greater, crown raise to 15 feet.

 Tree: 30 inch white pine in back yard, overlooking sea. Maintenance Prune – crown clean 2 inches or greater, vista prune south side to improve view of sea.

Tree: 10 inch redbud in front yard. Maintenance prune – crown thin, ½ inch or greater.

Tree: 19 inch red maple in back yard. Hazard Reduction Prune – crown clean dead wood only 2 inches or greater, crown reduction prune away from antenna on house.

The American National Standard for tree pruning is ANSI A300. The American National Standards Institute approved its development process. This pruning standard should be followed where possible in all pruning situations to remain consistent with industry standards. Please note that the A300 standard has been drafted to address pruning specifications across all geographic areas. Knowledge of the growth habits of certain tree species within a given environment may alter how the recommendations of A300 are interpreted.



Purpose    Right Tree / Right Place    Selecting Trees    Transplanting Trees    Mulching & Staking    Summary Diagram     Pruning Trees    Topping Hurts!      Protecting Trees     Tree Root Myths     Pine Bark Beetles     Live Christmas Trees     Glossary     List of Figures    List of Video Vignettes    Related Links     Bibliography is maintained by: Douglas Airhart, Ph.D. Certified Arborist & Jeff Plant, Ph.D, Last Updated on: 07/11/03