Abstract
The upper limits on silviculture cost that will allow a forest manager to produce a profit under the optimized controllable variables of given profit models can be defined as the allowable upper limits. A simple calculation method for determining these limits will be useful for designing a subsidy system and examining its validity. In this paper, we derived a simple calculation method with the following simplifications: only rotation age is the only controllable variable; thinning profits and upkeep costs are ignored. The formula can be applied in cases where either the both soil expectation value (SEV) or net present value of the yields (NPV) is defined as the management criterion of the forest. The formula is derived from a hypothesis that the net profit at clear cutting grows according to a Richards or Gompertz function. If the following conditions are met, the formula can be applied: the height of dominant trees grows according to these functions (Richards or Gompertz), the relationship between the height of dominant trees and yield volume per area is exponential, and the net profit per volume at clear cutting is constant. Using the formula, the upper limits on the silviculture cost for four major species planted sites of each quality at Nagano Prefecture were calculated. The calculation shows that the silviculture cost should be controlled at less than 1 million yen/ha except for Hinoki and Sugi at the best quality site, and the subsidy for silviculture rate should be more than 50% except for Japanese larch at the best quality site.
