Direct estimation of stand increments. (III)

Individual tree sampling

Abstract

Using the data of the permanent sample plot (Japanese larch) on the Kawanishi working unit of Nagano Regional Forestry Office, we estimated the stand increment by means of the regression method.
If the present d. b. h. and the past one by increment boring of individual tree be measured, we can determine the present volume and the past one by the volume table, and then the volume increment can be obtained by these two differences. Using volume equations where V=a+bD²H, V=a+bD² and V=aD^b, we estimated the stand increment volume (I) by the simple regression method and the curvilinear regression method. Dependent variables were present d. b. h. and present volume (Assumption 1), and past d. b. h. and past volume (Assumption 2). These calculated results are shown in Table 2, 4, 6. 7, 8 and 9.
Results obtained were as follows:
1. Tere were no differences in the estimated stand increments by various regression equations. So we had better use the regression equation I=a+bD² and the volume equation V=aD^b.
2. The results of Assumption 2 were an over-etimate as compared with that of Assumption 1, but without the actual increment on this permanent sample plot, we could not pass judgement whether the latter assumption was better than the former or not.