Arboriculture Glossary of Terms

There are 1070 entries in this glossary.



ABC (aerial bundle cable): system of reducing the physical hanging space of aboveground electrical conductors.
abiotic: nonliving.
abiotic disorder: plant malady caused by nonliving, environmental, or man-made agents.
abscisic acid (ABA): plant hormone that stimulates stomatal closure and promotes seed and bud dormancy. Inhibits shoot growth but may promote root growth. Plays a role in wounding responses and in abscission of leaves and fruit.
abscission: leaf or fruit drop induced by hormonal changes.
abscission zone: area at the base of the petiole where cellular breakdown leads to leaf and fruit drop.
absorbing roots: fine, fibrous roots that take up water and minerals. Most absorbing roots are within the top 12 inches (30 centimeters) of soil.
absorption: taking up. Contrast with adsorption.
acceleration: rate of change of the velocity of an object. Acceleration is a vector quantity. See vector and velocity.
access line: (1) second climbing line hung in a tree in case it is needed to reach a victim in an emergency. (2) climbing line installed in a tree to gain access to, but not used to work, the tree.
access route: defined entrance and exit route for a property during construction, tree work, or landscape operations.
acclimation: physiological adaptation process of plants and other living organisms to a climate or environment different from their native environment or where originally grown.
acid: having a pH less than 7.0. Contrast with alkaline.
acidity: state or quality of being acid. Contrast with alkalinity. See pH.
actinomycetes: group of soil bacteria resembling fungi. Actinomycetes play a role in the decomposition of organic matter and the release of mineral elements.
action: pertaining to carabiners and snaps, the number of distinct motions for the gate to be opened. A nonlocking carabiner is single action, requiring one movement for the gate to be opened.
acuminate: term describing leaves that taper sharply at their tip (apex).
acute: disorder or disease that occurs suddenly or over a short period of time. Contrast with chronic.
adaptability: genetic ability of plants and other living organisms to adjust or acclimate to different environments.
adjustable balancer: adjustable rigging sling used to balance limbs in rigging operations.                                                                               adpressed: in close, tight proximity. Pressed close to or lying flat against something. Appressed.
adsorption: adhesion on contact of the molecules of gases, dissolved substances, or liquids to the surface of solids or liquids with which they are in contact. Contrast with absorption.
adventitious: arising from parts of the root or stem and having no connection to apical meristems.
adventitious bud: bud arising from a place other than a leaf axil or shoot tip, usually as a result of hormonal triggers.
adventitious roots: roots arising from roots or stems and having no connection to apical meristems.
aeration: provision of air to the soil to alleviate soil compaction and improve its structure.
aeration system: set of holes or trenches created in the tree
aerial device (aerial lift device): truck with booms and a bucket for elevating a worker to the proximity of a tree
aerial rescue: method of bringing an injured worker down from a tree or aerial lift device.
aesthetic: pleasing to the senses, visually or otherwise. Artistic.
aggregate: close cluster or mix of small particles of soil and/or organic matter of varying size that are bonded together; sand, gravel, or small rocks in soil; and/or sand, gravel, or small rocks used under paved surfaces. Also clusters of flowers or fruits that appear as a single unit. Also individual tree crowns that form a canopy.
air excavator: device that directs a jet of highly compressed air to excavate soil. Used within the root zone of trees to avoid or minimize damage to the roots, or near underground structures such as pipes and wires to avoid or minimize damage to them.
air terminal: uppermost point of a tree lightning protection system.
alkaline: having a pH greater than 7.0. Contrast with acid.
alkalinity: state or quality of being alkaline. Contrast with acidity. See pH.
all: two parallel rows of trees, usually of the same species, form, and age, often having canopies that have grown together.
allelochemicals: substances produced naturally by plants as part of a defense against pests and other plants. May adversely affect the growth and development of other plants.
allelopathy: chemical effect or inhibition of growth or development of plants that is induced by allelochemicals.
alternate: pertaining to bud or leaf arrangement, one leaf or bud at each node, situated at alternating positions along the stem. In this arrangement, the leaves are not directly across from each other. Contrast with opposite and whorled.
