References of "Doucet, Jean-Louis"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailNew data on the recent history of the littoral forests of southern Cameroon: an insight into the role of historical human disturbances on the current forest composition
Biwolé, Achille ULg; Morin-Rivat, Julie ULg; Fayolle, Adeline ULg et al

in Plant Ecology and Evolution (in press)

Background and aims – Prior to European colonisation of Central Africa, human populations were dispersed through the forests, where they practiced slash-and-burn cultivation. From the 19th century they ... [more ▼]

Background and aims – Prior to European colonisation of Central Africa, human populations were dispersed through the forests, where they practiced slash-and-burn cultivation. From the 19th century they were progressively concentrated in villages along roads, leaving large areas of forest derelict. In south-western Cameroon, and elsewhere in Central Africa, forest canopy is dominated by long-lived lightdemanding tree species, suggesting a possible role of human disturbance. The aim of this study was to bring new insights into the possible effect of historical human disturbances in terms of timing and spatial extent on the current forest composition. Location – Wet evergreen littoral forest in south-western Cameroon. Methods and key results – A combined vegetation sampling and archaeobotanical survey were conducted. Potsherds, oil-palm endocarps, and charcoal were found throughout the study area, suggesting generalised human occupation and anthropogenic fire. Human occupancy occurred in two periods: between 2200 and 1500 BP, and, more recently, beginning three centuries ago. High frequency of fire and the presence of Elaeis guineensis both dated recently (between 260 and 145 BP) suggest slash-and-burn shifting cultivation practices. These human-induced disturbances may coincide with the age of the current emergent lightdemanding species, the age of which can be estimated around 200 years, or with the phases of drying climate recorded in the Central African forest in the early 18th century. Conclusions – These results support the idea that historical human disturbances are one of the major factors that shaped the current forest composition in Central Africa. [less ▲]

Detailed reference viewed: 44 (17 ULg)
Full Text
Peer Reviewed
See detailExplorer la banque de graines du sol pour mieux comprendre la dynamique de régénération des forêts tropicales africaines (synthèse bibliographique)
Douh, Chauvelin ULg; Daïnou, Kasso ULg; Loumeto, Jean Joël et al

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (in press), 18(4),

La banque de graines du sol des forêts denses humides africaines a été très peu étudiée, alors qu’elle pourrait jouer un rôle déterminant dans les cycles sylvigénétiques naturels. Elle pourrait également ... [more ▼]

La banque de graines du sol des forêts denses humides africaines a été très peu étudiée, alors qu’elle pourrait jouer un rôle déterminant dans les cycles sylvigénétiques naturels. Elle pourrait également être avantageusement utilisée dans les programmes de restauration, à l’instar de ce qui se fait sur d’autres continents. La présente synthèse bibliographique fait le point sur les connaissances actuelles relatives à la banque de graines du sol, en mettant l’accent sur le continent africain. Elle montre qu’une meilleure caractérisation de la banque de graines du sol des différentes communautés végétales constituerait une contribution notable pour la gestion durable des forêts tropicales d’Afrique. [less ▲]

Detailed reference viewed: 25 (2 ULg)
See detailIntegrating phylogenetic and environmental niche models to explore speciation mechanisms in the Erythrophleum genus in tropical Africa
Gorel, Anaïs ULg; Fayolle, Adeline ULg; Doucet, Jean-Louis ULg et al

Conference (2014, December 10)

In the context of global climate change, it is of primary importance to understand the species response to climate (habitat tracking or adaptation). In this study we investigated the evolutionary history ... [more ▼]

