Abstract
In this paper, the author studied on the characters of volume-diameter curve in each stand of Sugi in Oita district. It was comprehended that the volume-diameter curve given with the equation V=aDb, is of the following characters:
(1) The narrow variation in the values of bin each stand is caused not by the difference of factors (e. g. average stand height) but by the biological variation among the stands. Therefore, we may think that the volume-diameter curves nearly keep going side by side. In the case of Oita Sugi, the average of b and its error are rounded up
b=2.20±0.20
(2) When b is considered a constant (2.20) in the equation above described, that of volume-diameter curve is
V=a1D2.20
The value of a1, which widely varies in this equation according to stands, can be computed by a pair of D and V residing on the volume-diameter curve under review. As D, average stand diameter and stand age, as V, average stand height, average volume of trees and average height of trees in average stand diameter are looked upon. Judging from their correlation to a1 and correctness of measurement in addition to readiness, average stand diameter and average height of the trees can be deemed most proper as the factors for estimation of a1.
(3) Using these two factors, the value of a1 can be found out precisely with
a1=pDq×Hr
As for Oita Sugi, the above regression equation, the standard error of which is 2.5 per cent, is shown as
a1=0.00075D-0.273×H0.895
In view of the results so far achieved, it may be concluded that the volume-diameter curve in each stand can be standardized, which is applicable to the construction of a new tree volume table.
