Stem volume estimation of Japanese Larch (Larix kaempferi) in Hokkaido based on the variable relative stem taper curve

Using 4, 562 cross section data collected from 630 trees of widely various diameter at breast height (DBH) classes (9∼56 cm) and height classes (10-34 m), we ascertained the relative stem taper curve and estimated the stem volume of Japanese larch (Larix kaempferi) trees in Hokkaido, Japan. We applied a cubic function and power function for relative stem taper curves, hypothesizing that the coefficients are affected by tree height and DBH. We used all data or data measured for the upper 1. 3 m to exclude the influence of butt swell. The cubic function obtained using data measured for the upper 1. 3 m was selected as the best model, having the least root mean square error of the expected diameter for almost all relative height classes except for the top and bottom of the stem. The effects of height and DBH were excluded from the coefficient of the third-order term, but they remained for the coefficients of first-order and second-order terms of the best model. Stem volume estimated using the best model had higher accuracy than that estimated using the Nakajima stem volume table and the theoretical volume equation of Inoue and Kurokawa.