Quelques représentations d'embarcations monoxyles en Asie du Sud-Est

Seront évoquées ici les modalités de deux occurrences des représentations relatives aux embarcations monoxyles, faites à des époques fort différentes et sur des subjectiles très dissemblables. Celles, d'une part, qui apparaissent sur les tambours de bronze de la civilisation de Dông-so'n (Viêt Nam), d'autre part, certaines de celles que l'on découvre dans les bas-reliefs de deux grands temples khmers datés de la fin du XIIe ou du début du XIIIe siècle.We will evoke the modalities of two occurrences that were determining factors of representations, relative to monoxyla boats built during different epochs and from different supports. On the one hand, those found on the bronze drums of the Dong So'n (Viet Nam) civilization and those discovered on the bas-reliefs of two important khmer temples dating from the end of the XIInd century or the beginning of the XIIIrd century.Serán evocadas aquí las modalidades de dos ocurrencias de las representaciones relativas a las embarcaciones monoxilas hechas en épocas completamente diferentes y sobre soportes muy desiguales. Por una parte, las que aparecen sobre los tambores de bronce de la civilización Dông So'n (Viet Nam) ; por otra parte, algunas de las que se descubren en los bajorrelieves de dos grandes templos kmer datando de fines del siglo XII o principios del XIII

How does replacing natural forests with rubber and oil palm plantations affect soil respiration and methane fluxes?

This research was conducted under the REDD-ALERT project (Grant Agreement # 226310) with financial support from the European Commission Seventh Framework Programme [FP7/2007-2013]. It was also generously funded by the Australian Agency for International Development (AusAID) (Grant Agreement # 46167) and the Norwegian Agency for Development Cooperation (NORAD) (Grant Agreement #QZA-10/0468). This work is part of the Consultative Group on International Agricultural Research (CGIAR) programs on Trees, Forests and Agroforestry (FTA) and Climate Change, Agriculture and Food Security (CCAFS). Authors extend their gratitude to staff from Brawijaya University in Malang, the Indonesian Soil Research Institute (ISRI) in Bogor, and Balai Lingkungan Pertanian in Jakenan for laboratory support. We also thank Robbin Matthews and John Hillier, whose insights, feedbacks and recommendations contributed to improve the quality of the manuscript and to the modeling team of the School of Biological and Environmental Science from the University of Aberdeen for constructive discussions. Furthermore, we are very thankful to all assistants and to the REDD-ALERT Indonesia team who supported field work in Jambi. Finally, we are very grateful to the two anonymous reviewers for their constructive comments which contributed to improve this manuscript.Peer reviewedPublisher PD

A cost-efficient method to assess carbon stocks in tropical peat soil

Estimation of belowground carbon stocks in tropical wetland forests requires funding for laboratory analyses and suitable facilities, which are often lacking in developing nations where most tropical wetlands are found. It is therefore beneficial to develop simple analytical tools to assist belowground carbon estimation where financial and technical limitations are common. Here we use published and original data to describe soil carbon density (kgC m<sup>−3</sup>; C<sub>d</sub>) as a function of bulk density (gC cm<sup>−3</sup>; <i>B</i><sub>d</sub>), which can be used to rapidly estimate belowground carbon storage using <i>B</i><sub>d</sub> measurements only. Predicted carbon densities and stocks are compared with those obtained from direct carbon analysis for ten peat swamp forest stands in three national parks of Indonesia. Analysis of soil carbon density and bulk density from the literature indicated a strong linear relationship (C<sub>d</sub> = <i>B</i><sub>d</sub> × 495.14 + 5.41, <i>R</i><sup>2</sup> = 0.93, <i>n</i> = 151) for soils with organic C content > 40%. As organic C content decreases, the relationship between C<sub>d</sub> and <i>B</i><sub>d</sub> becomes less predictable as soil texture becomes an important determinant of C<sub>d</sub>. The equation predicted belowground C stocks to within 0.92% to 9.57% of observed values. Average bulk density of collected peat samples was 0.127 g cm<sup>−3</sup>, which is in the upper range of previous reports for Southeast Asian peatlands. When original data were included, the revised equation C<sub>d</sub> = <i>B</i><sub>d</sub> × 468.76 + 5.82, with <i>R</i><sup>2</sup> = 0.95 and <i>n</i> = 712, was slightly below the lower 95% confidence interval of the original equation, and tended to decrease C<sub>d</sub> estimates. We recommend this last equation for a rapid estimation of soil C stocks for well-developed peat soils where C content > 40%