In the context of global climate change, it is of primary importance to understand the species response to climate (habitat tracking or adaptation). In this study we investigated the evolutionary history of the climatic niche between and within closely related tropical tree species of the Erythrophleum genus (Fabaceae, Caesalpinioideae): E. ivorense, E. suaveolens and E. africanum. Two major hypotheses, the refuge theory and the ecological gradient hypothesis, have been developed to explain the current distribution of tree clades across tropical Africa. To identify the speciation mechanisms, we used a combination of geographic data and environmental factors to quantify the degree of niche conservatism (or divergence). We used two sets of distribution data for the purpose of this study. Species distribution data for the whole of tropical Africa were gathered from herbarium records. Distribution data of the two sister species E. ivorense and E. suaveolens assigned to genetic cluster were available for the lowland tropical forests of western and central Africa. Using a Species Distribution Model (SDM) approach based on MaxEnt algorithm, we tested for the environmental differences (BIOCLIM data) between species and genetic clusters within species. We developed SDMs for each of the three Erythrophleum species (over the whole range) and for each of the five genetic clusters. We quantified the niche overlap using new niche similarity metrics. At species level, the climatic niches differed significantly and overlapped only sligthly, suggesting a parapatric speciation along a climatic gradient. Within the two sister species, the niche of the parapatric central African clusters strongly overlapped, suggesting a secondary contact following the recolonization from different forest refugia. The west African cluster however showed contrasted climatic niches possibly due to either recent (< 100 yrs) climate change in west Africa, or ongoing differentiation on the dry part of the climatic gradient. [less ▲]

Detailed reference viewed: 34 (4 ULg)
Full Text
Peer Reviewed
See detailStand structure and species co-occurence in mixed and monodominant Central African tropical forests
Djuikouo, Marie Noël K.; Peh, Kelvin S.H.; Nguembou et al

in Journal of Tropical Ecology (2014), 30(5), 447-455

Detailed reference viewed: 27 (19 ULg)
Full Text
See detailSeed dispersal by western lowland gorillas: what about gut passage effect?
Haurez, Barbara ULg; Petre, Charles-Albert ULg; Doucet, Jean-Louis ULg

Conference (2014, July 21)

Animal-mediated seed dispersal is an essential ecological process in the tropics. Among African primates, the critically endangered western lowland gorilla (WLG) seems to fulfill many characteristics of ... [more ▼]

Animal-mediated seed dispersal is an essential ecological process in the tropics. Among African primates, the critically endangered western lowland gorilla (WLG) seems to fulfill many characteristics of an effective seed disperser. WLG preferentially disperses species of various seed-size into open canopy habitats suitable for seedling growth. However, few studies have addressed the effects of the passage through the digestive tract on germination. Thus, the effectiveness of WLG in ecological processes governing forest dynamics and regeneration is still poorly known. Seed dispersal by WLG was studied in Central Gabon and Southeast Cameroon. Dispersed seed were identified from fresh fecal samples. Comparative germination trials based on 5 treatments (seeds from fresh fruits, seeds from fresh fruits surrounded by pulp, seeds from fresh fruits with fecal matrix, seeds from feces and seeds from feces with fecal matrix) were realized for 13 species. We recorded germination success for all species and germination delay for 6 species. Our results suggest a neutral gut passage effect for 54% and positive effect for 40% of tested species. Germination success enhancement was linked to another factor than pulp suppression. For two species, pulp suppression enhanced germination success, but not gut passage. The presence of pulp or fecal matrix surrounding the seed seemed to longer germination delay, while gut passage would not fasten germination. Globally, we conclude that WLG dispersed seeds are not damaged by gut passage. Consequently, WLG is thought to provide effective ecological services that could be essential to the maintenance and the recovery of forest ecosystems. [less ▲]

Detailed reference viewed: 27 (4 ULg)
Full Text
See detailWestern lowland gorilla in a logging concession: comparison of density and nesting behavior before and after logging
Haurez, Barbara ULg; Petre, Charles-Albert ULg; Doucet, Jean-Louis ULg

Conference (2014, May 22)

Timber exploitation is rapidly expanding throughout the Congo Basin. In Gabon, timber industry is currently the second working sector and logging concessions cover 45% of the country forest area, largely ... [more ▼]

