TREE PRUNING BASICS
Trees are complex living organisms whose growth, appearance, condition and longevity are greatly influenced by environmental factors. Useful generalizations concerning pruning practices can be made to improve the health, structure, aesthetics, and safety of trees, even though tree species may vary in their cultural requirements, and even within a species individual trees differ
in branch configuration.
There are four classes of pruning established by the Tree Care Industry Association to accommodate varying work needs.
CLASS I - FINE PRUNING
Fine pruning is recommended for premium quality work with an emphasis on aesthetic considerations in addition to structural enhancement. Fine pruning consists of the removal of dead, dying, diseased, decayed, interfering, objectionable, obstructing, and weak branches, as well as selective thinning to lessen wind resistance. The removal of such described branches is to include those on the main trunks, as well as those inside the leaf area . An occasional undesirable branch up to one-half inch (1.25 cm) in diameter, as described above, may remain with the main leaf area to its full length when it is not practical to remove it.
CLASS II - STANDARD PRUNING
Standard pruning is recommended where aesthetic considerations are secondary to structural enhancement and tree health concerns. Standard pruning consists of the removal of dead, dying, diseased, decaying, interfering, objectionable, obstructing, and weak branches, as well as selective thinning to lessen wind resistance. The removal of such described branches is to include those on the main trunks, as well as those inside the leaf area. An occasional undesirable branch up to one inch (2.5 cm) in diameter may remain within the main leaf area where it is not practical to remove it.
CLASS III - HAZARD PRUNING
Hazard pruning is recommended where safety considerations are paramount. Hazard pruning consists of the removal of dead diseased, decayed, and obviously weak branches, two inches (5 cm) in diameter or greater.
CLASS IV - CROWN REDUCTION PRUNING
Crown reduction pruning consists of the reduction of tops, sides or individual limbs. It involves the removal of a parent limb or dominant leader at the point of attachment of a lateral branch.
This practice is to be undertaken only for the following reasons:
a. In situations where branches interfere with utility lines.
b. When there has been significant crown dieback.
c. When it is necessary to achieve specific topiary training or dwarfing.
d. In cases where, due to storm damage or prior incorrect pruning, it is appropriate to prune for safety and aesthetic reasons.
The terms "cutting back" and "drop crotch pruning" are sometimes used interchangeable with the term crown reduction pruning. By contrast, the term "topping" is often used to refer to a generally unacceptable pruning practice.
GENERAL PRUNING RECOMMENDATIONS
a. All cuts on live branches should be made as close as possible to the trunk or parent limb, without cutting into the branch collar or leaving a protruding stub. Bark at the edge of all pruning cuts should remain firmly attached. Cuts on dead branches should be
made as close as possible, without causing injury, to the callus tissue, when evident.
b. All branches too large to support with one hand should be precut to avoid splitting or tearing of the bark. Where necessary, ropes or other equipment should be used to lower large branches or stubs to the ground.
c. Treatment of cuts and wounds with wound dressing or paints has not been proven to be effective in preventing or reducing decay or insect and disease infection, and is not generally recommended for that reason. Wound dressing over infected wood may stimulate the decay process.
d. Old injuries should be inspected. Those not closing properly and where the callus growth is not already completely established should be bark traced if the bark appears loose or damaged. Such tracing shall not penetrate the xylem (sapwood), and margins shall be kept rounded.
e. Equipment that will damage the bark and cambium layer should not be used on or in the tree. For example, the use of climbing spurs (hooks, irons) is not an acceptable work practice for pruning operations on live trees. Sharp tools shall be used so that clean cuts will be made at all times.
f. All cut limbs should be removed from the crown upon completion of the pruning.
g. Trees susceptible to serious infectious diseases should not be pruned at the time of year during which the pathogens causing the diseases or the insect vectors are most active. Similarly, if pruning wounds may attract harmful insects, pruning should be timed so as to avoid insect infestation.
h. Removal of the weaker or less desirable of crossed or rubbing branches is recommended. Such removal, if possible, should not leave large open spaces in the general outline of the tree.
i. The presence of any disease condition, fungus fruit bodies, decayed trunk or branches, split crotches or branches, cracks, or other structural weakness should be reported to a supervisor and/or the owner to avoid leaving or creating a hazard tree.
j. When removing a parent leader of limb to a lateral branch, the final cut should be made as close to parallel as possible with the branch bark ridge and the lateral limb. The cut should be made as close to the bark ridge as possible without cutting into it. Care should be taken to avoid damaging the lateral limb when the final cut is made.
k. Generally in crown reduction pruning, not more than one-third of the total area should be removed in a single operation. Every effort should be made to cut back to a lateral at least one-third to one-half the diameter of the parent limb or leader that is being removed. Cuts not made to a suitable lateral, sometimes called topping cuts, should not be made.
l. Before a branch is cut back, the ratio of live wood in the branch to leaf surface area in the remaining branch should be considered carefully. The leaves maintain the wood in the remaining branch as well as send excess carbohydrates to the trunk and roots for storage and later use. Generally, not more that one third the total leaf surface area should be removed at any one time.
m. Trees should be pruned to a shape typical of their species.
n. To prevent sunburn on thin-barked trees, just enough limbs shall be removed to get the desired effect without admitting too much sunlight to the trunk of the tree or the top of large branches. Care should be taken with the following species: Linden (Tilia spp.), Maple (Acer spp.), Beech (Fagus spp.), Apple (Malus spp.), Oak (Quercus spp.) and other thin barked trees. The above damage may be minimized by doing work on susceptible species during the dormant season.
o. When removing the lower branches of trees for crown elevation or underclearance, care should be taken to maintain a symmetrical appearance, and cuts should not be made so large or so numerous that they will prevent normal sap flow.