References of "Doucet, Jean-Louis"
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See detailEntandrophragma cylindricum (Sprague) Sprague (Meliaceae), une espèce ligneuse concurrentielle en Afrique centrale (synthèse bibliographique)
Tabi Eckebil, Paule ULg; Verheggen, François ULg; Doucet, Jean-Louis ULg et al

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment (2017), 21(1), 80-97

Introduction. De nos jours, la gestion des ressources forestières ne se focalise plus sur l’exploitation exclusive du bois d’oeuvre, mais prend également en considération les produits forestiers non ... [more ▼]

Introduction. De nos jours, la gestion des ressources forestières ne se focalise plus sur l’exploitation exclusive du bois d’oeuvre, mais prend également en considération les produits forestiers non ligneux. Entandrophragma cylindricum (Sprague) Sprague, de son nom commercial « sapelli/sapele », de la famille des Meliaceae, illustre parfaitement cette situation. Le présent article fait un état de l’art des connaissances concernant E. cylindricum et présente quelques informations sur la chenille qui lui est inféodée. Littérature. Le sapelli est une des espèces ligneuses les plus exploitées d’Afrique centrale pour son bois d’oeuvre. Il est répandu dans la forêt dense humide semi-caducifoliée du domaine guinéo-congolais. C’est une espèce semi-héliophile, son mode de dispersion est anémochore et sa phénologie est régulière. Selon la sylviculture appliquée, sa croissance en diamètre peut atteindre jusque 0,82 cm par an. Cette essence est également l’hôte d’une espèce de chenille comestible riche en protéines, I. oyemensis Rougeot. Fortement appréciée par les populations locales, cette chenille fait également l’objet d’un commerce régional et international. Enfin, l’écorce du sapelli est reconnue pour son intérêt ethnobotanique, particulièrement en médecine traditionnelle. Conclusions. Les informations tirées de la littérature ont permis de mettre en évidence certaines lacunes relatives à l’écologie et au mode de reproduction de cette espèce et, ceci, en dépit de son importance pour le commerce du bois. De plus, les inconnues quant à la productivité et la saisonnalité des chenilles d’Imbrasia oyemensis sur cet arbre nécessitent de développer des recherches complémentaires pour garantir la durabilité de l’exploitation simultanée de la ressource ligneuse et non ligneuse et pour proposer des modes de gestion concertés entre exploitants industriels et populations locales. [less ▲]

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See detailLogging impact on biodiversity in Central Africa
Doucet, Jean-Louis ULg

Conference (2017, February 07)

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See detailHydraulic and wood traits of two congeneric tropical tree species in their core habitat
Gorel, Anaïs ULg; Steppe, kathy; Beeckman, Hans et al

Conference (2017, February 06)

Background: Strong niche partitioning across rainfall gradients has been identified for several tropical tree genera. The link between hydraulic and wood anatomical traits, associated with drought ... [more ▼]

Background: Strong niche partitioning across rainfall gradients has been identified for several tropical tree genera. The link between hydraulic and wood anatomical traits, associated with drought tolerance, however remains to be explored, in order to identify the mechanisms shaping the range limits of tropical tree species. Aim: In this study, we aimed to identify the differences in hydraulic and wood traits between two congeneric tree species with contrasting distributions in moist and wet tropical forests. Location: Central African moist and wet forests Methods: In the core habitat of Erythrophleum ivorense (wet forest) and of E. suaveolens (moist), we collected branches to construct vulnerability curves and measure hydraulic capacitance, and both stem and branch wood samples to link the hydraulic traits to wood anatomy. Major results: E. suaveolens, which is characteristic of drier forests, is clearly more resistant to cavitation than E. ivorense, and also possess a greater hydraulic capacitance (i.e. the capacity that species have to mitigate periods of water storage by using internally stored water). In agreement with this great drought tolerance for E. suaveolens, wood anatomy revealed a high number of small vessels associated with small intervessel pits, features minimizing cavitation risk but also reducing water transport. Main conclusions: Drought tolerance, as indicated by both hydraulic and wood traits, strongly differed between the closely related species and explained their contrasting distribution, and affinity for moist (E. ivorense) and wet (E. suaveolens) forests. However, phenotypic plasticity in hydraulic and wood traits remained to be addressed to examine the extent of water use differences between the two species. [less ▲]