Timber exploitation is rapidly expanding throughout the Congo Basin. In Gabon, timber industry is currently the second working sector and logging concessions cover 45% of the country forest area, largely overlapping with the range of western lowland gorilla (Gorilla gorilla gorilla WLG). Logging may negatively impact gorilla because of an increase in hunting pressure linked to human concentration and easier access to forest. On the other hand, WLG might benefit from forest opening and the associated growth in Terrestrial Herbaceous Vegetation, following timber felling and roads/trails implementation. In the present study, gorilla density and nesting behavior were studied in a 617,000-ha logging concession located in Central Gabon. A Standing Crop Nest Count census was realized 25 years after the first timber harvesting cycle, consisting in the assessment of the potentiality of logged forest to hold viable WLG populations. A second census was undertaken four to six months after the second logging wave. Comparing nesting behavior and estimated gorilla density between the two census allows to highlight the short-term effects of logging on gorilla populations. A relatively high WLG density was observed during the first census (2.1 weaned gorillas/km²). This figure dropped down to 1.0 weaned gorillas/km² after the second felling cycle. Both density values fall within the range of documented WLG densities documented at other sites. Gorillas consistently nested preferentially in open terra firme forest and built the majority of their nests using herbs of the Marantaceae and Zingiberaceae families. Both these observations underline the importance of Terrestrial Herbaceous Vegetation for nesting. The results of this study suggest that timber exploitation and WLG conservation are not mutually exclusive. The initial high density might traduce an effective anti-poaching strategy for now. The decline in gorilla density observed directly in the second census is probably linked with the avoidance of the disturbance of logging operations. Monitoring the evolution of WLG density would be important in order to control if the figure will rise over time to reach its initial value, but also to assess if a positive effect of Terrestrial Herbaceous Vegetation growth will be observed. [less ▲]

Detailed reference viewed: 32 (4 ULg)
Full Text
See detailDynamique d’une espèce ligneuse héliophile longévive dans un monde changeant le cas de Pericopsis elata (Harms) Meeuwen (Fabaceae) au sud-est du Cameroun
Bourland, Nils ULg; Doucet, Jean-Louis ULg

Scientific conference (2014, May 13)

Exposé sur l'origine et la dynamique des peuplements formés par Pericopsis elata au Sud-Est du Cameroon.

Detailed reference viewed: 11 (0 ULg)
Full Text
See detailRecords of human activity during the late-Holocene in the soils of the African dense humid forest
Morin-Rivat, Julie ULg; Biwolé, Achille; Bourland, Nils ULg et al

Conference (2014, April 30)

Recently, several authors gathered data about the presence of past human populations in tropical regions covered by dense forest nowadays. In central Africa, there is a growing body of evidence for past ... [more ▼]

Recently, several authors gathered data about the presence of past human populations in tropical regions covered by dense forest nowadays. In central Africa, there is a growing body of evidence for past human settlements along the Atlantic coast, but very little information is available further inland. In this perspective, soil records seem to be the most appropriated so as to appraise the spatial and temporal extent of human activity in the African dense humid forest. In this paper, we thus aimed to present a synthesis of the archaeological and archaeobotanical data obtained during several fieldwork campaigns in an archaeologically unexplored area of 200,000 km² located in southern Cameroon and the northern Republic of Congo. A total of 275 test pits, among them 30 pedological pits up to 150 cm deep, were excavated in the study area. So as to get a long temporal scale as well as a fine resolution spatial scale, we quantified wood charcoal and charred endocarps in soil samples by layers of 10 cm taken for 100 pits located along transects of systematic sampling. Spatial projections were performed using statistics together with multivariate analyses. AMS radiocarbon dating allowed interpreting the temporal framework. Evidence of past human activities through either artifacts or charred botanical remains was observed in all pits, in particular with the ubiquitous presence of charcoal at each site. Main charcoal peaks were interpreted as fields (slash-and-burn agriculture) in the vicinity of ancient villages, the later marked by the presence of both potsherds and oil palm endocarps. The dichotomy of these kinds of activities may have impacted differentially the environment during the past. The set of 73 radiocarbon dates extending from 15,000 BP to the present time provided more dates in the late-Holocene showing a bimodal distribution which was interpreted as two phases of human expansion with an intermediate phase of population crash. The 2300–1300 BP phase is correlated with the migrations of supposed farming populations from northwestern Cameroon. Between 1300 and 670 BP, less material could be dated. Following that population collapse, the 670–20 BP phase corresponds to a new period of human expansion known as the Late Iron Age. The dates obtained support the established chronology reported for whole central Africa. This study underlines the necessity of fieldwork efforts and of the usefulness of archives sealed in soil records so as to bring new, extensive and precise evidence of human activities in the Congo Basin. [less ▲]

