Abstract. Aedes albopictus (Diptera: Culicidae) was first reported in Central Africa in 2000, together with the indigenous mosquito species Aedes aegypti (Diptera: Culicidae). Because Ae. albopictus can also transmit arboviruses, its introduction is a public health concern. We undertook a comparative study in three Cameroonian towns (Sahelian domain: Garoua; equatorial domain: Douala and Yaoundé) in order to document infestation by the two species and their ecological preferences. High and variable levels of pre-imaginal Ae. aegypti and Ae. albopictus infestation were detected. Only Ae. aegypti was encountered in Garoua, whereas both species were found in Douala and Yaoundé, albeit with significant differences in their relative prevalence. Peridomestic water containers were the most strongly colonized and productive larval habitats for both species. No major differences in types of larval habitat were found, but Ae. albopictus preferentially bred in containers containing plant debris or surrounded by vegetation, whereas Ae. aegypti tended to breed in containers located in environments with a high density of buildings. These findings may have important implications for vector control strategies.

In an area of savanna-forest (S-F) mosaic of Cameroon, at Kandara near Bertoua, an enclosed savanna bordered by young semi-deciduous forests was selected for detailed studies of vegetation and soil carbon isotope compositions with a view to estimating the rate of forest advance into savannas. Forest floristic composition and structure were analysed in small plots along two S-F transects and within two large stands. Tree species counts and basal area (BA) measurements gave convergent results defining (1) an edge forest with low BA values that forms an irregular strip parallel to the S-F border, (2) a large colonization zone zone composed of pioneer species (Albizia species, with individuals of very large diameter) and (3) a mature forest composed of abundant Rinorea individuals and large individuals of Triplochiton scleroxylon and Piptadeniastrum africanum. Carbon stable isotopes were deter mined from organic matter of soil profiles sampled at various depths in savanna, colonization-zone and mature forest. In the deep soil horizons (40-50 cm) of the colonization-zone profiles, δ13C values similar to those of the present savanna reveal the past existence of a large-tree savanna. In subsurface horizons (15-20 cm), δ13C values intermediate between those of savanna and mature forest prove the encroachment of the forest ecosystem on savanna. Using 14C measurements, the mean residence time (MRT) of soil organic matter of these last horizons was determined with precision owing to the atmospheric 14C pulse from nuclear bomb tests prior to 1964. By assuming an exponential age distribution of organic compounds and by taking account of MRT and remaining carbon from the savanna, the coloniza tion zone was found to be 60-80 y old. The age of the colonization zone being the same near the present savanna and near the mature forest, it seems that the forest advance was probably not a linear process but would result from the coalescence of Albizia thickets born in savanna.

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The aim of this study was to make an inventory of the trees and estimate hedgerows and eucalyptus plantations carbon stocks in comparison with that of the Kouoghap sacred forest which is the only landscape having retained its original character. This study was conducted in the sacred forest, hedgerows and Eucalyptus plantations, which are the predominant land use type of Batoufam locality. Inventory data of trees with diameter ≥10 cm were made in 5 transects of 800 m x 5 m for the sacred forest and 10 transects of 300m x 5m for hedgerows and Eucalyptus plantations. The above and below ground biomass of trees was estimated using allometric equations; that of litter collected in 30 square plots of 0.5m x 0.5m, was estimated by the destructive method. A total of 70 and 11 trees species were respectively recorded in the sacred forest and hedgerows. However, Eucalyptus plantations are monospecific (only one trees species was found). The Shannon index (3.51) showed a rich floristic diversity in the sacred forest and weak diversity in hedgerows (1.94). The abundance of trees decreases with the increase in diameter classes of the sacred forest and hedgerows therefore forming and irregular appearance in the Eucalyptus plantations. No significant difference was found between these three land use according to the carbon stocks which varied from 130 to 196 tC.ha -1 for aboveground and from 31 to 47 tC.ha -1 for belowground carbon. As compared to, that of litter which was significantly different between the sacred forest (6.40 tC.ha -1 ), hedgerows (9.39 tC.ha -1 ) and Eucalyptus plantations (10.96 tC.ha -1 ). This study confirmed the conservation of biodiversity through sacred forest and also the need to take into account other types of lands use in policies to fight against climate changes given the amount of carbon they store.