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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.

Summary The evolution of angiosperms was accompanied by the segregation and specialisation of their xylem tissues. This study aimed to determine whether the fraction and arrangement of parenchyma tissue influence the hydraulic efficiency–safety trade‐off in the basal angiosperms. We examined xylem anatomical structure and hydraulic functioning of 28 woody species of Magnoliids in a tropical rainforest of Madagascar and reported, for the first time, quantitative measurements that support the relationship between vessel‐to‐xylem parenchyma connectivity and the hydraulic efficiency–safety trade‐off. We also introduced a new measurement – the distance of species from the trade‐off limit – to quantify the co‐optimisation of hydraulic efficiency and safety. Although the basal angiosperms in this study had low hydraulic conductivity and safety, species with higher axial parenchyma fraction (APf) had significantly higher hydraulic conductivity. Hydraulic efficiency–safety optimisation was accompanied by higher APf and vessel‐to‐axial parenchyma connectivity. Conversely, species exhibiting high ray parenchyma fraction and high vessel‐to‐ray connectivity had lower Ks and were further away from the hydraulic trade‐off limit line. Our results provide evidence that axial parenchyma fraction and paratracheal arrangement are associated with both enhanced hydraulic efficiency and safety.

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