Classifying Plantation Forests in a Snowy Region According to Cutting Age using GIS: A Case Study of Private Forests in Sanpoku Town, Niigata Prefecture

摘要

Forest stands must be evaluated before making zoning or harvest plans. This paper evaluated the net income of managed sugi (Japanese cedar, Cryptomeria japonica D. DON) plantations in private forests in a snowy region and classified sugi plantations according to the probability of harvesting, using a geographic information system (CIS), in a case study of private forests in Sanpoku Town, Niigata Prefecture. The town includes both low coastal and mountainous inland areas and the snow depth varies markedly. Two transfer points were assumed: a timber market and a local wood-related complex. First, log production was predicted according to site quality, using an existing stand density management diagram, as well as height growth curves to obtain log volumes according to log length and top diameter class. Gross income was estimated from log prices and the predicted log production according to site quality. Then, the total cost from planting through to logging was estimated for standard conditions of productivity, necessary workforce and wages, using four factors: site quality, yarding distance, the deepest snow depth and slope angle. The cost of plantation forest management included the regeneration cost for establishing new plantations and the loggingcost for final cutting. Forest net income was evaluated for three cutting ages: short, intermediate and long rotation. Finally, sugi plantations were classified according to the probability of harvest and the area of each class was obtained using CIS onthe assumption of present, 10% higher and 10% lower log prices. Site quality was the more important factor in sugi plantation management; it was more important than yarding distance or the deepest snow depth. Prices 10% lower than present prices on theNiigata Timber Market were the minimum necessary to maintain timber production from sugi plantations in private forests, given present costs and subsidies.