Modeling long-term carbon accumulation of tropical peat swamp forest ecosystems

Peatlands play an important role in the global climate system and carbon cycle; their large carbon stocks could be released to the atmosphere due to climate change or disturbance, resulting in increased climate forcing. I modified the Holocene Peat Model (HPM), a process-based model coupling water and carbon balance for simulating carbon dynamic over millennia, to be applicable for tropical peatlands. HPMTrop outputs are generally consistent with the field observations from Indonesia. The simulated long-term carbon accumulation rate for coastal and inland peatlands were 0.63 and 0.26 Mg C ha-1 y -1, and the resulting peat carbon stocks at the end of the simulations were 3,150 Mg C ha-1 and 3,270 Mg C ha-1, respectively. The simulated carbon loss for the coastal scenario caused by forest conversion to oil palm plantation with periodic burning was 1,500 Mg C ha-1 y-1over 100 years, which is equivalent to ∼3,000 years of peat accumulation

Impacts of land use, restoration, and climate change on tropical peat carbon stocks in the 21st century: Implications for climate mitigation

The climate mitigation potential of tropical peatlands has gained increased attention as Southeast Asian peatlands are being deforested, drained and burned at very high rates, causing globally significant carbon dioxide (CO2) emissions to the atmosphere. We used a process-based dynamic tropical peatland model to explore peat carbon (C) dynamics of several management scenarios within the context of simulated twenty-first century climate change. Simulations of all scenarios with land use, including restoration, indicated net C losses over the twenty-first century ranging from 10 to 100 % of pre-disturbance values. Fire can be the dominant C-loss pathway, particularly in the drier climate scenario we tested. Simulated 100 years of oil palm (Elaeis guineensis) cultivation with an initial prescribed burn resulted in 2400–3000 Mg CO2 ha−1 total emissions. Simulated restoration following one 25-year oil palm rotation reduced total emissions to 440–1200 Mg CO2 ha−1, depending on climate. These results suggest that even under a very optimistic scenario of hydrological and forest restoration and the wettest climate regime, only about one third of the peat C lost to the atmosphere from 25 years of oil palm cultivation can be recovered in the following 75 years if the site is restored. Emissions from a simulated land degradation scenario were most sensitive to climate, with total emissions ranging from 230 to 10,600 Mg CO2 ha−1 over 100 years for the wettest and driest dry season scenarios, respectively. The large difference was driven by increased fire probability. Therefore, peat fire suppression is an effective management tool to maintain tropical peatland C stocks in the near term and should be a high priority for climate mitigation efforts. In total, we estimate emissions from current cleared peatlands and peatlands converted to oil palm in Southeast Asia to be 8.7 Gt CO2 over 100 years with a moderate twenty-first century climate. These emissions could be minimized by effective fire suppression and hydrological restoration

The Eco-hydrology of Tropical Peatlands Associated with Land Cover Changes

Tropical peatlands play an important role in global climate system by storing an immense of carbon that had been accumulated over thousands of years. Peatlands provide another important ecosystem service by regulating the hydrology. It is believed that peatlands act like a giant sponge by absorbing substantial amounts of water in wet season and gradually releasing the water in the following dry season. Nonetheless, there is a lack of information about the hydrological processes that occur in tropical peatlands, especially the effects of land cover change on peat and peat hydraulic properties. In this study, I conducted field surveys to evaluate two main peat hydraulic properties: saturated hydraulic conductivity (Ks) and moisture retention characteristics at different land cover types in tropical peatlands of West Kalimantan, Indonesia. I also explored the potential of ground penetrating radar (GPR) to determine peat properties in tropical peatlands. Across all sites, Ks varied over four orders of magnitude with depth (ca 0.001 – 13.9 m d-1). The saturated hydraulic conductivity in forested sites at the depth of 50-100 cm (1.08 ± 0.39 m day-1) was significantly higher than Ks at deeper layers. In addition, Ks at the upper layer of forested sites was significantly higher than Ks at the same depth in other land cover types, i.e., recently burned forests, seral community, and oil palm plantation. The best-approximating hierarchical model for estimating Ks included depth, forest cover, a depth and forest cover interaction, and the von Post degree of decomposition. There was no evidence that Ks was related to other peat physical and chemical properties.The peat moisture retention characteristics presented in the van Genuchten (VG) model indicated that bulk density was strongly and negatively related to the α parameter and there was no evidence that peat properties were strongly related to the m shape parameter of VG model. The proportion of macro-porosity in the drained sites with the distance 50 m from canal and forested sites. Peat pore distribution (i.e., the proportion of macro-, meso- and micro-porosity) also was strongly related to bulk density.The GPR results indicated that dielectric varied from 5.8 to 84.9 across all sites and were significantly lower at the 50-100 cm depth than those measured at 300- 400 cm and 500-600 cm. Parameter estimates from hierarchical models indicated that ash content and carbon concentration were strongly positively related to dielectric and the relationship varied among sites.My results suggest that tropical peatlands provide essential environmental services by storing huge amounts of water. We estimated that the potential amount of water that can be stored by undrained peat swamp forests in Borneo, Sumatra, and Peninsular Malaysia was about 51.1 – 52.5 km3 of freshwater. However, the tropical peatlands release water relatively easily when the water table is lowered since it is mostly composed by macro-porosity. Therefore, maintaining the water table close to the peat surface is crucial to prevent water loss from peat. My results also suggest that GPR can be useful for mapping peatland distribution, providing estimates of peat depth and insights into its properties. However, the manual coring is still needed to improve the accuracy and quality of peat property measurement data.Keywords: retention curve, moisture characteristic, peat porosity, ground penetrating radar, tropical peatlands, hydraulic properties, hydraulic conductivit

