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Abstract Many peatlands in Europe and North America have been developed for agriculture for over a century, whilst in Southeast Asia development has largely occurred since 1990. Cultivation of drained peatlands now supports the livelihoods of large numbers of people, and the ongoing economic development of countries such as Indonesia and Malaysia. However, peat subsidence linked to plantation drainage represents both an environmental and a socio-economic challenge, associated with elevated CO 2 emissions, impacts on adjacent forest habitat, and long-term changes in plantation drainability. Whilst the fundamental challenges presented by peat subsidence are broadly recognised, the long-term rates and the potential for mitigation or avoidance of subsidence remain uncertain. We analysed over 2000 site-years of subsidence measurements from 312 sites in Sumatra, Indonesia, collected under Acacia pulpwood plantation and adjacent native forest, representing the largest peat subsidence dataset published to date. Subsidence averaged 4.3 cm yr−1 in the Acacia plantations, and extended at least 300 m into adjacent forest. Mean water table depth (WTD) was the best predictor of subsidence rate in both plantation and forest areas. We did not find conclusive evidence that subsidence was intrinsically faster under Acacia plantation than under native forest or (by comparison with previous studies) oil palm plantations for the same level of drainage. Our results suggest that raising average WTDs to the Indonesian Government's 40 cm target could – if practically and economically viable means of achieving this can be developed – reduce current plantation subsidence rates by 25–30%. Whilst some degree of peat subsidence under any form of plantation management may be unavoidable, these reductions would – if achieved at scale – both increase the economic lifetime of the plantations, and simultaneously deliver reductions in CO 2 emissions of national and global significance. Highlights • We analysed the largest current dataset of cultivated peatlands subsidence rates • Peatlands drained for Acacia in Indonesia are subsiding at over 4 cm yr−1. • Plantation drainage also leads to subsidence in adjacent natural forest • Drainage depth influences subsidence rate in both plantations and forests • Raising water tables to 40 cm could reduce subsidence and CO 2 emissions [ABSTRACT FROM AUTHOR]

We present an alternative equation for estimating carbon density of tropical peatlands. We compiled a dataset of tropical peatlands with various land uses and found that when carbon content is greater than 0.5 g g − 1 , there is no relationship between carbon content and bulk density. Thus, carbon density can be estimated from an average carbon content (0.5501 ± 0.0225 g g − 1 ) multiplied by the measured bulk density. This simple model is in contrast with previous studies, where a linear regression model is fitted to the carbon density and bulk density data. We tested the model to the data and demonstrated its high accuracy and applicability across land uses. [ABSTRACT FROM AUTHOR]

• Temporal dynamics of tropical peat subsidence are related to water table depth. • Management-related subsidence rates appear to be gradually slowing over time. • The 2015-16 El Nino drought caused rapid and sustained subsidence. • Intensifying climate extremes may lead to accelerated peat subsidence and associated carbon loss. 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. [ABSTRACT FROM AUTHOR]

Abstract: Extensive peatlands in Indonesia are a major store of carbon. Deforestation, conversion to other land uses, especially plantations of oil palm and pulpwood trees, and recurrent fires have recently caused the release of large amounts of this carbon to the atmosphere. If these large emissions from degrading peatlands are taken into account Indonesia is one of the largest emitters of CO2 worldwide. To improve estimates of the amount of carbon stored in Indonesian peatlands we applied 3D modelling based on the combined analysis of satellite imagery (Landsat ETM+, SRTM) and 750 in situ peat thickness measurements. We demonstrate that SRTM radar data can be used to determine the extent and topography of the dome shaped surface of a selection of peatlands in Central Kalimantan, South Sumatra and West Papua. A strong correlation was obtained between the convex peat dome surface and the underlying mineral ground, which was used to calculate the peat volume and carbon store. Conservatively, we estimate that at least 55±10 Gt of carbon are stored in Indonesia''s peatlands. This amount is higher than previous results published because it takes into account the biconvex nature of the tropical peatlands. With this huge carbon storage and the current rate of degradation the tropical peatlands of Indonesia have the power to negatively influence the global climate. [Copyright &y& Elsevier]

Abstract: Peat domes in Kalimantan (Indonesia) are reported to loose their dome shape as a result of disturbance such as logging and artificial drainage. The loss of the dome shape can be caused by (a combination of) two major processes: compaction and oxidation. Because natural, undisturbed peat is a major sink for atmospheric CO2, the distinction between the two processes is of utmost importance with regard to carbon storage. In case of compaction, no CO2 need to be lost to the atmosphere. In case of oxidation, either as a result of increased decomposition upon improved drainage or by burning, all CO2 produced goes to the atmosphere. To estimate the contribution of oxidation and compaction to the loss of peat dome shape, research was conducted in the Mawas area in Central Kalimantan. Physical and chemical parameters of an intact and collapsed dome were compared. Increased bulk densities in the collapsed peat dome showed that considerable compaction has occurred. Depending on the initial bulk density, compaction has probably caused a subsidence from 2.2 to 4.0 m. According to ash content measurements, no significant oxidation has taken place, but increased EC found at the collapsed dome can be due to oxidation of at least 2.3 cm to 46.9 cm peat, which implies an emission of respectively 4.2 to 85.9 kg CO2 m−2 over the 6 years since collapse. Compaction appeared to be a more important factor in the loss of dome structure than oxidation based on the estimated possible ranges in peat loss. Collapse of the dome had only minor influence on its chemical parameters. Regrowth did not seem to be hindered by the collapse and its consequences, but it was less at sites that had suffered recent fires. If peat growth resumes, collapse need not be detrimental to carbon storage. [Copyright &y& Elsevier]