インドネシア, 東ジャワ, マディウンにおけるチーク林の現存量と一次生産量

Abstract

ジャワ島東部のマディウンにおいて, 若いチーク人工林の生産量と比較するために, より年齢が大きく, 一般的なチーク人工林, 植栽後10年から40年までのチーク人工林に, 0.1ヘクタールの調査区22個を設定し, それらの現存量と生産速度を推定した.推定に先立って2000年, 2001年の4月に樹木個体間の相対成長関係を調べるために, 調査地周辺の個体から, 胸高直径, 枝下幹直径等の測定を行った.2000年と2001年の9月に調査区の毎木調査を行い, その間の現存量の差と月2回の落葉量調査から森林の純生産量を推定した.年齢の大きなチーク林での純生産速度は, 若いチーク林の値に比べると低く, それらの半分ほどの値であった.年齢の高いチーク林が示した低い生産力の値でも, 日本の落葉広葉樹林, インド, タイでのチーク林の純生産速度に比べるとより高い値であった.若いチーク林では, 林内で生産される農作物等のための耕耘, 施肥等の効果, 熱帯の長い生育期間とジャワ東部の多い降水量によって, 高い生産力が維持されていたと推測された.

Permanent plots of 0.1 ha were established at 22 forests in the Forest District in Madiun, East Java. The biomass and productivity of planted teak forests (Tectona grandis Linn.) in old stands of 10 to 40-year-old were estimated and compared with those of young stands, already investigated in our previous study. In April 2000, sample trees selected around the plot were felled for collecting of stem weight and other related data needed for estimating the allometric relationships of various dimensions of individual trees e.g. stem diameter at breast height DBH and stem diameter at the lowest branch D_B. Tree censuses were conducted in the plots twice in September of 2000 and 2001. The productivity was estimated using the biomass increment during the period between the censuses and leaf production, which was estimated by measuring litter fall two times every month. The old stands showed lower net primary production (NPP), about half of the values for the young stands fertilized as one of the agroforestry practices. However, the NPP were higher than deciduous forests in Japan and teak stands in India and Thailand. The higher NPP in early stage seemed to be maintained by the intensive agricultural practices such as fertilization and tillage for agroforestry and by a long tree growth period in East Java under tropical climate.