GHG emission under different cropping systems in some Histosols of Malaysia

Oil palm is the fastest expanding equatorial crop, and is one of the biggest threats to carbon-rich tropical peatlands in Malaysia. Smallholder plantations cover a vast area of peatlands in Peninsular Malaysia and follow varied cropping systems. Here we analyse the impacts of specific crops and the effects of proximity to such crops, upon GHG emissions from the soil, and the soil microbial community phenotype. We found that only mature oil palm plants in 1st generation oil palm mono-cropping potentially had significant autotrophic contributions to total CO2 emissions with 33.5% increase in locations closer to mature oil palm stems. The sampling locations closer to younger oil palms and other crops did not significantly increase total CO2 emissions. CH4 emissions were significantly greater for sampling locations near plants with adventitious root system such as yam and pineapple crops. However CH4 emissions were very low in comparison to CO2 emissions, and their contribution to carbon loss was limited in these sites. Surface peat microbial community structure was unaffected by proximity to different crops within each cropping system, possibly due to a lack of influence of rhizosphere in the surface peat layers (0–5 cm). The results suggest that most of the total CO2 emissions from these agro-ecosystems contribute to C loss due to microbial decomposition of the peat soil, unlike greater autotrophic contributions to total emissions in forested peatlands reported in other studies. Hence without appropriate above-ground vegetation or hydrology conducive to peat formation, ancient carbon stored in these peatlands is gradually lost into the atmosphere via greater heterotrophic respiration under agricultural management on such peat-based ecosystems

Characterizing degradation of palm swamp peatlands from space and on the ground: an exploratory study in the Peruvian Amazon

Peru has the fourth largest area of peatlands in the Tropics. Its most representative land cover on peat is a Mauritia flexuosa dominated palm swamp (thereafter called dense PS), which has been under human pressure over decades due to the high demand for the M. flexuosa fruit often collected by cutting down the entire palm. Degradation of these carbon dense forests can substantially affect emissions of greenhouse gases and contribute to climate change. The first objective of this research was to assess the impact of dense PS degradation on forest structure and biomass carbon stocks. The second one was to explore the potential of mapping the distribution of dense PS with different degradation levels using remote sensing data and methods. Biomass stocks were measured in 0.25 ha plots established in areas of dense PS with low (n = 2 plots), medium (n = 2) and high degradation (n = 4). We combined field and remote sensing data from the satellites Landsat TM and ALOS/PALSAR to discriminate between areas typifying dense PS with low, medium and high degradation and terra firme, restinga and mixed PS (not M. flexuosa dominated) forests. For this we used a Random Forest machine learning classification algorithm. Results suggest a shift in forest composition from palm to woody tree dominated forest following degradation. We also found that human intervention in dense PS translates into significant reductions in tree carbon stocks with initial (above and below-ground) biomass stocks (135.4 ± 4.8 Mg C ha−1) decreased by 11 and 17% following medium and high degradation. The remote sensing analysis indicates a high separability between dense PS with low degradation from all other categories. Dense PS with medium and high degradation were highly separable from most categories except for restinga forests and mixed PS. Results also showed that data from both active and passive remote sensing sensors are important for the mapping of dense PS degradation. Overall land cover classification accuracy was high (91%). Results from this pilot analysis are encouraging to further explore the use of remote sensing data and methods for monitoring dense PS degradation at broader scales in the Peruvian Amazon. Providing precise estimates on the spatial extent of dense PS degradation and on biomass and peat derived emissions is required for assessing national emissions from forest degradation in Peru and is essential for supporting initiatives aiming at reducing degradation activities

