Dictionary
Area at the base of the petiole where cellular breakdown leads to leaf and fruit drop
The degree or amount of risk that the owner, manager, or controlling authority is willing to accept
The highest level of risk that does not exceed the owner/manager’s tolerance
An assessment performed to provide detailed information about specific tree parts, defects, targets, or site conditions. Specialized equipment, data collection and analysis, and/or expertise are usually required
Branch arising from a stem or parent branch and having no connection to apical meristems.
Roots arising from roots or stems and having no connection to apical meristems
Inspection of the upper tree parts not readily accessed from the ground; typically done by climbing or from an aerial lift.
Overflights of utility right-of-way, large areas or individual trees in a defined area to record the location of trees that are likely to fail or cause harm
Detailed examination of the elements or structure of something
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)
Rings of xylem that are visible in a cross section of the stem, branches, and roots of some trees. In temperate zones the rings typically represent one year of growth
A chemical and anatomical barrier formed by the cambium present at the time of wounding in response to wounding. Inhibits the spread of decay into xylem tissue formed after the time of wounding. Wall 4 in the CODIT model (contrast with reaction zone)
Increased wood growth in the area near or where the trunk and roots come together
Detailed visual inspection of a tree and surrounding site that may include the use of simple tools. It required that a tree risk assessor inspect completely around the tree trunk looking at the visible aboveground roots, trunk, branches and site.
A turning, bending or twisting force exerted by a lever, defined as the force (acting perpendicular to the lever) multiplied by the length of the lever (see moment).
The study of the action of forces on living trees
Leans characterized by the top of the tree bending over more than the lower trunk, creating a curve
Metal rod used to support weak sections of crotches of a tree
The fruiting body of a decay fungus (see conk)
Failure to take reasonable care to avoid injury or damage to a person or property in a situation where the law imposes a duty of care.
Fungal wood rot characterized by the breakdown of cellulose (contrast with soft rot and white rot)
Failure mode characteristic of collapsing under compressive stress
Swellings on branches, trunk, or root flares: often caused by new tissue formed as a response to movement and that reinforces the wood structure at the weak area.
Decay of the lower trunk, trunk flair, or buttress roots
Roots at the trunk base that help support the tree and equalize mechanical stress.
Installation of steel or synthetic cable in a tree to provide supplemental support to weak branches or branch union.
Undifferentiated tissue formed by the cambium, usually as the result of wounding (contrast with woundwood)
Thing layer(s) of meristematic cells that rive rise (outward) to the phloem and (inward) to the xylem, increasing stem and root diameter
localized diseased area on stems, roots, and branches. Often shrunken and discolored.
Open or closed hollow within a tree stem, branch or root usually associated with decay
Complex carbohydrate found in the cellular walls of the majority of plants, algae, and certain fungi.
The point toward or from which a force acts; the resultant point of aggregate forces
The person or organization for whom professional services are rendered. Usually, the owner or manager responsible for the trees.
Instrument used for measuring the height of a tree or other structure.
Acronym for compartmentalization of Decay in Trees (see compartmentalization)
forked branches nearly the same size in diameter, arising from a common junction and lacking a normal branch union
Wood decay inside a tree that extends longitudinally up and down a stem or through a branch.
Natural defense process in trees by which chemical and physical boundaries are created that act to limit the spread of disease and decay organisms (see CODIT)
In mechanics, the action of forces to squeeze, crush, or push together any material or substance (contrast with tension)
Fracture caused by compressive stress.
Reaction wood in gymnosperms, and some angiosperms, that develops on the underside of branches or leaning trunks and is important in load bearing (contrast with tension wood).
The summary and result of a risk assessment.
Fruiting body or nonfruiting body (sterile conk) of a fungus. Often associated with decay (see bracket)
Outcome of an event
Personal injury, property damage, or disruption of activities due to the failure of tree or tree part.
A target is present at nearly all times, 24 hours a day, 7 days a week.
Tree lean characterized by a leaning lower trunk and a top that is more upright as a result of self-correction; sweep
Separation in wood fibers; narrow breaks or fissures in stems or branches. If server, may result in tree or branch failure
Process of degradation by microorganisms.
An instrument or tool developed to detect decay in tree parts.
The breakdown or separation of a substance into simpler substances.
An imperfection, weakness, or lack of something necessary. In trees, defects are injuries, growth patterns, decay, or other conditions that reduce the tree’s structural strength
An indicator that decay is definitely present.
The amount or extent of injury, damage, or disruption
The length of a straight line through the center of a circle
A measuring tape scaled such that when it encircles a tree trunk, the diameter can be read directly
Wood response of a tree to microorganisms, including bacteria and non-decay-causing fungi, resulting in dead, darkened wood with little strength
A delay or interruption of progress or continuity.
