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Use of a tree volume equation based on two lower-stem diameters to estimate forest volume from sample tree counts

Lynch, T.B.

Canadian Journal of Forest Research 25(6): 871-877

1995

A recently developed method of individual-tree volume prediction uses measurements of two lower-stem diameters, rather than the more traditional DBH and height measurements, to estimate stemwood. One form of the equation is linear with respect to volume between the two diameter measurements, as computed by Smalian's formula, and can be algebraically rearranged into the sum of two equations, one linear with respect to the square of the topmost lower-stem diameter, the other linear with respect to the square of the bottom lower-stem diameter. These two equations have the same form as local volume equations that are linear functions of the square of diameter. Because of this, a variation of horizontal point sampling can be used to select trees with probability exactly proportional to each of the equations. Forest volumes can be estimated from counts of trees obtained by comparing the point sampling gauge angle with individual tree diameters at the lower-stem diameter measurement points used by the individual-tree volume equation. To account for the negative intercept term in the linear equations, trees within a small fixed-radius plot are not included in the counts.

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