Abstract. In temperate regions the chemistry of the lower troposphere is known to be significantly affected by biogenic volatile organic compounds (VOCs) emitted by plants. The chemistry of the lower troposphere over the tropics, however, is poorly understood, in part because of the considerable uncertainties in VOC emissions from tropical ecosystems. Present global VOC models predict that base emissions of isoprene from tropical rainforests are considerably higher than from savannas. These global models of VOC emissions which rely mainly on species inventories are useful, but significant improvement might be made with more ecologically based models of VOC emissions by plants. Ecosystems along a successional transect from woodland savanna to primary rainforest in central Africa were characterized for species composition and vegetation abundance using ground surveys and remotely sensed data. A total of 336 species (mostly trees) at 13 sites were recorded, and 208 of these were measured for VOC emissions at near-optimal light and temperature conditions using a leaf cuvette and hand-held photoionization detector (PID). A subset of 59 species was also sampled using conventional VOC emission techniques in order to validate the PID technique. Results of ecological and VOC emission surveys indicate both phylogenetic and successional patterns along the savanna-rainforest transect. Genera and families of trees which tend to emit isoprene include Lophira, Irvingia, Albizia, Artocarpus, Ficus, Pterocarpus, Caesalpiniaceae, Arecaceae, and Moraceae. Other taxa tend to contain stored VOCs (Annonaceae and Asteraceae).Successional patterns suggest that isoprene emissions are highest in the relatively early successional Isoberlinia forest communities and progressively decrease in the later successional secondary and primary rainforest communities. Stored VOCs appear to increase along the savanna-rainforest succession, but these data are more tentative. These findings are consistent with successional patterns of isoprene and terpene fluxes in North American forests and highlight the feasibility of constructing better predictive models of VOC emissions.

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.

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Individual density and social group formation of a western lowland gorilla population were estimated by (1) the line transect method with direct detection and (2) reconstruction of social groups from direct observation and bed count in the Ndoki Forest, northern Congo. The line transect method gave an estimate of 4-5 gorillas per sq km along the transect course in the roughly 24 sq km study site. The small range of the strip width in dense vegetation, detectability of all members in a group, uncovered vegetation type by the census course, and the contagious distribution of the animals in space may affect the results. The reconstruction suggested the presence of 7 social groups as well as solitaries in the same gorilla popUlation, although individual identification will be necessary for more accurate results. In other study sites of lowland gorillas, the densities have been reported to be lower in primary forests than those in secondary regenerating forests. Aboundant fibrous foods, such as certain aquatic plants found in the marshy grassland, may increase the carrying capacity and allow for the high density of gorillas in this primary forest, Key Words: western lowland gorilla / density estimates / social group / tropical forest / Congo Nest census along line transect(s) (nest census) has been a common approach to estimate density in several western lowland gorilla populations with incomplete habituation and identification of gorilla individuals. This approach is validated by the gorilla's typical nestbuilding behavior, i.e., nest-builders usually make a new nest each night, and few cases of reuse occur.On the other hand, the nest census will underestimate densities in certain forest types, probably because of decreased detectability of certain types of old nests (Remis, 1993 in this volume). Remis (1993) reports such a case of underestimation and its reasons at the Bai Hokou Study Site in the Central African Republic, which is near the present site.

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.