Tree taper

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

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

d ( h ) 2 = D 2 ( H − h H − h b ) 1.6

where:

d ( h ) = stem diameter at height h,

D = tree diameter at breast height,

H = tree total height,

h height of interest (h ≤ H), and

h b = breast height.

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