環境

近年，都市近郊の里山の面積は，孤立・分断化によって年々縮小している。このような里山の植生は，人為的な影響を強く受け，より詳細な植物の記録が必要とされるが，全植物の調査を行うことは不可能である。一方，都市近郊の里山には，未記録の巨木が数多く生育しているが，環境の悪化による巨木の活力の衰えも散見され，一刻も早くその種や大きさ等の記録が必要である。里山の定義は曖昧であるが，本研究では「自然緑地」の概念に近いものとして捉え，1.研究対象地の「里山」が，どのような地形に成立しているのかを調べ，あわせて面積を求めた。2.複雑な地形を成すことが多い多摩川周辺の里山において，特定の種（例えばジャノヒゲ）が特定の地形に多い要因（光や水分）や，アズマネザサの刈込み等の人為的な影響について調べた。3.都市近郊に生育する「巨木」に着目して81 箇所の里山を踏査し，41 種，1072 本（株）の巨木の種別の本数，最大幹周，幹周の総和を因子として，里山を類型化した。4.各里山で報告されている植物リストの文献を集め，一覧表をつくった。5.里山の植物の生育に及ぼす諸要因に関する踏査を行い，各里山を最も特長づける因子と考えられたヤマザクラの巨木下で，管理状態との関係を明らかにするために，植生調査を行った。また，多くの里山には，これまで長く人と関わってきたと思われる信仰対象があり，その有無を調査した。

In recent years, areas of suburban satoyama are decreasing year by year, owing to their segmentation and isolation. Being susceptible to human activities, vegetation of these satoyama needs to be recorded in detail even if it is impossible to research them all. On the other hand, there are many unrecorded giant trees growing in suburban satoyama, and they are weakening due to environmental degradation. Hence we should lose no time to collect detailed data (such as species and size) of these trees. While the definition of satoyama is ambiguous, this study uses the term to mean a concept close to “natural green area.” In our study we have done the following:

1. We investigated the topography of satoyama in the targeted areas of the study and calculated their size;

2. Since satoyama along the Tama River rather have complex topographic features, we identified what factors (sunlight and moisture level) contribute to the growth of specific species, such as dwarf lilyturf, in specific topography, and also investigated anthropogenic influence, such as trimming of Pleioblastus chino, on them;

3. Focusing on the giant trees that grow in suburban areas, we conducted field investigations in 81 satoyama areas. Then we classified them by the number of trees and species (we found in the investigations a total of 1072 giant trees (trunks) of 41 species), by maximum tree circumference and the total sum of tree circumference;

4. We collected documents on recorded plants in each satoyama and made a listing of them; and

5. We conducted a field investigation on the factors that affect the growth of plants in satoyama. And to assess the conservation state of satoyama we surveyed vegetation under the Prunus jamasakura, which is considered most characteristic of satoyama. We have also investigated the existence of the objects of worship that seemed to have a long history with the local people in each satoyama.

亀山慶晃　東京農業大学地域環境科学部・植物生態学

Yoshiaki Kameyama, Plant Ecology, Faculty of Regional Environment Science, Tokyo University of Agriculture