Environmental characteristics of tropical peat swamp forests and development of reforestation techniques for degraded peat land

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In Thailand, natural peat swamp forests (42,000ha) can be found in Narathiwat, the extreme south province of the country. But, recently, the wide area of these swamp forests reclaimed rapidly for agriculture. The effects of deforestation or reclamation for natural peat swamp forests were estimated with carbon dynamics. The annual amounts of net carbon absorption were estimated at 5.32tC/ha/year and 5.22 tC/ha/year for the primary peat swamp forest and the secondly forest, respectively. A great amount of net carbon absorption, 9.69 tC/ha/year, was expected, assuming that the ground surface in the secondary forest remained under waterlogged conditions throughout a year. On the other hand, a net emission of carbon, -0.40 tC/ha/year, was expected, assuming that the soil in the secondary forest remained under dry conditions throughout a year. Carbon dioxide emissions by peat and litter decomposition and by tree respiration were measure in natural peat swamp forest. Annual CO_2 emission from the forest ecosystem was estimated to 8.84tC/ha/year on the carbon weight basis. The horizontal distribution of thickness of peat layer at Bacho swamp was investigated with the assistance of GPS for localization. It was estimated that the average thickness of peat layer was 1.1m. It was clarified that thick peat layer located parallel to coastal line with striped pattern. Peat subsidence of the development zone was 2.72〜5.21cm/year. This means that the ecosystem emits 16.1〜30.8 tC/ha/year, that is to change from a carbon sink to carbon source by the deforestation or reclamation. These results show that water management is quite important for the secondary forest after development with drainage, to restrict peat decomposition and keep the forest as a carbon sink ecosystem. Some tree species (Melaleuca cajuputi, etc.) were found as promising species to be planted at peat swamp and acidic sulfate soil.