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

For the nine tree species studied, this assertion was true for Type 2: C. gabunensis ; E. cylindricum ; E. utile ; E. suaveolens ; M. excelsa and P.soyauxii . The opposite shade-tolerant species systematically showed high wood density values. In our study, shade-tolerant species were not available. But Chao et al. (2008) and King et al. (2006) formulated the hypothesis that slow- growing species that invest in dense wood were shade- tolerant, in particular during the early stages of their lives. Other studies also reported that shade tolerant species tend to have a much higher WD than do pioneer species (King et al. 2006; Ramananantoandro et al. 2016). One explanation were that pioneer species produce a low WD to grow taller than their neighbors, thereby acquiring more resources (i.e., light) quickly (Woodcock & Shier 2002).The observations of these six listed tree species were unlikely to persist in old-growth forests, supporting the assumption that strictly light- demanding species present decreasing trends in wood density from bark to pith (Nock et al. 2009; Wiemann & Williamson 1988). Type 1: A. bipendensis presents an increasing trend in wood density from bark-to-pith. This observation was confirmed by Woodcock & Shier (2002), who corroborated that the increase in wood density from bark-to-pith is often attributed to increased light exposure and improved growth conditions in the later stages. With possible access to the canopy for some trees during ontogeny (Brienen & Zuidema 2006). All of this supports the idea that a species' regeneration guild may differ between places (Hawthorne 1985) and should only be assigned with care. This finding emphasises the significant correlation between wood density and regeneration guild and backs up the notion of a comprehensive wood economic spectrum (Chave et al. 009). It’s clear that the evergreen species invest in denser wood, the production of this denser wood induct the difficulty of detection of tree ring boundaries in wood samples of this species. And the evergreen species growth in entire year and during the drought periods. All these nine studied timber tree specie’s, were deciduous, and there were no a significant difference between them (brevidecidious and deciduous). Only two: C. gabunensis and P. soyauxii were brevidecidious with a second highest density for C. gabunensis: 0.79 ± 0.14 g.cm 3 . The other seven timber tree species were deciduous with highest density for E. suaveolens 0.81 ± 0.03 g.cm 3 ; and lowest density for T. scleroxylon 0.44 ± 0.07 g.cm 3 . At the light of this exception and results, it’s appeared clear that brevidecidious present more heavy wood than deciduous species. c) Comparison between Different Wood Densities The specific wood density of A. bipendensis in this study is 83 percent lower than the value obtained by (Sallenave 1964; 1971), 96 percent lower than that obtained by Zanne et al. (2009), and 106 percent higher than that obtained by Fayolle et al. (2013). For C. gabunensis, these values were 94 percent lower than those of Sallenave (1955) and were equal to the value obtained by Zanne et al. (2009). In E. cylindricum, they were equal to the value obtained by Sallenave (1955), 113 percent higher than those of Fayolle et al. (2013), and 121 percent higher than those of Zanne et al. (2009). For E. utile, the value obtained was 80 percent lower than that of Sallenave (1955), 91 percent lower than that of Sallenave (1964), and 101 percent higher than that of Zanne et al. (2009). The WD value of E. suaveolens was 102 percent higher than Sallenave (1971), 82 percent lower than the value of Fayolle et al. (2013), and 105 percent higher than the value of Zanne et al. (2009). In M. altissima, the WD values obtained in this study were 106 percent higher than those of Sallenave (1964), 85 percent lower than those of Fayolle et al. (2013), and 112 percent higher than the value of Zanne et al. (2009). In M. excelsa, they were 103 percent higher than those of Sallenave (1964) and 112 percent higher than those of Zanne et al. (2009). The WD value in P. soyauxii was 95 percent lower than that of Sallenave (1964) and 97 percent lower than that of Zanne et al. (2009). Finally, the WD values obtained in T. scleroxylon were 118 percent higher than those of Sallenave (1955), 125 percent higher, and 133 percent higher, respectively, than those of Fayolle et al. (2013) and Zanne et al. (2009). C onclusion In this study, we characterised detailed bark-to- pith WD profiles between and within nine harvested tropical tree species. Our study on WD radial gradients in Congo Basin tropical tree species showed an exclusively significant positive, neutral, and negative pith-to-bark WD gradient. These unique, site-specific details are not included in the global databases that are currently in use, which could result in assessments of species' functional attributes and estimates of tree biomass that are inadequate and erroneous. We advise extreme caution when performing meta-analyses based on global functional trait databases to prevent mistakes brought on by insufficient data collection and storage. Regional biomass estimates will be improved, and our understanding of the functional strategies and successional behaviour of tropical tree species will be increased by future studies documenting trends in WD variance in new locations and forest types. V. 1 Year 2023 73 © 2023 Global Journals 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 Particularly, this study recommends that future studies of wood density 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