Glossary of Tree Terms

The cultivation, management, and study of individual trees, shrubs, vines, and other perennial woody plants.  A person who practices or studies arboriculture can be termed an ‘arborist’ or an ‘arboriculturist’.

A ridged area located at the union of a branch to a trunk or stem.

Trunk tissue that forms around the base of a branch between the main stem and the branch, or between a main branch and a lateral branch. As a branch decreases in vigour or begins to die, the collar usually becomes more pronounced and completely encircles the branch.

Form of decay where cellulose is degraded, while lignin is only modified.

Roots that emerge from the base of the tree stem, normally large and well developed that rapidly reduce in diameter to create the Root Plate this offers structural support for the tree. Buttress roots divide rapidly forming the connection between the stem and the transport roots.

Installation of steel cables, attached to lag screws or bolts placed in tree limbs, to provide additional support or to limit movement and stress of limbs. Recent developments have established non-injurious flexible systems that enable the partial movement of parts within reasonable limits enabling the trees to produce reaction growth and forms an excellent alternative to propping. The installation of such features does require legal interpretation.

Undifferentiated cells often formed at the edges of recent injuries. This tissue quickly becomes differentiated, forming cells of the type characteristic of that position on the tree (e.g. forming wood, bark, roots, etc.) see wound response tissue.

A thin layer of actively growing and dividing cells, located between the xylem (sapwood) and bark of a plant; the part responsible for radial growth of a tree stem or branch.

A localised area of dead bark and cambium on a stem or branch, caused by fungal or bacterial organisms, characterised by woundwood development on the periphery. This may be annual or perennial.

An open and exposed area of wood, where the bark is missing and internal wood has been decayed and dissolved.

Also Chlorosis. A condition of the plant marked by yellowing of normally green foliage, often indicating nutrient deficiency or plant dysfunction.

Devices that measures vertical angles, and provides direct height measurements of objects by triangulation.

Are forked branches or trunks of nearly the same size in diameter and lacking a normal branch union.

Soils in which the air-space (oxygen space) has been reduced or eliminated, reducing water infiltration and percolation, reducing root presence and inhibiting new root development.

The physiological process that creates the chemical and mechanical boundaries that act to limit the spread of disease and decay organisms.

A sample of wood extracted from a trunk or branch, using an increment borer tool. The resulting core can be analysed for characteristics of growth, wood strength, structure, decay, and for species identification.

The union of two or more branches; the auxiliary zone between branches.

Crown Lift The removal of the lowest branches, usually to a given height. It allows more residual light and greater clearance underneath for vehicles etc.

The reduction of a tree’s height or spread while preserving its natural shape.

The removal of some of the density of a tree’s crown, usually 5-25% allowing more light through its canopy and reducing wind resistance.

Deadwood is often present within the crown or on the stems of trees. In some instances is may be an indication of ill health, however, it may also indicate natural growth processes. If a target is present beneath the tree, deadwood may fall and cause injury or damage and should be removed, otherwise deadwood can remain intact for conservation purposes (insects, fungi, birds etc.).

The removal of dead branches from a tree’s canopy, usually of a specified size (in diameter).

Progressive deterioration of organic tissues, usually caused by fungal or bacterial organisms, resulting in loss of cell structure, strength, and function. In wood, the loss of structural strength.

The assessment of decay within a tree has been traditionally difficult, but recent advances have made it possible to achieve accurate representations of the internal section of a tree in both 2D and 3D, removing doubt over the condition of the tree and allowing accurate management decisions.

In relation to tree hazards, any feature of a tree which detracts from the uniform distribution of mechanical stress, or which makes the tree mechanically unsuited to its environment.

Progressive death of buds, twigs and branch tissues, on individual limbs resulting in Deadwood, or throughout the canopy, extreme cases can result in Stag Heading.

A projected line on the ground that corresponds to the spread of branches in the canopy; the farthest spread of branches.

Fast growing, weakly attached shoots/branches that often grow as a response to stress factors upon a tree or branch removal. They usually appear on the stem arising from suppressed buds in the bark. 

‘in urban environments most common cause may be severe crown pruning and pollarding but environmental stress on the tree, alteration of soil conditions, e.g. water-logging, soil sealing, and root severance during site development, or colonisation of roots by pathogens, may all be sufficient to initiate epicormic shoot formation.’ – Arboricultural Advisory & Information Service.

The many direct and indirect contributions provided to humanity by a healthily functioning ecosystem. We rely on ecosystem services to provide clean air and drinking water, agriculture, forestry, ocean health, flood control and much more. Ecosystem services can be categorised as cultural services, provisioning services, regulating services or habitat services.

In trees and shrubs, a pruning cut close to the parent stem, which removes the branch bark ridge.

The trimming of a tree to remove weaknesses and irregularities which may lead to problems. The formative pruning operation is aimed at reducing the potential for future weaknesses or problems within the tree’s crown.

In woody plants, any form of damage that destroys the bark and / or the Cambium all the way around the stem, branch or root, normally resulting in death of the damaged section.

In woody plants, a root that grows across the buttress, or across other roots, eventually causing constriction of the radial growth.

Inner non functioning tissues that provide structural support to trunk.

In relation to shrinkable clay soils, expansion due to rewetting of a volume of soil previously subjected to the removal or water by plant / trees following felling or root severance. Also in relation to root growth, the lifting of pavements and other structures by radial expansion. Also in relation to tree stability, the lifting of one side of a wind rocked root plate.

