Northeastern Gabon Research Articles

Evidence for circulation of Rift Valley fever virus in wildlife and domestic animals in a forest environment in Gabon, Central Africa.

Rift Valley fever (RVF) is a mosquito-borne viral zoonosis caused by the Rift Valley fever virus (RVFV) that can infect domestic and wild animals. Although the RVFV transmission cycle has been well documented across Africa in savanna ecosystems, little is known about its transmission in tropical rainforest settings, particularly in Central Africa. We therefore conducted a survey in northeastern Gabon to assess RVFV circulation among wild and domestic animals. Among 163 wildlife samples tested using RVFV-specific RT-qPCR, four ruminants belonging to subfamily Cephalophinae were detected positive. The phylogenetic analysis revealed that the four RVFV sequences clustered together with a virus isolated in Namibia within the well-structured Egyptian clade. A cross-sectional survey conducted on sheep, goats and dogs living in villages within the same area determined the IgG RVFV-specific antibody prevalence using cELISA. Out of the 306 small ruminants tested (214 goats, 92 sheep), an overall antibody prevalence of 15.4% (95% CI [11.5-19.9]) was observed with a higher rate in goats than in sheep (20.1% versus 3.3%). RVFV-specific antibodies were detected in a single dog out of the 26 tested. Neither age, sex of domestic animals nor season was found to be significant risk factors of RVFV occurrence. Our findings highlight sylvatic circulation of RVFV for the first time in Gabon. These results stress the need to develop adequate surveillance plan measures to better control the public health threat of RVFV.

Molecular Identification of Enteric Viruses in Domestic Animals in Northeastern Gabon, Central Africa.

Astroviruses (AstVs), enteroviruses (EVs), and caliciviruses (CaVs) infect several vertebrate taxa. Transmitted through the fecal-oral route, these enteric viruses are highly resistant and can survive in the environment, thereby increasing their zoonotic potential. Here, we screened for AstVs, EVs, and CaVs to investigate the role of domestic animals in the emergence of zoonoses, because they are situated at the human/wildlife interface, particularly in rural forested areas in Central Africa. Rectal swabs were obtained from 123 goats, 41 sheep, and 76 dogs in 10 villages located in northeastern Gabon. Extracted RNA reverse-transcribed into cDNA was used to detect AstVs, EVs, and CaVs by amplification of the RNA-dependent RNA polymerase (RdRp), or capsid protein (VP1) gene using PCR. A total of 23 samples tested positive, including 17 goats for AstVs, 2 goats, 2 sheep, 1 dog for EVs, and 1 dog for CaVs. Phylogenetic analyses revealed that AstV RdRp sequences clustered with sheep-, goat-, or bovine-related AstVs. In addition, one goat and two sheep VP1 sequences clustered with caprine/ovine-related Evs within the Enterovirus G species, and the CaV was a canine vesivirus. However, human-pathogenic Evs, EV-B80 and EV-C99, were detected in goats and dogs, raising questions on the maintenance of viruses able to infect humans.

Prevalence and Cardiovascular Risk Factors Associated with Obesity/ Overweight in Adult Patients Living with HIV/AIDS: Case of the Makokou Outpatient Treatment Center, Ogooué-Ivindo, North-Eastern Gabon

