Definition

Taper is the degree to which a tree's stem or bole decreases in diameter as a function of height above ground. Trees with a high degree of taper are said to have poor form, while those with low taper have good form. The form of a tree is sometimes quantified by the Girard form class

Girard form class

Girard Form Class is a form quotient calculated as the ratio of diameter inside bark at the top of the first 16 foot log to the diameter outside bark at breast height . Girard form class is the primary expression of tree form in the United States....

, which is the ratio, expressed as a percentage, of the butt-log scaling diameter to diameter at breast height

Diameter at breast height

Diameter at breast height, or DBH, is a standard method of expressing the diameter of the trunk or bole of a standing tree. DBH is one of the most common dendrometric measurements....

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Taper is often represented by mathematical functions fitted to empirical data, called taper equations. One such function, attributed to Ormerod, is



where:

= stem diameter at height h,

= tree diameter at breast height,

= tree total height,

height of interest (h ≤ H), and

= breast height.

Once developed, taper equations can be used to predict the diameter at a given height, or the height for a given diameter.