The tree or trees in a stand that are typically larger in height (taller), diameter, and crown spread that all the adjacent trees.
Wind resistance
Imaginary line defined by the branch spread of a single plant or group of plants
Limited visual inspection from only one side of the tree, performed from a slow-moving vehicle. Also, may be called a windshield assessment.
Legal obligation that requires an individual to apply reasonable actions when performing tasks that may potentially harm others
Study of how objects move under the action of forces.
Portion of an annual right (growth ring) that forms during spring, characterized by large-diameter cells and thin walls. Also called springwood (contrast with latewood).
A tree on the edge of a stand, growing under conditions of light and exposure different from those prevailing within the stand.
The body of moral principles or values governing a group or individual’s conduct
Occurrence of a particular set of circumstances. In tree risk assessment, a tree or tree part falling and impacting a target.
Defined by its placement in the risk rating matrix (Matrix 2); failure is imminent with a high likelihood of impacting the target, and the consequences of the failure are severe.
Breakage of stem, branch, or roots, or loss of mechanical support in the root system.
Location/manner in which failure could or has occurred; for example, stem failure, root failure or soil failure.
Elongated, tapering, thick-walled cell that provides strength to wood
A long, narrow opening or split
Response growth triggered by the continued flexing of a tree stem or branch
Any action or influence causing an object to accelerate/decelerate. Calculated as mass multiplied by acceleration. Is a vector quantity.
A group of trees in a wooded setting
Frost crack; vertical split in the wood of a tree, often near the base of the bole, caused by internal stresses and low temperatures
The target zone Is occupied for a large portion of the day or week.
Vertical split in the wood of a tree, often near the base of the bole, caused by internal stresses and low temperatures
The reproductive structures of a fungus (conks, brackets, mushrooms).
Group of organisms from the kingdom Fungi, including yeasts, molds, mushrooms, and smuts. Typically multicellular, saprophytic, or parasitic and lacking vascular tissue and chlorophyll. Reproduces vegetatively and by various types of spores borne in fruiting bodies.
Root that encircles all or part of the tree trunk or the tree’s other roots, constricting the vascular tissues and inhibiting secondary growth and the movement of water and photosynthates.
A topographic alteration to the surface of the round
The force that attracts a body toward the center of the earth
A nondestructive device that uses radar pulses to image the subsurface
1) A steel or synthetic-fiber cable between a tree or branch and an external anchor (another tree, the ground, or other fixed object) to provide supplemental support.
2) A steel cable between a utility pole and external anchor (another pole, the ground, or other fixed object, which may sometimes be a tree) to keep the pole upright. Guys act in tension (contrast of prop)
Plants with exposed seeds, usually within cones (contrast with angiosperm)
A load test that involves installing a line in a tree, and then pulling and releasing the line several times to move the tree or branch. Most commonly used in a pre-work inspection but can be used as part of an advanced tree risk assessment.
Personal injury or death, property damage, or disruption of activities.
situation or condition that is likely to lead to a loss, personal injury, property damage, or disruption of activities; likely source of harm. In relation to trees, a hazard is the tree part(s) identified as a likely source of harm.
A tree identified as a likely source of harm
Wood that is altered (inward) from sapwood and provides chemical defense against decay-causing organisms and continues to provide structural strength to the trunk. Trees may or may not have heartwood (contrast with sapwood)
Any of several types of fungal decay of tree heartwood, often beginning with infected wounds in the living portions of wood tissue. Also called heart rot.
The failed tree or tree part is likely to impact the target. This is the case when there is a constant target, with no protection factors, and the direction of fall is toward the target.
Defined by its placement in the risk rating matrix (Matrix 2); consequences are significant, and likelihood is very likely or likely, or consequences are severe and likelihood is likely
Study of the properties, distribution and effects of water on the Earth’s surface, underground, and the atmosphere.
Failure has started or is most likely to occur in the near future, even if there is no significant wind or increased load. The imminent category overrides the stated time frame.
Striking a target or causing a disruption that affects activities
The tree or tree part is not likely to fail during normal weather conditions and may not fail in extreme weather conditions within the specified time frame.
Bark that becomes embedded in a crotch (union) between branch and trunk or between codominant stems. Causes a weak structure.
An organized and systematic examination.
The number of inspections per given unit of time (for example, once every three years)
Time between inspection
A tree within a stand of trees, protected from wind exposure
Disruptions to a terrestrial site, community or ecosystem that alters the physical environment.