alternate host: one of a number of separate obligate hosts to the different life stages of certain pathogens, such as rusts, which must alternate between hosts.                                                                                                                                                                                                                     amon-eye nut: specialized nut used in cabling trees that has a large eye for attaching a cable to a threaded rod.
ampere (amp, A): (1) measure of electrical current flow through an electrical conductor; the flow of one volt through a wire with a resistance of one ohm. (2) the current draw or power rating of electrical power tools and appropriately sized power cords and sources and circuit breakers. Important to understand for efficient and safe use of such tools.
anatomy: (1) study of the structure and composition of plants and other living organisms. (2) structure and composition of plants and other living organisms. Contrast with morphology, physiology, and taxonomy.
anchor: (1) in cabling, hardware to which support cable is affixed. (2) in rigging, the point at which the rigging system is secured or where friction is controlled.
anchor block: in a mechanical advantage system that employs pulleys, the stationary block in a block and tackle system.
anchor force: sum of the forces acting on the anchor point(s) in a rigging system.
anchor hardware: hardware to which the cable termination is affixed in a cabling or guying installation.
anchor hitch: knot commonly used to attach a line to a piece of hardware. Anchor bend.
angiosperm: plant with seeds borne in an ovary. Consists of two large groups: monocotyledons (grasses, palms, and related plants) and dicotyledons (most woody trees, shrubs, herbaceous plants, and related plants). Contrast with gymnosperm.
anion: ion that carries a negative charge. Contrast with cation.
annual: plant living only one year. Compare to biennial and perennial.
annual rings: see growth rings.
ANSI: acronym for American National Standards Institute.
ANSI A300: in the United States, industry-developed, national consensus standards of practice for tree care.
ANSI Z133.1: in the United States, industry-developed, national consensus safety standards of practice for tree care.
ANSI Z60.1: in the United States, industry-developed, national consensus standards for nursery stock.
anthocyanin: red or purple pigment responsible for those colors in some parts of trees and other plants. Compare to carotenoid and xanthophyll.
anthracnose: group of fungal diseases of trees that affect the leaves, stems, flowers, or fruit, causing spotting, blotching, or necrosis.
anti gibberellin: plant growth regulator that inhibits the action of the plant hormone gibberellin, which, among other things, regulates cell elongation.
antitranspirant: substance applied to the foliage of plants to reduce water loss (transpiration).                                                                                 anvil-type pruning tool: hand pruning tool with a sharp, straight blade that cuts against a flat metal surface. Cuts across fibers and may crush adjacent fibers. Intended for cutting single, small-diameter stems. Also called hand pruners or hand snips.
apical: having to do with the tip of a leaf or stem.
apical bud: see terminal bud.
apical control: inhibition of lateral buds, decreasing from the top down, by apical buds over many seasons, resulting in trees with an excurrent growth form.
apical dominance: condition in which the terminal bud inhibits the growth and development of the lateral buds on the same stem formed during the same season.
apical meristems: growing points at the tips of shoots and roots.
apoplasm: free spaces in plant tissue. Includes cell walls and intracellular spaces. Contrast with symplasm.
appraisal: (1) placing a monetary value on a tree, other plant, other landscaping, including hardscape, or an entire property. (2) a report stating an opinion of appraised value. (3) particularly outside the United States, an evaluation of nonmonetary landscape or plant characteristics.
approach distances: minimum distances that must be maintained between conductors and other energized equipment and qualified line-clearance personnel or persons other than line-clearance personnel and their bodies or tools. Approach distances vary with qualifications of personnel and with voltages.
appropriate response process (ARP): method of systematically assessing plant health and client needs to determine which course of action, if any, is recommended.
approved: in the context of guidelines, standards, and specifications, that which is acceptable to federal, state, provincial, or local enforcement authorities or is an accepted industry practice.
arboriculture: practice and study of the care of trees and other woody plants in the landscape.
arborist: professional who possesses the technical competence gained through experience and related training to provide for or supervise the management of trees and other woody plants in residential, commercial, and public landscapes.
arborist block: heavy-duty pulley with an integrated connection point (bushing for attaching a rope sling), a rotating sheave for the rope, and extended cheek plates. Used in tree rigging operations.
artificial respiration: forcing air into the lungs of a person who has stopped breathing. See also cardiopulmonary resuscitation (CPR).
