Terms and Definitions

Aeration & Decompaction – Creating natural pockets in the soil for air and water to promote tree health and root growth.
Airknife – A specialized tool used to move soil safely around any root zone, without worry of harm to the trees, plants or buried utilities.
Aerial Root – a root originating from a branch or trunk that eventually touches the ground and takes root in the soil.
Aggressive Branches (limbs) – fast growing stems.
Amenity Value – The environmental and landscape benefits of trees as opposed to their commercial value for timber.
Ansi A300 – The American National Standards Institute standard for pruning trees and shrubs in landscapes.
Ansi Z60.1 – The American National Standards Institute standard for nursery stock.
Ansi Z133.1 – The American National Standards Institute standard for safe working practices in and near trees.
Anvil Pruner – A tool designed to cut by passing a sharpened blade through a twig against a metal anvil.
Apoplast – Network of open, dead conducting elements in xylem.
Appraisal – Estimates the defined value of personal property, including plants. The tree appraisal process is used to develop a supported estimate of current value. The purpose of an appraisal is defined by the clients’ needs. These needs may include tort claims, insurance claims, tax deductions, real estate assessment and proactive planning.
Arborist – A person with technical knowledge of tree care practices gained through experience and training. They are professionals who possess the technical competence gained through experience and related training to proved for or supervise the management of trees and other woody plants I residential, commercial and public landscapes.
Arboriculture – Management of individual trees or groups of trees primarily for their amenity value.
Architectural Pruning – Shapes and maintains trees to a specific form and size with regular pruning.
At Risk – see hazardous condition.
Auxin – A plant growth regulator that inhibits shoot formation in high concentrations and initiates roots.
Balancing – removes branches to redistribute weight.
Balled And Burlapped (B&B) – A tree or other plant prepared for transplanting by allowing the roots to remain covered by a ball of soil around which canvas or burlap is tied.
Bare Root – A tree or other planted prepared for transplanting by having all or most of the soil removed from about its roots.
Bark Inclusion – see included bark.
Best Management Practice – The best available treatment, considering the benefits and drawbacks, based on current knowledge.
Bonsai – A technique combining root and shoot pruning designed to keep a plant very small.
Border Tree – A tree jointly owned by adjacent property owners due to its location on the property line.
Bracing – Placing a stiff support under a low limb to prevent it from falling from the tree; securing stems together.
Branch – A stem arising from a larger stem; a subdominant or subordinate stem; the pith in true branches has no connection to the parent stem.
Branch Angle – The angle formed in the union between stem and branch.
Branch Arrangement – Orientation and distribution of branches along a trunk.
Branch Bark Ridge – A more or less commonly occurring raised area of bark tissue in the union of two branches or two stems or in the union of branch and stem.
Branch Collar – A swelling at the base of a branch where it joins the trunk or larger branch resulting from overlapping trunk and branch tissue.
Branch Protection Zone – A thin zone of starch-rich tissue at the base of a branch where chemicals are deposited to retard the spread of discoloration and decay.
Branch Reduction – A pruning method which reduces the length of each branch to make them shorter. All branches are cut back to a suitable fork or bud. This method is not suited to all trees and where applied to the whole tree canopy should not exceed 30% of the foliage bearing structure. The natural shape of the crown is retained and minimizes hazards of dysfunctional problems in tree circulation.
Branch Stub – The part of the branch beyond the collar inadvertently left following branch removal.
Branch Union – The place where two branches or stems join or where a branch meets a trunk. See crotch.
Bypass Pruner – A tool that pushes a sharp blade through a twig past a hooked or curved metal anvil.
Caliper – Trunk diameter measured 6 inches from the ground; if caliper is greater than 4 inches, the measurement is taken at 12 inches from the ground.
Callus – Undifferentiated, meristematic tissue with little lignin formed by the cambium layer; callus can form sprouts.
Cambium – The layer of dividing meristematic cells beneath bark giving rise to xylem, phloem, and more cambium.
Canker – A depression or opening in the bark usually caused by a fungus or bacterium.
Canopy – The portion of the tree with foliage from the lowest branch to the topmost part of the tree; synonymous with crown.
Carpenter’s Saw – A saw designed to cut through dried lumber, not fresh wood.