Actions, events, or changes that have taken place on a site
Portion of an annual ring (growth ring) that have taken a place on a site
Predominant angle of the trunk from vertical
A principle or rule established by a prior court or other decision-making body
The distance between the applied force (or center of force) and the point where the object will bend or rotate.
Categorization of the breadth and depth of analysis
Something for which one is responsible. Legal responsibility
A remote sensing method that uses laser technology to measure tree size and location in relation to the target of concern
Hardware installed in a tree to conduct the charge of a lighting strike to ground
Organic substance that impregnates certain cell walls to thicken and strengthen the cell to reduce susceptibility to decay and pest damage.
The chance of an event occurring. In the context of tree failure, the term may be used to specify:
1) the chance of tree failure occurring
2) the chance of impacting a specified target
3) The combination of the likelihood of a tree failing and the likelihood of impacting a specified target.
A tool for categorizing the combined likelihood of a failure impacting a target.
The chance of a tree or tree part failure occurring within the specified time frame
The chance of a tree failure occurring and impacting a target within the specified time frame.
The chance of a tree failure impacting a target during the specified time frame.
Define by its placement in the likelihood matrix (matrix 1); imminent likelihood of failure and medium likelihood of failure of impact, or probable likelihood of failure and high likelihood of impact
Restraints or factors that restrict the precision, applicability, or extent of something
A visual assessment from a specified perspective such as a foot, vehicle, or aerial (airborne) patrol of an individual tree or a population of trees near specified targets to identify conditions or obvious defects of concern.
The ratio of crown length to total tree height
1) A general term used to indicate the magnitude of a force, bending moment, torque, or pressure applied to a substance or material.
2) Cargo; weight to be borne or conveyed.
In advanced tree risk assessment, pulling tests to measure or observe the amount of inclination and/or deformation to assess stability
There is a slight chance that the failed tree or tree part will impact the target
Defined by its placement in the risk rating matrix (matrix 2); consequences are negligible, and likelihood is unlikely, or consequences are minor, and likelihood is somewhat likely
A broad-headed hammer made of wood, plastic, or resin used for “sounding” a tree
A process by which the amplitude of oscillations is reduced; in trees, motion created by the forces of wind or rigging operations may be reduced through branch movement
A rectangular array of rows and columns used to facilitate problem solving or decision making
A measure of the internal forces acting within a deformable body; force per unit area
study of forces and their effects on bodies at rest or in motion.
The failed tree or tree part could impact the target, but is not expected to do so
Undifferentiated tissue in which active cell division take place. Found in the root tips, buds, cambium, cork cambium, and latent buds.
Minor personal injury, low- to moderate-value property damage, or small disruption of activities.
In tree risk management, the process for reducing risk
Alternatives for reducing risk
Established hierarchy for mitigation of risks based on risk ratings, budget, resources, and policies
a target that is in motion or intermittently moving
Defined by its placement in the risk rating matrix (Matrix 2); consequences are minor and likelihood is very likely, or likelihood is somewhat likely and consequences are significant or severe
a turning, bending, or twisting force exerted by lever, defined as the force (acting perpendicular to the lever) multiplied by the length of the lever.
Target that can be relocated
The concept that any tree, part, or failure mode could represent more than one type of risk.
Failure to use reasonable care, resulting in damage or injury to another.
No personal injury, low-value property damage, or disruptions that can be replaced or repaired.
An imaginary plane where there is neither tension nor compression
The target zone is occupied by people or other targets infrequently or irregularly
seeping or exudation from a tree cavity or other opening.
A tree that has grown with exposure to wind and other elements from all directions.
Branch that extends outside the normal crown area.
The person or entity responsible for tree management
Thin walled, living cells essential in photosynthesis, radial transport, energy storage, and production of protective compounds.
Causal agent of disease. Usually refers to micro-organisms
Common modes of tree failure within a tree species or failure of multiple trees in a contiguous area that share similar site histories or environmental conditions.
Plant vascular tissue that transports photosynthates and growth regulators. Situated on the inside of the bark, just outside the cambium. Is bidirectional (transports up and down) (contrast with xylem)
Failure may be expected in extreme weather conditions, but it is unlikely during normal weather conditions within the specified time frame.
An indicator that decay might be present.
any form of water that falls to the Earth’s surface, such as rain, snow, or sleet
A process for ranking targets according to importance or value.
The measure of the chance of occurrence expressed as a number between 0 and 1 (0-110%), where 0 is impossibility and 1 is absolute certainty. Often expressed as a percentage.
Failure may be expected under normal weather conditions within the specified time frame.
