How Much Carbon Do the Soils of Papua New Guinea Forests Contain?: A Preliminary Assessment Based on the Multipurpose National Forest Inventory Soil Survey

Preliminary assessment of carbon in forest soils of Papua New Guinea (PNG) was done for 53 sites. Simple soil-landscape model was constructed to explain how soil carbon relates to landscape position and landform processes. Despite limitations of the soil survey, sufficient data have been obtained to indicate that the amount of carbon in forest soils surveyed so far is related primarily to their carbon-complexing capacity (CCC) which, in turn, depends on their geological parent material and parent rock. Soils were grouped into six categories based on their carbon content. The six categories ranged from very low 0–50 t/ha to extremely high 601–1,000 t/ha. Amalgamating the areas of mapped geological units on the basis of their likely CCC and their median carbon content has enabled the total carbon content of all forest soils in PNG to be estimated as 7,727 × 10⁶ t. This figure is approximate and will be modified as more results are obtained and more sophisticated GIS-based landscape analysis is undertaken. The total carbon in forest biomass, as measured in this National Inventory and estimated for roots, is 4,006 × 10⁶ t. Thus, the total carbon in PNG’s forests at present is estimated to be 11,733 × 10⁶ t, with 66% stored in the soil and 34% in the biomass. The high proportion of ecosystem carbon held in the soil emphasises the importance of implementing soil conservation measures to maintain the total carbon resource in PNG’s forests.