横浜市道志水源かん養林の形成過程

Abstract

近年，森林の公益的機能に対する一般の関心が高まりつつある。特に森林の水源かん養機能は森林管理とも密接に関係している。筆者は既に東京都水源林及び横浜市道志水源かん養林を対象とした経営計画の変遷，東京都水源林及び甲府市水源林の形成過程を明らかにしてきた。今回は，横浜市により水道水源かん養のために所有・直接管理されている横浜市水源林（大正5（1916）年経営開始，山梨県南都留郡道志村）を対象として取り上げた。水源林問題は河川をめぐる上下流の相互関係とも捉えられ，水源林問題の解明に当たってはこの上下流の関係成立過程が極めて重要な意味を持つ。そこで本研究では，横浜市水源林の経営前史における上下流の相互関係について明らかにすることを目的とした。分析に当たっては(1)上下流対立の発生と調整過程(2)森林の所有と利用の変遷(3)当時の森林経営計画の3点に着目した。 Yokohama City's water resource conservation forest, which located in Doshi village in Yamanashi prefecture, has been managed since 1916 in order to conserve water resources. This paper is intended to clarify the formation process of Yokohama City's water resource conservation forest. Especially, this study pays attention to: 1) conflicts between economic activity in Doshi-gawa headwater areas and water resource conservation of Yokohama City, 2) changes of forest usage, 3) a forest management plan (FMP) proposed in the formation process of the forest. The following is results of the analysis based on materials such as history of Doshi village and that of Yokohama City's waterworks. First, there was often friction between Doshi-gawa headwater areas and Yokohama City in the view of water usage and landuse. Since the citizens of Yokohama used the river for drinking, they were interested in the safety of the water supply. This interest conflicted with economic activities in the headwater area, such as copper mine development, construction of hydroelectric power plant, and logging fuel wood. The forest management for water resources conservation by Yokohama City had begun with an action against deforestation in the Doshi-gawa headwater area. At first, Yokohama City tried to restrict logging in headwater area, next it made subsidy for afforestation and tried to establish a proceeds-sharing forest. At last Yokohama City bought the forest at a bargain. Second, the demand of the local people on forest increased because of diversification of forest usage and increase of population in Doshi-gawa headwater areas. They utilized forest in various ways, such as production of charcoal and fuelwood, clearing for silkworm raising, and logging for handicraft and timber. Especially, they lived mainly by processing charcoal, so they saw hardwood resources and the grass were important. This interest compromised with that of Yokohama City, because they saw it was important for water resource conservation to plant conifers on the grass. Third, in this formation process, well-organized FMP was not established. Because local people overexploited the forest as their commons, it was hard to develop a modern FMP. Since forest owners, the Imperial Forest Agency and Yamanashi prefecture or Doshi village, did not develop an effective FMP, eventually forest resources were almost exhausted. Yokohama City begun the forest management by itself for water resource conservation.