Amenity value.  The environmental and landscape benefits of trees as opposed to their commercial value for timber. Many of these benefits are intangible or difficult to measure.

Arboriculture. Management of individual trees or groups of trees primarily for their amenity value.

Compensation (in relation to defects). Defects such as branch wounds can be compensated by the continued radial growth of new wood, especially in young and mature trees. In this case the new wood strengthens the defects and renders them progressively less significant. 

 Coppice. Coppice growth consists of shoots arising from the stump of a tree felled at ground-level. The growth ultimately gives rise to a multi-stemmed tree, often with the stems arranged in a circle.

 Crown thinning, crown reduction and crown raising. Crown thinning is the removal of branches from the crown without necessarily reducing the extent of the crown. Crown reduction decreases the extent of the crown without decreasing its density. A sympathetic reduction minimizes the appearance of decapitation by cutting back to smaller branches so that the extremity of the crown looks relatively natural. Crown raising increases the headroom to the base of the canopy.

 Hanger. Dead branch fallen from the crown but caught by, and resting on, branches lower down. 

 Hazard, risk and target. A hazard has the capacity to cause harm, which may be more or less serious. Risk is the likelihood that a hazard eventuates. A target is the subject of injury or damage within range of a hazard.

 Loading. Loading refers to the mechanical stresses imposed by the weight, orientation etc. of trees and branches in relation to the site, the architecture of the tree and the weather.

 Maturity. The crowns of mature trees have attained full size. 

 Pollard. Pollarding is the decapitation of a tree at a certain height above ground level (traditionally above the browsing height of farm animals), and may involve leaving a framework of larger branches. Re-growth typically develops from near the point or points of decapitation. Once a tree is pollarded it is common to re-pollard periodically to avoid over-dense crowns and high loadings on the (often complex) union between framework and re-growth. Alternatively, in a lapsed pollard, this complex architecture may be accepted indefinitely.

 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.

 Safe. Safe means not significantly weakened by any defect. To judge the significance of a defect requires knowledge and experience. 

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.

 Shrinkable. Soils that shrink on drying (and swell on re-wetting) are shrinkable. Tree roots can dehydrate soil, and if they do this below a structure, having grown under the foundations, the affected part may subside, causing cracks.

 Tree surgeon. A contractor skilled in performing aerial operations in trees, as is often necessary near buildings, roads etc.

Young. The crown of a young tree has not yet reached full size (ie. maximum leaf area).