References of "Doucet, Jean-Louis"
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See detailCpDNA-based species identification and phylogeography: application to African tropical tree species
Duminil, Jérôme; Heuertz, Myriam; Doucet, Jean-Louis ULg et al

in Molecular Ecology (2010), 19(24), 5469-5483

Despite the importance of the African tropical rainforests as a hotspot of biodiversity, their history and the processes that have structured their biodiversity are understood poorly. With respect to past ... [more ▼]

Despite the importance of the African tropical rainforests as a hotspot of biodiversity, their history and the processes that have structured their biodiversity are understood poorly. With respect to past demographic processes, new insights can be gained through characterizing the distribution of genetic diversity. However, few studies of this type have been conducted in Central Africa, where the identification of species in the field can be difficult. We examine here the distribution of chloroplast DNA (cpDNA) diversity in Lower Guinea in two tree species that are difficult to distinguish, Erythrophleum ivorense and Erythrophleum suaveolens (Fabaceae). By using a blind-sampling approach and comparing molecular and morphological markers, we first identified retrospectively all sampled individuals and determined the limits of the distribution of each species. We then performed a phylogeographic study using the same genetic data set. The two species displayed essentially parapatric distributions that were correlated well with the rainfall gradient, which indicated different ecological requirements. In addition, a phylogeographic structure was found for E. suaveolens and, for both species, substantially higher levels of diversity and allelic endemism were observed in the south (Gabon) than in the north (Cameroon) of the Lower Guinea region. This finding indicated different histories of population demographics for the two species, which might reflect different responses to Quaternary climate changes. We suggest that a recent period of forest perturbation, which might have been caused by humans, favoured the spread of these two species and that their poor recruitment at present results from natural succession in their forest formations. [less ▲]

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See detailDiversity and aboveground biomass in three tropical forest types in the Dja Biosphere Reserve, Cameroon
Djuikouo, Marie Noël Kamdem; Doucet, Jean-Louis ULg; Nguembou, Charlemagne K. et al

in African Journal of Ecology (2010), 48

We present tree community diversity, species composition, basal area and aboveground biomass of three forest types in the Dja Biosphere Reserve, in South-East Cameroon, part of the contiguous tropical ... [more ▼]

We present tree community diversity, species composition, basal area and aboveground biomass of three forest types in the Dja Biosphere Reserve, in South-East Cameroon, part of the contiguous tropical forest of the Congo Basin. A total of fourteen, 1 ha, plots were established in heterogeneous terra firme forests (TFF), Gilbertiodendron dewevrei forests (GDF) and periodically flooded forests (PFF). A total of 281 tree species with diameter ‡10 cm were recorded. The Shannon diversity index was significantly higher in TFF (5.7 ± 0.28) and PFF (5.6 ± 0.23) than in GDF (2.29 ± 0.48) (ANOVA, F2,11 = 139.75, P < 0.001). While tree density did not differ between forest types (F2,11 = 3.50, P = 0.06), basal area differed significantly (F2,11 = 7.38, P = 0.009), as did aboveground biomass (F2,11 = 17.95, P < 0.001). Mean AGB values were respectively, 596.1 ± 62.24, 401.67 ± 58.06 and 383.14 ± 61.91 Mg ha)1 in GDF, TFF and PFF. Variation in the abundance of trees with large diameter was the main reason for these differences. Few dominant species made the greatest contribution to the AGB. G. dewevrei, accounted for 83% of AGB in GDF, Penthaclethra macrophylla for 9.9% in TFF and Uapaca heudolotii for 10.6% in PFF. The importance of preserving G. dewevrei forest in the context of ‘Reducing Emissions from Deforestation and forest Degradation’ (REDD) policies is discussed. [less ▲]

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See detailForest refugia revisited: nSSRs and cpDNA sequences support historical isolation in a wide-spread African tree with high colonization capacity, Milicia excelsa (Moraceae)
Daïnou, Kasso ULg; Bizoux, Jean-Philippe ULg; Doucet, Jean-Louis ULg et al

in Molecular Ecology (2010)

The impact of the Pleistocene climate oscillations on the structure of biodiversity in tropical regions remains poorly understood. In this study, the forest refuge theory is examined at the molecular ... [more ▼]

The impact of the Pleistocene climate oscillations on the structure of biodiversity in tropical regions remains poorly understood. In this study, the forest refuge theory is examined at the molecular level in Milicia excelsa, a dioecious tree with a continuous range throughout tropical Africa. Eight nuclear microsatellites (nuSSRs) and two sequences and one microsatellite from chloroplast DNA (cpDNA) showed a deep divide between samples from Benin and those from Lower Guinea. This suggests both that these populations were isolated in separate geographical regions, probably for several glacial cycles of the Pleistocene, and a poor mixture of gene pools despite M. excelsa’s wind-pollination syndrome. The divide can also be related to seed dispersal patterns, which should be largely determined by the migration behaviour of M. excelsa's main seed disperser, the frugivorous bat Eidolon helvum. Within Lower Guinea, a north-south divide, observed with both markers despite weak genetic structure (nuSSRs: FST=0.035, cpDNA: GST=0.506), suggested the existence of separate Pleistocene refugia in Cameroon and the Gabon/Congo region. We inferred a pollen-to-seed dispersal distance ratio of 1.76, consistent with wide-ranging gene dispersal by both wind and bats. Simulations in an Approximate Bayesian Computation framework suggested low nuSSR and cpDNA mutation rates but imprecise estimates of other demographic parameters, probably due to a substantial gene flow between the Lower Guinean gene pools. The decline of genetic diversity detected in some Gabonese populations could be a consequence of the relatively recent establishment of a closed canopy forest which may negatively affect M. excelsa's reproductive system. [less ▲]