AS 4373-1996, Pruning of Amenity Trees: in Australia, industry-developed, national consensus standards of practice for pruning.
ascender: piece of gear that enables a climber to ascend a rope. Attached to the rope, it will grip in one direction (down) and slide in the other (up). Contrast with descender.                                                                                                                                                                                     asymptomatic: without symptoms.
auger: tool that bores holes in wood or other materials while carrying cuttings away from the bored hole. Fitted with a cross handle for hand use.
auger bit: tool that bores holes in wood or other materials while carrying cuttings away from the bored hole. Fitted with a hex, round square, or threaded shank for insertion into a power drill or driver.                                                                                                                                                 auxin: plant hormone or substance that promotes or regulates the growth and development of plants. Produced at sites where cells are dividing, primarily in the shoot tips. Auxinlike compounds may be synthetically produced.
available water: water remaining in the soil after gravitational water has drained and before the permanent wilting point has been reached. Compare to field capacity, gravitational water, permanent wilting point, and saturation point.
axial transport: movement of water, minerals, or photosynthates longitudinally within a tree.
axil: point of attachment of a leaf petiole to a stem.
axillary bud: bud in the axil of a leaf. Lateral bud.                



back cut: cut made on a tree trunk or branch, opposite from and toward the notch, face cut, or undercut, to complete felling or branch removal. Contrast with bore cut.
back feed: process whereby electricity is fed back into downed lines, usually from a home generator that can re-energize the lines. Voltage can be modified if it passes through a transformer.
backfill: (1) soil or amended soil used to fill the hole when planting a tree. (2) soil, common fill, aggregates, or contaminants in various combinations put back into an excavation. May not be hospitable for tree root growth and function.
bacteria: single-celled organisms having a cell wall but no organized nucleus. A few species are plant pathogens.
balance: in rigging, a technique for lowering a limb without allowing either end to drop.
balancer: rigging sling(s), usually with at least one spliced eye and a Prusik to position the load line. Used to rig a limb in a balanced configuration.
balled and burlapped (B&B): ree or other plant dug and removed from the ground for re-planting, with the roots and soil wrapped in burlap or a burlaplike fabric. Contrast with bare root, container grown, containerized, and in-ground fabric-bag grown.
barber chair: dangerous condition created when a tree or branch splits upward vertically from the back cut, slab up.
bare root: tree or other plant removed from the ground for re-planting without soil around the roots. Contrast with balled and burlapped, container grown, containerized, and in-ground fabric-bag grown.
bark: protective outer covering of branches and stems that arises from the cork cambium or cambium.
bark tracing: cutting away torn or injured bark to leave a smooth edge.
barrier: see root barrier and tree protection zone barrier.
barrier zone: chemically defended tissue formed by the still-living cambium, after a tree is wounded or invaded by pathogens, to inhibit the spread of decay into new annual growth rings. Wall 4 in the CODIT model. Contrast with reaction zone.
basal bark application: application of herbicides, usually mixed with penetrating oil, to the lowest 12 to 18 inches (30 to 45 centimeters) of the main stem(s) of unwanted vegetation.
bearing: device, often relying on balls or rollers, to reduce friction between mechanical parts such as a wheel or a pulley sheave and an axle or a shaft and case connecting rod. Contrast with bushing.
becket: an auxiliary attachment point on a block or pulley, usually 180 degrees from the main attachment, that is used to reeve the rigging line in a set of blocks.
beer knot: knot commonly used to join two ends of a piece of tubular webbing to create a loop. See water knot.
belay: means of securing or slowing a climbing line by using wraps around a cleat, carabiner, or other device.
belay device: piece of equipment used to provide friction for belaying a climber.
bend: type of knot used to join two rope ends together. Contrast with hitch.                                                                                                                 bend radius: radius of an object around which a line passes.
bend ratio: ratio of the diameter of a branch, sheave, or other object to the diameter of the rope that is wrapped around it.
