Beneath the forest, carbon is stored in the soil, but also in the peat layer. Most of the carbon is stored in the wet anaerobic conditions within the peat layers, below ground. Peat accumu- lation takes place very slowly, over thousands of years and can lead to peat layers of several meters deep (Rieley et al. 2008). Peatlands are therefore one of the most area-efficient carbon stores of any terrestrial ecosystem and they are also home to the highest densities of Sumatran orangutans (Jaenicke et al. 2008).
Te three coastal peat swamps of Tripa, Kluet and Singkil to- gether represent the most important habitat for Sumatran oran- gutan populations in terms of density (van Schaik et al. 1995). When considering that the depth of the peat exceeds more than
five metres in many parts of Aceh’s peatlands, these coastal peat swamp forests represent by far the largest carbon stocks per unit area for the areas where Sumatran orangutans occur (Wahyunto et al. 2003; Agus and Wahdini 2008) (Map 22).
In the Tripa peat swamps alone, the total carbon stock has been estimated at between 0.05 – 0.1 Gt (PanEco 2008). Te most important single factor leading to carbon loss from In- donesia’s peatlands is conversion of forest to agriculture, and the associated drainage and burning of the peat that accom- panies this process.
As elsewhere in Indonesia, all three of Aceh’s main remaining peat swamp forests are being damaged in this way, but by far the