USE OF A TREE VOLUME EQUATION BASED ON 2 LOWER-STEM DIAMETERS TO ESTIMATE FOREST VOLUME FROM SAMPLE FREE COUNTS

A recently developed method of individual-tree volume prediction uses measurements of two lower-stem diameters, rather than the more traditi onal DBH and height measurements, to estimate stemwood. One form of th e equation is linear with respect to volume between the two diameter m easurements, as computed by Smalian's formula, and can be algebraicall y 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 equ ations have the same form as local volume equations that are linear fu nctions of the square of diameter. Because of this, a variation of hor izontal point sampling can be used to select trees with probability ex actly proportional to each of the equations. Forest volumes can be est imated from counts of trees obtained by comparing the point sampling g auge angle with individual tree diameters at the lower-stem diameter m easurement points used by the individual-tree volume equation. To acco unt for the negative intercept term in the linear equations, trees wit hin a small fixed-radius plot are not included in the counts.