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.

A study on the change of forest cover was carried out in the Department of Likouala, Republic of Congo for the period from 1986 to 2015. It was intended to calculate the areas of the different land conversions in the study period, but also to identify the causes of deforestation and forest land Landsat TM (1986), Etm + (2001), and Oli (2015) images were treated with the method of supervised classification "Maximum Likelihood" was applied to obtain the different maps of land type. The results revealed the lost of forest, with 133.624 hectares of intact forests in1986, 126980.89 ha of intact forests in 2001 and 114.166 ha of intact forests in 2015. There were also increases and regressions in areas of other types of land tenure. This study shows that agriculture is the main driving force for the conversion of forest land to non-forest land. Given the importance of the coverage of lost forests, it appears urgent to strengthen the sustainable management of these ecosystems with a view to combating climate change.Keywords: Forest, deforestation, Landsat, Likouala, Republic of Congo RésuméUne étude sur le changement de la couverture forestière a été réalisée dans le département de la Likouala en République du Congo dans la période de 1986 à 2015. Celle-ci avait pour but de calculer les superficies des