best management practices (BMP): best-available, industry-recognized courses of action, in consideration of the benefits and limitations, based on scientific research and current knowledge.
better half hitch: half hitch(es), typically two or more, added to other knots for additional security. Also called 
biennial: plant living two years. Usually grows vegetatively the first year, then flowers and fruits the second year. Compare to annual and perennial.
bifurcation: natural division of a branch or stem into two or more stems or parts.
bight: curve or arc in a rope between the working end and the standing part.
biodegradable: capable of being broken down by natural, organic processes and reabsorbed into the environment.
biological control: method of managing plant pests or weeds through the use of natural predators, parasites, or pathogens.
biotic: pertaining to living organisms.
biotic disorder: disorder caused by an infectious living agent.
bipinnate: double pinnate. Contrast with palmate and pinnate.
blade: (1) expanded body of a leaf. (2) sharp, cutting part of a tool.
Blake: friction knot climbers use, sometimes in place of the tautline hitch or Prusik knot.
bleeding: (1) flow of sap from plant wounds, injuries, or pathogen invasion. (2) flow of blood from a human or animal wound.
blight: any disease or disorder, regardless of the causal agent, that kills young plant tissues.
block: heavy-duty pulley used in rigging. Designed for dynamic loading.
block and tackle: system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.
blocking: method of using an arborist block to rig down trunk sections. Contrast with butt-hitching.
body-thrust: method of ascending a tree using a climbing rope.                                                                                                                                     bole: main trunk of a tree below the branches, usually used in reference to a tall tree whose first branch is high off the ground.
bollard: post on which wraps can be taken with a rope to tie it off or to provide friction for control.
bolt: (1) lag- or machine-threaded cable anchor or bracing rod; used with a nut and washer in supplement support systems in trees. (2) a machine-threaded fastener used with a nut and washer in various equipment or structures.
bonding conductor: conductor that connects a tree support cable or metal conduit to a lightning protection system.
bonsai: art of pruning and managing tree growth through root pruning to maintain a miniature size.
boom: long, movable arm of an aerial device or crane.
bore cut: using the tip of a chain saw to cut into or through the middle of a piece of wood. Back-cut technique in which the hinge is established by plunge cutting through the stem, then cutting back away from the hinge. Plunge cut. Contrast with back cut.
botanicals: compounds (pesticides, oils, etc.) made from plants.
bowline: loop knot used to form single or double endline loop(s) in a rope, often to attach items to the rope.
bowline on a bight: knot used to form two loops in the standing part of a rope.
box cable system: tree cabling system that forms closed polygons. Used to join together more than three stems. Contrast with direct cable system and triangular cable system.
bracing: installation of metal rods through portions of a tree for supplemental support.
bracing rod: metal rod used to support weak sections or crotches of a tree.
braided rope: rope construction in which the strands are woven together in a diagonal pattern. Contrast with 3-strand rope.
branch: stem arising from a larger stem. A subdominant stem. Pith in true branches has no connection to the parent stem.
branch bark ridge: raised strip of bark at the top of a branch union, where the growth and expansion of the trunk or parent stem and adjoining branch push the bark into a ridge.
branch collar: area where a branch joins another branch or trunk that is created by the overlapping vascular tissues from both the branch and the trunk. Typically enlarged at the base of the branch.
branch protection zone: chemically and physically modified tissue within the trunk or parent branch at the base of a smaller, subordinate branch that retards the spread of discoloration and decay from the subordinate stem into the trunk or parent branch.
branch union: point where a branch originates from the trunk or another branch. Fork. Crotch.
breaking strength: force at which a new piece of equipment or rope fails under a static load.                                                                                 bridge graft: method to repair a semi-girdled to completely girdled trunk in which scion wood is grafted above and below the trunk injury to reconnect the trunk vascular cambium.
broadcast fertilization: application of fertilizer over the soil surface. Contrast with drill-hole fertilization and liquid fertilization.
brown rot: fungal wood rot characterized by the breakdown of cellulose. Contrast with soft rot and white rot.
brownout: term describing the brown appearance of dead foliage, usually following the application of herbicide.
brush chipper: see chipper.
