冷温帯下部天然生林の更新技術 II : 天然生林の林分構造および蓄積の標高, 地形の違いによる変化

Abstract

京都大学芦生演習林の天然生林毎木調査結果から, 標高, 地形の違いによる中・大径木 (DBH＞10cm) の樹種構成の違いについて, 本数や材積割合を用いて量的に検討した。その結果 1) 天然生林の直径階別本数の度数分布は, DBH 10-20cmに度数の高いL型分布を示すが, 沢部ではピークの度数は低い。沢部平坦地では一部直径階と無関係に不連続な度数分布を示すもの, あるいはDBH 20-50cmにピークをもつものも認められた。2) DBH 10cm以上では立木本数, 蓄積ともに尾根部が高い値を示す。3) 本地域の標高600m以上の天然生林は, スギ, ブナ, ミズナラの占める割合が高く, 大径木 (DBH＞30cm) の本数, 材積の65 - 85％を占め, これら3樹種の分布の中心である標高700-800mの沢部, 800m付近の尾根部で蓄積が最も高い。4) DBH 10cm以上の立木のうち中径木 (DBH 10-30cm) の占める本数割合は尾根部で4/5, 沢部で2/3と極めて多いが, 材積は尾根部で1/4, 沢部で1/8と比較的少ない。5) 中径木には針葉樹あるいは有用な高木性広葉樹の割合が高く, 択伐後の後継樹として次期の森林の主体をなすものと期待される。

The relation of distribution of each tree species in population and growing stock to the altitude and topographical factor was investigated with the data taken by random sampled plots in natural forest stand of Kyoto Univ. Forest in Ashu which located at the northeastern part of Kyoto Prefecture. This forest is situated on the lower limit of cool temperate deciduous broad-leaved forest zone. The results are summarized as follows; 1) The frequency distribution of DBH class of plots shows L type and the frequency of 10-20 cm DBH class is high in general. The peak of frequency on valley plot is slightly lower than that on ridge plot. But on valley plots it is observed often that the distribution is irregular or the peak of frequency is in range of 20-50 cm DBH class. 2) Tree number and total volume of stands (DBH>10 cm) are generally higher on ridge plots than that on valley plots. 3) Sugi (Cryptomeria japonica), Buna (Fagus crenata) and Mizunara (Quercus mongolica var. grosseserrata) are dominant species above 600 m in altitude. Growing stock is the highest in the range of 700-800 m in altitude on valley plots and in the neighborhood of 800 m on ridge plots, where are in the center of distribution of these three species. 4) There is a lot of middle DBH class trees (DBH 10-30 cm) in each plots and most of which are important tree species and will dominate the upper layer of succeeding forest after selection cutting.