by Jack Rieley
Tropical peatlands are one of the largest carbon stores
on earth, release of which has implications for climate change (Page 2002).
In a natural state, lowland tropical peatlands support a luxuriant growth of
peat swamp forest (PSF) overlying peat deposits up to 20 metres thick, but any
persistent environmental change, particularly decrease in wetness, threatens
their stability and makes them susceptible to fire.
Fires were widespread on the extensive peatlands of Indonesia during the 1997 El Niño and recurred in 2002 and 2004. By using satellite imagery and ground measurements within a 2.5 million hectare study area in Central Kalimantan it was determined that 32% (0.79 Mha) of the area burned in 1997, of which peatland accounted for 91.5% (0.73 Mha), releasing 0.19-0.23 Gt of carbon to the atmosphere through peat combustion. It was estimated that between 0.81-2.57 Gt of carbon were released to the atmosphere from Indonesia’s peatlands in 1997 as a result of burning peat and vegetation. This is equivalent to 13-40% of the mean annual global carbon emissions from fossil fuels and contributed greatly to the largest increase in atmospheric CO2 content detected since records began in 1957. Forest and peat fires in 2002 burned much of the same area that was affected in 1997 releasing probably around 25% of the carbon that was lost in the previous burn.
In addition to fire, tropical peatland cleared for agriculture and settlement subsides at rates between 2 and 10 cm per year, slowly releasing stored carbon to the atmosphere. Tropical peatlands cover approximately 20 million hectares (Mha) in Indonesia, constituting nearly 11% of the total land area of the country. More than 50% of the peat exceeds 2 metres in thickness, ranging from 0.5 m to 20 m. The vast majority of these peatlands are lowland, rain-fed ecosystems with a natural vegetation cover of peat swamp forest. Studies of the ecology and environmental importance of the tropical peatland resource have been carried out since 1993, in Central Kalimantan (the Indonesian part of the island of Borneo) Province of Indonesia, which has approximately 5 million hectares of peatland. This research project was already established when Indonesia was affected by the 1997 El Niño-Southern Oscillation (ENSO) event and therefore well placed to observe and measure some of its environmental consequences.
The climatic changes brought about by ENSO events have global consequences, with effects particularly pronounced in Indonesia and other parts of the Western Pacific where drought often results. ENSO events have occurred several times over the last three decades, resulting in extended dry seasons with droughts of varying severity. Prior to 1997, the most prolonged dry period was in 1982/83 when there were severe forest fires in East Kalimantan and more than 3 Mha of land burned, including 0.55 Mha of peat swamp forest. There were less severe droughts and associated fires in 1987, 1991, and 1994. In Central Kalimantan, in non-ENSO years, there is a dry season of usually three or four month’s duration between May/June and September. Normal dry seasons are, however, usually relatively wet. During the 1997 ENSO, the dry season began as early as March and continued through into December, i.e. there were eight months without appreciable rainfall. At the start of the 1997 dry season, as is normal in every dry season, many fires were started by local farmers and estate managers in order to clear deforested land of vegetation in preparation for planting domestic and plantation crops.
Many of these fires spread into forest areas where they burned with great intensity. In Kalimantan, South Sumatra, and Irian Jaya, fires were started on, or reached areas of peatland, burning both the vegetation and the underlying peat. In Central Kalimantan, the situation was exacerbated by a massive peatland conversion project - the so-called Mega Rice Project (MRP). This scheme was initiated in 1995 with the aim of converting 1 Mha of wetland, mostly peatland, to agricultural use. Throughout the MRP area extensive, deep drainage and irrigation canals were excavated, much of the peat swamp forest was logged over and, during 1997, fire was being used as a rapid land clearance tool. Various estimates have been made of the amount of land in Indonesia that was damaged by the 1997 fires. Initial estimates indicated that approximately 4.5 Mha of land had been affected, but more detailed assessments doubled this figure to 9 Mha. Of this latter area, as much as 1.45 Mha was believed to be peat and swamp forest although no one made credible estimates of the area of peatland affected by fire at the time.
We presented evidence to show that it was probably much larger than previously believed, between 2.4 and 5.8 million hectares, with correspondingly much greater transfers of carbon to the atmosphere of 0.81 to 2.57 Giga (Billion) tonnes. The two most intensivee sources of smoke and particulate matter were the fires centred on the peatlands of Central Kalimantan and the Riau area of South Sumatra. Here both vegetation and underlying peat caught fire, contributing greatly to the so-called haze (particulate-laden smog), which blew north-westwards to affect Singapore and Malaysia. During this time solar radiation in Central Kalimantan was reduced to 40% of normal levels whilst visibility was reduced to 25 metres.
It has been estimated that the financial consequences of the fires were over US$ 3 billion from losses in timber, agriculture, non-timber forest products, hydrological and soil conservation services, and biodiversity benefits, whilst the haze cost an additional US$ 1.4 billion, most of which was borne by Indonesians for health treatment and lost tourism revenues. At the present time, the peatlands of Southeast Asia represent a globally important carbon store, which has accumulated over 26,000 years or more. In recent decades, however, an increasing proportion of this store has been converted to a carbon source, through a combination of deforestation, land-use change and fire. The widespread peatland fires that occurred throughout Indonesia during the strong ENSO-related drought of 1997 resulted in the combustion of 0.87-2.57 Gt (Bt) of stored carbon that took between 1000 and 2000 years to accumulate, with up to 8% of the total carbon store within the peat being released in a few months (Page et al., 2002).
At the current estimated rate of carbon accumulation in Central Kalimantan peatlands of 85 g m-2 yr-1, this single fire event represents an approximate loss of between 70 and 200 years of carbon sink function. The Southeast Asian region is currently subject to increasing climatic variability (Easterling et al., 2000; Heaney, 1991) and it is predicted that seasonal precipitation extremes associated with future ENSO-events are likely to become more pronounced (Meehl & Washington, 1996). This may lead to reduced water supply to and retention by peatlands, leading to a lowering of water tables. This will limit the rate of peat accumulation where it is still taking place, enhance degradation and oxidation on peatlands that are no longer actively forming peat, and greatly increase the likelihood of peatland fires, with consequent rapid loss of stored carbon. In conclusion, increased climatic seasonality and variability has the potential to switch the tropical peatland ecosystems of Southeast Asia from carbon sinks to carbon sources.
Unless land use policies are changed to control logging and to drain and clear peatland for plantations, recurrent fires will lead to a complete loss of Indonesia’s peat swamp forests and continued, high emissions of CO2 to the atmosphere. Scientists are demanding intensive national and international efforts to avoid further fires in the tropical peat swamp forests of Southeast Asia that lead to the release of huge amounts of carbon dioxide. They ask politicians to act now.
ReferencesPage et al., 2002: “The amount of carbon released from peat and forest fires in Indonesia during 1997”. Nature, 420: 61-65.
More information
is available from Jack Rieley: rieleyconsultants@btinternet.com