Background: Designed to fight HIV/AIDS, antiretroviral drugs (ARVs) may be responsible for certain cardiometabolic abnormalities in people living with HIV (PLWHIV). To this end, the present study evaluates the prevalence and impact of obesity/overweight on the development of cardiovascular risk factors in patients at the outpatient treatment center (CTA) of Makokou, in the Ogooué-Ivindo region, North-eastern Gabon.
 Materials and Methods: This is a cross-sectional and descriptive study, based on a retrospective analysis of the records of patients followed at the HIV/AIDS outpatient treatment center of Makokou from December 2015 to December 2020. A structured questionnaire was used to collect data such as age, gender, socio-economic level, daily habits such as alcohol consumption, tobacco consumption, and physical exercise. Other epidemiological parameters such as body mass index (BMI), and CD4 count were measured.
 Results: A total of 165 people living with HIV (PLHIV), the majority of whom were between 41 and 60 years of age (60.60%). treated with antiretrovirals from December 2016 to December 2021 were collected for this study. With a sex ratio (F/M) of 3.58, women (78.2%) were in the majority compared to men. The mean age was 51 ± 13 years. While 95.8% of the patients were from the different departments of the province of Ogooué-Ivindo, the remaining patients (4.8%) were from other provinces such as Estuaire, Haut-Ogooué or Ogooué-Lolo. Civil servants represented 21%. The self-employed represented 29%, and the unemployed represented 50%. Only 34% of the participants in the study, the majority of whom were women, engaged in regular physical activity. 5.4% of the patients, mostly men, were active smokers. 34%, especially women, consumed alcohol. 20% of the PLWHIV had a medical history of type 2 diabetes mellitus or hypertension (HTA), and the majority were female. 5.4% of the declared hypertensives were on treatment. 7.8% of the hypertensive patients were discovered in consultation. The remainder were normotensive (86.8%). A significant difference in hypertension was observed in patients aged between 41 and 60 years ( p= 0.0029*). The data revealed a positive correlation index (r=0.19) between BMI and hypertension. All the therapeutic combinations with which the patients were treated contained NRTIs, of which the most used were tenofovir disoproxil (TDF) 66.67% and lamivudine (3TC) 33.33% and finally the most used NRTI was Efavirenz (EFV) 76.36%. After 5 years of treatment, 89 PLWHIV ( 53.93%), had CD4 count ≥ 500 cells/mm3. 53 PLWHIV (32%) had CD4 count ranging from 200 - 499 mm3 and thus moderate immune deficiency and with CD4 count < 200 cell /mm3, 23 PLWHIV (14%) had severe immune deficiency. HIV-infected patients under 40 years of age had a mean CD4 count of 412 cell/mm3, which was lower than that of patients 40 years of age and older, which was 556 cell/mm3. It was noted that after 5 years, treatment with ARVs was significantly associated with an increase in BMI among PLHIV, (P=0.0210). It was indicated that the increase or decrease of CD4 count in PLWHIV, depended on BMI, after 5 years of ARV treatment.
 Conclusion: This study confirms the existence of an increase in overweight and obesity in people living with HIV/AIDS under antiretroviral treatment. It also shows that obesity had an impact on the development of certain cardiovascular risk factors in these people, which require careful vigilance of the health personnel on their weight gain, due to lipidic parameters such as cholesterol, HDL, Triglycerides.

Description of two new miniature species of Hylopanchax Poll & Lambert, 1965 (Cyprinodontiformes: Procatopodidae), from northeastern Gabon, with an updated diagnosis of the genus based on morphology, colouration and osteology.

Two new species of the lampeye genus Hylopanchax are described from the Ivindo River basin in the Ogowe River drainage. Hylopanchax multisquamatus, new species, and Hylopanchax thysi, new species, differ from congeners by the presence of a hyaline urogenital male papilla with small black spots and a dark-brown reticulate pattern on the flanks of both males and females in preserved specimens. Hylopanchax multisquamatus is distinguished from congeners by the number of scales on the mid-longitudinal series (27-30 vs. 19-26, respectively) and by the relative anterior/posterior flank scale depth ratio (140%-150% vs. 170%-220%). Hylopanchax thysi is distinguished from all other congeners, except Hylopanchax paucisquamatus, by the presence of vertebrae (30 vs. 31-33) and is further distinguished from H. multisquamatus by the presence of a deeper caudal peduncle and much larger anterior flank scales. It is distinguished from H. paucisquamatus by the presence of a hyaline urogenital male papilla with small black spots and a dark-brown reticulate pattern on the flanks of both males and females in preserved specimens. Osteological data of Hylopanchax are presented for the first time, and an updated diagnosis based on external morphology, colouration pattern and osteology is provided. An osteological comparison with closely related species belonging to the genera Procatopus, Hypsopanchax and "Hypsopanchax" is presented. (a) A truncate and slightly downward-directed anterior process of the angulo-articular and (b) a guitar-shaped lachrymal with both its anterior and posterior margins sharply curved are here considered as diagnostic features of Hylopanchax.

