Trees species diversity, richness, and similarity were studied in fifteen plots of the tropical rainforests in the northeast of the Republic of Congo, based on trees inventories conducted on fifteen 0.25 ha plots installed along different types of forests developed on terra firma, seasonally flooded, and on flooded terra. In all of the plots installed, all trees with diameter at breast height, DBH ≥ 5 cm, were measured. The Shannon diversity index, species richness, equitability, and species dominance were computed to see the variation in tree community among plots but also between primary forest and secondary forest. A total of 1611 trees representing 114 species and 35 families were recorded from a total area of 3.75 ha. Euphorbiaceae was the dominant family in the forest with 12 species, followed by Fabaceae-Mimosoideae (10 species) and Phyllanthaceae (6 species) and Guttiferae (6 species). The biodiversity did not vary greatly from plot to plot on the whole of the study area (3.75 ha). The low value of Shannon index was obtained in plot 11 ( = 0.75) whereas the highest value was obtained in plot 12 ( = 4.46). The values of this index vary from 0.23 to 0.95 in plots P11 and P15, respectively. Results obtained revealed high biodiversity of trees of the forest of Impfondo-Dongou. The information on tree species structure and function can provide baseline information for conservation of the biodiversity of the tropical forest in this area.

In order to improve the knowledge of the functioning of tropical rainfall forests in the Congo basin ,a study on the quantification of the stocks of carbon in coarse woody debris was done in Likouala's area, in Republic of Congo. To achieve this goal,14 squares plots of 50mx50m had installed on the whole study area, including ten plots in primary forest and four in secondary forests. The method used was to make an inventory of woody debris lying on the ground or Log and snags in the different study plots. There sults of this study revealed average stocks of 603.45kg MS.ha -1 in primary forests, 468.64 kg MS.ha -1 in secondaryforestsand392.68 kgMS.ha -1 in agroforestry, with no significant differences between stocks in primary forests and secondary forests (P = 0.05). In addition this study revealed that carbon stocks varied from one locality to another in all the study area, as well as between the experimental plots (p = 0.005). This study helps to understand that the Chablis played a key role in the production of large woody debris. Keywords

In order to know the role of plant woody debris in the carbon cycle, a study of carbon stocks and carbon flow of plant woody debris was conducted in the natural forests of the centre of the republic of Congo in the Bateke Plateau. Allometric equations were used to measure the carbon stock of in dead wood debris of Lesio-louna tropical rainforest. Three plots of 40 m × 40 m were delimited in each forest types. All plots were within 300 m of each other. The average stocks of carbon in coarse woody debris obtained are 10993 g•m −2 and 14172 g•m −2 , respectively, in the Gallery forest (GF) and the hill-slope forest clump (HF), the difference of carbon stock between the two forests is not significant (p = 0.78). The interannual mean flow in both forests is respectively 1776 and 545 g•m −2 •an −1 in the FG and the MSDS; this medium is not significant (p = 0.10). Carbon stocks of fine woody debris are respectively 965 and 83 g•m −2 in the GF and HF, difference is significant (p = 0.0013). The interannual mean flow of carbon in fine woody debris in the GF and the HF were respectively 310 g•m −2 •an −1 and 51 g•m −2 •an −1 .

The study of structural and tree flora biodiversity of the forest of the Mbomo-Kellé UFA was done on an area of 88.5 ha (0.014% of the total UFA area). The inventory was carried out in plots of 200 m × 25 m (0.5 ha), arranged in a contiguous way along the opened trails in the forest with an equidistance interval of 2 km. 11,012 trees of DBH ≥20 cm were counted, divided into 107 genera, 31 families and 133 species including 121 completely identified and 12 defined only in terms of genus. Data analysis consisted of calculating relative and weighted frequencies, the Shannon and Weaver diversity indexes, Pielou's evenness index, and the Jaccard and Sorensen similarity indices. Relative frequencies showed that the most representative family in terms of species is the Fabaceae-Caesal piniodeae with 18.05% of species and the most representative in terms of individuals is the Burseraceae with 19.17% of inventoried trees. The principal components analysis allowed to show inter-and intrablock heterogeneities.

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