This dissertation addresses gaps of knowledge associated with how ecosystem carbon stocks and greenhouse gas emissions are affected by land use land cover change in tropical peatlands. This was the first study that paired peat swamp forests with oil palm plantations and analyzed site scale variation on greenhouse gas emissions. This study was conducted over 16 months (September 2012 to December 2013) at Tanjung Puting, Central Kalimantan province, Indonesia. Three main objectives of this study were: 1) to quantify the total ecosystem carbon stocks and potential carbon emissions from peat swamp forest conversion to oil palm plantations; 2) to measure annual soil emissions of CO₂, CH₄ and N₂O emissions from forests and oil palm plantations; and 3) to assess the effects of fertilizer application on nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄) emissions in the immature oil palm plantations.
The ecosystem carbon stock of primary peat swamp forests (1770 ± 123 Mg C/ha) was 2.3 times greater than in oil palm plantations (759 ± 36 Mg C/ha). The estimate of potential emissions from forest conversion on shallow peat in this study (3710 ± 321 Mg CO₂e/ha) was one of the highest emissions derived from land use change activity in the tropics. Most of the total carbon losses were produced from belowground carbon pool, which mainly due to the depletion of soil C pools. These findings suggest that the conversion of shallow peat swamp forest may result in emissions that are as high as those arising from conversion on deep peats.
We found that the conversion of tropical peat swamp forests resulted in lower CO₂ and methane emissions but higher N₂O emissions. Soil CO₂ emissions were higher in the forests (14.9 ± 0.6 Mg C ha⁻¹ yr⁻¹) than in the oil palm plantations (12.1 ± 0.4 Mg C ha⁻¹ yr⁻¹). Methane emissions were insignificant (0.4 ± 2.0 kg C ha⁻¹ yr⁻¹) in the drained plantations and high (52.4 ± 10.6 kg C ha⁻¹ yr⁻¹) in the swamp forests. The annual N₂O emissions were negligible in the peat swamp forests (0.5 ± 0.2 kg N ha⁻¹ yr⁻¹) and were substantially higher in plantations (5.5 ± 0.8 kg N ha⁻¹ yr⁻¹).
In the fertilized area, we found that N addition stimulated N₂O and CO₂ emissions, but had no significant effect on CH₄ emissions. Based on local standard fertilization practices, the mean daily N₂O and CO₂ emissions were 3.5 and 1.2 times higher in the fertilized treatment than in the control treatment. The presence of oil palm in the under canopy area significantly reduced N₂O emissions but increased CO₂ emissions following nitrogen addition. However, fertilization did not affect N₂O and CO₂ emissions at a plot level in the immature oil palm plantations.
Overall, our results emphasize the high urgency to conserve remaining tropical peat swamp forests by restricting oil palm plantation expansion on peat in support of global climate change mitigation efforts.