Assessing the effects of elephant foraging on the structure and diversity of an Afrotropical forest

AbstractAfrican forest elephants (Loxodonta cyclotis) are ecosystem engineers that browse and damage large quantities of vegetation during their foraging and movement. Though elephant trail networks and clearings are conspicuous features of many African forests, the consequences of elephant foraging for forest structure and diversity are poorly documented. In this study in northeastern Gabon, we compare stem size, stem density, proportional damage, species diversity, and species relative abundance of seedlings and saplings in the vicinity of seven tree species that produce elephant‐preferred fruits (“elephant trees”) relative to control trees that do not. Across 34 survey trees, with a combined census area of 2.04 ha, we recorded data on 26,128 woody stems in three sizes classes. Compared with control trees, the area around elephant trees had the following: (a) a significantly greater proportion of damaged seedlings and a marginally greater proportion of damaged saplings (with 82% and 24% greater odds of damage, respectively); (b) no significant difference in stem density or species diversity; and (c) a significantly greater relative abundance of seedlings of elephant tree species. Increasing distance away from focal elephant trees was associated with significantly reduced sapling stem damage, significantly increased sapling stem density, and significantly increased sapling species diversity. Considered in sum, our results suggest that elephants can affect the structure and diversity of Afrotropical forests through their foraging activities, with some variation based on location and plant size class. Developing a more complete understanding of elephants’ ecological effects will require continued research, ideally with manipulative experiments.Abstract in French is available with online material.

High Circulation of Malaria and Low Prevalence of Bacteremia in Febrile and Afebrile Children in Northeastern Gabon.

The epidemiology of febrile illness etiologies is under-explored in resource-poor settings. Establishing a local repertory of microorganisms circulating in blood of febrile and afebrile people is important for physicians. Blood was collected from 428 febrile and 88 afebrile children in Makokou (Gabon) and analyzed using polymerase chain reaction. Plasmodium spp. were the pathogens, which were most detected in febrile children (69.6%; 298/428) and in afebrile children (31.8%; 28/88) (P < 0.0001). Plasmodium falciparum was the most prevalent species in both febrile and afebrile children (66.8% and 27.3%, respectively). No differences were observed between febrile and afebrile children for Plasmodium malariae and Plasmodium ovale (8.2% versus 10.2% and 3.3% versus 3.4%, respectively). Triple infection with P. falciparum, P. malariae, and P. ovale was also detected in 1% of febrile children (4/428). Filariasis due to Mansonella perstans was detected in 10 febrile patients (2.3%), whereas Loa loa was detected in both febrile and afebrile children (1.4% and 2.3%, respectively). Bacterial DNA was detected in only 4.4% (19/428) of febrile children, including 13 (68.4%) who were coinfected with at least one Plasmodium species. These were Haemophilus influenzae (1.6%, 7/428), Streptococcus pneumoniae and Staphylococcus aureus (1.2%, 5/428), and Rickettsia felis (0.9%, 4/428). Coxiella burnetii, Bartonella spp., Borrelia spp., Tropheryma whipplei, Anaplasma spp., Leptospira spp., Streptococcus pyogenes, and Salmonella spp. were not detected. This study also highlights the over-prescription and the overuse of antibiotics and antimalarials. Overall, malaria remains a major health problem in Makokou. Malaria control measures must be reconsidered in this region.