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See detailEnjeux fonciers et exploitation du bois-énergie en périphérie de Kinshasa, RDC
Vermeulen, Cédric ULg; Mutambwe, Shango; Dubiez, Emilien et al

Conference (2010)

L’identification des acteurs, des finages, des dynamiques sociales locales et du rapport à la terre et aux ressources naturelles constitue un préalable à toute intervention dans les zones péri-urbaines ... [more ▼]

L’identification des acteurs, des finages, des dynamiques sociales locales et du rapport à la terre et aux ressources naturelles constitue un préalable à toute intervention dans les zones péri-urbaines soumises à forte pression anthropique. En République Démocratique du Congo, la capitale Kinshasa, mégapole en pleine extension, engendre une pression considérable sur les ressources ligneuses dans les finages des villages situés dans sa grande périphérie. La présente communication décrit les rapports des acteurs aux espaces-ressources dans deux zones (Bas-Congo et plateau Bateke) situées en périphérie de cette ville, zones considérées comme des bassins d’approvisionnement en bois-énergie. Les deux sites différent en termes de pression foncière (très élevée dans le Bas-congo, centrée sur les forêts galerie sur les plateaux Bateke) mais présentent les mêmes faciès de surexploitation des ressources ligneuses. Dans les deux cas, la gestion locale, aux mains des chefs de villages ou des chefs de lignée, a failli. La volonté de reboisement est aussi grande au Bas-Congo qu’elle semble moins développée sur les plateaux. Dans les deux situations, la pratique du retour rapide sur la formation végétale (pour l’agriculture ou pour l’exploitation du charbon de bois) hypothèque la possibilité de régénération de la plupart des essences locales. [less ▲]

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See detailEtude de l'écologie de Pericopsis elata (afrormosia) au sud-est du Cameroun
Bourland, Nils ULg; Doucet, Jean-Louis ULg

Scientific conference (2009, June 03)

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See detailPeut-on expliquer les patrons d’agrégation spécifiques d’arbres tropicaux à partir de leurs traits ? Une analyse de l’échelle locale à l’échelle régionale.
Rejou-Mechain, Maxime; Bourland, Nils ULg; Flores, O. et al

in Laboratoire d'Ecologie de la FUSAGx (Ed.) ECOVEG 5 - Cinquième colloque d'écologie des communautés végétales (2009, April 08)

Les processus qui génèrent la répartition spatiale des arbres tropicaux ont fait l’objet de nombreuses études. Trois processus semblent déterminants pour la répartition des végétaux : la dispersion ... [more ▼]

Les processus qui génèrent la répartition spatiale des arbres tropicaux ont fait l’objet de nombreuses études. Trois processus semblent déterminants pour la répartition des végétaux : la dispersion limitée, l’histoire de la zone (perturbations anthropiques et histoire climatique) et la différenciation de niche. Leur importance relative est aujourd’hui largement débattue et dépend certainement de l’échelle spatiale considérée. Dans cette étude notre objectif général est de comprendre quels sont les principaux mécanismes qui génèrent les patrons spatiaux des espèces et à quelles échelles ils interviennent. Les données traitées proviennent d’inventaires botaniques réalisés à grande échelle (460000 ha) par des sociétés forestières, en Afrique Centrale (Cameroun et République Centrafricaine). Des mesures d’agrégation spatiale sont réalisées sur 121 espèces d’arbre (individus > à 30 cm de diamètre), dans 4 sites différents et à 3 échelles spatiales : l’échelle locale (0-1 km), l’échelle intermédiaire (1-10 km) et l’échelle du paysage (> à 10 km). Nous testons la relation entre l’agrégation spatiale spécifique et une série de caractéristiques propres aux espèces : le type de diaspore, la tolérance à l’ombre, le type biologique, le système de reproduction et le type phytogéographique. Nos résultats montrent que les patrons d’agrégation spécifiques sont cohérents à travers les sites, jusqu’à l’échelle intermédiaire, mais que les caractéristiques propres aux espèces permettent peu de les prédire. La variation de l’agrégation entre sites pour une même espèce est toutefois très importante et suggère que les patrons d’agrégation observés sont en grande partie dépendants des sites et de leur histoire. Nos résultats suggèrent que les patrons spatiaux spécifiques sont liés à une dispersion limitée à une échelle très locale alors que les patterns observés à des échelles supérieures sont principalement dus à l’histoire des sites et dans certains cas à une forte hétérogénéité environnementale. [less ▲]