A stiff, small-diameter rod, stick, or wire that is inserted into a cavity or crack to estimate its size or depth
rigid brace, acting in compression, to support a tree, tree branch, or utility pole. Prop pole (contrast with guy)
Structures, trees, branches, or other factors that would prevent or reduce harm to targets in the even of a tree failure
Removing branches (or occasionally roots) from a tree or other plant, using approved practice, to achieve a specified objective
In utility and municipal arboriculture, the time scheduled between pruning events that is established as a guideline for providing reasonable clearance between trees and conductors.
A process using ratings of consequences and likelihood to determine risk significance levels (e.g. extreme, high, medium, or low) and to evaluate the level or risk against qualitative criteria
A process to estimate numerical probability values for consequences and to calculate numeric values for risk
Distance from the center of the perimeter of a circle. One half of diameter
Inward curling formation of woundwood resembling the horns of a ram
The target zone is not commonly used by people or other mobile/moveable targets
Parenchyma tissues the extend radically across the xylem and phloem of a tree and function in transport, storage, structural strength, and defense.
Wood formed in leaning or crooked stems, or on upper or lower sides of branches, as a means of counteracting the effects of gravity (see compression wood and tension wood).
Natural boundary formed chemically within a tree to separate damaged wood from existing healthy wood. Important in the process of compartmentalization (contrast with barrier zone).
One or many alternatives that are promoted to achieve a desired outcome, based on professional judgment.
Presenting the client with a summary statement describing in detail the results of an assessment.
Risk remaining after mitigation
A device consisting of a specialized micro-drill bit that drills into trees and graphs resistance to penetration; used to detect internal differences in the wood, such as decay
New wood produced in response to loads to compensate for higher strain in outermost fibers; includes reaction wood (compression and tension), flexure wood, such as decay.
The recommendation to keep a tree and conduct follow-up assessments after a stated inspection interval.
Natural process during which an overly mature tree reduces its crown and increases its girth to consolidate resources and increase longevity; the deliberate process of reducing tree height to mimic natural processes.
a root-like aggregation of fungal hyphae.
Longitudinal bulge of response wood growth.
The combination of the likelihood of an event and the severity of the potential consequences. In the context of trees, risk is the likelihood of a conflict or tree failure occurring and affecting a target, and the severity of the associated consequences.
The consideration of risks and combination
The systematic use of information to identify sources and to estimate the risk.
The process of risk identification, analysis, and evaluation
The process of assigning risk and risk factors to categories based on severity or hierarchy.
The process of comparing the assessed risk against given risk criteria to determine the significance of risk
The application of policies, procedures, and practices used to identify, evaluate, mitigate, monitor, and communicate risk
The subjective perceived level of risk from a situation or object, often differing from the actual level of risk
The level of risk combining the likelihood of a tree failing and impacting a specified target, and severity of the associated consequences.
A tool for ranking and displaying risk by assigning ratings for consequences and likelihood
Degree of risk that is acceptable to the owner, manager, or controlling authority
Process of removing soil to expose and assess the root collar (root crown) of a tree
Decay located in the roots; root decay is usually developed from the bottom up, and crown symptoms may or may not be visible.
Organism that lives on and may act to decay dead organic matter
Outer wood (xylem) that is active in longitudinal transport water and minerals
Decay located in the sapwood. Bark and/or cambium may be damaged or dead. Signs of the classification of rot are usually numerous, but small, fruiting bodies along the bark’s surface are common.
The defined project objectives and requirements.
lines formed where two edges of bark meet at a crack or wound
Xylem produced to the interior of the vascular cambium during secondary growth
Serious personal injury or death, high-value property damage, or major disruption of important activities.
1) in mechanics, the movement of failure of materials, especially laminar material such as wood, by sliding side by side.
2) A tool used to cut small-diameter plant material, including secateurs and snips, as well as long-bladed hand tools and power tools used to cut hedges.
3) To cut; often used to describe cutting foliage or stems to a single plane as in a hedge.
A crack at the neutral plane between tension and compression stresses
The remaining solid wood around a cavity or internal wood decay.
Substantial personal injury, moderate- to high-value property damage, or considerable disruption of activities
Decay of plant tissues characterized by the breakdown of tissues within the cell walls (contrast with brown rot and white rot)
Compression of the soil, often as a result of vehicle or heavy-equipment traffic, that breaks down soil aggregates and reduces soil volume and total pore space, especially macropore space.
The vertical extent of soil present below ground
Defined by its placement in the likelihood matrix (Matrix 1); imminent likelihood of failure and low likelihood of impact, or probable likelihood of failure and medium likelihood of impact, or possible likelihood of failure and high likelihood of impact.
A process of measuring wood density, or other mechanical properties, using an instrument that transmits, receives, and records and velocity of sound or electric waves through wood.