Seed traits, not density or distance from parent, determine seed predation and establishment in an Afrotropical forest

AbstractSeed predators drive patterns in seed mortality and seedling establishment and are posited to contribute to the maintenance of plant species diversity through several mechanisms. Negative density dependence and spatially restricted recruitment are apparently widespread in Neotropical forests, but are little studied in Afrotropical forests, where generalist vertebrates may contribute more to seed mortality than do specialized invertebrates and fungi. We experimentally assessed the roles of seed density and distance from the parent tree for ten tree species in a forest in northeastern Gabon, using exclosures to isolate the effects of different seed predator types. Vertebrates caused greater seed losses than all other mortality agents combined. Unexpectedly, seeds under fruiting conspecific trees had significantly lower removal and higher seedling establishment than those under heterospecific trees or in neutral non‐fruiting locations. Seed density did not significantly affect seedling establishment. Vertebrate seed removal ranged from 0 percent to 100 percent among focal species and was positively correlated with seed mass but had no relationship with species commonness (adult tree density). Seed traits strongly affected patterns of seed removal and seedling establishment and may contribute more to the likelihood of success for an individual seed than do its density or distance from parent. Our results highlight an apparent divergence in patterns of seed mortality and seedling establishment between tropical forest regions and emphasize the need for further comparative study.

Co-variation in biomass and environment at the scale of a forest concession in central Africa

Abstract:Drivers of forest structure in central African rain forests are largely unknown. Using forest inventory data (3024 0.4-ha plots) in a forest concession of 154 456 ha in north-eastern Gabon covering an altitudinal gradient (from 485 to 1009 m asl), relationships between above-ground plot biomass and environmental variables (soil type, altitude, slope, aspect) and floristic composition (score given by an ordination method) were tested. After controlling for confounding variables, biomass was significantly related to altitude (with a modal response peaking at 346 Mg ha–1 on western slopes at an altitude of 707 m asl) and to aspect (additional 18.3 Mg ha–1 on eastern slopes) but not to floristic composition. Biomass and basal area responded differentially to the environment. Mean wood density was significantly related to soil, altitude and floristic composition, with a predicted minimum of 0.60 g cm–3 at an altitude of 1009 m asl in stands characterized by Scorodophloeus zenkeri and a maximum of 0.69 g cm–3 at an altitude of 458 m asl in monodominant Gilbertiodendron dewevrei stands. Variation in forest structure in the concession was primarily driven by altitude while floristic composition played a role in differentiating the variation in biomass and basal area.

We Descended the Ivindo: Baka Migration and Mobility to Northeastern Gabon from the 1960s to Today

We Descended the Ivindo: Baka Migration and Mobility to Northeastern Gabon from the 1960s to Today

A new species of Poropoea Foerster from Africa (Hymenoptera, Chalcidoidea, Trichogrammatidae).

A new species of Poropoea Foerster (Hymenoptera, Chalcidoidea, Trichogrammatidae) was obtained from eggs of attelabid beetles (Coleoptera: Attelabidae) associated with Combretum sp. (Myrtales, Combretaceae). This species is described from Ogooué-Ivindo province in north-eastern Gabon. The new species is easily distinguished from the known members of the genus Poropoea by the following combination of characters: female antennal club unsegmented, premarginal vein of the fore wing with a nodular premarginal vein and the stigma of the stigmal vein black, the wing lacks the RS1 track; front and hind legs more robust than the middle leg and with coxa and femur markedly enlarged, and ovipositor exserted to one-third of the gaster length. Morphological features of this new species are discussed and illustrated. A key to females of Poropoea species lacking the Rs1 track in the fore wing has been constructed and is presented here.