Bark that becomes embedded in a crotch between branch and trunk or between co-dominant stems, usually found in narrow or tight crotches, and causes a weak structure.

A tool that cuts and extracts a narrow cylinder of wood from a tree for analysis of the wood tissue and growth increments.

A large lateral branch growing from the main trunk or from another larger branch.

Often the result of poor pruning practices; the main leader or branches are largely devoid of side branches, growth is restricted to the end of branches and is likely to suffer damage through end loading.

In trees, a general term that related to the removal of branches from a tree.

A mass of growing filaments (hyphae) formed by fungi.

A term given to the symbiotic relationship between roots and certain beneficial fungi. Mycorrhizae are the combined root / fungal growth.

The NTSG is a multi-organisation partnership striving to develop national standards and guidelines for the safe management of trees. The group’s approach is to strike the correct balance between the risks and benefits of trees.

Present in a defined place for a certain period and not brought there by human intervention. Native tree species are those that became established in the British Isles after the last interglacial period some 11,000 years ago.

General term for the wood, cambium and bark that develops around the site of a wound on a woody plant. In arboriculture occlusion is a commonly used verb referring to the trees process of progressively closing a wound by forming occluding tissue around it.

The principle conductive tissue that the products of photosynthesis are transported around the plant by.

The complete or partial removal of the crown of a young tree so as to encourage the development of numerous branches either for amenity or historically as fodder, repeated management is required cyclically to maintain the feature

Selective removal of woody plant parts of any size, using saws, Loppers, Secateurs, or other pruning tools.

Wood with distinctive anatomical and physical characteristics, formed in parts of leaning or crooked stems and in branches to provide additional strength / support. In hardwoods, tension wood usually forms. In conifers, compression wood is usually found.

The raising or lowering of a soil profile from its original grade.

In tree hazard management, action to mitigate or remove the risk of injury to persons or property.

The removal of old stubs, deadwood, epicormic growth, rubbing or crossing branches and other unwanted items from the tree’s crown.

Invasive decay detection technique whereby the resistance offered by the timber to a spinning probe is measured and plotted. Invasive though very small hole diameter.

Artificial Girdling of the stem, to result in the death of a tree. May be used in habitat creation were the retention of dead standing trees is required.

Both Buildings and services can benefit from the installation of root barriers to protect a soil volume from the ingress of roots.

The basal area of the tree; transition zone from trunk to root. Also sometimes called trunk flare.

The primary support area for the tree; an area of the root system close to the base that structurally anchors the tree to the soil.

Either a general term for decay within the wood of the lower stem / buttress roots, or a disease in which the fine roots are killed.

The area and volume of soil around the tree in which roots are expected. May extend to three or more times the branch spread of the tree, or several times the height of the tree.

In arboriculture, a general description for the wind intercepting area of a trees live crown. This can vary with both orientation and season.

Xylem wood tissue, usually light in colour, representing the outer growth rings of the wood. Usually living, reactive wood tissue, in a healthy tree. See heartwood

The branches that from the main network framework of the crown of a tree.

A kind of wood decay, were a fungi degrades cellulose within the cell wall, without causing overall degradation.

The compression of soil, causing a reduction of pore space and an increase in the density of the soil. Air is squeezed out and nutrients become locked. Tree roots cannot grow in compacted soil.

Non invasive method whereby sound waves are passed through the tree and the speed is measured. Slow speeds indicate decay and a tomography picture representing the inner stem is produced.

In a tree, a state of dieback were dead branches protrude beyond the current living crown.

In relation to vegetation, the removal of water by plant growth resulting in localised shrinkage in the soil volume.

Same as sprout.

Trees which are dominated by surrounding vegetation and whose crown development is restricted from above.

Affecting the whole plant or organism. A systemic compound is carried throughout the entire plant to all parts through the vascular system.

Reaction wood typically formed on the upper side of limbs or curved stems; characterized by lack of cell wall lignifications (higher ratios of cellulose to lignin).

Also, narrow crotch. A crotch with a narrow angle between branches, often having included bark.

The comparison of sound or stress waves through the tree allows the creation of a 2D or 3D representation of the internal structure of a stem or branch section and highlights areas of damage. Virtually non-injurious.

The practice of cutting large limbs back severely, without regard to form or habit of the tree. Cuts are usually made between lateral branch nodes. This practice is extremely injurious to trees, and promotes decay and structural weakness within the canopy.

Trees and other woody vegetation considered collectively within the built environment over a large area such as a city or urbanised local authority area.

Active, healthy growth of plants: ability to respond to stress factors.

An assessment of the mechanical condition of trees based upon their ‘body language’. Trees are dynamic and respond to faults / decay / environmental factors in various ways, these responses can be indicative of structural integrity.

A kind of wood decay were a fungi attacks the lignin within the wood matrix

Forces placed upon tree canopy, branches, trunk and roots of a tree under windy conditions.

The failure of a tree due to wind loading.

A deformed or unusual growth of twigs from adventitious buds, caused by insects, disease, or dieback of twigs and buds.

Wood with atypical anatomical features, formed in the vicinity of a wound and a term to describe the occluding tissues around a wound

Vascular plant tissues with special function of translocation of water and dissolved nutrients from the roots through to the aerial part of the plant and to the leaves and buds.