Detailed reference viewed: 66 (20 ULg)
Full Text
See detailQuaternary rainforests of the Northern Congo Basin: contribution of charcoal analysis
Morin-Rivat, Julie ULg; Bremond, Laurent; Gillet, Jean-François ULg et al

Conference (2014, March 27)

In comparison with the wood charcoals uncovered in the soils of the temperate regions, charcoals from the tropical regions remain little studied yet, in particular those from the dense humid forests of ... [more ▼]

In comparison with the wood charcoals uncovered in the soils of the temperate regions, charcoals from the tropical regions remain little studied yet, in particular those from the dense humid forests of Central Africa. Here we aim at showing the interest of the analysis of soil charcoals so as to understand the current environments through some examples of taxonomical identifications conducted on charcoals sampled in several soil pits in Cameroon and in the Republic of the Congo. These charcoals were hand-split then observed under an incident light microscope. The anatomical features that are hold in the charcoals and described according to a standard method were compared to wood samples from the reference collection of the RMCA. Results demonstrated that the identified species are still present in the vegetal environment today and that only limited changes occurred over the past two millennia. Charcoal analysis can thus allow a better understanding of the past history of the forests in relationship with the ancient disturbances. The temporal and spatial framework of human settlements as well as the impact of the colonial period on the evolution of the forest is also discussed. [less ▲]

Detailed reference viewed: 85 (6 ULg)
Full Text
See detailIdentification des charbons de bois pour connaître l'histoire passée des forêts tropicales africaines
Morin-Rivat, Julie ULg; De Weerdt, Joëlle; Hubau, Wannes et al

Scientific conference (2014, March 26)

Nous présentons ici différents aspects de l’étude des charbons de bois à travers l’exemple de l’Afrique tropicale

Detailed reference viewed: 45 (8 ULg)
Full Text
See detailHistoire humaine des forêts tropicales du nord du Bassin du Congo durant les deux derniers millénaires
Morin-Rivat, Julie ULg; Biwolé, Achille; Bourland, Nils ULg et al

Scientific conference (2014, March 26)

Identifier les indices d’activités humaines anciennes et les mettre en relation avec la composition floristique actuelle grâce à une approche multidisciplinaire.

Detailed reference viewed: 49 (15 ULg)
Full Text
See detailRapport final du projet FRFC n° 2.4577.10. Dynamique des populations d’arbres et d’herbacées héliophiles en relation avec les anciennes perturbations anthropiques et climatiques
Doucet, Jean-Louis ULg; Hardy, Olivier

Report (2014)

L’objectif principal de ce projet était d’étudier dans quelle mesure l’organisation de la biodiversité végétale des forêts d’Afrique centrale a été influencée par les activités anthropiques et les ... [more ▼]

