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.

The functioning and productivity of pre-Columbian raised fields (RFs) and their role in the development of complex societies in Amazonian savannas remain debated. RF agriculture is conducted today in the Congo Basin, offering an instructive analogue to pre-Columbian RFs in Amazonia. Our study of construction of present-day RFs documents periodic addition of organic matter (OM) during repeated field/fallow cycles. Field investigations of RF profiles supported by spectrophotometry reveal a characteristic stratigraphy. Soil geochemistry indicates that the management of Congo RFs improves soil fertility for a limited time when they are under cultivation, but nutrient availability in fallow RFs differs little from that in uncultivated reference topsoils. Furthermore, examination of soil micromorphology shows that within less than 40 years, bioturbation almost completely removes stratigraphic evidence of repeated OM amendments. If Amazonian RFs were similarly managed, their vestiges would thus be unlikely to show traces of such management centuries after abandonment. These results call into question the hypothesis that the sole purpose of constructing RFs in pre-Columbian Amazonia was drainage. Recent research in Amazonia has revealed that centuries of human occupation before European arrival have in many sites profoundly altered soils and landscapes 1,2. The widespread presence of Terra preta do indio and similar Anthrosols, collectively termed Amazonian Dark Earths (ADEs) 3,4 , and tree species composition altered by human activities 5-7 , belie previous perceptions of 'pristine' Amazonian forests. Seasonally inundated savanna regions of Amazonia offer other striking examples of human-transformed landscapes: large areas of pre-Columbian wetland raised fields (RFs). These are elevated earthen structures of varying size and shape, from round mounds < 2 m in diameter to platforms up to 100 m broad and hundreds of meters long, on which farmers grew flood-intolerant crops 8. RFs were an important component of subsistence systems for people living in these environments 8,9. However, soils of RF landscapes have received much less attention than the ADEs that are widespread in forested Amazonia, and how RF soils were managed remains poorly understood 8,10. Knowledge on the functioning of RF soils is crucial for a better understanding of the societies that depended on them. It could also be useful in conceiving sustainable ways to use similar environments today 11. In Amazonia, as elsewhere, one key function of RFs was to provide well-drained ground for crops 8,9,12-14. But whether making RFs in Amazonian savannas conferred other benefits has been much debated, and the predominant opinions have shifted over time. Early research on Amazonian RFs was inspired by comparisons

Methodology and results: Cowpea leaves were collected at 1, 2 and 3 months after sowing. Dried in an oven at 60 ° C to constant weight, they were subjected to chemical analysis in the laboratory. The results show that the levels of various minerals behave differently during the development cycle of the plant. Conclusion and application of results: Overall, the levels of major elements and trace elements can cover the needs of growth, maintenance, reproduction and milk production of animals during three months of the cycle. However the period of one month after sowing seems most favorable to harvest the leaves.

Climate‐driven environmental changes bring new risks but also opportunities to populations living along the world's major rivers. Based on ethnoecological fieldwork, in this paper we examine how people living in the cuvette centrale of the Congo basin have adopted flood‐recession agriculture on islands in the Congo River, taking advantage of a secular shift since the 1980s in the hydrological regime of the Congo River. Analyses of the hydrological data reveal that this shift decreased flood risk and significantly extended the growing season on the islands, long enough to enable cultivation of fast‐maturing varieties of manioc and other crops. Flood‐recession farming on islands in the river is today not only an important source of food, but also a source of income for women, who are primarily responsible for seasonal cultivation of fields during the low‐water season. Hydrological changes alone are insufficient to explain the adoption of the new agricultural practice; adoption also arose as a result of dynamic interactions among river fishing, trading, and broader socio‐economic forces. Climate‐change models project an increased frequency of extreme floods. Our results suggest that this change may limit island cultivation in the future. More generally, our findings point to the importance of looking beyond single‐factor, solely environmental explanations in studies of climate‐change adaptation.

Effet des arbustes sur la diversité floristique et la production herbacée dans les pâturages au ranch d'Essimbi à Boundji (République du Congo)