森林立地学会誌森林立地51(2),2009,105〜115

Jpn.J.For.Environment 51(2), 105-115 2009

 

Effects of light intensity and soil physico-chemical properties on seedling mortality and growth of six dipterocarp species planted for rehabilitation of degraded grassland, secondary forest and logged forest in Sarawak, Malaysia

 

Daisuke Hattori¹, Tanaka Kenzo², Joseph Jawa Kendawang³

Kazuo Okamura Irino⁴, Sota Tanaka⁵, Tomoaki Ichie⁶

Ikuo Ninomiya⁷and Katsutoshi Sakurai⁶

¹The United Graduate School of Agricultural Sciences, Ehime University,

²Forestry and Forest Products Research Institute, ³Sarawak Planted Forest

⁴Center for Cooperative Research and Development,Ehime University

⁵Graduate School of Kuroshio Science, Kochi University

⁶Faculty of Agriculture, Kochi University, ⁷Faculty of Agriculture, Ehime University

 

Enrichment planting with dipterocarps is required in order to rehabilitate degraded vegetation in tropical Southeast Asia, since tropical rainforests have been damaged by various anthropogenic activities. This study investigated the effects of light and soil properties on the mortality and growth of six dipterocarp species in grassland, secondary forest, and logged forest in the Niah Forest Reserve, Sarawak, Malaysia. Relative light intensity was much higher in the grassland than the forested area, whereas large variations in soil properties were not found. Seedling mortality, height and diameter over 81 months were higher in the grassland than the forested area. Strong light intensity killed many seedlings in the grassland during the first 24 month, though it enhanced the growth of theseedlings that survived. Few survived large seedlings could be one of the targets for ecosystem rehabilitation in the grassland, if the seedlings can dominate the forest structure in the future. In the secondary forest and logged forest, lower light intensity led to lower mortality and growth rate than in the grassland. In the secondary forest, pioneer trees fostered seedlings and produced suitable conditions for their survival. Careful thinning of local trees may enhance the growth of seedlings if necessary. On the other hand, we found interspecific variations. For example, Parashorea macrophylla showed the highest survival rate in the secondary forest, but it did not like very dark conditions. Shorea macrophylla was easily attacked by herbivores. Shorea virescens showed a higher growth rate in the grassland. These interspecific variations should be considered when selecting species for enrichment planting.

Key words：dipterocarp, enrichment planting, light intensity, rehabilitation, soil properties.

 

服部大輔，田中憲蔵，ジョセフ・ジャワ・ケンダワン，入野（岡村）和朗，田中壮太，市栄智明，二宮生夫，櫻井克年：マレーシア・サラワク州における荒廃した草地，二次林，択伐林の修復のために植栽された６種のフタバガキ苗の枯死率と成長に光及び土壌環境が与える影響．森林立地 51:105-115, 2009

東南アジアでは，人為的な撹乱により多くの低地熱帯雨林が荒廃しており，その修復のためにはフタバガキを用いたエンリッチメント・プランティング手法の開発が必要である。本研究では，マレーシア・サラワク州ニア森林保護区内の焼畑放棄草地，二次林，択伐林に植栽した６種のフタバガキ苗の枯死率と成長に光と土壌が与える影響について調査を行った。相対照度は，林内より草地で極端に高かった。しかし，土壌特性については顕著な差は見られなかった。調査期間内（81ケ月間）の苗の枯死率，高さ，直径は，いずれも草地で高く林内で低かった。草地では，はじめの24ケ月間で強光により多くの苗が枯死したが，生残苗は高い成長率を示した。草地での植林は，成長の良い個体が少数でも生存すれば十分に森林を修復できると考えられた。一方，林内では草地より照度が低いため苗の生存率は高かったが成長率は低かった。二次林では，先駆樹種が植栽苗の保育樹としての役割を果たしており，高い生存率を保ったと考えられた。必要に応じて先駆樹の間伐を行うことにより植栽苗の生育を促進できると考えられた。一方，種間差も観察され，Parashorea macrophyllaは二次林での生存率が高いものの，極端な暗所での生育はよくなかった。また，Shorea macrophyllaは，野生動物の食害が観察された。Shorea virescensは，草地での成長率が高かった。今後植林の際には，このような種特性を考慮し植栽種の選択を行う必要があるだろう。

キーワード：フタバガキ，エンリッチメント・プランティング，光強度，修復，土壌特性