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Tree Care: A Glossary of Arborucultural Terms

In an effort to help our clients and tree enthusiasts alike understand a few definitions of words and terms used in the tree service and tree care industry, we offer the following glossary of Arboricultural terms. Enjoy!

Diameter At Breast Height (DBH)

How a trees size is measured. At a point 54 inches above the base of a tree, a measuring tape is wrapped around the trunk. We use diameter as the measurment but some cities ask for the circumference.  


The upper part of a tree, measured from the lowest branch, including all the branches and foliage out to the end of the longest branch, up to the highest point atop the tree.

Thin Crown

Often followed by a percentage. A preferred method of pruning by removing interior growth and selectively thinning out branch tips. Overall size of the tree remains the same and retains its natural form. Although, the tree will appear lighter, airier, and one should be able to see attractive branch structure; the crown should retain even branch coverage with out holes or gaps. This method of pruning rids the tree of extra weight, and allows even passage of wind, reducing windsail effect. (reducing a windsail effect is not necessarily applicable nor required for every species of tree). It also allows the passage of air and light into the tree's interior which has the added benefit of helping to control certain pest infestations: A.K.A. a cultural approach to pest control.

Clean Crown

Generally involves only the removal of dead, dying, and/or diseased stems, branches, and stubs from throughout the crown. A.K.A. remove deadwood.

Raise Crown

Removal of lowest lateral branches back to their source on the main trunk, (branch attachment), to enable access or sight lines to remain clear. Raising the crown a "bit" doesn't necessarily involve the removal of whole stems at their branch attachments rather just the removal of some of the smaller stems hanging vertically.

Reduce Crown

Usually a percentage of reduction will follow the term, (e.g. reduce crown by approximately 25%). This describes a method of physical size reduction of the tree crown, (the crown being the portion starting at the lowest branch and ending at the very tips of the branches). The height and spread of the tree is reduced by shortening back leaders and laterals to suitable smaller branches, leaving a more compact tree.

Thin, Clean, Raise And Reduce Crown By 25%

The highest level of tree pruning  allowed by industry standards and best management practices. No more than 25% of the total living crown is removed. The living crown includes wood, stems, branches and leaves. The tree should maintain its natural structure and character. A 25% reduction does not mean an overall reduction in height by 25%. The total density and mass of foliage, stems, branches, and wood removed is considered. It is our experience that those clients who wish to have their trees topped consider this approach inadequate. 

Top (Topping)

This word sends a shudder through the Arboricultural world!
It is a seriously detrimental tree practice, which should not be encouraged. It leads to wounds which never heal (compartmentalize) leading to decay and structural weakness, weak sprout attachment and danger of limb shed in future years. Trees that require "topping" should be considered as candidates for removal (abatement) and replacement.


A drastic means of pruning mature trees, involves removal of all green growth, leaving a "hat rack" impression. Not recommended for maturing and mature trees. It leads to weak sprout attachment and if not attended to regularly, can cause dangers of limb shed. It can be a useful way of controlling certain species of trees if the process is started when the tree is young (less than 5 years), and then done annually.

Structural Prune/Formatively Prune

Usually, only done to young, developing trees. It involves the elimination, (where possible), of structural faults, such as tight, (compression), forks, (which may later on in life lead tomajor limb shed), crossing and rubbing branches, imbalances of crown and giving the trees a "direction" to grow in . Often, it is not possible to eliminate such problems in mature trees. Structure pruning in mature trees is normally only done to attempt to balance the crown of a tree after suffering the loss of a large stem or stems during inclement weather or high winds.

Skirt Raise

The pruning of the tips of lower branches frequently done on weeping type trees to enable access or keep sight lines clear. (raise it just a "bit" please!) Also extensively used to describe the method used to remove living fronds from palm trees, (e.g. raise skirt to 45 degrees).

Head Back

The shortening of long, lateral branches, (can be considerable), on a particular section of a tree, (usually specified), used to lighten stresses on suspect limb branch attachment points, to enable access for vehicles, etc. and to prevent limbs from touching buildings or structures.

Tuck Back

Shortening of lateral limbs, for same purposes as above, however, it should signify the amount of shortening to the operator. Tucking back involves less severe pruning than heading back.

Clip Back

Shortening of lateral limbs on a specific part of a tree. Involves minor work, but for the same purposes as the above.


Read both terms to be the same. Involves minor works to trees to trim minor branches or trees to maintain natural shape or form. The removal of "vagrant" branches is included and usually it only involves a light pruning, (where needed), to the periphery of the tree.