Central Leader – A dominant stem located more or less in the center of the canopy.
Certified Arborist – An arborist who has passed an exam and receives, on a regular basis, continuing education administered by the International Society of Arboriculture (Champaign, IL).
Chain Saw – A power tool designed to cut through large branches and stems.
Christmas Tree – Spruces, pines, firs, Douglas firs, cedars, Junipers, and other evergreens marketed as decorative trees for the holidays.
Clean (cleaning) – Removes dead, broken, rubbing, or diseased branches and foreign objects; could also include removing or subordinating weakly-attached branches.
Clear Trunk – The lower portion of a trunk lacking lateral branches on nursery tree.
Clustered Branches – branches that are closely spaced, originating from nearly the same position on the trunk.
Co-dominant Stem – A stem growing at about the same rate, and with nearly the same diameter, as another stem originating from the same union; often the piths are connected in the union.
Collar – see branch collar.
Collar Cut – see removal cut.
Compartmentalization – The boundary-setting process that resists loss of normal wood function and resist the spread of discoloration and decay process that separates injured or decayed tissue from healthy tissue.
Crotch – See branch union.
Conservation Area – Section 69 of the Civic Amenities Act 1967 gives local councils the power to designate as Conservation Areas, “areas of special architectural or historic interest, the character or appearance of which it is desirable to preserve or enhance”. Designation gives control over the demolition of buildings and provides the basis for policies designed to preserve or enhance all the aspects of character or appearance that define an area’s special interest, including trees.
Crotch Spreading – Increasing the angle of a branch union by placing a wooden dowel or stick in union.
Crown – Refers to the part of the tree consisting of the limbs, branches, twigs and leaves.
Crown Cleaning – The removal of dead, dying, diseased, crowded, weakly attached and low vigor branches from the crown of the tree
Crown Thinning – 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.
Crown Raising – Removes the lower branches from a tree in order to provide clearance for buildings, vehicles, pedestrians, and vistas.
Crown Reduction – Reduces the size (height or spread) of the tree, often for clearance for utility lines. Arboriculture (ar●bor●cul●ture) [arbori – culture] is the practice and study of the care of trees and other woody plants in the landscape. A term developed to cover the broad spectrum of the green (trees, wood shrubs, plants, etc.) industry.
Crown Lifting – Involves the removal of lower branches to provide a desired amount of clearance above ground level. This can be achieved either by the complete removal of a branch or only parts of which extend below the desired height.
Cultivar – A cultivated variety of species typically propagated by cuttings, tissue culture, grafting or budding.
Cultural Problems – Too little or too much sunlight, water, fertilizer, air, pest infestations, or other factors resulting in poor growth.
Curtain – Creates a flat wall-like surface of foliage and twigs with regular shearing.
DBH (Diameter Breast Height) – Tree diameter at breast height. This has traditionally been the location on a tree where measurements are taken and a multitude of calculations are made to determine things like growth, volume, yield and forest potential. Breast height is defined as 4.5 feet above the soil line.
Decay – Degradation of tissue caused by biological organisms; the orderly breakdown of tissue resulting in strength loss.
Decurrent – Round-headed tree form; no leader to the top of the canopy in an open landscape pruning.
Defects – Cracks, poor branch or trunk structure, included bark, and other conditions that can reduce a plant’s utility or value.
Directional Pruning – Guides the tree to grow in a certain direction by removing live branches from another portion of the tree.
Discoloration – Darkened tissue in the xylem resulting from the orderly response of the tree to microorganisms.
Dogleg – Typically, an S-shaped bend in the tree.
Dominant Leader/trunk – The one stem that grows much larger than all other stems and branches. At least 1/3 bigger than lateral branches located nearby.
Double Leader – Two co dominant stems originating more or less in the center of the tree and jointly assuming the role of the leader.
Drop Crotch Cut– See reduction cut.
Drop Cut – Making tree cuts, beginning with an n undercut, to remove a branch to prevent bark peeling.
Edge Trees – Trees with access to sunlight from only one side that grows more on that side.
Eradication – Removes branches with pest infestations or disease.
Excurrent – Conically shaped tree form with a dominant leader or trunk extending to the top of the tree.
