A tropical ombrotrophic peatland ecosystem is one of the largest terrestrial carbon stores. Flux rates of carbon dioxide (CO 2 ) and methane (CH 4 ) were studied at various peat water table depths in a mixed-type peat swamp forest floor in Central Kalimantan, Indonesia. Temporary gas fluxes on microtopographically differing hummock and hollow peat surfaces were combined with peat water table data to produce annual cumulative flux estimates. Hummocks formed mainly from living and dead tree roots and decaying debris maintained a relatively steady CO 2 emission rate regardless of the water table position in peat. In nearly vegetation-free hollows, CO 2 emission rates were progressively smaller as the water table rose towards the peat surface. Methane emissions from the peat surface remained small and were detected only in watersaturated peat. By applying long-term peat water table data, annual gas emissions from the peat swamp forest floor were estimated to be 3493 AE 316 g CO 2 m À2 and less than 1.36 AE 0.57 g CH 4 m À2 . On the basis of the carbon emitted, CO 2 is clearly a more important greenhouse gas than CH 4 . CO 2 emissions from peat are the highest during the dry season, when the oxic peat layer is at its thickest because of water table lowering.

Tropical peatlands have accumulated huge soil carbon over millennia. However, the carbon pool is presently disturbed on a large scale by land development and management, and consequently has become vulnerable. Peat degradation occurs most rapidly and massively in Indonesia, because of fires, drainage, and deforestation of swamp forests coexisting with tropical peat. Peat burning releases carbon dioxide (CO2) intensively but occasionally, whereas drainage increases CO2 emission steadily through the acceleration of aerobic peat decomposition. Therefore, tropical peatlands present the threat of switching from a carbon sink to a carbon source to the atmosphere. However, the ecosystem‐scale carbon exchange is still not known in tropical peatlands. A long‐term field experiment in Central Kalimantan, Indonesia showed that tropical peat ecosystems, including a relatively intact peat swamp forest with little drainage (UF), a drained swamp forest (DF), and a drained burnt swamp forest (DB), functioned as net carbon sources. Mean annual net ecosystem CO2 exchange (NEE) (± a standard deviation) for 4 years from July 2004 to July 2008 was 174 ± 203, 328 ± 204 and 499 ± 72 gC m−2 yr−1, respectively, for the UF, DF, and DB sites. The carbon emissions increased according to disturbance degrees. We found that the carbon balance of each ecosystem was chiefly controlled by groundwater level (GWL). The NEE showed a linear relationship with GWL on an annual basis. The relationships suggest that annual CO2 emissions increase by 79–238 gC m−2 every 0.1 m of GWL lowering probably because of the enhancement of oxidative peat decomposition. In addition, CO2 uptake by vegetation photosynthesis was reduced by shading due to dense smoke from peat fires ignited accidentally or for agricultural practices. Our results may indicate that tropical peatland ecosystems are no longer a carbon sink under the pressure of human activities.

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Peat fire in tropical peatland not only releases a large amount of carbon into the atmosphere, but also causes significant damage to peatland ecology and the landscape. It is important to understand peat fire and to establish more effective methods to control peat fire. In this paper, the results of field and laboratory research elucidate the combustion and thermal characteristics of peat fire. Field studies were carried out at 9 study plots in actual peat fire areas along the Trans Kalimantan Highway of Central Kalimantan in 2002. Laboratory analyses using a bomb calorimeter and TG-DTA were carried out to obtain low and high ignition temperatures and calorific values of various peat fire fuels. Results of field studies on weather conditions, temperatures in peat layers during fire, patterns of peat fire fronts, peat fire spreading speeds, fuel composition, moisture contents and fuel losses during fires are described in this paper. This study clarified the nature of fire movement and the smoldering process in an actual peat fire in tropical peatland. Based on our results, a more effective method for controlling peat fire can be developed. Miyanishi (2001) elucidated the processes of smoldering combustion and pyrolysis in a shallow duff layer with a numerical simulation model. The results of numerical simulation showed that both pyrolytic and oxidative degradation of duff occur down to a depth of about 1 cm and that only endothermic pyrolysis occurs below that depth due to a lack of oxygen.The results of the studies mentioned above give an excellent overview of similar aspects of peat fire processes in tropical peatland. In spite of the very different climate, peat material and social economical conditions in which peat fires occur, there are some common physical factors that play major roles in determining the incidence and propagation of peat fires. These factors are the main subject of this paper.The aim of this study is to clarify the physical aspects of peat fire characteristics in tropical peatland of Central Kalimantan, including the weather in the dry season, peat combustion properties and characteristics of fuel materials. STUDY SITES AND METHODS Study sitesAs shown in Fig 1, Nine study plots along the highway were selected for field observations of wildfire in peatland during the dry season in 2002.The wildfires in each plot were caused independently. The distances between plots ranged from about 1 to 30 km.The depths of the peat layer at the nine plots were about 1-3 m ( RePPProT, 1990).