L’objectif principal de ce projet était d’étudier dans quelle mesure l’organisation de la biodiversité végétale des forêts d’Afrique centrale a été influencée par les activités anthropiques et les changements climatiques qui se sont déroulés au cours des quelques derniers millénaires. A cette fin, cinq disciplines ont été utilisées : (1) l'archéologie afin de dater et de quantifier l’intensité de l’occupation humaine ; (2) l'anthracologie pour reconstituer la végétation présente lors du passage des feux ; (3) la dendrochronologie en vue d’établir des corrélations entre les événements passés et l'âge des arbres ; (4) l'écologie des communautés pour permettre de tester l’existence d’une corrélation entre l’abondance d’espèces héliophiles et les indices d’occupation humaine ; (5) la génétique des populations afin d'identifier des signatures génétiques d’anciens évènements de fragmentation et de changement démographique. [less ▲]

Detailed reference viewed: 9 (5 ULg)
Full Text
See detailThe end of roaming in the forest causes a loss of timber resources: the paradox of slash-and-burn agriculture
Morin-Rivat, Julie ULg; Fayolle, Adeline ULg; Favier, Charly et al

Conference (2014, February 27)

Tropical forests are not believed as pristine anymore. Their structure and specific composition are induced by past climatic and human disturbances over years. In the African moist forests, the emergent ... [more ▼]

Tropical forests are not believed as pristine anymore. Their structure and specific composition are induced by past climatic and human disturbances over years. In the African moist forests, the emergent trees are mainly light-demanding. These trees are considered to derive from the recent disturbances of the last centuries. Most of them are exploited for their timber. However, several of these tree species are currently suffering from a lack of regeneration that threatens the specific diversity of the forests and the sustainability of timber exploitation. Through dendrometric and radiocarbon analyses we found that the majority of the trees of the Congo Basin are not older than 160 years. This corresponds to about the year 1850 when the Europeans colonized the inner regions of Central Africa. By reassembling people along the road axes, the colonial administration reduced the forest roaming. Former activities such as slash and burn agriculture created large openings in the canopy that allowed light-demanding tree species to establish. Currently we observed that timber logging does not provide openings large enough for the recruitment of these species. We thus anticipate that adjustments in forest management strategies shall be made to preserve the forest resources, for instance by recreating the conditions of slash and burn agriculture. [less ▲]

Detailed reference viewed: 66 (9 ULg)
Full Text
Peer Reviewed
See detailSpeciation slowing down in widespread and long-living tree taxa : insights from the tropical timber tree genus Milicia (Moraceae)
Daïnou, Kasso ULg; Mahy, Grégory ULg; Duminil, Jérôme et al

in Heredity (2014)

The long generation time and large effective size of widespread forest tree species can result in slow evolutionary rate and incomplete lineage sorting, complicating species delimitation. We addressed ... [more ▼]

The long generation time and large effective size of widespread forest tree species can result in slow evolutionary rate and incomplete lineage sorting, complicating species delimitation. We addressed this issue with the African timber tree genus Milicia that comprises two morphologically similar and often confounded species: M. excelsa, widespread from West to East Africa, and M. regia, endemic to West Africa. We combined information from nuclear microsatellites (nSSRs), nuclear and plastid DNA sequences, and morphological systematics to identify significant evolutionary units and infer their evolutionary and biogeographical history. We detected five geographically coherent genetic clusters using nSSRs and three levels of genetic differentiation. First, one West African cluster matched perfectly with the morphospecies M. regia that formed a monophyletic clade at both DNA sequences. Second, a West African M. excelsa cluster formed a monophyletic group at plastid DNA and was more related to M. regia than to Central African M. excelsa, but shared many haplotypes with the latter at nuclear DNA. Third, three Central African clusters appeared little differentiated and shared most of their haplotypes. Although gene tree paraphyly could suggest a single species in Milicia following the phylogenetic species concept, the existence of mutual haplotypic exclusivity and nonadmixed genetic clusters in the contact area of the two taxa indicate strong reproductive isolation and, thus, two species following the biological species concept. Molecular dating of the first divergence events showed that speciation in Milicia is ancient (Tertiary), indicating that long-living tree taxa exhibiting genetic speciation may remain similar morphologically. [less ▲]

Detailed reference viewed: 22 (12 ULg)