Summary 1.Regional above-ground biomass estimates for tropical moist forests remain highly inaccurate mostly because they are based on extrapolations from a few plots scattered across a limited range of soils and other environmental conditions. When such conditions impact biomass, the estimation is biased. The effect of soil types on biomass has especially yielded controversial results. 2. We investigated the relationship between above-ground biomass and soil type in undisturbed moist forests in the Central African Republic. We tested the effects of soil texture, as a surrogate for soil resources availability and physical constraints (soil depth and hydromorphy) on biomass. Forest inventory data were collected for trees ‡20 cm stem diameter in 2754 0.5 ha plots scattered over 4888 km 2 . The plots contained 224 taxons, of which 209 were identified to species. Soil types were characterized from a 1:1 000 000 scale soil map. Species-specific values for wood density were extracted from the CIRAD's data base of wood technological properties. 3. We found that basal area and biomass differ in their responses to soil type, ranging from 17.8 m 2 ha )1 (217.5 t ha ). While shallow and hydromorphic soils support forests with both low stem basal area and low biomass, forests on deep resource-poor soils are typically low in basal area but as high in biomass as forests on deep resource-rich soils. We demonstrated that the environmental filtering of slow growing dense-wooded species on resource-poor soils compensates for the low basal area, and we discuss whether this filtering effect is due to low fertility or to low water reserve. 4. Synthesis. We showed that soil physical conditions constrained the amount of biomass stored in tropical moist forests. Contrary to previous reports, our results suggest that biomass is similar on resource-poor and resource-rich soils. This finding highlights both the importance of taking into account soil characteristics and species wood density when trying to predict regional patterns of biomass. Our findings have implications for the evaluation of biomass stocks in tropical forests, in the context of the international negotiations on climate change.

In carbon cycle research, tree wood density is used to compute forest carbon stock and assess the role of forests in mitigating climate change (Pan et al., 2011;Vieilledent et al., 2016) or evaluate the impact of deforestation on climate (Achard et al., 2014). In community ecology, wood density is a proxy for species performance (Lachenbruch and McCulloh, 2014), reflecting a trade-off between growth potential and mortality risk from biomechanical or hydraulic failure (Díaz et al., 2016). Fast-growing, short-lived species tend to have a lower wood density, while slow-growing, long-lived species tend to have a higher wood density (Chave et al., 2009;Greenwood et al., 2017). In wood technology, most physical and mechanical properties of wood (e.g., strength, stiffness, porosity, heat transmission, yield of pulp per unit volume) are closely related to wood density (Sallenave, 1955;Thibaut et al., 2001;Shmulsky and Jones, 2011). This explains why wood density has been commonly measured in forestry institutes, where wood was principally studied for construction or paper making.Wood density was originally measured at ambient air moisture after air drying (Glass and Zelinka, 2010), but is now measured at a fixed moisture content, such as 15% or the international standard of 12% (Sallenave, 1955). In temperate countries, construction wood is at equilibrium with ambient air at an average moisture close to 12%. Wood density at 12% moisture is the ratio between the mass

The Vibrio splendidus clade has previously been associated with epidemic outbreaks of various aquatic animals, as in the case of the cupped oyster, Crassostrea gigas. To investigate whether involved strains could present a clonal origin and to identify possible alternative background carriage animals or zooplankton, a large epidemiological survey was conducted on isolates of the splendidus clade. For this purpose, Vibrio strains were isolated from various samples including oysters, mussels, sediments, zooplankton, and sea water on the basis of a North/South gradient of the European sea water zone (Ireland, The Netherlands, France, Italy, and Spain). A total of 435 isolates were successfully associated to the V. splendidus clade using real time polymerase chain reaction with 16S specific primers and probes. A multiple-locus variable-number tandem-repeat analysis (VNTR) was conducted on all isolates based on a multiplex PCR-VNTR with a set of primer pairs designed from the V. tasmaniensis LGP32 genome. Preliminary validation of the primers on a set of collection strains from the V. splendidus clade confirmed that the former V. splendidus-related LGP32 and relative strains were related to V. tasmaniensis rather than to the type strain V. splendidus LMG 4042. The VNTR analysis was then successfully conducted on 335 isolates which led to the characterization of 87 different profiles. Our results showed that (1) the high diversity of VNTR did not enlighten significant correlation between a specific pattern and the origin of collected samples. However, populations isolated from animal samples tend to differ from those of the background environment; (2) oyster mortality events could not be linked to the clonal proliferation of a particular VNTR type. However, few different patterns seemed successively associated with samples collected during peaks of oyster's mortality. (3) Finally, no correlation could be seen between specific VNTR patterns and sequence phylogeny of the virulence factors vsm and ompU that were detected among strains isolated during as well as outside mortality events. These results, combined with incongruence observed between the ompU and vsm phylogenetic trees, suggested both large diffusion of strains and massive lateral gene transfer within the V. splendidus clade.