BSI: acronym for British Standards Institution.
buck strap: strap used in tree climbing, often employed for ascending trees with climbing spurs. Similar to a work-positioning lanyard.
bud: small lateral or terminal protuberance on the stem of a plant that may develop into a flower or shoot. Undeveloped flower or shoot containing a meristematic growing point.
bud trace: vascular connection extending from the base of latent buds inward to near the pith. Grows in length with each annual increment and appears as a thin, continuous line when viewed in longitudinal section.
buffering capacity: ability of a soil to maintain (i.e., resist change in) its pH.
bulk density: mass of soil per unit volume. Often used as a measure of compaction.
buntline hitch: simple hitch commonly used to attach a line to a piece of hardware.
burl (burr, in British English): an abnormal swelling of a tree trunk characterized by swirling wood grain and meristematic tissue. Wood with these structures is prized for woodworking. Contrast with gall.
burlap: (1) strong, coarsely woven cloth made from fibers of jute, flax, or hemp. (2) a burlaplike fabric made of synthetic fibers. Both are used for containing soil in a root ball. See balled and burlapped.
bushing: (1) metallic tube or lining, without moving parts, to reduce friction between mechanical parts such as a pulley sheave and an axle; also the nonrotating sheave used to increase the bend radius for the sling attachment. Contrast with bearing. (2) a device, often made of rubber or plastic, to reduce vibration or wear between mechanical parts. (3) a fitting used to connect plumbing parts of different diameters (such as in spray equipment).
butt rot: decay of the lower trunk, trunk flare, or buttress roots. See crown rot.
butt-hitching: method of lowering pieces when the rigging point is below the work, traditionally without the use of a block. Contrast with blocking.
butt-tying: tying off a limb at the butt (larger) end for rigging.
butterfly knot: knot that can be used to form a loop in the standing part of a line.
buttress roots: roots at the trunk base that help support the tree and equalize mechanical stress.


cable aid: device used to tighten lags and aid in cable installation.
cable anchor: hardware to which a cable termination is affixed in a cabling or guying installation.
cable clamp: double-bolted, U-shaped clamp, sometimes used to secure tree cables. Not acceptable or approved for tree support systems in the United States.
cable grip: mechanical device that grasps and holds the cable during installation.
cabling: installation of steel or synthetic cable in a tree to provide supplemental support to weak branches or crotches.
callus: undifferentiated tissue formed by the cambium, usually as the result of wounding. Contrast with woundwood.
cambium: thin layer(s) of meristematic cells that give rise (outward) to the phloem and (inward) to the xylem, increasing stem and root diameter.
canker: localized diseased area on stems, roots, and branches. Often shrunken and discolored.
canopy: collective branches and foliage of a tree or group of trees
can't hook: lever with an adjustable hook and having a blunt end instead of a spike. Used for handling and rolling logs. Traditionally made with a stout wooden lever but now often made of metal. Contrast with peavey.
carabiner (karabiner): connecting device. Oblong metal ring used in climbing and static rigging that is opened and closed by a spring-loaded gate. Contrast with snap.
compound, combining carbon, hydrogen, and oxygen, that is produced by plants as a result of photosynthesis. Sugars and starches.
cardiopulmonary resuscitation (CPR)
procedure used by a trained person to force air into the lungs and to force blood circulation in a person whose heart has stopped beating. See also artificial respiration.
yellow, orange, or red pigment responsible for those colors in some parts of trees and other plants. Compare to anthocyanin and xanthophyll.
positively charged ion. In soils, the most abundant cations are calcium (Ca), magnesium (Mg), potassium (K), sodium (Na), and aluminum (Al). Contrast with anion.
cation exchange capacity (CEC)
ability of a soil to adsorb and hold cations. Affected by soil pH. Measures soil fertility, clay composition, and engineering characteristics.
causal agent
biotic or abiotic agent that induces a disease or disorder.
open or closed hollow within a tree stem, usually associated with decay.
basic structural and functional unit of living organisms.
cellulose complex carbohydrate found in the cellular walls of the majority of plants, algae, and certain fungi.