Global Journal of Science Frontier Research, H: Environment & Earth Science, Volume 23 Issue 2

IV. D iscussion a) Wood Density Intra and Inter-Radial Variation The first aim of our study was to compare the variation in WD among and within nine harvested tropical tree species, including radial variation within individuals. At the light of this analysis conducted on stem discs. This results show that specie’s explained most wood density radial variance whereas individuals explained only a minor part from pith-to-bark. These results were consistent with previous observations in different part of world (Parolin 2002 Woodcock & Sheir 2002; Nock et al. 2009; Onada et al. 2010; Hietz et al. 2013; Osazuwa-Peters et al. 2014; Bastin et al. 2015; Plourde et al. 2015; Lehnebach et al. 2019). And globally among tropical tree species (Zanne et al. 2009). Importantly, the WD values between 0.44 and 0.81 g.cm - 3 from this present study were within the range (0.11 to 1.39 g.cm -3 ) reported for 2,456 tropical forest tree species (Chave et al. 2006). The differences in WD between our study and other studies may be due to aspects of the growing environment (biotic and abiotic) factors. Particularly, the observation of variations in WD from bark to pith enabled three qualitative types of radial patterns to be distinguished. Type 1 was represented by a tree species in which WD increased from bark to pith: Species No. Samples/Ste m discs measured Average WD ± STD (g.cm -3 ) at humidity 8 % Range WD (g.cm -3 ) [Min-Max] No. values are given in GWDD WD value GWDD ± STD (g.cm -3 ) WD value GWDD ran ge (g.cm -3 ) Afzelia bipendensis (Fabaceae) 01/02 0.70 (±0,05) [0.65 – 0.75] 11 0.73 ± 0.05 0.66 – 0.82 Cylicodiscus gabunensis (Fabaceae) 01/02 0.79 (±0.14) [0.65 – 0.93] 18 0.79 ± 0.07 0.62 – 0.97 Entandrophragma cylindricum (Meliaceae) * 01/02 0.69 (±0.05) [0.64 – 0.74] 16 0.57 ± 0.04 0.50 – 0.63 Entandrophragma utile (Meliaceae) 01/01 0.55 (±0.03) [0.51 – 0.58] 18 0.54 ± 0.04 0.44 – 0.58 Erythropheum suaveolens (Fabaceae) * 01/02 0.81 (±0.03) [0.78 – 0.84] 20 0.77 ± 0.06 0.69 – 0.87 Mansonia altissima (Malvaceae) * 01/03 0.63 (±0.02) [0.61 – 0.65] 23 0.56 ± 0.03 0.47 – 0.63 Milicia excelsa (Moraceae) * 01/03 0.65 (±0.08) [0.45 – 0.73] 24 0.58 ± 0.06 0.44 – 0.67 Pterocarpus soyauxii (Fabaceae) 01/03 0.64 (±0.05) [0.59 – 0.69] 14 0.66 ± 0.07 0.57 – 0.81 Triplochiton scleroxylon (Malvaceae) * 01/03 0.44 (±0.07) [0.37 – 0.63] 24 0.33 ± 0.03 0.28 -0.41 A. bipendensis . Type 2 corresponded to tree species in which WD decreased from the bark to the pith: C. gabunensis ; E. cylindricum ; E. utile ; E.suaveolens ; M. excelsa; and P. soyauxii . And type 3 was represented by tree species in which WD values were substantially equal from bark-to-pith: M. altissima and T. scleroxylon . These results confirms the effect of heartwood on WD radial variations already suspected (Parolin 2002; Hietz et al. 2013). These findings contrast with the bulk of studies on WD radial variations (Parolin 2002; Woodcock & Sheir 2002; Nock et al. 2009; Hietz et al. 2013; Osazuwa-Peters et al. 2014; Plourde et al. 2015), which reported both negative and positive gradients. We presume that this difference is mainly due to the failure to take into account the presence of heartwood that was previously hypothesized by several authors (Parolin 2002; Hietz et al. 2013). b) Wood Density Shade Tolerance and Phenology Wood density profiles with a decreasing trend from bark to pith and a low wood density were not systematic for pioneer and non-pioneer light-demanding species, but our results demonstrated that the pioneer species E. suaveolens showed the very highest wood density value, the second highest wood density value was for C. gabunensis, and the lowest wood density value was found for the pioneer species T. sceroxylon . For the nine tree species studied, this assertion was true © 2023 Global Journals 1 Year 2023 72 Global Journal of Science Frontier Research Volume XXIII Issue ersion I VII ( H ) Wood Density Variations of Tropical Trees Differing in Shade-Tolerance and Leaf Phenology of the Congo Basin Table 2: WD of the Measured Samples Per Species Compared to the WD Values in the GWDD. WD Values from the GWDD Were Taken for Species Occurring in Africa, as the Measured Species all Originate From Central Africa. an Asterisk (*) Next to a Species Name Indicates a Significant Difference (P < 0.05) Between the Mean of the Measured Values and the Mean of That Species in the GWDD