Although formed in historic (Holoceen) rather than prehistoric times, peatlands cover extensive areas in the lowlands of Sumatra, Kalimantan, Sulawesi and Irian Jaya. Taking up large quantities of carbon dioxide and regulating water flows, they perform important chemical and hydrological services for mankind, both on a local scale and globally.
Formation of most peatswamp forests in Indonesia started approximately 5,000 to 8,000 years ago. At that time extensive alluvial plains formed along the shores of Kalimantan, Sumatra and Irian Jaya as a result of accretion of clay particles and a sea level drop of several meters. The mangroves that initially developed on those plains, were gradually replaced by other plant species as accumulation of organic materials caused a change in growth conditions. Slowly, the tidal (salt water) mangrove swamps turned into elevated (rainwater fed) peatswamp forests.
As peatswamp forests are purely rainwater-fed, they have specific chemical characteristics. The waters are very acid (pH 3.0-4.5) and nutrient poor as there are no nutrients or buffering components flowing in from outside the area. The peat soil in undisturbed circumstances consists of 80 to 90 percent water. Due to their capacities to store and maintain large quantities of water, peatswamp forests play an important role in flood mitigation and ensure a continuous water supply. Peatswamp forests are often characterised as Blackwater Systems, as the waters flowing out of these areas are heavily stained by tannins released from the peat soils, giving the water a dark ‘cola’colour.
The rate of peat accumulation changes over time. Young peats accumulate at a maximum rate of 4.7 millimetres per year. This rate decreases as peats grow older, often to less than 2.2 millimetres per year. The depth of the peat layer strongly differs among locations, ranging from less than a metre in young peats to an impressive 24 metres in old peat bogs in Riau province, Sumatra. The peat formation is highly linked to the capacity to hold water, and the peat is therefore dome shaped, like a drop of water on a flat floor. The system depends on the hydrostatic equilibrium that enables the peat to hold the rain water above the normal ground water level. If something disturbs this equilibrium, for instance by digging a small drainage channel, the balance of the huge ‘water bell’ is disturbed leading to desiccation and peat soil subsidence over large areas. This also leads to oxidation of the drained areas, resulting in carbon molecules linking to oxygen, thus creating carbon-dioxide, a greenhouse gas that then automatically is emitted into the atmosphere.
Tropical peats are widely distributed throughout the world. Small tracts are found in parts of Latin America, Africa and the Caribbean. The vast majority however is found in Southeast Asia. The total amount of peatlands in this region is estimated at 33 million hectares. Most peatlands, approximately 27 million hectares, are found in the lowlands of Indonesia. Smaller tracts are a found in Malaysia, the Philippines Thailand and Vietnam. Many countries already lost considerable amounts of their peat resources. Ongoing disturbances like fires, land conversion and logging will lead to further decrease of peat coverage.