Usually followed by an object such as building, light or sign. The object is to trim away to prevent encroachment of branches that may damage paint, gutters, fixtures, etc. It may also pertain to the clearance of braches by lights to emit more light in certain areas.


Involves the judicious removal of water sprouts, epicormic growth, (suckers), often not all are removed to allow branches to fill gaps in the future and to develop better branch structure.


Often trees that have single predominant leaders, will throw out competing leaders, (twin forks), that result in serious structure problems in later life and can lead to complete tree failure. The location of the co-dominant stem plays a significant role in performing hazard tree risk assessment.
Singling-up involves the removal of the least desirable of those co-dominant stems, (best suited for young specimens). In most but not all mature trees with co-dominant stems the least desirable stem is reduced in height or length to suppress its growth rate rather than removing the whole stem. Coast Redwood (Sequoia sempervirens) is aspecies most suseptible to this type of phenomenon.


Compartmentalization Of Decay In Trees. Get it?! This is tree care 101. Learn it, know it, love it!


This term is used to describe treatments, (through pruning), for the purpose of the tree's well being. This is the primary goal. It involves all advantageous cultural pruning techniques as required by the tree for the best health and structure. It involves as needed: crown thinning, end weight removal, correction, (if possible), of structural faults, removal of dead, dying and diseased tissue, and correction of imbalances, (if possible). Where needed, it can also take into account owner needs such as clearance.

Remove Deadwood/Clean

Usually stated as remove major deadwood. It involves removal of the majority of deadwood, dying and diseased branches throughout the tree's canopy. Depending upon the size of the tree, wood down to pencil size is removed.

Root Prune

This involves the severance of sections of roots that are causing or are likely to cause damage to hard surfaces, foundations, etc. Root barriers can often be inserted following this mechanical operation to prevent further encroachment.

Remove To Near Grade

Tree removal to as near to ground level as possible, without causing damage to the operators machinery.

Grind Stump To Below Grade Into Mulch

The mechanical grinding only of stumps from just below grade (ground level) to a maximum of 12" below grade, (depending upon the machine used and location of stump), resulting in a pile of dirt and wood chips that may be used as an acceptable mulch in many circumstances. When large stumps are gound to below grade, significant amounts of dirt and mulch will accumulate that is overwhelming for most yards, grindings can be removed if you wish!

Deep Root Fertilize

The insertion, (by means of high pressure hydraulic action), of a dilute liquid fertilizer. This is injected directly into the root zone, and is primarily used for trees on soils with poor nutrient status or obvious deficiencies.


The control of insects or disease by hydraulic spraying of insecticides, fungicides, etc.

Pull Stakes

Removal of supporting tree stakes, (that may cause root girdling), that are no longer required.

Other useful terms associated with tree work

Adaptive growth

An increase in wood production in localised areas in response to a decrease in wood strength or external loading to maintain an even distribution of forces across the structure.

Adventitious/epicormic growth

New growth arising from dormant or new buds directly from main branches/stems or trunks.


Bracing is a term used to describe the installation of cables, ropes and/or belts to reduce the probability of failure of one or more parts of the tree structure due to weakened elements under excessive movement.

Branch bark ridge and collar

See diagram 3 section 3. Natural features of a fork or union that may or may not be visually obvious. Neither the branch bark ridge nor collar should be cut.


Undifferentiated tissue initiated as a result of wounding and which become specialised tissues of the repair over time.


A void within the solid structure of the tree, normally associated with decay or deterioration of the woody tissues. May be dry or hold water, if the latter it should not be drained. Only soft decomposing tissue should be removed if necessary to assess the extent. No attempt should be made to cut or expose living tissue.

Co-dominant stems

Two or more, generally upright, stems of roughly equal size and vigour competing with each other for dominance. Where these arise from a common union the structural integrity of that union should be assessed.


The foliage bearing section of the tree formed by its branches and not including any clear stem/trunk.


Non-living branches or stems due to natural ageing or external influences. Deadwood provides essential habitats and its management should aim to leave as much as possible, shortening or removing only those that pose a risk. Durability and retention of deadwood will vary by tree species.


When a tree exhibits signs of a lack of vitality such as reduced leaf size, colour or density.


Tips of branches exhibit no signs of life due to age or external influences. Decline may progress, stabilize or reverse as the tree adapts to its new situation.


The inactive condition of a tree, usually during the coldest months of the year when there is little or no growth and leaves of deciduous trees have been shed.

