抄録
In this study, we evaluate the risk of snow damage to sugi plantations in Japan. We examine the optimal rotation age (ORA) which maximizes the land expectation value (LEV), and the economic effects of snow damage. We considered two types of stem breaking damage. One is the thinning type and the other is the domino type of damage. In the case of the thinning type, if there are subsidies or higher prices, long rotations are suitable. This is because the damage ratio is lower in stands. In the case of the domino type damage, the ORA is similar to cases without damage. Snow risk has two apparently contradictory effects. One is a rotation shortening effect - harvest before the stand is damaged by snow. The other is a rotation lengthening effect, i.e. harvest later to recover, the increased management costs of snow damage. If the probability of snow damage is high for matured stands, a shorter rotation is advantageous, even in cases of thinning type damage. This is similar to the case of forest fire in preceding studies. However, if the probability of snow damage is lower for mature stands, the rotation shortening effect is often cancelled out by the rotation extending effect of increased management costs. Furthermore, if damage ratios in the stands over 30 years old are sufficiently low, even where there is domino type damage, the ORA is higher than in stands without damage under subsidy or higher price. From this, it is clear that the damage ratio at older ages is a key factor determining rotation age. The decrease in LEV following domino type damage is twice as much as that of thinning type damage. In cases, where the probability of domino type damage and damage of older stands can not be reduced to reasonable levels at a reasonable cost, natural forest management may be more appropriate than plantation management.
