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No.45 (1998/12) >

 
Title :複層林に関する研究 : 2. 上層が天然生広葉樹林の場合について
Title alternative :Studies on the Multiple Storied Forest : 2. A case of a nutural broad leaved forest as an upper story
Authors :平田, 永二
安里, 練雄
新本, 光孝
新里, 孝和
Authors alternative :Hirata, Eiji
Asato, Isao
Aramoto, Mitsunori
Shinzato, Takakazu
Issue Date :1-Dec-1998
Abstract :天然生広葉樹林を上層とする複層林について, 名護市及び国頭村で調査を行い, 上層の林分構造を明らかにすると共に, 下層木のイスノキ及びイヌマキの樹高成長について検討した。その結果を要約するとおよそ次の通りである。1) 施業林分は18∿50年生(平均38年)の壮齢林分で, 天然生広葉樹林の現実林林分材積収穫表(平均地位)と比較して, 直径及び樹高は類似しているが, 本数及び材積についてはかなり高い数値を示している。2) 上層を天然生広葉樹林とする複層林は, 沖縄県の複層林施業指針に示されたリュウキュウマツを上層とする林分の基準本数をかなり上まわっているが, 育成天然林の基準の相対幹距15%と比較すると, およそその線に沿っており, けっして過密状態とはいえない。3) 相対樹高80%以上の上層樹冠は, その大半(75%)がイタジイ及びイジュで占められ, ほかの樹種は少ない。4) 相対幹距は9∿33%の範囲で, 平均約17%となるが, これは, スギ林の中庸度の間伐に相当する。また, 開空率は平均約24%となっていて, 複層林施業指針で示されている30∿40%に比べるとやや低くなっている。5) 下層植生の植被率は相対幹距及び開空率の増加に伴って増加し, 相対幹距約20%, 開空率約40%でほぼ最大に達し, それ以降は一定(約80%)の値を示す。6) 天然生広葉樹林-イスノキの林型では, イスノキの成長は良好で, 健全に生育しているものが多い。連年成長量は平均約16cmで, 相対幹距及び開空率が大きくなるのに伴って増加する。7) 天然生広葉樹林-イヌマキの林型では, イヌマキの連年成長量は9cmであるが, キオビエダシャクの被害が大きく, そのため植栽本数が著しく減少し, 生育不良のものが多くなっている。8) 天然生広葉樹林-フクギ, リュウキュウコクタン特殊林型については, 施業事例が少ないので, 今の段階では, その良否を判断することはできない。しかし, 立地環境に適した複層林施業を目指す上からは, いろいろな林型について積極的に試みるべきであろう。
On the multiple storied forest with a natural broad leaved forest as an upper story, this investigation was carried out in Nago city and Kunigami village to elucidate the stand structure of an upper story as well as the height growth of Distylium racemosum and Podocarpus macrophyllus as lower story trees. The results of the investigation are summarized as follows : 1) The working stand was a middle aged stand of 18∿50 years old (38 years in an average value). In comparison to the yield table of actual broad leaved forest (middle site quality), the values of diameter and height were similar while number of trees per ha. and volume per ha. gave extremely high values. 2) The multiple storied forest with a natural broad leaved forest as an upper story had values higher than standard number of trees in the stand of Pinus luchensis as the upper story, shown in the guideline for working of multiple storied forest in Okinawa, however, it belonged to the level similar to the value of 15% in the standard relative spacing of raising natural broad leaved forest, showing not necessarily overpopulated condition. 3) A greater portion (75%) of the crown of upper story having the value higher than 80% in relative height was occupied by Castanopsis sieboldii and Schima wallichii. 4) The relative spacing was in a range of 9∿33%, 17% in average value, indicating the value being a middle degree of thinning for Cryptomeria japonica forest. And an average value of crown densities was 24%, showing a value rather lower than the value (30∿40%) presented in the quideline for working of multiple storied forest in Okinawa. 5) The cover rate of understory vegetation increased with an increase in relative spacing and crown density, reached the maximum value at about 20% in relative spcing and 40% in crown density, and then maintained a constant value of about 80%. 6) In the forest type of natural broad leaved forest of Distylium racemosum, the growth of Distylium racemosum was excellent, being mostly in healthiness. The annual increment of height of Distylium racemosum was 9cm in an average value, increasing with increases in relative spacing and crown density. 7) In the forest type of natural broad leaved forest of Podocarpus macrophyllus, the annual increment of height of Podocarpus macrophyllus was 9cm. This value was not much different from that of the stand having Pinus luchensis as upper story, indicating for the forest type to be promising. 8) In the special forest type of natural broad leaved forest of Garcinia subelliptica and Diospyros ferrea, at the present, too little working instances to give a proper evaluation of its annual increment of height. Nevertheless, to find working of multiple storied forst in Okinawa being fit for site environment, various forest types are needed to be working positively.
Type Local :紀要論文
ISSN :0370-4246
Publisher :琉球大学農学部
URI :http://hdl.handle.net/20.500.12000/3693
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.45 p.209 -219
Appears in Collections:No.45 (1998/12)

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