A B S T R A C TSustainability criteria for palm oil production guide new planting toward non-forest land cover on mineral soil, avoiding carbon debts caused by forest and peat conversion. Effects on soil carbon stock (soil C stock ) of land use change trajectories from forest and non-forest to oil palm on mineral soils include initial decline and subsequent recovery, however modeling efforts and life-cycle accounting are constrained by lack of comprehensive data sets; only few case studies underpin current debate. We analyzed soil C stock (Mg ha À1 ), soil bulk density (BD, g cm À3 ) and soil organic carbon concentration (C org , %) from 155 plots in 20 oil palm plantations across the major production areas of Indonesia, identifying trends during a production cycle on 6 plantations with sufficient spread in plot age. Plots were sampled in four management zones: weeded circle (WC), interrow (IR), frond stacks (FS), and harvest paths (HP); three depth intervals 0-5, 5-15 and 15-30 cm were sampled in each zone. Compared to the initial condition, increases in C org (16.2%) and reduction in BD (8.9%) in the FS zone, was compensated by decrease in C org (21.4%) and increase in BD (6.6%) in the HP zone, with intermediate results elsewhere. For a weighted average of the four management zones and after correction for equal mineral soil basis, the net temporal trend in soil C stock in the top 30 cm of soil across all data was not significantly different from zero in both forest-and non-forest-derived oil palm plantations. Individual plantations experienced net decline, net increase or U-shaped trajectories. The 2% difference in mean soil C stock in forest and nonforest derived oil palm plantations was statistically significant (p < 0.05). Unless soil management changes strongly from current practice, it is appropriate for C footprint calculations to assume soil C stock neutrality on mineral soils used for oil palm cultivation. 2015 Z. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Most attention in quantifying carbon dioxide (CO2) emissions from tropical peatlands has been on large-scale plantations (industrial timber, oil palm (Elaeis guinensis)), differing in drainage and land-use practices from those of smallholder farms. We measured subsidence and changes in bulk density and carbon organic content to calculate CO2 emissions over 2.5 years in a remnant logged-over forest and four dominant smallholder land-use types in Tanjung Jabung Barat District, Jambi Province, Sumatra, Indonesia: (1) simple rubber (Hevea brasiliensis) agroforest (> 30 years), (2) mixed coconut (Cocos nucifera) and coffee gardens (Coffea liberica) (> 40 years), (3) mixed betel nut (Areca catechu) and coffee gardens (> 20 years), and (4) oil palm plantation (1 year). We quantified changes in microtopography for each site for greater accuracy of subsidence estimates and tested the effects of nitrogen and phosphorus application. All sites had a fibric type of peat with depths of 50 to > 100 cm. A recently established oil palm had the highest rate of peat subsidence and emission (4.7 cm year−1 or 121 Mg CO2 ha−1 year−1) while the remnant forest had the lowest (1.8 cm year−1 or 40 Mg CO2 ha−1 year−1). Other land-use types subsided by 2–3 cm year−1, emitting 70–85 Mg CO2 ha−1 year−1. Fertilizer application did not have a consistent effect on inferred emissions. Additional emissions in the first years after drainage, despite groundwater tables of 40 cm, were of the order of belowground biomass of peat forest. Despite maintaining higher water tables, smallholder landscapes have CO2 emissions close to, but above, current IPCC defaults.

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