A System to Predict Diameter Distribution in Pure Even-aged Hinoki (Chamaecyparis Obtusa Sieb.) Plantations (III) -Extension to Stand Volume Prediction-

摘要

We developed a height-diameter curve estimation model for even-aged hinoki (Chamaecyparis obtusa Sieb.) plantations to develop a height-diameter curve that could be applied to any stands at any stand age using diameter distribution and stand characteristics. We used generalized allometric equation for the height-diameter curve equation and assumed that allometric coefficient was equal to 1 (constant) and that maximum height was the upper-asymptote of the site index curve. We performed stepwise multiple regression analysis to derive the remaining parameter related to the slope of curves (referred to here as the 'shape parameter'). For the multiple regression analysis, we used stand age, density, mean basal area and site index as explanatory variables. To validate the model, we estimated the mean tree height of each DBH class and compared the predicted and observed heights. Furthermore, we predicted stand volume by combining the height-diameter curve estimation model and a diameter distribution prediction system developed in a previous study, and compared the predicted and observed data. From the regression analysis, we obtained a linear equation for the shape parameter as a function of stand age, density and mean basal area. The results of model validation indicate that the height-diameter curve estimation model is capable of estimating mean tree height for DBH classes with less bias, and would be useful for diameter distribution-based stand volume prediction. The results of stand volume prediction indicated that when initial stand age was greater than 30 years, the prediction error of both basal area and stand volume were small, while they were over-predicted when initial stand age was less than 30. These results suggest that the predictive error for stand volume was dependent upon the diameter distribution prediction system.