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See detailÉtude du comportement de Baillonella toxisperma Pierre (moabi) dans les trouées d’abattage enrichies
Kouadio, Y. L.; Doucet, Jean-Louis ULg

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2009), 13(2), 317-324

The moabi (Baillonella toxisperma Pierre) is a commercial tree in central Africa. Although forest gaps are generally considered as favorable to the regeneration of this species, in this study, a ... [more ▼]

The moabi (Baillonella toxisperma Pierre) is a commercial tree in central Africa. Although forest gaps are generally considered as favorable to the regeneration of this species, in this study, a preliminary inventory conducted within a selective exploitation located in the Dja district, southeastern Cameroon, found a low density of 12.7 seedlings.ha-1 within logging gaps. This suggests that the species was in fact poorly represented in logging gaps. In order to further study the behavior of the moabi in logging gaps, 795 seeds were planted in 15 logging gaps and 410 saplings from a tree nursery were introduced in 15 other gaps. A biannual monitoring spanning a period of 30 months showed a 75.9% survival rate for seedlings and 95.5% for saplings. Despite our observation of a significant difference in growth rates between both methods during the first semester, after 30 months of monitoring, seedlings and saplings had reached similar growth rates (167.5 cm and 160.6 cm for seedlings and saplings, respectively). On average, 6.1% of B. toxisperma saplings emerged naturally from the competitive vegetation and had a higher growth rate than other plants species. Growth differences between plants were mainly explained by the geographical orientation of the logging gap (N-S unfavorable) and the density of Macaranga spp. whose abundance inhibits the development of B. toxisperma. In conclusion, both the high survival rate of B. toxisperma in logging gap and its 10 fold higher growth rate in the latter environment when compared to canopy cover suggest the implementation of forestry methods using logging gap during reforesting operations. [less ▲]

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See detailSpatial genetic structure in Milicia excelsa (Moraceae) indicates extensive gene dispersal in a low-density wind-pollinated tropical tree
Bizoux, Jean-Philippe ULg; Daïnou, Kasso ULg; Bourland, Nils ULg et al

in Molecular Ecology (2009), 18

In this study, we analysed spatial genetic structure (SGS) patterns and estimated dispersal distances in Milicia excelsa (Welw.) C.C. Berg (Moraceae), a threatened windpollinated dioecious African tree ... [more ▼]

In this study, we analysed spatial genetic structure (SGS) patterns and estimated dispersal distances in Milicia excelsa (Welw.) C.C. Berg (Moraceae), a threatened windpollinated dioecious African tree, with typically low density ( 10 adults ⁄km2). Eight microsatellite markers were used to type 287 individuals in four Cameroonian populations characterized by different habitats and tree densities. Differentiation among populations was very low. Two populations in more open habitat did not display any correlation between genetic relatedness and spatial distance between individuals, whereas significant SGS was detected in two populations situated under continuous forest cover. SGS was weak with a maximum Sp-statistic of 0.006, a value in the lower quartile of SGS estimates for trees in the literature. Using a stepwise approach with Bayesian clustering methods, we demonstrated that SGS resulted from isolation by distance and not colonization by different gene pools. Indirect estimates of gene dispersal distances ranged from rg = 1 to 7.1 km, one order of magnitude higher than most estimates found in the literature for tropical tree species. This result can largely be explained by life-history traits of the species. Milicia excelsa exhibits a potentially wideranging wind-mediated pollen dispersal mechanism as well as very efficient seed dispersal mediated by large frugivorous bats. Estimations of gene flow suggested no major risk of inbreeding because of reduction in population density by exploitation. Different strategy of seed collection may be required for reforestation programmes among populations with different extent of SGS. [less ▲]

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See detailSpecies delimitation and phylogeography of an African tropical tree species complex
Duminil, J.; Heuertz, M.; Bourland, Nils ULg et al

Poster (2009)

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See detailDe nouveaux enjeux sur l’espace : la délimitation des premières forêts communautaires au Gabon
Vermeulen, Cédric ULg; Schippers, C.; Ndouna, A. A. et al

in International Journal of Biological and Chemical Sciences (2009), 3(5), 1171-1181

Le Gabon s’est doté il y a quelques années d’une nouvelle loi forestière intégrant les populations locales dans la gestion durable des massifs forestiers à travers le concept de « forêts communautaires » ... [more ▼]

Le Gabon s’est doté il y a quelques années d’une nouvelle loi forestière intégrant les populations locales dans la gestion durable des massifs forestiers à travers le concept de « forêts communautaires ». L’une des premières étapes dans la mise en place de ces forêts communautaires est la délimitation de celles-ci. Cet article aborde le cas concret de la délimitation d’une première forêt communautaire dans ce pays, le cas du regroupement de villages de Ebe Messe Melane. La délimitation suit une approche intégrée afin de concilier d’une part les contraintes légales et d’autre part l’occupation de l’espace actuelle par les populations villageoises. Cet exemple permet d’illustrer les différents enjeux que soulève la délimitation des forêts communautaires. Des enjeux spatiaux, financiers ou identitaires qui impliquent les acteurs aux intérêts parfois divergents que sont les communautés villageoises, l’Etat et les opérateurs forestiers privés. [less ▲]

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