Extension Pruners – A bypass pruner with integrated extension pole.
Fail – to break or fall.
Faults – See defects.
Feature Trees – Trees located by themselves with few other trees nearby surrounded by turf, ground cover, or shrubs.
Flush Cut – A destructive pruning cut made on the trunk side of the branch bark ridge or through the collar.
Foresters – have a 4-year degree in forestry from an accredited college or university. They do the management of forests, woodlots and urban forestry landscapes and cityscapes to provide a variety of benefits including timber, aesthetics, wildlife habitat and health and care of trees.
Formal Hedge – A shrub maintained as a sharply defined geometric shape by shearing regularly.
Frost Crack – A visible vertical crack in a trunk or branch usually originating from a rig crack inside the tree; a split or crack in wood that extends out through the bark.
Good Compartmentalizer – A plant with good resistance to movement of discoloration and decay.
Good Quality Trees– Trees with a good trunk, branch, and root structure.
Good Structure (architecture or form) – Branch and trunk architecture resulting in a canopy form that resists failure.
Growth Ring – A new layer of xylem produced by the secondary growth system (cambium) typically demarcated by visible change in color.
Hand Pruners – Mechanical, single-handed pruners designed to cut twigs up to about ½ inch diameter.
Hanger – Dead branch fallen from the crown but caught by, and resting on, branches lower down.
Hazard Reduction – Reduces potentially hazardous conditions.
Hazardous Condition – A condition in a tree that could result in injury to people or damage to property.
Heading Cut – A type of pruning cut that prunes a shoot no more than 2 years old back to a bud; cutting an older stem back to a lateral branch less than 1/3 the diameter of the cut stem; cutting a stem to an indiscriminate length.
Healing – A physiological, regenerative process not known to occur in plants.
Heartwood – Xylem in the center of a trunk or branch that receives deposits from other portions of the tree; wood lacking living cells.
Hedging Shear – A two-handed mechanical or power tool designed to cut many shoots at once.
Included Bark – Bark pinched or embedded between two stems or between a branch and a trunk preventing formation of a branch bark ridge; an indication of a weak union; a crack in the union.
Informal Hedge – A shrub maintained by making heading or reduction cuts only on the longest shoots, 6 to 18 inches back inside the outer edge of the hedge.
Large Caliper Trees – Nursery trees greater than about 4 inches trunk diameter.
Large Maturing Trees – Trees that grow to a height or spread greater than about 40 feet.
Large Wound – A wound that can lead to defects.
Latent Bud – A suppressed bud lying just beneath bark, capable of forming a shoot, which grows enough each year to stay even with the bark.
Lateral Branch – A stem arising from a larger stem.
Lateral Pruning (cut) – See reduction.
Leader – A stem that dominates a portion of the canopy by suppressing lateral branches.
Leader Training Process – The technique that leads to development of one leader.
Limb – A large branch that is among the biggest on a tree.
Liners – Young seedlings planted in a container or field nursery for growing on to landscape sized trees.
Lions Tailing – The improper practice of removing all or most secondary and tertiary branches from the interior portion of the canopy leaving most live foliage at the edge of the canopy.
Live Crown Ratio – The ratio of the top portion of the tree baring live foliage to the cleared lower portion that includes the trunk, without live foliage.
Lopper – A tool best suited for cutting branches once they have been removed from a tree; a tool with two long handles used to cut stems on shrubs up to an inch diameter.
Lopping – A term used to describe topping.
Lowest Permanent Limb – The lowest large branch or scaffold limb that will remain on the tree for a long time.
Main Branches – Those that are the largest several on the tree. See also scaffold limbs.
Major Limbs – See scaffold limbs.
Matching Trees – A set of trees of the same species or cultivar with like sizes and shapes.
Maturity – The trees have attained full size.
Mature Trees – Trees that have reached at least 75 percent of their final height and spread.
Maximum Critical Diameter – The largest diameter pruning cut you are willing to make on a certain species.
Medium Aged Shade Trees – Trees more than about 15 to 20 years old that are not yet mature.
Modified Central Leader – A system of training small maturing trees to a single, short trunk with five to eight scaffold limbs.
