Tropical peatland is a complex and globally important wetland ecosystem, storing an enormous amount of the Earth's terrestrial carbon from centuries of organic material accumulation. In this ecosystem, peat swamp forests developed over an ombrogenous peat where hydrology influences its physico-chemical properties, one of which is fluctuation of the peat surface. While several studies of tropical peatland surface fluctuation have been reported, most are based on relatively short measurement periods or focused on drained areas. Hence, the objective of this study is to determine the long-term dynamics of peat surface fluctuation from an undrained peat swamp forest in relation to its water table depth. Peat surface level, water table, and rainfall were measured monthly at three experimental sites in a peat swamp forest in Sarawak, Malaysia over a period of about 10 years (2011-2020). The sites were different in soil structure and vegetation community; namely mixed peat swamp, Alan Batu, and Alan Bunga forests. Throughout the measurement period the peat surface in all sites exhibited consistent oscillating movement that generally follow the fluctuation of water table, with swelling and subsidence occurring after water table increase following high rainfall and receding water during dry spells respectively. Positive linear relationships were also found between peat surface level and water table (p < 0.05). Both the surface level and water table at all sites fell to their lowest during an intense dry period in 2019. Surface fluctuation at the Alan Batu site was most affected by seasonal changes in water table, which may be due to presence of vacant zones in the peat profile.
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