[A-CG37] 陸域生態系の物質循環

[ACG37-02] 熱帯泥炭林のオイルパーム農園への転換で発生した粗大有機物の分解量評価

*平野 高司¹、村田 祥子²、Wong Guan Xhuan³、Waili Joseph Wenceslaus³、Lo Kim San³、Kiew Frankie³、Aeries Edward Baran³、平田 竜一⁴、白石 知弘⁴、林 真智⁶、伊藤 雅之⁵、Melling Lulie³ (1.北海道大学大学院農学研究院、2.科学技術振興機構、3.サラワク州熱帯泥炭研究所、4.国立環境研究所、5.兵庫県立大学、6.宇宙航空研究開発機構)

キーワード：熱帯泥炭地、粗大有機物、オイルパーム農園、分解、CO2放出

Tropical peatlands are widely distributed in Indonesia and Malaysia and have accumulated a huge amount of biomass and soil carbon as peat, coexisting with swamp forest. Recently, however, the huge carbon pool has been threatened by deforestation and peat decomposition through land conversion to oil palm plantations. The land conversion produces a large amount of coarse woody debris (CWD). The CWD is usually piled high in a row (stacking rows) in plantations and would become a large CO₂ source through decomposition, though quantitative information on CO₂ emission is still lacking. Thus, we conducted a field experiment to quantify how much CO₂ is emitted through CWD decomposition.

The study was conducted in a newly developed oil palm plantation from a tropical peat swamp forest in Sarawak, Malaysia. After land preparation, CWD was piled up at the center of each subrow (0.3 ha). We measured the effective volume of a 90-m-long stacking row four times between November 2011 and May 2020, assuming that the shape of a cross section is a triangle. In addition, we determined the moisture and carbon content of CWD samples taken from the stacking row.
The width and height of the stacking row had decreased gradually. The mean cross-sectional areas of the first three measurements were 4.9, 4.1 and 3.5 m², respectively. The total amount of carbon in the stacking row was estimated at 19.0 t in November 2018 and 9.0 t in May 2019 from the effective volume and carbon content. The carbon amount was converted to 56.8 and 30.1 t C ha^-1, respectively, which indicates that 26.7 t C ha^-1 (= 16.1 g C m^-2 d^-1) was lost between the two measurement dates for 166 days.