Mop Top – Trees that will grow as a ground cover or sprawling or mounded shrub if not pruned initially to an upright trunk; plants trained with many weeping branches on top of one straight trunk.
Multiple Leaders (trunks) – A group of two or more leaders or trunks with a similar diameter.
Natural Tree Form – The form that develops in the tree’s native habitat without disturbance from human activities.
Neglected Tree – A poorly formed tree that has not been pruned for some time, or that has never been structurally pruned.
Node – The point on a stem where a leaf and bud emerge. Branches emerge from nodes.
Open Center System (open vase) – A training technique used on fruit trees that allows sunlight to reach developing fruit from above.
Open Landscape – An area with few trees within a few dozen feet.
Ornamental Tree – Those that never reach a large size.
Overthinning – Removal of too much foliage typically from the interior portion or lower portion of the canopy.
Permanent Branches (permanent Limbs) – Those that will remain on the tree for many years, perhaps until maturity.
Permanent Canopy – That portion of the tree that will remain for a long time.
Permanent Nursery Canopy – The portion of a nursery tree canopy that will be present when the tree is sold.
Phloem – Living cells located just outside the cambium that move sugars and other components about the plant.
Photosynthesis – The process that turns light energy into chemical energy in green plants.
Pinching – The equivalent of heading performed on a soft young stem.
Pith – The center, typically soft portion of a branch or stem that forms the first year that lacks living tissue.
Pleaching – Intertwines branches and trunks to form a hedge, archway, or tunnel.
Pole Saw – A saw with a long handle several feet long.
Pole Lopper – A device on a pole that passes a sharp blade past an anvil operated from the ground or in a tree used to remove small diameter branches.
Pollarding – This involves the removal of whole branches to leave only the main trunk. In species such as willows and poplars, such significant pruning is acceptable as new branches develop from the pollard heads. Secondary pruning of the new wood can help form a new canopy to the tree several years after the initial pollard.
Pollard Head – The starch-rich swollen living tissue comprised of callus, collars, and buds at the end of a branch or stem resulting from many years of removing shoots back to the same point.
Pollarding – The specialized training technique used to maintain a tree at a specified height with regular heading to the exact same position; not same as topping.
Pollarding Cut – A pruning cut that removes sprouts back to the same location annually or every other year.
Poor Compartmentalize – A plant with poor resistance to movement of discoloration and decay; decay could move rapidly through the plant following mechanical injury.
Poor Structure (form) – Branch and trunk architecture resulting in a canopy form that could lead to premature failure of a tree part.
Potentially Hazardous – See hazardous condition.
Pot In Pot – Arrangement of nursery containers so that one touches the others.
Preventive Arboriculture – Tree care practices and techniques incorporating strategies designed to prevent problems from occurring on trees in urban and suburban landscapes.
Preventive Tree Care – See preventive arboriculture.
Primary Branches – Branches attached directly to the trunk.
Production Protocol – A written plan for nursery trees detailing what is to be performed and when.
Pruning – Removal of plant parts.
Pruning Cycle – The interval or time between each pruning.
Pruning Dose – The amount of live tissue removed at one pruning; can be used in a whole-tree sense, or on one stem only.
Pruning Objectives – What is to be accomplished by pruning, for example, create and maintain strong structure by guiding a tree’s architecture.
Pruning Types – Includes clean, thin, reduce, raise, balance, risk reduction, restore, directional prune, vista, root prune, eradicate and structural pruning.
Quality Nursery Tree – Trees with good root and branch structure, typically with no circling or kinked roots and a dominant leader (for shade trees).
Quaternary Branches – Branches growing from tertiary branches.
Radial Crack – A crack beginning from a ring crack that forms along a ray and may extend to the bark.
Raise (raising) – Provides vertical clearance under canopy.
Rays – Long groups or plates of living cells that extend from the phloem into the xylem toward the center of the trunk.
Reduce (reduction) – Decreases height or spread on entire tree, or one section only, using reduction cuts; also referred to as reduction or reduction pruning.
Reduction Cut (drop-crotch cut) – Reduces the length of a branch or stem back to a live lateral branch large enough to assume the apical dominance – this is typically at least one third the diameter of the cut stem.
Regular Pruning – Pruning at a more-or-less set interval, such as yearly or every five years.
