多摩地区を中心とした東京における緑地環境の変化と管理
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概要
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Present vegetation, changes in green spaces, and present status of their management in Tokyo are reviewed to introduce adequate management conditions in three areas of Tokyo 23 special wards, Tama, and Okutama, with special reference to the Tama area. The present natural vegetation in each of the three areas is as follows. The 23 special wards have a scarcity of green spaces, but there are major remnants of such evergreen broad-leaved forests as Machilus thunbergii forest, Castanopsis cuspidata forest, and Quercus myrsinaefolia forest. The Tama area is traditionally thought to be climatically an area dominated by evergreen broad-leaved forests of Quercus myrsinaefolia, with deciduous broad-leaved oak forest in the Tama area being secondary. However, this review takes a new view contrasting with the traditional interpretation that Castanea crenata-deciduous Quercus species forests also constitute important parts of the natural forest of the Tama area. These forests originate from remnants of forests of the Late Glacial in the Kanto district. The Okutama area is dominated by Cryptomeria japonica and Chamae-cyparis obtusa plantations. The natural forests of the area consist of cool temperate Quercus serrara, Quercus crispula, Fagus japonica forest, and subalpine Tsuga diversifolica forest. Regarding changes in green spaces, increments of such unique plant species as Trachycarpus fortunei, Neolistea aciculata, and Idesia polycarpa are obvious, especially in remnant forests in the 23 special wards. In the Tama area, forest fragmentation is serious and results in a decline of plant species diversity. Bamboo invasion destroys secondary Castanea crenata-deciduous Quercus species forests. In the Okutama area, increases in the Sika deer population cause long-term destruction of plant communities. Regarding green-space management, green spaces in the 23 special wards, which play an important role as fire shelters, should maintain fire-resistant tree species such as evergreen broad-leaved species. In the Tama area, a moderately strong forest management was proposed to maintain the plant species diversity of Quercus secondary forests. To conserve the diversity of species in forests through non-traditional management, it is necessary to manage forests continuously without long periods of neglect. It is concluded that to manage Quercus secondary forests appropriately, long-term changes in species composition need to be monitored. In the Okutama area, the Tokyo government is attempting a forest reconstruction enterprise to recover declining forests through forest management.
- Tokyo Geographical Societyの論文
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