Telemetric tracking of scatterhoarding and seed fate in a Central African forest

AbstractIn seed predation studies, removal of a seed is only the first step of a dynamic process that may result in dispersal rather than seed death. This process, termed seed fate, has received little attention in African forests, particularly in Central Africa. We experimentally assessed the initial steps of seed fate for two tree species—the large‐seeded Pentaclethra macrophylla and the relatively small‐seeded Gambeya lacourtiana—in northeastern Gabon. Specifically, we evaluated whether seed size and seed consumer identity are important determinants of seed fate. We established experimental stations under conspecific fruiting trees, each comprising three seeds fitted with telemetric thread tags to facilitate their recovery, and a motion‐sensitive camera to identify visiting mammals. In total, animals removed 76 tagged seeds from experimental stations. Small Murid rats and mice primarily removed small Gambeya seeds, whereas large‐bodied rodents and mandrills primarily removed large Pentaclethra seeds. Gambeya seeds were carried shorter distances than Pentaclethra seeds and were less likely to be cached. The two large‐bodied rodents handled seeds differently: Cricetomys emini larderhoarded nearly all (N = 15 of 16) encountered Pentaclethra seeds deep in burrows, while Atherurus africanus cached all (N = 5 of 5) encountered Pentaclethra seeds singly under 1–3 cm of leaf litter and soil, at an average distance of 24.2 m and a maximum distance of 46.3 m from experimental stations. This study supports the hypothesis that seed fate varies based on seed size and seed consumer identity, and represents the first telemetric experimental evidence of larderhoarding and scatterhoarding in the region.

Hunting-induced defaunation drives increased seed predation and decreased seedling establishment of commercially important tree species in an Afrotropical forest

Human hunting is widespread in tropical forests and can substantially alter the plant-animal interactions that drive tree recruitment. Seed predation is a strong determinant of plant reproductive success, but it remains unclear how defaunation modifies this process. We examined the effects of hunting-induced defaunation on seed predation and seedling establishment, using replicated exclosure treatments at six sites across a defaunation gradient in northeastern Gabon. We monitored 5580 seeds of eight commercially important tree species that varied in seed traits such as size and dispersal mode. Rodents caused the greatest seed mortality for all species, removing ∼60% of accessible seeds. In comparison, invertebrates and fungi together caused just 6% of seed mortality. With protection from rodents, more than twice as many seeds established as seedlings, demonstrating that vertebrate seed predation was a strong filter on recruitment. With increasing defaunation, the proportion of seeds removed by rodents increased significantly, and seedling establishment decreased significantly, for most species. In heavily defaunated sites, with the lowest abundances of large mammals, seed removal by rodents increased by 63% and seedling establishment decreased by 42% compared to sites with intact fauna. Diminished seedling establishment is likely to reduce the regeneration of many tree species – including some with commercial importance – in hunted forests, with detrimental economic consequences. In turn, declines in timber regeneration may increase the likelihood that selectively logged forests are converted to non-forest land uses with little conservation value. Appropriate management could preclude these outcomes, to the benefit of both wildlife and natural timber regeneration.

High Frequency of Trypanosoma congolense Savannah Type (Kinetoplastida: Trypanosomatidae) Among Tsetse Flies (Diptera: Glossinidae) in a Historic Trypanosoma Foci in North-Eastern Gabon: Preliminary Study [corrected

Human African trypanosomiasis became a neglected disease after the 1960s, when case numbers dropped dramatically. It again became a public health problem in sub-Saharan Africa at the end of the 1990s, when new cases were reported, notably in Central Africa, and specifically in Gabon, where historic foci existed and new cases have been reported. Therefore, the present study reports on an entomological survey conducted in May 2012 to determine the pathogenic trypanosome infection rate in tsetse flies and characterize the diversity of Trypanosoma species in the Ivindo National Park (INP) in northeastern Gabon. Nine Vavoua traps were used to catch tsetse over a 7-days period. All tsetse flies captured were identified to species, dissected, and trypanosome species identified using polymerase chain reaction (PCR). In total, 160 tsetse flies were analyzed, including Glossina palpalis palpalis, Glossina fusca congolense, and Glossina tachinoïdes The trypanosome infection rate of the flies was 6.3 and 31.9% using microscopy and PCR, respectively. The species identified were Trypanosoma congolense savannah type, Trypanosoma brucei brucei, Trypanosoma brucei gambiense, Trypanosoma vivax, and Trypanosoma congolense forest type. Trypanosoma risk index was 0.75 and 7.05 for humans and for animals, respectively. This study illustrates the diversity of Trypanosoma species infecting the tsetse flies in the INP. The simultaneous occurrence of Trypanosoma and tsetse from the palpalis group may suggest that the reservoirs of African animal trypanosomiasis should be carefully monitored in this area.

