Japanese forecasting of log output employs a stochastic felling model called gentan probability theory. Usually this theory is applied to those forests thought to be under active management. In this paper the opposite stance is adopted. Forests are divided into two groups, a managed group, the rotation age of which is determined by the Faustmann formula and an unmanaged group which is modelled using gentan probability theory. The proportion of forests in the Faustmann group and the parameters of the gentan probability distribution are estimated using a data set from Aichi Prefecture.
The results show that the proportion of Japan’s man-made forests in the Faustmann group has fallen. Also, the mean and variance of the gentan probability distribution have increased, implying that the felling intensity in ‘unmanaged’ forests is also falling. Reasons for these trends are speculated upon and forecasts for Japanese log output are presented under different assumptions about the proportion of forests under active management.
