Modeling the effects of growth rate on the intra-tree variation in basic density in hinoki cypress (Chamaecyparis obtusa)

Abstract

The purpose of this study is to evaluate the effect of growth rate on intra-tree variation in basic density of hinoki cypress (Chamaecyparis obtusa) quantitatively using the statistical modeling technique. Nineteen sample trees were harvested from 50-year-old hinoki stand which consists of two different growth rate plots. Disks were cut from sample trees at height positions of 2, 4 m, and then 4 m intervals until 16 m position. Radial strips were cut from the disks, and ring widths and basic density were measured at 5-ring intervals. The basic density decreased with age at any height positions. The linear mixed model was fitted to the age trend data having two nested grouping levels, i.e., tree and position within tree. Models having various mean and covariance structures were tested in devising an appropriate wood density model. The model, consisting of the mean structure with quadratic function of cambial age was able to describe the intra-tree variation in basic density. The model containing the random effects which consist of effect of the tree level and vertical stem position level explained the density variation adequately. The growth rate did not show the significant effect on the basic density variation within the stem.