Removal Cut – Removes a branch from the trunk or parent branch.
Renovate – Cutting a shrub back to the ground or nearly so in order to increase vigor.
Restore (restoring, restoration) – The process of improving the structure of a tree that was previously topped, damaged, vandalized, or over-thinned.
Resistograph Decay Testing – Performed using the IML Resistograph. This test allow us “see” the sound and decayed wood in 1:1 ratio at almost any area of the tree. This test allows us to make much more precise judgments in the assessment of decay (especially in trees with more advanced issues).
Ring Crack – A crack that forms along a wall 4.
Risk Assessment (tree risk assessment) – Visual tree assessment; VTA Level 1: Performed from the ground using basic inspection tools. Each tree is given a numerical risk rating and for each rating, a definition and basic actions are described. VTA Level 2: Performed using more entailed testing equipment as well as time. Each tree is given a numerical risk rating as well as more detailed mitigation actions. VTA Level 3: Performed from the ground as well as aloft (climbing involved) to inspect upper sections of the tree. Each tree is given a numerical risk rating and detailed mitigation action.
Root Collar Excavation (RCE) – By moving the soil away from the root zone we can inspect them for any underground issues. (I.e. planting depth, twine, burlap, or stem girdling roots.) In many cases, these issues can be corrected at time of excavation/inspection, and the tree can make a good recovery. May only be for diagnostic purposes.
Root Problems (defects) – Conditions in the root system that could lead to poor health, or plants falling over such as circling roots, cut roots, decayed roots, no trunk flare, and deep planting.
Root Protection Area (RPA) – The RPA of a tree is the area around its base that contains sufficient rooting volume to ensure the survival of the tree in the event of nearby soil disturbance (as on a development site). The RPA is calculated using guidelines in BS 5837 (2005) Trees in relation to construction – Recommendations
Root Pruning – Removes circling and girdling roots around trunk base; a technique of cutting many roots on a tree growing in a field nursery or landscape to prepare it for digging; cutting roots regularly to help keep a plant small.
Rounding Over (round over) – Reducing the size of a tree by pruning the outer edge of a canopy with small-diameter (typically less than 2 inches) heading cuts; diameter of the cuts are typically small compared to a tree that was topped.
Sapling – A young tree about 1 to 3 years old.
Scaffold Limb – A branch that is among the largest in diameter on the tree.
Senescence – The third phase of a tree’s life, after youth and maturity, when the leaf area of the crown tends to diminish. Veteran trees are generally senescent.
Secondary Branches – branches growing from primary branches.
Seedling – A young tree less than about 1 year old.
Shade Tree – Those that grow to be more than about 35 feet at maturity.
Shears – A tool used to cut many small diameter stems at once.
Single Leadered Tree – A tree with a dominant trunk.
Small Maturing Tree – A tree that reaches about 25 to 30 feet in height at maturity.
Species Selection – The process of choosing a plant for a specific location.
Specifications – Describe what pruning types should be performed and provide other details of the pruning required for the job.
Splints – Stakes that have no contact with the ground used in a nursery to forma straight trunk.
Standard – A tree or large shrub trained into one short, straight trunk with a small dense, round canopy.
Standards – Industry accepted definitions and principles.
Starch – A chain of sugars linked together that stores chemical energy for later use by the plant.
Stem – Slender woody structure bearing foliage and buds that gives rise to other stems.
Stem Bark Ridge – Raised bark in the union of two stems.
Stomata – Pores or openings in leaves, typically on the undersides, through which gases such as CO2, O2 and water vapor pass.
Stooling – Cutting a plant nearly to the ground each year.
Structural Pruning – Pruning that influences the orientation, spacing, growth rate, strength of attachment, and ultimate size of branches and stems resulting in a strong tree.
Structure – The spacing, orientation, and size of branches relative to the trunk; the arrangement of trunk and branches; the tree’s architecture.
Stub – The piece of branch left beyond the collar after a removal cut.
Stump Grinding – A term used to describe a method of removing a stump after a tree has been cut. A specialized piece of machinery with a large wheel and teeth is used to chip away the stump to below the surface of the ground.
