秩父地方山地帯天然林の更新に関する基礎的研究3 : 約１４５年前に生じた人為的撹乱がヒノキ林の更新に与えた影響

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1．秩父山地のヒダナ沢流域に分布するヒノキ林において，過去に発生した攪乱の影響とその後の更新過程を明らかにする目的で，標高1,450mに50×50mの調査区を2箇所設置し，林冠構成木の樹齢と直径成長について調査を行った。2．二つの調査区（AとB）は林冠構成種の違いによって，A区はツガとヒノキ，B区はツガ，ヒノキおよび広葉樹類が優占するパッチに明瞭に区分された。3．成長錐を用いてコア試料を採取した個体には樹齢131～140年のものが最も多くを占め，なかでも樹齢146年以上のものには約145年前に胸高直径の成長量が増大している個体が多かった。したがって，約145年前に調査区内で何らかの攪乱が生じたと推定された。4．約145年前に攪乱があったと推定されたヒノキと広葉樹類の優占するパッチの林床には腐朽した根株が数多く認められ，それらの根株の8割以上がヒノキであった。ヒダナ沢流域の森林では，西暦1844年にヒノキを含む有用樹数種の「御伐出願い」が出されいる。この史実はコア試料の解析結果と一致することから，145年前の攪乱は伐採による人為的攪乱であると推察された。5．攪乱後の樹種構成は，その時に残った前生樹の樹種，サイズ，本数に因るところが大きかった。現在ツガの優占するパッチは，約145年前の攪乱発生時に直径15cm以上のツガが多く残った箇所，逆にヒノキの優占するパッチは直径15cm以下のヒノキが数多く残った箇所であることが明らかになった。一方，広葉樹類が優占するパッチは，攪乱発生時に樹高1.3m以上の個体が全て失われたた箇所であった。したがって，攪乱の程度はツガの優占するパッチに小さく，広葉樹類のそれに最も大きいことが推定された。1. In order to clarify the distrubance occurred in the past and its effect on the regeneration processes of natural forest stands mainly dominated by Hinoki Cypress (Chamaecyparis obtusa Endl.) which distribute at the area of Hidana watershed in the Chichibu Mountains, Central Japan. We made a research on the age and diameter growth of canopy trees within the two plots (A and B) of 50m×50m, established at an altitude of ca. 1450m a.s.l.. 2. Based on the dominant species of the canopy, each plot was divided into a few patches i.e., Hemlock (Tsuga sieboldii Carr.) and Hinoki patches in plot A and Hemlock, Hinoki and broad-leaved tree patches in plot B, respectively. 3. From the analyses of age composition and growth pattern of canopy trees in each patch, trees aged 131-140 years were most abundant among the trees from which core were sampled by increament borer. And trees which showed the obvious increment of diameter at breast height (DBH) at about 145 years ago were also abundant among the trees older than 146 years. Therefore, it was assumed that a kind of strong distrubance had occurred at about 145 years ago (in 1845) within the plots. 4. A large number of decayed stumps mostly composed of Hinoki were found on the forest floor within Hinoki and broad-leaved tree patches in which the disturbance had occurred in ca. 1845. This disturvance was supposed to be caused by logging, because we found a written petition for having logged several useful species including Hinoki from the research area, which had been submitted by villagers of Tochimoto in 1844. 5. A large number of Hemlock trees with DBH larger than 15cm were saved from the disturbance and survived in the Hemlock patches. On the contrary, only advance growth of Hinoki with DBH less than 15cm abundantly survived in Hinoki patches. While in a broad-leaved tree patch, all of the trees with height taller than 1.3m were completely destroyed by the disturbance. Therefore, it was supposed that the degree of disturbance was the smallest in the Hemlock patches, and it was the largest in the broad-leaved tree patch, and that the species composition of canopy trees at present in each patch depends largely on the kind of species, density and size of advance growth which survived against the disturbance.
東京大学大学院農学生命科学研究科附属演習林,The Tokyo University Forests,東京大学農学部附属北海道演習林,東京大学農学部附属秩父演習林,The University Forest in Hokkaido, Faculty of Agriculture, University of Tokyo,The University Forest at Chichibu, Faculty of Agriculture, University of Tokyoの論文

秩父地方山地帯天然林の更新に関する基礎的研究3 : 約１４５年前に生じた人為的撹乱がヒノキ林の更新に与えた影響

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