h i g h l i g h t sDifferent surface treatments are applied on oil palm shell (OPS). Effects of treated OPS on physico-mechanical properties of concrete are studied. Lime treatment increases the mechanical properties of OPS concrete. Sodium silicate treatment has not enhanced the bond between cement paste and OPS. Prewetting OPS and PVA treatment reduces the shrinkage and thermal conductivity. The overuse of natural aggregates for construction causes many environmental problems. In light of their environmental impact, the discussion has increasingly focused on using alternative plant-based materials and processes such as oil palm shells (OPS). However, previous studies show that OPS have a weak adhesion with cement paste, which results in a decrease in the physical and mechanical properties of OPS concretes. One of the solutions for this problem is to carry out a surface treatment on OPS before using them in concrete. This study has examined the influence of five treatments on the physical and mechanical properties of concrete: treatment with lime (CH), sodium silicate (SS), polyvinyl alcohol (PVA), heat treatment (TH) and OPS saturation (SAT). Lime treatment (CH) on OPS showed good improvement in the mechanical properties of concrete, compared to untreated OPS.

Variability in the chemical composition of 614 species is described in a database containing measurements of wood polymers (cellulose, lignin and pentosan), as well as overall extraneous components (ethanol-benzene, or hot water extracts and ash, with a focus on silica content). These measurements were taken between 1945 and 1990 using the same standard protocol. In all, 1,194 trees belonging to 614 species, 358 genera and 89 families were measured. At species level, variability (quantified by the coefficient of variation) was rather high for density (27%), much lower for lignin and cellulose (14% and 10%) and much higher for ethanol/benzene extractives, hot water extractives and ash content (81%, 60% and 76%). Considering trees with at least five different specimens, and species with at least 10 different trees, it was possible to investigate within-tree and within-species variability. Large differences were found between trees of a given species for extraneous components, and more than one tree should be needed per species. For density, lignin, pentosan and cellulose, the distribution of values was nearly symmetrical, with mean values of 720 kg/m3 for density, 29.1% for lignin, 15.8% for pentosan, and 42.4% for cellulose. There were clear differences between species for lignin content. For extraneous components, the distribution was very dissymmetrical, with a minority of woods rich in this component composing the high value tail. A high value for any extraneous component, even in only one tree, is sufficient to classify the species in respect of that component. Siliceous woods identified by silica bodies in anatomy have a very high silica content and only those species deserve a silica study.

Grain deviations and high extractives content are common features of many tropical woods. This study aimed at clarifying their respective impact on vibrational properties, referring to African Padauk (Pterocarpus soyauxii Taub.), a species selected for its interlocked grain, high extractives content and uses in xylophones. Specimens were cut parallel to the trunk axis (L), and local variations in grain angle (GA), microfibril angle (MFA), specific Young's modulus (E0L/q, where q stands for the density) and damping coefficient (tandL) were measured. GA dependence was analysed by a mechanical model which allowed to identify the specific Young's modulus (E03/q) and shear modulus (G0/q) along the grain (3) as well as their corresponding damping coefficients (tand3, tandG). This analysis was done for native and then for extracted wood. Interlocked grain resulted in 0-25_ GA and in variations of a factor 2 in E0L/q and tandL. Along the grain, Padauk wood was characterized, when compared to typical hardwoods, by a somewhat lower E03/q and elastic anisotropy (E0/G0), due to a wide microfibril angle plus a small weight effect.(Résumé d'auteur

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Basic wood density is an important ecological trait for woody plants. It is used to 2 characterize species performance and fitness in community ecology, and to compute 3 tree and forest biomass in carbon cycle studies. While wood density has been histor-4 ically measured at 12% moisture for construction purpose, it is convenient to convert 5 this measure to basic wood density, i.e. the ratio of dry mass over green volume. 6Basic wood density can then be used to compute tree dry biomass from living tree 7 volume. 9Here, we show that previous conversion factors used to convert densities at 12% mois-10 ture into basic wood densities are inconsistent. We derive a new, exact formula to 11 compute the basic wood density D b from the density at moisture content w denoted 12 D w , the fibre saturation point S, and the volumetric shrinkage coefficient R. We Based on theory and data, we found that basic wood density could be inferred from