Wood specific gravity within tree trunk variation: the case study of Legumes representatives in French Guiana

Over the past decade, much attention has been devoted to the development of forest biomass estimation methods at a stand scale, leading to the establishment of allometric models (Chave, et al. 2014). These allometric equations use a unique wood specific gravity value (WSG) per species, but neglect the within tree variations of WSG found by others (Wiemann & Williamson, 1989). The main objectives of this study are to (1) illustrate the diversity of radial and vertical patterns of WSG variation within tree trunks belonging to different ecological groups (from pioneer to sciaphilic species) and to (2) develop an estimation method of trunk biomass taking into account WSG variations. We sampled 33 young trees (10trunk of each tree. We observed different radial (from pith to bark) and longitudinal (from bottom to top) patterns of WSG variation. Pioneers and heliophilic species show both radial and longitudinal increases in WSG, while shade-tolerant and sciaphilic species show the reverse pattern. Hemi-tolerant species show an intermediate pattern, with WSG increasing radially, but decreasing or increasing longitudinally. Thus, combinations of both radial and longitudinal patterns differentiate the different ecological groups and their growth strategies. We also developed a biomass model, implemented under Xplo software (Griffon, et al. 2011) to infer trunk biomass from WSG profiles, allowing comparisons of both single- and varying-WSG model. (Texte integral)