アーバン・フリンジにおける風致林計画 : 京都市双ケ丘を事例として

Abstract

本報告は大都市圏のアーパン・フリンジに立地する森林について, 京都市双ヶ丘を事例として調査・計画したものである。無秩序な都市スプロールの結果として, 山地は見離され荒廃化が進んでいる。それを再生する手段は容易でない。然し一方で, 風土的かつ自然的アメニティ基盤としての周辺山林に対する都市サイドからのニーズは極めて高いものがある。双ヶ丘の場合は特にそうした意識の高まりもあって都市風致林としての位置付けが前提にされてきたといってよい。調査編において, 「歴史環境」では奥行と豊かさが述べられ, 「自然環境」では都市近郊林の土壌立地と植生の貧弱さが明らかにされた。「景観・社会環境」では双ヶ丘の可視圏の特性さらに眺望景観の質が述べられ, 次に周辺社会との関わりについて述べられている。計画編ではアカマツ林を風致林の軸として設定し, 市街地との緩衝帯として疎生林帯を計画した。又現植生を踏まえて風致施業区が設定された。施設は山内の文化財の鑑賞や緑地的機能の補完を目的に動線を中心に計画されている。

This paper describes a case of amenity forest planning on urban fringe on Kyoto. First we mention natural condition, in which secondary vegetation has been evolved through human activities. Then, scenic views of forest, which have been established by specific urban cultures, are mentioned. It reflects the historical backgrounds. Thirdly we consider the structural character of Kyoto. The consideration reveals especially when urban growth has been caused by some socio-economic conditions. In Japan urban fringe is located between urban district and forest land in many cases. Synchronically urban fringe is characterized by the coexistence of forest, farm, housing or road site and others. Diachronically the structure is unstable and changeable. On one hand, open space, such as farm and forest land, is changed into fragments and urbanized It can be called intensive land use in an area. It causes competition and "confusion" of land use. On the other hand, devastated land increases with extensive use of forest and farmland, which has been produced by the decline of agricultural activity and the change of life style. It is extensive land use. It brings about some negative effects on conservation of scenic beauty and on prevention of disasters and crimes. This simultaneaus process of the both land uses is the definite character of urban fringe. A preceding condition of forest planning is an organic contact with the land uses which surround the forest. Land use planning, therefore, should be done ahead of forest planning. An ideal forest image appears in the process of the land use control. Next come the treatment planning and the utility planning which are the central issues of forest planning. For the former, we consider a treatment methodology shoud be established according to each scenic viewpoints in the entire city. The latter plays an important role in connecting urban district with the forest areas and it is expected that this planning should lead people to act more significantly in the forest. Here forest should be considered to function not only as a landscape but as a ground for amenity experience. This report contains a case study of Narabigaoka Hill in Kyoto around where the urban fringe is typically Japanese. Urban growth in the 60's made the hillside of Narabigaoka a residential district. Although there was the claim for historic landscape protection, only limited open space of the hill could be conserved. Since Heiankyo, the oldest city of Kyoto, was founded in the eighth century, the historical environment of Narabigaoka has been modified in accordance with the urban growth. Even today we Japanese project our historical image on Narabigaoka. We never fail to imagine the pine forest there, through a scene of the medieval literature. In Omuro area that includes Narabigaoka, the temples, founded before the middle ages, exist to this day. And this is familiar to the urbanites as a recreational or meditative space. In natural environment of the hill, broad leaved trees are invading and pine trees regressing. One reason is that forest land use such as gathering wood for fuel or fire has become obsolete, and hence this makes regeneration condition worse. The other reason is the death of mature trees by insect damage. Artifitial silvicultural condition for pine trees is neither good. On the ridgeline the topsoil has become thin, and bare land is seen in no small quantities. Due to the spatial development of Kyoto, surroundings of Narabigaoka has become housing area, and agricultural land use is rarely seen. We conclude that the neighborhood community has hardly the facilities to use Narabigaoka. Now Narabigaoka is nothing more than a portion of urban landscape. Narabigaoka should be rearranged for a park to be connected with the community people. In order to position Narabigaoka in the urban structure of Kyoto, landscape analysis is effective. We analyzed the visibility of Narabigaoka Hill from Kyoto, and the view of Kyoto from the hill. As a result we found that the forest landscape of the hill itself is meaningful only in the short distance, when we make an amenity forest planning. Here we can propose two planning strategies. (1) Silviculture planning of amenity forest consisting mainly of pine trees. (2) Park facilities design to make Narabigaoka connected with urban district.