Subordination (Subordination Pruning, Suppression) – Removing the terminal, typically upright or end portion of a parent branch or stem to slow growth rate so other portions of the tree grow faster.
Sunscald – A flattened, dried, or sunken area of the bark resulting from overexposure to the sun.
Suppression – See subordination.
Symplast – Network of living cell contents.
Taper – The thickening of a stem or branch toward its base.
Temporary Branch – A branch that will remain on the tree for only a short period; not a permanent limb.
Terminal Bud Cluster Pruning – Removing all buds except for the terminal from the end portion of a dormant twig.
Tertiary Branches – Branches growing from secondary branches.
Thin (thinning) – Removes lateral branches from the edge of the canopy; increases light and air penetration, or reduces weight by removing branches primarily from the outer edge of the canopy.
ThinningCut – See removal cut.
Tipping – similar to topping except heading cuts.
Topiary – A training system that creates an animal, column, ball or other shape with regular heading or shearing.
Topping – An inappropriate technique to reduce tree size that makes heading cuts through a stem more than 2 years old; a type of pruning cut destroys tree architecture and serves to initiate discoloration and perhaps decay in the cut stem.
Transpiration – Evaporation of water vapor from foliage.
Tree Evaluation – The process of determining what actions should be taken to improve plant health and reduce risk.
Tree Habit – The form or shape taken on by the canopy.
Tree Inspection – The careful process of checking for defects that could lead to tree failure while climbing.
Tree Preservation Order (TPO) – A Tree Preservation Order (TPO) is an order made by us which in general makes it an offence to cut down, lop, top, uproot, willfully damage or willfully destroy a tree without first getting permission from us. Tree Preservation Orders are usually made to protect trees that make a significant contribution to the amenity of an area. They may particularly be made when it is felt that a tree may be under threat. For further information, please visit our Tree Preservation Order page.
Tree Shelters – Tubes 2 to 4 inches in diameter, about 3 to 4 feet long made from various materials that are placed around the trunk of young saplings.
Tree Surgeon – A contractor skilled in performing aerial operations in trees near buildings and roads.
Trimming – Clipping the ends of young branches using heading cuts; see tipping.
Trunk – The main woody part of a tree beginning at the ground and extending up into the canopy from which primary branches grow.
Union (crotch) – The junction between stem and branch or between stems.
Urban Forestry – the management of naturally occurring and planted trees and associated plants in urban areas. Urban forestry came from the forestry management when the management of trees (forests) were expanded into public areas—communities with development of electrical and telephone lines (utility lines) around the nation and world around, 1924-1926 in the state of Michigan and perhaps earlier in other parts of the nation.
Utility Arborist – An arborist with specialized training who prunes trees near energized wires and other utility equipment.
Utility Tree Care – Tree practices near overhead lines and other potentially hazardous structures.
Vigorous Branches – Those that grow at a fast rate compared to most other branches on the tree; aggressive branches.
Vista Pruning – A combination of pruning types including; thinning, raising, and others designed to enhance a view.
Wall 1 – A term used to describe the boundary formed by plugging of xylem vessels, sometimes in response to injury; the weakest boundary that resists movement of discoloration and decay up and down the xylem.
Wall2 – A term used to describe the boundary between one growth ring and the next; a boundary that resists movement of discoloration and decay in toward the pith usually considered stronger than wall.
Wall3 – A term used to describe the boundary formed by rays; a boundary that resists movement of discoloration and decay around the trunk along growth rings usually considered stronger than wall 2.
Wall4 – A term used to describe the boundary formed by a reaction zone along the cambium in response to injury; the strongest boundary that resists movement of discoloration and decay into wood formed after injury.
Water Sprouts – Stems arising from interior branches often growing upright and vigorously, often as a result of a stress such as overpruning, drought, or root damage.
Weak Crotch (union) – A union with included bark; a union that is relatively weak compared to other unions.
Wind Throw – When a tree falls over due to a strong wind.
Wound Closure – The process of forming callus and wound wood over a wound such as a pruning cut.
Wound Dressing – A substance, solution or formulation developed for application over a recent pruning cut.
Woundwood – Differentiated woody tissue forming around a wound, such as a pruning cut. See callus for comparison.
Xylem – The woody part of the tree that begins on the inside of the cambium.