International audienc

& Key message In a tropical rainforest of Madagascar, tree species differed in average wood density depending on their light requirements and on the soil type. Tree diameter had no effect. None of these factors influenced the variation of density related to the distance to the pith. & Context Wood density (WD) is an important wood property as it correlates with several functional tree traits and mechanical wood properties. Furthermore, wood density is often used in forest biomass and carbon stock estimates. The variation in wood density depends on a range of intrinsic or environmental factors. & Aims This study investigated the effect of species, tree diameter, soil types and the distance from the pith on wood density in native hardwood species from a natural, midelevation rainforest in Madagascar. & Methods We extracted pith-to-bark core samples from the trunk of 204 trees from 23 species. Each wood core was sectioned into 1 cm-long segments on which measures of volume and weight were performed. Within-tree and between-tree variations of wood density were analysed. & Results Average wood density was higher on shade-tolerant than on light-demanding species. It was higher on poor ferralitic than on fertile lowland soils. Tree diameter had no influence on average wood density. Regarding within-tree variation, wood density does not vary from pith to bark. & Conclusion These results help fill the gaps in wood properties database for tree forest species in Madagascar.

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To generate carbon credits under the Reducing Emissions from Deforestation and forest Degradation program (REDD?), accurate estimates of forest carbon stocks are needed. Carbon accounting efforts have focused on carbon stocks in aboveground biomass (AGB). Although wood specific gravity (WSG) is known to be an important variable in AGB estimates, there is currently a lack of data on WSG for Malagasy tree species. This study aimed to determine whether estimates of carbon stocks calculated from literature-based WSG values differed from those based on WSG values measured on wood core samples. Carbon stocks in forest biomass were assessed using two WSG data sets: (i) values measured from 303 wood core samples extracted in the study area, (ii) values derived from international databases. Results suggested that there is difference between the field and literaturebased WSG at the 0.05 level. The latter data set was on average 16 % higher than the former. However, carbon stocks calculated from the two data sets did not differ significantly at the 0.05 level. Such findings could be attributed to the form of the allometric equation used which gives more weight to tree diameter and tree height than to WSG. The choice of dataset should depend on the level of accuracy (Tier II or III) desired by REDD?. As higher levels of accuracy are rewarded by higher prices, speciesspecific WSG data would be highly desirable.