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See detailLe rôle des rongeurs dans la dispersion des diaspores en milieu forestier (synthèse bibliographique)
Evrard, Quentin ULg; Haurez, Barbara ULg; Doucet, Jean-Louis ULg

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment (2017)

Introduction. Seed dispersal is a key interaction that influences a number of ecological processes that are important to the maintenance of diversity in forest ecosystems. Rodents, mainly considered as ... [more ▼]

Introduction. Seed dispersal is a key interaction that influences a number of ecological processes that are important to the maintenance of diversity in forest ecosystems. Rodents, mainly considered as seed predators, can carry, hide and discard seeds, often transporting them over considerable distances from the parent tree and thus leading to an enhanced germination rate. The role of rodents on forest regeneration therefore depends upon several environmental variables influencing their behavior. Literature. Many publications demonstrate that rodents are mostly seed predators for many species. Nevertheless, because it is hard to define their movement pattern, the role of rodents on regeneration could be underestimated. Through scatter-hoarding, rodents may play a crucial role, particularly in those forests where anthropogenic pressures have led to a reduction in the density of large mammals. However, very few studies have been conducted in African moist forests where defaunation can be high, and the role of rodents has been very poorly studied. Conclusions. To understand the phenomenon, we suggest to further investigate the interactions between seeds and rodents by employing methods that have been commonly used on other continents. [less ▲]

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See detailA look at Intact Forest Landscapes and their relevance to Central African forest policy
Haurez, Barbara ULg; Daïnou, Kasso ULg; Vermeulen, Cédric ULg et al

Conference (2017, February)

Tropical forests are important providers of natural resources and ecosystem services but their ecological functions are facing increasing human pressure, linked to economic development. The preservation ... [more ▼]

Tropical forests are important providers of natural resources and ecosystem services but their ecological functions are facing increasing human pressure, linked to economic development. The preservation of tropical forest ecosystems is interrelated with effective land use planning and identification of priority areas for conservation. Initially defined by Greenpeace and the World Resources Institute (WRI) in 2000, Intact Forest Landscapes (IFLs) are large areas of forest minimally impacted by human activities. IFLs were identified by mapping industrial activities, road networks and infrastructure using remote sensing. Since 2014, when IFLs were recognized and adopted by the certification scheme Forest Stewardship Council (FSC), the IFLs have become integrated into forest management policies. In order to trace the history and evaluate the applicability of IFLs for forest management policy in the Central African context, we searched for documents related to the IFL method, and previous similar concepts. The IFL method is simple and cost-effective and enables the monitoring of forest degradation at a global scale. However, the approach mainly considers forest cover and is imprecise at the local scale. For example, hunting, one of the main threats faced by Central African ecosystems, cannot be detected by satellite imagery and is therefore disregarded in IFL identification processes. In contrast, there are other considered anthropogenic activities, such as reduced-impact selective logging, which may be compatible with forest ecosystem conservation. To better tailor the IFL approach to Central African forests, we recommend (i) the consideration of wildlife communities distribution in the analysis of disturbance, (ii) a thorough evaluation of the impacts of different human activities on forest ecosystems, and (iii) the integration of local stakeholders and governments in the design of land management strategies devised to address social, economic and environmental needs. [less ▲]

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See detailDiversity and carbon storage across the tropical forest biome
Sullivan, Martin J.P.; Talbot, Joey; Lewis, Simon L. et al

in Scientific Reports (2017), 7(39102),

Tropical forests are global centres of biodiversity and carbon storage. Many tropical countries aspire to protect forest to fulfil biodiversity and climate mitigation policy targets, but the conservation ... [more ▼]