Greenhouse gas fluxes from agricultural soils of Kenya and Tanzania

Knowledge of greenhouse gas (GHG) fluxes in soils is a prerequisite to constrain national, continental, and global GHG budgets. However, data characterizing fluxes from agricultural soils of Africa are markedly limited. We measured carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) fluxes at 10 farmer-managed sites of six crop types for 1 year in Kenya and Tanzania using static chambers and gas chromatography. Cumulative emissions ranged between 3.5–15.9 Mg CO2-C ha−1 yr−1, 0.4–3.9 kg N2O-N ha−1 yr−1, and −1.2–10.1 kg CH4-C ha−1 yr−1, depending on crop type, environmental conditions, and management. Manure inputs increased CO2 (p = 0.03), but not N2O or CH4, emissions. Soil cultivation had no discernable effect on emissions of any of the three gases. Fluxes of CO2 and N2O were 54–208% greater (p < 0.05) during the wet versus the dry seasons for some, but not all, crop types. The heterogeneity and seasonality of fluxes suggest that the available data describing soil fluxes in Africa, based on measurements of limited duration of only a few crop types and agroecological zones, are inadequate to use as a basis for estimating the impact of agricultural soils on GHG budgets. A targeted effort to understand the magnitude and mechanisms underlying African agricultural soil fluxes is necessary to accurately estimate the influence of this source on the global climate system and for determining mitigation strategies

Impacts of conversion of tropical peat swamp forest to oil palm plantation on peat organic chemistry, physical properties and carbon stocks

Ecosystem services provided by tropical peat swamp forests, such as carbon (C) storage and water regulation, are under threat due to encroachment and replacement of these natural forests by drainage-based agriculture, commonly oil palm plantation. This study aims to quantify how the chemical and physical properties of peat change during land conversion to oil palm. This will be addressed by comparing four separate stages of conversion; namely, secondary peat swamp forests, recently deeply drained secondary forests, cleared and recently planted oil palm, and mature oil palm plantation in North Selangor, Malaysia. Results indicate accelerated peat decomposition in surface peats of mature oil palm plantations due to the lowered water table and altered litter inputs associated with this land-use change. Surface organic matter content and peat C stocks at secondary forest sites were higher than at mature oil palm sites (e.g. C stocks were 975 ± 151 and 497 ± 157 Mg ha− 1 at secondary forest and mature oil palm sites, respectively). Land conversion altered peat physical properties such as shear strength, bulk density and porosity, with mirrored changes above and below the water table. Our findings suggest close links between the organic matter and C content and peat physical properties through the entire depth of the peat profile. We have demonstrated that conversion from secondary peat swamp forest to mature oil palm plantation may seriously compromise C storage and, through its impact on peat physical properties, the water holding capacity in these peatlands

A cost-efficient method to assess carbon stocks in tropical peat soil

Estimation of belowground carbon stocks in tropical wetland forests requires funding for laboratory analyses and suitable facilities, which are often lacking in developing nations where most tropical wetlands are found. It is therefore beneficial to develop simple analytical tools to assist belowground carbon estimation where financial and technical limitations are common. Here we use published and original data to describe soil carbon density (kgC m⁻³; C[subscript d]) as a function of bulk density (gC cm⁻³; B[subscript d]), which can be used to rapidly estimate belowground carbon storage using B[subscript d] measurements only. Predicted carbon densities and stocks are compared with those obtained from direct carbon analysis for ten peat swamp forest stands in three national parks of Indonesia. Analysis of soil carbon density and bulk density from the literature indicated a strong linear relationship (C[subscript d] = B[subscript d] × 495.14 + 5.41, R² = 0.93, n = 151) for soils with organic C content > 40%. As organic C content decreases, the relationship between C[subscript d] and B[subscript d] becomes less predictable as soil texture becomes an important determinant of C[subscript d]. The equation predicted belowground C stocks to within 0.92% to 9.57% of observed values. Average bulk density of collected peat samples was 0.127 g cm⁻³, which is in the upper range of previous reports for Southeast Asian peatlands. When original data were included, the revised equation C[subscript d] = B[subscript d] × 468.76 + 5.82, with R² = 0.95 and n = 712, was slightly below the lower 95% confidence interval of the original equation, and tended to decrease C[subscript d] estimates. We recommend this last equation for a rapid estimation of soil C stocks for well-developed peat soils where C content > 40%