Wood Density Variations of Tropical Trees Differing in Shade-Tolerance and Leaf Phenology of the Congo Basin
Abstract- Wood density (WD) is not only a key element in tropical forest ecology to estimate tree biomass but also an indicator of timber quality, and it integrates many aspects of tree mechanical properties and functioning. Notably, contrasting patterns of radial variation of WD have been demonstrated and are related to regeneration guilds (light- demanding vs. shade-bearing) but haven’t been demonstrated to be related to leaf phenology (deciduous vs. evergreen). With the destructive method and the “archimed” principle, we investigated the WD radial variation of nine timber tree species harvested in the eastern region of Cameroon. The result showed that WD differed significantly among these nine species (P > 0.05). Their average WD was 0.70 ± 0.05; 0.79 ± 0. 14; 0. 69 ± 0.05; 0.55 ± 0.03; 0.81 ± 0.03; 0.63 ± 0.08; 0.65 ± 0.08; 0.64 ± 0.05; 0.44 ± 0.07 g.cm3 for Afzelia bipendensis; Cylicodiscus gabunensis; Entandrophragma cylindricum; Entandrophragma utile; Erythrophleum suaveolens; Mansonia altissima; Milicia excelsa; Pterocarpus soyauxii and Triplochiton scleroxylon. Variation in WD from bark-to-pith enabled three distinct patterns: type 1 in which WD increases (A. bipendensis); type 2 in which WD decreases (C. gabunensis; E. cylindricum; E. utile; E. suaveolens; M. excelsa and P. soyauxii); and type 3 in which WD values are substantially equal (M. altissima and T. scleroxylon). All nine timber tree species were deciduous. At the level of light requirement succession, the pioneer species were E. suaveolens, M. excelsa, T. scleroxylon and the other one was non-pioneer light demander species: C. gabunensis, A. bipendensis, E. cylindricum, P. soyauxii, M. altissima and E. utile. In addition, we found that WD in this study compared to the DRYAD global repository may strongly differ depending on the species (up to 133% for T. scleroxylon and less than 96% for A. bipendensis). Therefore, when estimating forest biomass in specific sites, we recommend that future studies on WD include the analysis of the effect of vertical variation with long-term phenological data and anatomical analysis in the same species and use a large sampling size, including individuals of both the same and different species.
