Regeneration of Castanopsis sieboldii forest : 1. Studies on stratification and age structure of a natural stand (Department of Forestry)

1.イタジイの優占する森林内で, 階層構造を調べ, 375m^2内の立木を伐採して樹幹解析を行なった。2.斜面下部は, 高木層(10m以上), 亜高木層(9∿6m), 低木層(5m以下)が認められたが, 稜線部は層化が不明瞭であった。高木層を構成するのはイタジイ, イジュであるが, イタジイは低木層にみられないが, イジュはほぼ一様に分布していた(斜面下部)。3.イタジイの生長速度は全生育期間を通してあまり変わらなかったが, 直径生長は後に発生した個体ほど緩慢になる傾向がみられた(斜面下部)。4.最高年齢は43年(イタジイ, イジュ)で, 高木層の年齢は39∿41年に集中した。イタジイは15年以下の年齢層にみられず, イジュはほとんど連続的に分布していた。5.年輪幅から求めた平均生長速度は, 高木, 亜高木, 低木の順にほぼ小さくなる傾向がみられた。6.イタジイは胸高直径3cm未満の稚樹層には多くの個体がみられ, 森林の再生に大きな役割をはたすのではないかと考えられた。7.以上の結果から, 調査した森林は約40年前(大戦前後)に伐採され, その後萌芽したものや亜高木∿低木層を構成する樹種の発生したものが発達しながら現在に至ったと推定された。1. The process of regeneration was studied in middle-aged schottky forest of the university forest, Kunigami, Okinawa Island, based on the tree census of two plots and the stem analysis data obtained by clear cutting of a 375 m^2 sample plot in January 1985. 2. Component species of the three layers, tall-tree (taller than 10m), mid-tree (9∿6m), and shrub (ca. 5m) were found on the lower slope, and the layers on the upper slope were indistinct, due to the many species present and the abundant pole timbers. The tall-tree layer consisted mainly of Castanopsis sieboldii (Cs) and Schima wallichii ssp. liukiuensis (Sw). On the lower slope the Cs trees were not recognized in the shrub layer, of the Sw trees found was a even distribution among the three layers. 3. The Cs trees tended to show a growth rate more or less constant during the all stage of their height growth, but the diameter growth of younger trees was found at a slower rate. 4. The oldest individuals of Cs and Sw were counted 43-years-old and the tall-tree layer were mostly between 39 and 41 years in age. The Cs trees were not found in a group under 15-years-old in the shrub layer, while the Sw were distributed from the crown to the shrub layer. 5. The mean rate of stem diameter increment tended to decrease in the order of tall-tree, mid-tree and shrub. 6. The Cs trees with DBH less than 3cm increased remarkably in the sapling layer. It was regarded as an indication that these saplings would play an important function in regeneration of the natural forest of Cs. 7. From the above it was interpreted that the forest investigated here was once exposed to very intensive cutting about 40 years ago, a little before and after the Second World War, and that the sprouts and the recruits then started to reconstruct the present forest