Impacts of land use, restoration, and climate change on tropical peat carbon stocks in the twenty-first century: implications for climate mitigation

The climate mitigation potential of tropical peatlands has gained increased attention as Southeast Asian peatlands are being deforested, drained and burned at very high rates, causing globally significant carbon dioxide (CO2) emissions to the atmosphere. We used a process-based dynamic tropical peatland model to explore peat carbon (C) dynamics of several management scenarios within the context of simulated twenty-first century climate change. Simulations of all scenarios with land use, including restoration, indicated net C losses over the twenty-first century ranging from 10 to 100 % of pre-disturbance values. Fire can be the dominant C-loss pathway, particularly in the drier climate scenario we tested. Simulated 100 years of oil palm (Elaeis guineensis) cultivation with an initial prescribed burn resulted in 2400–3000 Mg CO2 ha−1 total emissions. Simulated restoration following one 25-year oil palm rotation reduced total emissions to 440–1200 Mg CO2 ha−1, depending on climate. These results suggest that even under a very optimistic scenario of hydrological and forest restoration and the wettest climate regime, only about one third of the peat C lost to the atmosphere from 25 years of oil palm cultivation can be recovered in the following 75 years if the site is restored. Emissions from a simulated land degradation scenario were most sensitive to climate, with total emissions ranging from 230 to 10,600 Mg CO2 ha−1 over 100 years for the wettest and driest dry season scenarios, respectively. The large difference was driven by increased fire probability. Therefore, peat fire suppression is an effective management tool to maintain tropical peatland C stocks in the near term and should be a high priority for climate mitigation efforts. In total, we estimate emissions from current cleared peatlands and peatlands converted to oil palm in Southeast Asia to be 8.7 Gt CO2 over 100 years with a moderate twenty-first century climate. These emissions could be minimized by effective fire suppression and hydrological restoration

Ecosystem modelling of tropical wetlands

4.1 Background Modelling is essential for enhancing our understanding of the functioning of tropical wetland ecosystems, and for simulating future trajectories and testing for system thresholds. Anthropogenic activities such as drainage and land-use change can be integrated in models and their impacts on fluxes of greenhouse gas concentrations simulated. Models can also be used to test the response of peatlands and mangroves to climate extremes, variability and change, and to estimate reference levels and greenhouse gas emissions scenarios in the framework of climate change mitigation projects such as REDD+. In coastal settings, models are used to explore wetland resilience to sea-level rise. Finally, models can also be developed to support the decision making process by providing policyrelevant information on the consequences and trade-offs of adopting different management and climate scenarios

Impact of forest plantation on methane emissions from tropical peatland

Tropical peatlands are a known source of methane (CH4) to the atmosphere, but their contribution to atmospheric CH4 is poorly constrained. Since the 1980s, extensive areas of the peatlands in Southeast Asia have experienced land‐cover change to smallholder agriculture and forest plantations. This land‐cover change generally involves lowering of groundwater level (GWL), as well as modification of vegetation type, both of which potentially influence CH4 emissions. We measured CH4 exchanges at the landscape scale using eddy covariance towers over two land‐cover types in tropical peatland in Sumatra, Indonesia: (a) a natural forest and (b) an Acacia crassicarpa plantation. Annual CH4 exchanges over the natural forest (9.1 ± 0.9 g CH4 m−2 year−1) were around twice as high as those of the Acacia plantation (4.7 ± 1.5 g CH4 m−2 year−1). Results highlight that tropical peatlands are significant CH4 sources, and probably have a greater impact on global atmospheric CH4 concentrations than previously thought. Observations showed a clear diurnal variation in CH4 exchange over the natural forest where the GWL was higher than 40 cm below the ground surface. The diurnal variation in CH4 exchanges was strongly correlated with associated changes in the canopy conductance to water vapor, photosynthetic photon flux density, vapor pressure deficit, and air temperature. The absence of a comparable diurnal pattern in CH4 exchange over the Acacia plantation may be the result of the GWL being consistently below the root zone. Our results, which are among the first eddy covariance CH4 exchange data reported for any tropical peatland, should help to reduce the uncertainty in the estimation of CH4 emissions from a globally important ecosystem, provide a more complete estimate of the impact of land‐cover change on tropical peat, and develop science‐based peatland management practices that help to minimize greenhouse gas emissions