Tropical forests are global centres of biodiversity and carbon storage. Many tropical countries aspire to protect forest to fulfil biodiversity and climate mitigation policy targets, but the conservation strategies needed to achieve these two functions depend critically on the tropical forest tree diversity-carbon storage relationship. Assessing this relationship is challenging due to the scarcity of inventories where carbon stocks in aboveground biomass and species identifications have been simultaneously and robustly quantified. Here, we compile a unique pan-Tropical dataset of 360 plots located in structurally intact old-growth closed-canopy forest, surveyed using standardised methods, allowing a multi-scale evaluation of diversity-carbon relationships in tropical forests. Diversity-carbon relationships among all plots at 1 ha scale across the tropics are absent, and within continents are either weak (Asia) or absent (Amazonia, Africa). A weak positive relationship is detectable within 1 ha plots, indicating that diversity effects in tropical forests may be scale dependent. The absence of clear diversity-carbon relationships at scales relevant to conservation planning means that carbon-centred conservation strategies will inevitably miss many high diversity ecosystems. As tropical forests can have any combination of tree diversity and carbon stocks both require explicit consideration when optimising policies to manage tropical carbon and biodiversity. [less ▲]

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See detailPresent-day central African forest is a legacy of the 19th century human history
Morin, Julie ULg; Fayolle, Adeline ULg; Favier, Charly et al

in eLife (2017)

The populations of light-demanding trees that dominate the canopy of central African forests are now aging. Here, we show that the lack of regeneration of these populations began ca. 165 ya (around 1850 ... [more ▼]

The populations of light-demanding trees that dominate the canopy of central African forests are now aging. Here, we show that the lack of regeneration of these populations began ca. 165 ya (around 1850) after major anthropogenic disturbances ceased. Since 1885, less itinerancy and disturbance in the forest has occurred because the colonial administrations concentrated people and villages along the primary communication axes. Local populations formerly gardened the forest by creating scattered openings, which were sufficiently large for the establishment of light-demanding trees. Currently, common logging operations do not create suitable openings for the regeneration of these species, whereas deforestation degrades landscapes. Using an interdisciplinary approach, which included paleoecological, archaeological, historical, and dendrological data, we highlight the long-term history of human activities across central African forests and assess the contribution of these activities to present-day forest structure and composition. The conclusions of this sobering analysis present challenges to current silvicultural practices and to those of the future. [less ▲]

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See detailThe influence of spatially structured soil properties on tree community assemblages at a landscape scale in the tropical forests of southern Cameroon
Vleminckx, Jason; Doucet, Jean-Louis ULg; Morin, Julie ULg et al

in Journal of Ecology (2016)

Species distribution within plant communities results from both the influence of deterministic processes, related to environmental conditions, and neutral processes related to dispersal limitation and ... [more ▼]

Species distribution within plant communities results from both the influence of deterministic processes, related to environmental conditions, and neutral processes related to dispersal limitation and stochastic events, the relative importance of each factor depending on the observation scale. Assessing the relative contribution of environment necessitates controlling for spatial dependences among data points. Recent methods, combining multiple regression and Moran's eigenvectors maps (MEM), have been proved successful in disentangling the influence of pure spatial processes related to dispersal limitation, pure environmental variables (not spatially structured) and spatially structured environmental properties. However, the latter influence is usually not testable when using advanced spatial models like MEM. To overcome this issue, we propose an original approach, based on torus-translations and Moran spectral randomizations, to test the fraction of species abundance variation that is jointly explained by space and seven soil variables, using three environmental and tree species abundance data sets (consisting of 120, 52 and 34 plots of 0·2 ha each, located along 101-, 66- and 35-km-long transect-like inventories, respectively) collected in tropical moist forests in southern Cameroon. The overall abundance of species represented by ≥30 individuals, and 27% of these species taken individually, were significantly explained by fine-scale (<5 km) and/or broad-scale (5–100 km) spatially structured variations in soil nutrient concentrations (essentially the concentration of available Mn, Mg and Ca) along the 120-plots area. The number of significant tests considerably decreased when investigating the two smaller data sets, which mostly resulted from low statistical power rather than weaker floristic and/or edaphic variation captured among plots. Synthesis. Our results provide evidence that tree species turnovers are partly controlled by spatially structured concentrations in soil nutrients at scales ranging from few hundreds of metres to c. 100 km, a poorly documented subject in Central African forests. We also highlight the usefulness of our testing procedure to correctly interpret the space-soil fraction of variation partitioning analyses (which always accounted here for the most important part of the soil contribution), as this fraction was sometimes relatively high (R2 values up to c. 0·3) but nearly or not significant. [less ▲]

