Secondary Succession 13 Years after Natural Forest Clear-Cutting on Iriomote Island, The Ryukyus

亜熱帯西表島の森林資源回復に関する二次遷移について,1985年6月に天然林皆伐後,今回13年目における固定プロットの毎木調査の結果を用や宇する。実験林は西表島のやや内陸部,標高60m,緩傾斜面,面積0.869haで,4試験区に分割され,各試験区内のほぼ中央部に10m×10mの固定プロット(計4個)を設定した。4試験区のうち2試験区は対照区,残り2試験区は焼畑区である。生活形別の基底面積,立木本数は樹種の萌芽力に依存し,萌芽力の高いイタジイ,ホルトノキ,タブノキ,エゴノキ,フカノキ,シャリンバイ,シシアクチ,ボチョウジなどの数値が高い。樹高1m以上の個体の出現種で伐採後消滅した樹種は少なく,未発生の樹種はオオシイバモチ,モッコク,オオバルリミノキ,イヌマキなどである。侵入種には落葉性高木種のアカメガシワ,ハマセンダン,カラスザンショウ,イイギリなどがみられるが,これらの発生,成長は低下し,常緑性高木種の優占度が増大している。階層構造は未分化の状態にあるが,基底面積分布は常緑性高木種が上層に,立木本数分布では常緑性の低木種と小高木種が下層に増大し,また胸高直径分布でもややL字型となり,階層構造はやや複雑になりつつある。これら固定プロットにおける二次遷移の結果は,対照区でオキナワウラジロガシが増大し,焼畑区でアカメガシワが多いなど,多少の違いが見られるものの,対照区と焼畑区との間で明瞭な差異はないと考えられた。亜熱帯林における樹種の萌芽更新,雑木林,里山林の再生,利用について考察を加えた。Secondary succession 13 years after natural forest clear-cutting was studied. The experimental forest was set at the tropical biosphere research center, University of the RYukyus, on Iriomote Island in 1985. The antural forest was divided into four sections, two sections were left as the control, the other two were burned. Cut wood of the burned sections were incinerated two months after clear-cutting. In 1998, 13 years after the clear-cutting, a census of new growth of trees over 1.0m in height, which grew in the fixation plots was taken, end secondary succession was verified. Secondary succession is greatly dependent on the sprouting force of the tere species. The trees of Castanopsis siebolidii, Eleaeocarpus sylvestris, Persea thunbergii, Styrax japonicus, Ardisia quinquegona, Psychotria rubra, etc. with high sprouting force had the higher values for basal area and amount of new growth than the others. Generation and growth of Mallotus japonica, Euodia meliifolia, Zanthoxylum ailanthoides, etc., which are deciduous trees, were gradually lower. Relatively, the dominance of the evergreen trees increased. Stratification of the forest had become complicated. In the overstory, the basal area of evergreen trees was high, and in the understory, the amount of new growth of evergreen small tree species and shrub increased. In secondary succession, there was not difference between control plots and burned plots