輪伐期の研究
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概要
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1．輪伐期の計算式としてこれまで複数の式があげられているが，これらを次の2つの視点より分類した（表－1）。ひとつの視点は，林分を対象として計算式を考えているか，あるいは複数の林分の集合としての森林を対象として考えているかである。これは，土地純収益説と森林純収益説との論争に関係のあるひとつの事柄である。他方の視点は，目的生産物を立木と考えているか，あるいは丸太と考えているかである。1. In order to arrive at a figure for the rotation length, a log yield table of Sugi in Ryuujin village (Table 12) was constructed. This yield table is presented in terms of log volume and log value at the nearest market, rather than stumpage volume and value as is usual in yield tables constructed in Japan. 2. Rotation formulas are classified in Table 1 by the following two criteria. Does the rotation formula apply to a stand or to a forest unit composed of many stands? This question relates to controversies between soil rent theory and forest rent theory, which have continued for more than 100 years and have not yet been fully settled. The second question is whether the product in forestry is a log at a market or a stumpage at a stand. The authors prefered log prices to stumpage as the latter takes into account very different variables. 3. Whether a rotation fomula should be based on an individual stand or on a forest managed as a unit can be explained as follows. In forest rent theory, after the normal rotation aimed at in the forest unit, the cutting age of an individual stand is decided in some practical way based on the previously determined normal rotation age. In soil rent theory, after the rotation is determined at the stand level, the rotation in the forest unit is merely calculated as an average value of the rotations of the stands. Still more, soil rent theory divides the forest rent into soil rent, stumpage interest, etc. The rate of interest is presupposed in soil rent theory, whereas in forest rent theory it is derived from actual forest management. The authors considered this to be an advantage of forest rent theory, especially for practical purposes. 4. Before considering rotation fomulas, the authors start by considering the nature of forest management. In it's basic form, forest management presupposes the planning of annual cutting and of annual forestation determined by a reasonable forest rotation. 5. Using the log yeild table (constructed in this study), rotation ages suitable to this basic form of forest management for a forest of area u-hactares, have been calculated. The results are presented in Tables 14-18, e.g., the rotation age for the maximum log volume yield ranges from 55 years to 150 years (the maximum mean annual increment of log volume is 10.4m3/ha), the rotation age for the maximum money yield [Eu/u] and that for the highest forest rent [(Eu-k)/u] where k represents costs for harvesting and regeneration are not reached until 160 years. The rotation age for the highest rate of return [(Eu-k)/u/k] ranges from 85 years to 150 years (the highest rate of return is 5.96%). Moreover, in the case of a general normal forest, the results were similar to those in the case of a traditional normal forest (Table 19).
- 東京大学大学院農学生命科学研究科附属演習林,The Tokyo University Forests,東京大学農学部林学科,Department of Forestry, Faculty of Agriculture, University of Tokyoの論文