Sirvi Autor "Wong, Guan Xhuan" järgi

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Carbon dioxide dynamics across three stages of tropical peatland conversion to oil palm plantations
(2026) Kiew, Frankie; Hirata, Ryuichi; Hirano, Takashi; Wong, Guan Xhuan; Waili, Joseph Wenceslaus; Lo, Kim San; Soosaar, Kaido; Kasak, Kuno; Melling, Lulie; Mander, Ülo
This study represents the first long-term investigation spanning from a tropical peat swamp forest (PSF) to its conversion into an oil palm plantation (OPP), offering valuable data for assessing carbon dioxide (CO2) dynamics across different conversion stages. The conversion of tropical peat swamp forests to oil palm plantations has significant implications for CO2 dynamics. However, ecosystem-scale studies investigating CO2 dynamics across different stages of land conversion are lacking. This study used the eddy covariance (EC) technique to measure the net ecosystem exchange (NEE) of CO2 above a tropical peat swamp forest in Sarawak, Malaysia, from 2011 until it was cleared in 2017 and ultimately converted into an OPP in 2018. Our study found that the removal of forest biomass during land preparation led to a substantial increase in annual NEE from 25 ± 179 (2011 to 2016) to 2732 ± 655 g C m−2 year−1 (2017 to 2019). This increase was attributed to an 83 % reduction in gross primary productivity (GPP) and a 14 % reduction in ecosystem respiration (Reco). The near-ground environmental conditions also significantly changed across the conversion stages, inducing drier conditions compared to the forest. These changes were found to affect the controlling factors of nighttime NEE during conversion, resulting in a negative relationship with both air temperature and vapor pressure deficit above canopy, in contrast to the typical relationship with groundwater level observed before conversion. The conversion is also found to cause significant reduction in overall ecosystem photosynthetic activity as evidenced by the reduction in maximum gross photosynthetic rate (Pmax), photosynthetic photon flux density (PPFD), quantum yeild (α), and dark respiration (REd). Although ecosystem-scale assessments of CO2 dynamics provide insights into how ecosystems respond to changes in relation to land conversion, it is crucial to assess other respiration components, such as soil respiration and aboveground woody debris, for a more comprehensive analysis.
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Impact of land conversion on environmental conditions and methane emissions from a tropical peatland
(2025) Wong, Guan Xhuan; Hirata, Ryuichi; Hirano, Takashi; Kiew, Frankie; Waili, Joseph Wenceslaus; Mander, Ülo; Soosaar, Kaido; Melling, Lulie
Tropical peatlands are significant sources of methane (CH₄), but their contribution to the global CH₄ budget remains poorly quantified due to the lack of long-term, continuous and high-frequency flux measurements. To address this gap, we measured net ecosystem CH4 exchange (NEE-CH4) using eddy covariance technique throughout the conversion of a tropical peat swamp forest to an oil palm plantation. This encompassed the periods before, during and after conversion periods from 2014 to 2020, during which substantial environmental shifts were observed. Draining the peatland substantially lowered mean monthly groundwater levels from −20.0 ± 14.2 cm before conversion to −102.3 ± 31.6 cm during conversion and increased slightly to −96.5 ± 19.3 cm after conversion. Forest removal increased mean monthly soil temperature by 2.3 to 3.1 °C, reducing net radiation (Rn) and raising vapor pressure deficit (VPD). Following the tree removal, controlled burning temporarily warmed air temperature by 8 °C, increased VPD and significantly attenuated Rn, resulting in negative values owing to radiation interception by smoke and increased surface warming. Contrary to expectations that drainage would lower CH4 emissions, the site remained a consistent net source, with even higher emissions observed during and after conversion. The mean monthly NEE-CH4 during conversion (23.3 ± 8.6 mg C m−2 d−1) was about 2-times higher than before conversion (12.1 ± 5.3 mg C m−2 d−1) and about 1.5-times higher than after conversion (16.3 ± 4.1 mg C m−2 d−1). The heightened CH4 release is likely attributable to emissions from drainage ditches, underscoring their significant role in post-conversion CH4 dynamics. Despite its short duration, controlled burning substantially elevated NEE-CH4, ranging from 0.04 to 0.91 mg C m−2 s−1. Our findings highlight the substantial impact of land conversion on peatland CH4 dynamics, emphasizing the need for accurate flux measurements across various conversion stages to refine global CH4 budgets.