Process of striking a tree with a mallet or other appropriate tool and listening for tones that indicate dead bark, a thin layer of wood outside a cavity, or cracks in wood.
Degree of care that a reasonable person should exercise in performing duty of care; a measurement used to assess whether an individual acted in a reasonable manner.
In advanced tree risk assessment, a load test that measures outermost fiber stain in the stem or branches, and/or inclination at the root flare, in response to a controlled pull.
Target that cannot be easily moved
The deformation resulting from a stress measured as a change in specimen length per unit of total length.
A process for classifying targets according to importance or value
Degradation of the ability to withstand mechanical stress.
1) In Plant Health Care, a factor that negatively affects the health of a plant; a factor that stimulates a response.
2) in mechanics, a force per unit area.
Feature, condition, or deformity of a tree that indicates a weak structure or instability that could contribute to tree failure.
A device or mechanism providing supplemental support to individual branches and/or entire trees.
Understory trees in a stand or forest with growth somewhat restricted by larger nearby trees.
A waxy substance present in some cell walls.
Sudden, unanticipated failure of tree branch with little or no discernible defect: often associated with long, horizontal branches and warm temperatures.
Understory trees in a stand or forest with growth severely restricted by competing nearby trees.
Corrected tree lean characterized by a leaning lower trunk and a top that has grown back toward vertical
Change in diameter over the length of trunks, branches, and roots.
People, property, or activities that could be injured, damaged, or disrupted by a tree failure.
Acting to control the exposure of targets to risk
The monetary worth of something; the importance or preciousness of something.
The area where a tree or tree part is likely to land if it were to fail.
Risk mitigation actions aimed at reducing the likelihood of impact in the event of tree failure
In mechanics the action of forces to stretch or pull apart any material or substance (contrast with compression)
A form of reaction wood in broadleaved trees (hardwoods) that forms on the upper side of branches or the trunk of leaning tree (contrast to compression wood)
Time period for which an assessment is defined.
Time period for recommended mitigation.
Use if multiple sensors placed around a trunk or limb to record sound or magnetic waves traveling through the wood, with measurement resulting in a picture of internal density characteristics. Typically used in arboriculture to measure the extent of decay in trees.
The land and water features of an area, including changes in elevation
The action of twisting or being twisted
Elongated, tapering xylem cell adapted for the support and transport of water and elements.
The structural form and shape of a tree
An interference between the needs of a tree and society or infrastructure.
Chemical that can be applied to trees that slows terminal growth by reducing cell elongation.
A defined set, group, or collection of trees.
A systematic process used to identify, analyze, and evaluate tree risk
The process of comparing the assessed risk against given risk criteria to determine the significance of the risk.
The application of policies, procedures, and practices used to identify, evaluate, mitigate, monitor and communicate tree risk.
Risk mitigation actions aimed at reducing the likelihood of tree failure.
A degree of risk that exceeds the tolerance of the owner, manager, or controlling authority
Defined by its placement in the likelihood matrix (matrix 1); possible or probable likelihood of failure and low likelihood of impact, or possible likelihood of failure and medium likelihood of impact, or improbable likelihood of failure with any likelihood of impact rating, or any likelihood of failure rating with very low likelihood of impact.
Lateral meristem from which secondary xylem and secondary phloem originate (see cambium)
Oral report: results of the risk assessment delivered to the client orally.
defined by its placement in the likelihood matrix (Matrix 1): imminent likelihood of failure and high likelihood of impact.
The chance of the failed tree or tree part impacting the specified target is remote.
End-to-end, tub=like, water-conducting cells in the xylem of angiosperms.
A tree which, because of its great age, size, or condition, is of exceptional cultural, landscape, or nature conservation value.
Method of assessing the structural integrity of trees using external symptoms of mechanical stress (such as bulges, reactive growth ect.) and defects (cracks, cavities, etc.)
a limited visual inspection, usually from one side of the tree, performed as the tree risk assessor walks by the tree(s).
Fungal decay of wood in which both cellulose and lignin are broken down (contrast with brown rot and soft rot)
An environment suitable for sustaining one or more species of animals.
Exposure to the forces of wind
The force on a tree or structure
The speed of the wind
Uprooting and overthrowing of a tree caused by wind
The process of wood degradation by microorganisms
A written document detailing the work to be completed and authorizing performance of contracted work.
Lignified, differentiated tissues produced on woody plants as a response to wounding.
A document with text, images, and/or references, delivered in print or electronic form, containing the results of the risk assessment.
Main water- and mineral-conducting tissue in trees and other plants. Provided structural support (contrast with phloem)