From mobility to motility

This article introduces the concept of motility, the capacity to be mobile, as a more in-depth way to account for changes in forager mobility and social organization. research with Baka foragers in north-eastern Gabon shows how they are shifting their subsistence livelihoods by taking up artisanal gold mining, and an extended theoretical approach is called for to give greater acknowledgement to resulting social challenges and changes in these communities. The predominant focus in both archaeological and anthropological discussions has been on observable facts of resource-oriented mobility and human–environment interaction. Motility adds to the understanding of diversified mobilities by focusing not only on actualized observable mobility, but by also considering the choices and limitations, which precede movement. The notion of mobility capital is here introduced to evidence how changing individual and group mobilities challenge Baka egalitarian social organization.

Apparent sympatry of Stiphrornis pyrrholaemus Schmidt & Angehr, 2008and S. xanthogaster Sharpe, 1903 (Passeriformes: Muscicapidae) in Gabon, and taxonomic implications.

We report the occurrence of the recently-described Stiphrornis pyrrholaemus in the Makokou area, northeastern Gabon, more than 600 kilometers NE from its type locality, in areas covered by dense primary to secondary forest. The previous records of Stiphrornis from the same area were referred to S. xanthogaster. We confirm this attribution on the basis of museum specimens. Although several recent sources treat all Stiphrornis as a single species, our findings strongly suggest the sympatric coexistence of two Stiphrornis species and thus that they should be treated as separate species under the Biological Species Concept.

High Rate of Simian Immunodeficiency Virus (SIV) Infections in Wild Chimpanzees in Northeastern Gabon.

The emergence of HIV-1 groups M, N, O, and P is the result of four independent cross-species transmissions between chimpanzees (cpz) and gorillas (gor) from central/south Cameroon and humans respectively. Although the first two SIVcpz were identified in wild-born captive chimpanzees in Gabon in 1989, no study has been conducted so far in wild chimpanzees in Gabon. To document the SIVcpz infection rate, genetic diversity, and routes of virus transmission, we analyzed 1458 faecal samples collected in 16 different locations across the country, and we conducted follow-up missions in two of them. We found 380 SIV antibody positive samples in 6 different locations in the north and northeast. We determined the number of individuals collected by microsatellite analysis and obtained an adjusted SIV prevalence of 39.45%. We performed parental analysis to investigate viral spread between and within communities and found that SIVs were epidemiologically linked and were transmitted by both horizontal and vertical routes. We amplified pol and gp41 fragments and obtained 57 new SIVcpzPtt strains from three sites. All strains, but one, clustered together within a specific phylogeographic clade. Given that these SIV positive samples have been collected nearby villages and that humans continue to encroach in ape’s territories, the emergence of a new HIV in this area needs to be considered.

Social change mirrored in Baka dance and movement

This article discusses different dances and structured human movements of the Baka living along the River Ivindo in north-eastern gabon. Baka dancing in this region takes place in diverse ritual and social contexts. Movement theory and attention to body are used to show that dance analysis can provide a window on the challenges the Baka groups are experiencing to their egalitarian social organisation. The article addresses in particular how new technical influences are challenging long-standing movement values and ritualised male-female interaction of an egalitarian society. Social change is conceptualised from a perspective which gives primacy to human movement rather than material or environmental facts.

No evidence of decline in malaria burden from 2006 to 2013 in a rural Province of Gabon: implications for public health policy.

