The exploitation of tropical peatlands has triggered serious environmental problems such as deforestation and peat fires, loss of biodiversity, and emission of greenhouse gases. This process includes peat drainage and drying, followed by peat degradation. Dam construction is expected to decrease the vulnerability of peatlands to fires and improve the regeneration of degraded peatland. This study investigated the effects of dam restoration for peat swamp forests degraded by drainage on the dynamics of organic matter that regulate peat conditions. We compared the organic matter dynamics of three types of forest in Palagnkaraya, Central Kalimantan, Indonesia: less-drained (almost natural), drained (degraded), and dam-restored forest. Both drained and dam-restored forests experienced drainage in 1995; however, dams were constructed at the dam-restored site in 2005. Within each site, we measured litterfall, fine root production, and decomposition as indices of the peat accumulation rate, water table, and soil moisture. The mean groundwater level at the dam construction site was significantly higher than that of the drained forest. Litterfall was highest in the drained forest and lowest in the dam-restored site. The decomposition rates were not significantly different among the sites. We estimated the changes in peat mass using a model. The amounts of peat accumulation after 5 years were found to be 3.46, -1.60, and -2.86 kg/m2 in the less-drained, drained, and dam-restored sites, respectively. These results showed that peat deposition decreased at the dam construction site but decreased less in the drained forest. A possible explanation for the observed results is increased primary production in drained forests caused by reduced flooding stress and increased nutrient supply from oxidized peat for primary producers.
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