Estimation of carbon stocks in tropical lowland peats a case study

Estimates of the extent of lowland peatlands in the Tropics varies greatly with the source. Hence estimates of both the above ground biomass and the below ground carbon stocks in these tropical peatlands also vary greatly depending on the source. How these estimates are calculated, without systematic soil surveys, is questionable. Currently most estimates of carbon dioxide emissions and carbon stocks are made with little actual ground data. What ground data is used, is mainly through examinations at the edges of swamps. This paper, firstly questions how these data are estimated. Current estimates of above ground biomass do not take into consideration the significant changes in the biomass in the six phasic vegetational communities common in tropical peat domes. Examination of the vertical peat profile indicates layers of sapric, hemic and fibric materials with or without wood (logs) which can be decomposed or undecomposed. Without actual field surveys how are estimates of carbon stocks made when each of these organic layers have different carbon contents and bulk densities. This paper suggest that we need to have vegetational maps of an area to estimate the above ground biomass. Soil surveys of peat areas to characterize the soils, their layering of organic soil materials and the carbon content and bulk density of each layer have to be collected before more reliable estimates of below ground carbon stocks can be calculated. The author uses an Estate in the Baram Area, Miri Sarawak to illustrate how these estimates are to be made. For the above ground biomass the number, girth of the trees etc. in each phasic community are used to calculate the biomass. It is suggested that in the case of Shorea Afbida Alan Forests a discount should be used as these trees have hollow trunks. The biomass in these phasic communities ranges from 389 mt/ha in the Mixed Peat Swamp Forest through 986 mt/ha in the Alan Sunga Forest to 128 mt/ha in the Padang Paya Forests. A soil survey to characterize the soils and their morphology, bulk density and carbon contents of the same Estate was carried out Using these data the carbon stocks to 1m depth for each soil map unit is calculated. Again a discount for 'recalcitrant carbon' stored in the undecomposed wood should be given as these do not decompose readily. As the carbon loss is mainly from the upper one metre, it is not necessary to calculate carbon content to the underlying mineral substratum as the material below 100 cm is constant whether under natural conditions or agricultural development such as oil palm as the watertable remains within 80 cm of the soil surface. The paper suggests these methods of estimation of above ground biomass and below ground carbon stocks give more realistic estimates of carbon stored in tropical lowland peats compared to present estimates. Based on the case study of Baram Estate totaling 4,008 ha, the adjusted above ground carbon stock is estimated to be 530,630 mt while the below ground carbon stock to 100 cm depth was 2,272,567 mt.