Drop Crotching

Shortening branches by pruning off the end back to a lateral branch which is at least 1/3 of the diameter of the removed branch.


The application of a substance, usually to the tree’s rooting area (and occasionally to the tree), to promote tree growth or reverse or reduce decline. This will only be effective if nutrient deficiency is confirmed. If decline is the result of other factors such as compaction, physical damage, toxins etc., the application of fertiliser will not make any difference.

Formative pruning

Minor pruning during the early years of a tree’s growth to establish the desired form and/or to correct defects or weaknesses that may affect structure in later life.

Fungi/Fruiting bodies

A member of the plant kingdom that may colonize living or dead tissues of a tree or form beneficial relationships with the roots. The fruiting body is the spore bearing, reproductive structure of that fungus. Removal of the fruiting body will not prevent further colonization and will make diagnosis and prognosis harder to determine. Each colonization must be considered in detail by a competent person to determine the long term implications of tree health and structure when considered alongside the tree species, site usage etc.

Retrenchment pruning

A form of reduction intended to encourage development of lower shoots and emulate the natural process of tree aging.

Root pruning

The pruning back of roots (similar to the pruning back of branches). This has the ability to affect tree stability so it is advisable to seek professional advice prior to attempting root pruning.


See Lopping and Topping.


The degree of physiological and biochemical processes (life functions) within an individual, group or population of trees.

Main Pruning Definitions

Crown Thin

Crown thinning is the removal of a portion of smaller/tertiary branches, usually at the outer crown, to produce a uniform density of foliage around an evenly spaced branch structure. It is usually confined to broad-leaved species. Crown thinning does not alter the overall size or shape of the tree. Material should be removed systematically throughout the tree, should not exceed the stated percentage and not more than 30% overall. Common reasons for crown thinning are to allow more light to pass through the tree, reduce wind resistance, reduce weight (but this does not necessarily reduce leverage on the structure) and is rarely a once-only operation particularly on species that are known to produce large amounts of epicormic growth.

Crown Lift or Crown Raising

Crown lifting is the removal of the lowest branches and/or preparing of lower branches for future removal. Good practice dictates crown lifting should not normally include the removal of large branches growing directly from the trunk as this can cause large wounds which can become extensively decayed leading to further long term problems or more short term biomechanical instability. Crown lifting on older, mature trees should be avoided or restricted to secondary branches or shortening of primary branches rather than the whole removal wherever possible. Crown lifting is an effective method of increasing light transmission to areas closer to the tree or to enable access under the crown but should be restricted to less than 15% of the live crown height and leave the Crown at least two thirds of the total height of the tree. Crown lifting should be specified with reference to a fixed point, e.g. ‘crown lift to give 5.5m clearance above ground level’.

Crown Reduction

The reduction in height and/or spread of the crown (the foliage bearing portions) of a tree. Crown reduction may be used to reduce mechanical stress on individual branches or the whole tree, make the tree more suited to its immediate environment or to reduce the effects of shading and light loss, etc. The final result should retain the main framework of the crown, and so a significant proportion of the leaf bearing structure, and leave a similar, although smaller outline, and not necessarily achieve symmetry for its own sake. Crown reduction cuts should be as small as possible and in general not exceed 100mm diameter unless there is an overriding need to do so. Reductions should be specified by actual measurements, where possible, and reflect the finished result, but may also refer to lengths of parts to be removed to aid clarity, e.g. ‘crown reduce in height by 2.0m and lateral spread by 1.0m, all round, to finished crown dimensions of 18m in height by 11m in spread (all measurements approximate.)’. Not all species are suitable for this treatment and crown reduction should not be confused with ‘topping’, an indiscriminate and harmful treatment.

Illustrations courtesy of European Arboricultural Council.
Diagram 2 – examples of correct pruning cuts. Drawings courtesy of European Arboricultural Council.

The importance of correct pruning cuts

Every pruning cut inflicts a wound on the tree. The ability of a tree to withstand a wound and maintain healthy growth is greatly affected by the pruning cut – its size, angle and position relative to the retained parts of the tree. As a general rule branches should be removed at their point of attachment or shortened to a lateral which is at least 1/3 of the diameter of the removed portion of the branch, and all cuts should be kept as small as possible. Examples of correct pruning cuts are shown as follows.


Showing sequence of removal to avoid damage to the retained parts
Cypress Tree Care
Cypress Tree Care
33529 Fox Run Road, Frankford, DE 19945