@article{oai:soar-ir.repo.nii.ac.jp:00011271, author = {木平, 勇吉}, journal = {信州大学農学部演習林報告}, month = {Oct}, note = {The calculation method of the sustained yield which has been applied to the national forest for the long time seems to have some defects. For several years, the author has been engaged in introducing a computer system into this method and therefore, the problems on this method have gradually become clearer. In this paper, these problems are described as follows.(1) The regional forest planning ares which are treated as an unit of the sustained yield are classified into several groups by the tree species, forest type, felling method. Each one of the groups is the unit of the calculation. The Rule (established in 1969, partially revised in 1976) explains the details of the calculating process in each groups, but nothing is explained about the relation between each groups.(2) The formula which describes the transition of the each groups is very simple. a´=a-b (refer to the table 1). It is reasonable in the case of an even-aged forest, but in an uneven-aged forest or a selection forest, more logical formulas have to be made.(3) The next formula describes the process of the forest regeneration a_0+(∑b_i)=a_0´+a_1´ (refer to the table 2). The renewed species are not necessarilly the same to the former species, so the matrix which expresses the rate of the renewed species is more useful. The next formula seems to be more common and logically reasonable. _ka_0+m ∑ j=1((∑_jb_i)_jP_k)=_ka_0´+_ka_1´ (refer to the fig. 2, the table 3, the table 4. P; the matrix of the renewed species's rate). The concept of the matrix P is very fresh and important. (4) Assume that the total felling volume is given by the input data, how to allocate it to each forest groups is one of the most important process. But the Rule does not explain it. (refer to the fig. 4). Assume that the felling volume in each groups is given by some standard, how to allocate it to each forestage is also one of the most important process. Because the felling order influences the structure of the forest in future (refer to the fig. 8). The Rule does not explain it, and moreover, the concept of the structure about the normal forest has to be clearer. (5) The thinning process is not reasonable because the forest yield tables are not suited to the thinning standards which are decided from the viewpoint of the efficiency in the operation (refer to the table 8).(6) In practical business, this method is very troublesome and not efficient. To improve these problems, it seems to be most useful to put a computer for practical use.(7) Some kind of the input data are changeable, if the input data contain optimistic elements, the answer will be optimistic. Also, the unreliable input data make an unreliable answer. In this method, next data must be cautious. The yield table, the felling age, the felling method, the thinning standard, the matrix of the regeneration., Article, 信州大学農学部演習林報告 15: 37-63(1978)}, pages = {37--63}, title = {現行保続計算の問題点}, volume = {15}, year = {1978} }