栃木県における森林施業履歴を用いた林地残材発生量と収穫可能量推定モデルの構築

摘要

栃木県の森林は，森林面積349,228haで県土の54.5％を占めている。そのうち人工林は156,763haで，県内の全森林面積の449％を占め，人工林の蓄積は42,255,000m~3で，県内の全森林蓄積の62.4％を占める。これら人工林で深刻になった間伐遅れに対応するため，栃木県では，平成20年4月より導入した「とちぎの元気な森づくり県民税」の実施事業の中で，「奥山林整備事業」を開始した。%In Tochigi prefecture, some facilities to demand woody biomass resources such as the biomass power plant, chip production factories, and the pellet plant are located. These raw materials are mainly supplied by sawmill residues and construction wastes. However, since the number of entrepreneurs who set up the biomass power plants as a measure against climate change, it is worried about stringent supplies of those materials. Therefore, unused materials such as logging residues must be harvested and used near the future. In the previous study, we developed a method to estimate the harvesting volumes and costs of logging residues from subcompartments with plus balances, including both timber and logging residue harvesting at Sano city, Tochigi prefecture. In this study, we estimated the harvesting volumes and costs of logging residues for all cities and towns in Tochigi prefecture. Three factories in Sano city, Kanuma city, and Nasu-shiobara city, Tochigi prefecture were assumed as destinations, and set of the harvesting operation system based on each forestry cooperative. In addition, the previous study estimated these volumes and costs in whole city of Sano, but this study estimated these volumes and costs using forest management records. This could estimate these volumes and costs based on actual forest operations in this area. The model estimated these volumes and costs in the following order. 1) Selecting subcompartments conducting pre-commercial or commercial thinning operations from forest management records, 2) Setting extracting rates for timber and logging residues, 3) Estimating harvesting volumes of timber and logging residues, 4) Estimating logging distances, transporting distances, and inclinations of operation sites, 5)Estimating total expenses, 6) Estimat­ing incomes, 7) Estimating economic balances, 8) Estimating harvesting volumes from subcompartments with plus balances. The amount of logging residues from subcompartment with plus balances were 581 ton on the price of logging residues in this area: 3,000 yen/ton. If Feed-in Tariff (FIT) was established, the price of logging residues would be 10,000 yen/ton and the amount of logging residues from subcompartment with plus balances would be 134,198 ton/year which were almost equal to the demand of this area. The whole tree logging system may be more advantageous than the cut-to-length system for extracting logging resi­dues.