BackgroundThe morbidity of malaria has steady declined in the urban regions of Gabon between 2000 and 2008, but caution should be exercised before generalizing this trend to the whole country because this finding has not been systematically confirmed in remote rural provinces.MethodsWe conducted a retrospective survey using data on malaria cases recorded in North Eastern Gabon between 2006 and 2013 at health facilities in Makokou. Malaria data were analyzed, and associations with annual variations and patient age were assessed.ResultsA global increase in clinical and confirmed malaria cases was observed over the study period. The rate of infection was significantly higher in children aged between 0 to 4 years than in children of 5 years and above, and in adults. Contrary to prior observations in urban and semi-urban areas of Gabon, malaria burden remained mostly unchanged or even increased in Makokou in the Ogooué-Ivindo province during these last 8 years.ConclusionsThe persistence of Plasmodium falciparum pockets of sustained malaria transmission in rural Gabon may be related to an inadequate coverage of key interventions, to poor treatment seeking behavior and/or to a decline efficacy of treatments. Our results highlight the need to better adapt malaria control strategies to local epidemiological contexts and to environmental constraints. Equitable delivery of health service to hard-to-reach populations constitutes a challenging issue for the health authorities of Gabon.Electronic supplementary materialThe online version of this article (doi:10.1186/s12889-015-1456-4) contains supplementary material, which is available to authorized users.

Congruent phylogeographical patterns of eight tree species in Atlantic Central Africa provide insights into the past dynamics of forest cover

Cycles of Quaternary climatic change are assumed to be major drivers of African rainforest dynamics and evolution. However, most hypotheses on past vegetation dynamics relied on palaeobotanical records, an approach lacking spatial resolution, and on current patterns of species diversity and endemism, an approach confounding history and environmental determinism. In this context, a comparative phylogeographical study of rainforest species represents a complementary approach because Pleistocene climatic fluctuations may have left interpretable signatures in the patterns of genetic diversity within species. Using 1274 plastid DNA sequences from eight tree species (Afrostyrax kamerunensis, A.lepidophyllus, Erythrophleum suaveolens, Greenwayodendron suaveolens, Milicia excelsa, Santiria trimera, Scorodophloeus zenkeri and Symphonia globulifera) sampled in 50 populations of Atlantic Central Africa (ACA), we averaged divergence across species to produce the first map of the region synthesizing genetic distinctiveness and standardized divergence within and among localities. Significant congruence in divergence was detected mostly among five of the eight species and was stronger in the northern ACA. This pattern is compatible with a scenario of past forest fragmentation and recolonization whereby forests from eastern Cameroon and northeastern Gabon would have been more affected by past climatic change than those of western Cameroon (where one or more refugia would have occurred). By contrast, southern ACA (Gabon) displayed low congruence among species that may reflect less drastic past forest fragmentation or a more complex history of vegetation changes. Finally, we also highlight the potential impact of current environmental barriers on spatial genetic structures.

Site-specific versus pantropical allometric equations: Which option to estimate the biomass of a moist central African forest?

Fewer data on tree biomass and allometric equations are available in African tropical moist forests than in the other tropical continents. When needing a biomass allometric equation, one thus faces the dilemma of using either a pantropical equation with the risk that it is biased for Africa, or a site-specific equation that is imprecise. Using a data set on aboveground biomass for 101 trees destructively measured at Zadié in northeastern Gabon, we fitted site-specific allometric equations and assessed the validity of ten existing equations. The best fitted model without height as a predictor was: B=exp[-4.0596+4.0624lnD-0.228(lnD)2+1.4307lnρ], whereas the best fitted model with height was: B=exp[-2.5680+0.9517ln(D2H)+1.1891lnρ], where B is the aboveground biomass in kg, D the diameter at breast height in cm, H the height in m, and ρ the wood density in gcm−3. Separate allometric equations for the stem, stump, foliage and branches were also fitted. Chave et al. (2005)’s pantropical equations for moist forests, that are currently the most commonly used allometric equations in central Africa, were not valid at Zadié with an overestimation of biomass of about 40%. The allometric equations of the same authors for wet forests were valid at Zadié, even though the climatic zone does not correspond. More data on tree biomass are needed in central Africa to explore the natural range of variability in tree biomass and identify the factors that influence variations among sites.