沖縄やんばるの森林におけるマクロ土壌動物の個体数と多様性 : 森林下生えの刈り取りとも関連して(宇井純教授 大嶺哲雄教授退官記念論文集)

沖縄やんばるの3地域の、スダジイを優占種とする自然林および育成天然林整備(改良)という補助金により下生えを完全に刈り取られた森林のマクロ土壌動物を調査し、得られたデータを多様度指数を用いて解析した。1995年から1997年にかけて行った5回の調査で、ヤスデ綱13種、ムカデ綱23種、コムカデ綱1種が採集された。これらを合わせた多足類は、ダニ、クモ、昆虫を除くマクロ土壌動物相の29-85%(平均47%)を占めていた。このうち琉球列島から初めて記録されたのは次の13種である。ヤマトタマヤスデ、ブチダケヤスデ、オビヤスデ属の一種、リュウキュウヤハズヤスデ、ウチカケヤスデの一種、ミドリジムカデ?、ミドリジムカデ属の一種、シゴナガズジムカデ、ケナガトゲアシムカデ、イッスンムカデ属の一種、メナシムカデ属の一種、スコリジムカデ、トゲイシムカデ科の一種。ヤスデ綱とムカデ綱では下刈り区の個体数は自然林にくらべて減少していた。また後者では種数の減少も見られた。自然林の多足類の種多様度指数1-Dは、0.64-0.84、全マクロ土壌動物の指数値は0.72-0.83であった。各回別の計算では自然林と下刈り林の1-Dの値に有意差はみとめられなかったが、全データをまとめて計算したところ、下刈り林における全マクロ土壌動物の指数値は自然林のそれより有意に大きかった(ただし差は小さい)。この結果は同地区の昆虫、アリ、カブリダニにおいて下刈り林で種多様度が低下したという結果と異なる。この原因のひとつは、個体数の多いヤスデに下生え刈り取り区で激減した種があるとも考えられるが、サンプル数が小さいので調査区の地形、場所的条件などの影響も考えられ、今後の調査が必要である。
Soil macrofauna was studied in three forest areas of Yanbaru, northern part of Okinawa HontO(Okinawa Island), each area includes natural forests, dominated by Castanopsis sieboldii, and forests from which undergrowth was completely removed by subsidies from the government. Thirteen species of Diplopoda, 23 species of Chilopoda and 1 species of Symphyla were found during five surveys carried out from 1995 to 1997. The numbers of Myriapoda, including these three Classes, occupied 29-85% (mean, 47%) of total numbers of individuals of all macro-soil animals. Among them, 5 species of Diplopoda and 8 species of Chilopoda are new records from the Ryukyu Archipelago. In five surveys, numbers of individuals of Diplopoda and Chilopoda in forests from which undergrowth was removed (without-ug. forests) were smaller than those in natural forests, and numbers of species of Chilopoda were also smaller than those of natural forests. Values of Simpson diversity, 1 - D, of Myriapoda in natural forests were 0.64 to 0.84 and those of all macro-soil animals were 0.72 to 0.83. When diversity values of natural forests calculated for each survey were compared with those of without-ug. forests, there was no significant difference between two forest types. However, when 1 - lvalues were calculated using combined data of the all five surveys, the values of without-ug. forests were significantly larger, showing high species diversity, than natural forests, although the difference was small. This result is different from results of studies of species diversity of insects, ants and oribatid mites in natural and without-ug. forests of Yanbaru, in all of them, 1 - ^decreased in withoutug. forests. Notable decrease of some common diplopod species in withoutug. forests, effects of topography and place of survey plots and/or small sample size may be reason of this difference. But a general tendency of decrease of numbers of species and individuals in without-ug. forests as compared with with-ug. forests of the same area suggested harmful effects of undergrowth removal on species diversity of macro-soil animals.