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No.51 (2004/12) >

Title :沖縄の照葉樹林における帯状伐採施業7年後の保残区残存木の生育状態
Title alternative :Surviving States of Primary Trees in Residual Areas Seven Years after Strip Clear-cutting in a Natural Laurel Forest in Okinawa, Japan
Authors :新里, 孝和
呉, 立潮
新本, 光孝
Authors alternative :Shinzato, Takakazu
Wu, Lichao
Aramoto, Mitsunori
Issue Date :1-Dec-2004
Abstract :本論文は亜熱帯照葉樹林地帯において,天然更新を基盤とする各種天然林施栗法に関する研究の一環をなすものである.天然林施栗試験林は沖縄島北部と西表島西部にあり,沖縄島北部では琉球大学農学部附属亜熱帯フィールド教育研究センター・与那フィールドに皆伐施栗(1992年度),択伐施栗(1993年度),帯状伐施葉(1994年度)が設定された.帯状伐施業は天然林の面積3,600m^2で,斜面方向に10m幅の6帯状試験区A~Fが区画され,樹高1.2m以上の立木について樹種,樹高,胸高直径の毎本調査が行われた.保残区の直径分布はL字型を示し,材積64.7%のイタジイが優占した天然林であった.毎本調査の後レ6帯状試験区は交互にA,C,Eの伐採区とB,D,Fの保残区に区分され,伐採区は全立木が地上20cm高で伐採された.各帯状試験区には10m×10mの方形調査区2個,計10個が設定された.本論文では帯状伐施栗林設定7年後の保残区について,設定時の天然林残存本51種邱O個体の生育状態が調査,解析された.残存本の生育状態は7タイプに類型化され,胸高直径と生活形から考察された.生育状態は残存本の64.7%が健全で,35.3%が支降水であった.支障本35.3%の内訳は,枯死15.8%,頂端部の枯損12.9‰倒木6.6%であった.生存状態は胸高直径と生活形に関係していた.胸高直径1-2cmの小径群は枯死率がもっとも高く,胸高直径12cm以上の大径群は頂端部の枯損率が高くなった.生活形ではシシアクテのような低木種は枯死本のほとんどを占め,優占種であるイタジイは枯死率が6.3%で低く健全率が71.9%と高かった.シシアクチやタシロルリミノキのような林冠下に生育する低木種の枯死率が高いのは,伐採による生育環境の急激な変化,例えば強い光,乾燥,風の影響,また林冠木の折損枝の落下圧,さらに残存本の成長や新規発生木による密度圧などが考えられる.帯状伐施薬は森林の循環利用にとってきわめて有効であるが,その施栗法の確立のためには,保残区の残存本の生育,伐採区の二次遷移,根株の萌芽や実生,侵人種の更新,それらの相互作用など継続的な調査が必要である.
The effect of strip clear-cutting on surviving states of the primary trees 7 years post-cut in a subtropical laurel forest in Okinawa was studied. In the 3,600 m2 study area, six permanent plots named A to F were established by sequence in January 1995. A tree census was conducted; all trees with height equal to or higher than 1.2 m in the study plots were numbered and recorded with species name, height, and diameter at breast height (DBH). Strip clear-cutting was conducted after the tree census in February; the trees in plots A, C, E were clear-felled at the base at 20 cm height above the ground, versus the other trees in plots B, D and F, which remained. In the present study, a new tree census was performed in December 2002. The primary trees consisted of 51 tree species 550 tree stems in plots B, D and F were checked. Examined and measures were the surviving state, DBH and height. The current state of the primary trees was divided into seven types. The results showed the majority of stems (64.7%) remained in regular state without obvious damage, while 35.3% of them were in disturbance, i.e. 15.8% of them were dead, 12.9 % of them were living in standing state with breakdown at treetop or with withered tops, and 6.6% of them were living in falling state. The surviving states of primary trees differed by DBHs, life forms and tree species. The smallest DBH group (1-2 cm) had the highest mortality rate, versus the big DBH group (>12 cm) which had the highest rate of breakdown at treetop. Ardisia quinquegona, a kind of nanophanerophyte species, had the majority of the dead stems, while the dominant species, Castanopsis sieboldii, had the low mortality (6.3%), with most stems (71.9%) in regular state.
Type Local :紀要論文
ISSN :0370-4246
Publisher :琉球大学農学部
URI :http://hdl.handle.net/20.500.12000/3559
Citation :琉球大学農学部学術報告 = The Science Bulletin of the Faculty of Agriculture. University of the Ryukyus no.51 p.151 -157
Appears in Collections:No.51 (2004/12)

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