J. O. Rieley

The amount of carbon released from peat and forest fires in Indonesia during 1997

Tropical peatlands are one of the largest near-surface reserves of terrestrial organic carbon, and hence their stability has important implications for climate change. In their natural state, lowland tropical peatlands support a luxuriant growth of peat swamp forest overlying peat deposits up to 20 metres thick. Persistent environmental change—in particular, drainage and forest clearing—threatens their stability, and makes them susceptible to fire. This was demonstrated by the occurrence of widespread fires throughout the forested peatlands of Indonesia during the 1997 El Niño event. Here, using satellite images of a 2.5 million hectare study area in Central Kalimantan, Borneo, from before and after the 1997 fires, we calculate that 32% (0.79 Mha) of the area had burned, of which peatland accounted for 91.5% (0.73 Mha). Using ground measurements of the burn depth of peat, we estimate that 0.19–0.23 gigatonnes (Gt) of carbon were released to the atmosphere through peat combustion, with a further 0.05 Gt released from burning of the overlying vegetation. Extrapolating these estimates to Indonesia as a whole, we estimate that between 0.81 and 2.57 Gt of carbon were released to the atmosphere in 1997 as a result of burning peat and vegetation in Indonesia. This is equivalent to 13–40% of the mean annual global carbon emissions from fossil fuels, and contributed greatly to the largest annual increase in atmospheric CO2 concentration detected since records began in 1957 (ref. 1).

Effect of repeated fires on land-cover change on peatland in southern Central Kalimantan, Indonesia, from 1973 to 2005

Fire plays an increasingly important role in deforestation and degradation of carbon-dense tropical peatlands in South-east Asia. In this study, analysis of a time-series of satellite images for the period 1973–2005 showed that repeated, extensive fires, following drainage and selective logging, played an important role in land-cover dynamics and forest loss in the peatlands of Central Kalimantan, Indonesia. A study of peatlands in the former Mega Rice Project area revealed a rising trend in the rate of deforestation and identified fire as the principal factor influencing subsequent vegetation succession. A step change in fire regime was identified, with an increase in burned area and fire frequency following peatland drainage. During the 23-year pre-Mega Rice Project period (1973–1996), peat swamp forest was the most extensive land-cover class and fires were of relatively limited extent, with very few repeated fires. During the 9-year post-Mega Rice Project period (1997–2005), there was a 72% fire-related loss in area of peat swamp forest, with most converted to non-woody vegetation, dominated by ferns or mosaics of trees and non-woody vegetation, rather than cultivated land.

Peat fires detected by the BIRD satellite

Tropical peat swamp forests store huge amounts of carbon, which is released to the atmosphere as carbon dioxide during fires. Recurrent peat swamp forest fires are local catastrophic events that can have a serious impact on the global carbon balance. Urgent tasks in this regard are the provision of information on the fire locations and magnitude of the carbon emissions. The experimental Bi-spectral InfraRed Detection (BIRD) satellite enables early detection of peat swamp forest fires and retrieval of their quantitative characteristics, such as the effective fire temperature, area and radiative energy release. The combination of ground truth measurements and data obtained by BIRD can improve the accuracy of estimates of carbon emissions into the atmosphere and related trace gas composition.

Tropical Peatland water management modelling of the Air Hitam Laut catchment in Indonesia

Abstract Human induced land use change and associated fire alter profoundly the hydrology of tropical peatlands and thus affect the functioning of entire river catchments. The hydrological model SIMGRO was used to calculate the effects of drainage on peat water levels, peat surface morphology and river flows within the Air Hitam Laut catchment in Jambi Province, Sumatra, Indonesia. Model outcomes were calibrated and validated using groundwater levels monitored at several sites, discharges measured in the Air Hitam Laut River and flooding patterns derived from remotely sensed Radar images. The validated model was used to predict consequences of three possible scenarios: (i) expansion of oil palm plantations upstream, (ii) expansion of agriculture downstream and (iii) continuing fire damage. Oil palm plantation development results in changes to the drainage pattern of the catchment and reduces its natural extent. Lowered river discharge will have a detrimental affect upon the sustainability of Berbak National Park in the centre of the catchment and reduce prospects for agriculture and fisheries in the coastal zone. Expansion of agriculture downstream causes peat subsidence, resulting in exposure of underlying, acid sulphate soils and intrusion of saline sea water. Continuing fires will increase considerably the area of permanently flooded land and thus constrain peatland restoration options. For peatland restoration to be successful hydrological management must be accompanied by economic measures to improve the livelihoods of local people and by effective law enforcement.

Tropical Peatland of the World

In the tropics peat occurs mostly in sub-coastal lowlands and is formed from rainforest trees and associated higher plants. There are regional differences in the plant species involved and there are also changes with increase in altitude with a tendency to lower growing and more low temperature tolerant plants. The best estimate of the area of tropical peatland is 441,025 km2 which is about 11 % of the global peatland resource, although there is a wide range of estimate from 387,201 to 657, 430 km2 depending upon whether or not all Histosols and shallow organic soils are included. Current inventories of peatland area, peat thickness and carbon stores leave much to be desired and their accuracy varies not only from region to region but also country to country. The largest area of tropical peatland and peat carbon store is in Southeast Asia with 56 % of the former and 77 % of the latter owing to the large extent of peatlands and the considerable thickness of peat (regularly exceeding 10 m) in this region. Following Southeast Asia, South America contains the next largest area (24 %) of peatland but a smaller proportion of the global tropical peatland carbon store because of the thinner peat deposits. Africa contributes 13 % of the global area and 8 % of the carbon store, while Central America and the Caribbean, Mainland Asia and Australia and the Pacific contribute only 5 %, 1 % and <1 %, respectively and only 3 % of the carbon store, collectively. Tropical peatlands are now being subjected to intensive land use change and conversion to forms of agriculture including commercial plantations. This is well advanced in Southeast Asia, especially Indonesia and Malaysia where most of the peatland area has already been deforested, drained and converted often using fire as a land clearance tool. Apart from losses of biodiversity there have been immense emissions of greenhouse gases and large losses of carbon from the peat store, contributing to climate change processes. Other regions are further behind in these environmentally damaging impacts on the tropical peatland resource.