Long-term trajectory and temporal dynamics of tropical peat subsidence in relation to plantation management and climate

Disentangling land-use and climatic influences on peat subsidence, and establishing the long-term trajectory of subsidence, are necessary to determine the future economic and environmental sustainability of managed peatland landscapes. While many peatlands in temperate regions such as Europe have been drained for centuries, those of Southeast Asia have mostly been drained for agriculture and forestry practices within the last 30 years. These areas are subsiding rapidly, but few long-term subsidence records exist, and it is unclear whether currently high subsidence rates will be maintained in future. Furthermore, large-scale climate fluctuations associated with the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) exert a strong year-to-year influence on rainfall rates, affecting water table depth dynamics in both managed and intact peatlands. In this study, we analysed data collected over more than a decade of subsidence measurements from over 400 plantation and forest plots in Sumatra, Indonesia, including a unique set of 62 sites that have been continuously monitored since 2007. We show that spatial and temporal variations in subsidence rates are primarily determined by water table depth. We also find evidence of declining subsidence rates as a function of time since initial drainage, consistent with previous instrumental records from high-latitude peatlands and recent satellite data from tropical peatlands. Subsidence rates over the study period were strongly affected by the large ENSO/IOD-linked drought event in 2015–16, which caused an acceleration of subsidence across all sites. In plantation areas, we estimate that this climate perturbation caused around 14 % of subsidence observed over a twelve year period. At interior forest sites this rose to 32 %, and we found little evidence of ecosystem recovery to the end of 2018. This raises the possibility that repeated extreme droughts in the region could lead to long-term degradation of peat swamp forest ecosystems

The potential of Indonesian mangrove forests for global climate change mitigation

Mangroves provide a wide range of ecosystem services, including nutrient cycling, soil formation, wood production, fish spawning grounds, ecotourism and carbon (C) storage¹. High rates of tree and plant growth, coupled with anaerobic, water-logged soils that slow decomposition, result in large long-term C storage. Given their global significance as large sinks of C, preventing mangrove loss would be an effective climate change adaptation and mitigation strategy. It has been reported that C stocks in the Indo-Pacific region contain on average 1,023 MgC ha⁻¹ (ref. 2). Here, we estimate that Indonesian mangrove C stocks are 1,083 ± 378 MgC ha⁻¹. Scaled up to the country-level mangrove extent of 2.9 Mha (ref. 3), Indonesia’s mangroves contained on average 3.14 PgC. In three decades Indonesia has lost 40% of its mangroves⁴, mainly as a result of aquaculture development⁵. This has resulted in annual emissions of 0.07–0.21 Pg CO₂e. Annual mangrove deforestation in Indonesia is only 6% of its total forest loss⁶; however, if this were halted, total emissions would be reduced by an amount equal to 10–31% of estimated annual emissions from land-use sectors at present. Conservation of carbon-rich mangroves in the Indonesian archipelago should be a high-priority component of strategies to mitigate climate change

Net greenhouse gas balance of fibre wood plantation on peat in Indonesia

Tropical peatlands cycle and store large amounts of carbon in their soil and biomass1,2,3,4,5. Climate and land-use change alters greenhouse gas (GHG) fluxes of tropical peatlands, but the magnitude of these changes remains highly uncertain6,7,8,9,10,11,12,13,14,15,16,17,18,19. Here we measure net ecosystem exchanges of carbon dioxide, methane and soil nitrous oxide fluxes between October 2016 and May 2022 from Acacia crassicarpa plantation, degraded forest and intact forest within the same peat landscape, representing land-cover-change trajectories in Sumatra, Indonesia. This allows us to present a full plantation rotation GHG flux balance in a fibre wood plantation on peatland. We find that the Acacia plantation has lower GHG emissions than the degraded site with a similar average groundwater level (GWL), despite more intensive land use. The GHG emissions from the Acacia plantation over a full plantation rotation (35.2 ± 4.7 tCO2-eq ha−1 year−1, average ± standard deviation) were around two times higher than those from the intact forest (20.3 ± 3.7 tCO2-eq ha−1 year−1), but only half of the current Intergovernmental Panel on Climate Change (IPCC) Tier 1 emission factor (EF)20 for this land use. Our results can help to reduce the uncertainty in GHG emissions estimates, provide an estimate of the impact of land-use change on tropical peat and develop science-based peatland management practices as nature-based climate solutions

Denial of long-term issues with agriculture on tropical peatlands will have devastating consequences

Non peer reviewe