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See detailRevealing hidden species diversity in closely related species using nuclear SNPs, SSRs and DNA sequences - a case study in the tree genus Milicia
Daïnou, Kasso ULg; Blanc-Jolivet, Céline; Degen, Bernd et al

in BMC Evolutionary Biology (2016), 16(259), 15

Background: Species delimitation in closely related plant taxa can be challenging because (i) reproductive barriers are not always congruent with morphological differentiation, (ii) use of plastid ... [more ▼]

Background: Species delimitation in closely related plant taxa can be challenging because (i) reproductive barriers are not always congruent with morphological differentiation, (ii) use of plastid sequences might lead to misinterpretation, (iii) rare species might not be sampled. We revisited molecular-based species delimitation in the African genus Milicia, currently divided into M. regia (West Africa) and M. excelsa (from West to East Africa). We used 435 samples collected in West, Central and East Africa. We genotyped SNP and SSR loci to identify genetic clusters, and sequenced two plastid regions (psbA-trnH, trnC-ycf6) and a nuclear gene (At103) to confirm species’ divergence and compare species delimitation methods. We also examined whether ecological niche differentiation was congruent with sampled genetic structure. Results: West African M. regia, West African and East African M. excelsa samples constituted three well distinct genetic clusters according to SNPs and SSRs. In Central Africa, two genetic clusters were consistently inferred by both types of markers, while a few scattered samples, sympatric with the preceding clusters but exhibiting leaf traits of M. regia, were grouped with the West African M. regia cluster based on SNPs or formed a distinct cluster based on SSRs. SSR results were confirmed by sequence data from the nuclear region At103 which revealed three distinct ‘Fields For Recombination’ corresponding to (i) West African M. regia, (ii) Central African samples with leaf traits of M. regia, and (iii) all M. excelsa samples. None of the plastid sequences provide indication of distinct clades of the three species-like units. Niche modelling techniques yielded a significant correlation between niche overlap and genetic distance. Conclusions: Our genetic data suggest that three species of Milicia could be recognized. It is surprising that the occurrence of two species in Central Africa was not reported for this well-known timber tree. Globally, our work highlights the importance of collecting samples in a systematic way and the need for combining different nuclear markers when dealing with species complexes. Recognizing cryptic species is particularly crucial for economically exploited species because some hidden taxa might actually be endangered as they are merged with more abundant species. [less ▲]

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See detailBiomasse et stocks de carbone des forêts tropicales africaines (synthèse bibliographique)
Loubota Panzou, Grâce Jopaul ULg; Doucet, Jean-Louis ULg; Loumeto, Jean-Joël et al

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment (2016), 20(4), 508-522

Introduction. Quantifying the biomass and carbon stocks contained in tropical forests has become an international priority for the implementation of the REDD+ mechanism. Forest biomass is estimated at ... [more ▼]

Introduction. Quantifying the biomass and carbon stocks contained in tropical forests has become an international priority for the implementation of the REDD+ mechanism. Forest biomass is estimated at three successive levels: the tree, the stand and the region level. This paper reviews the state of the art regarding the estimation of biomass and carbon stocks in tropical African forests. Literature. This review highlights the fact that very few allometric equations, equations used for estimating the biomass of the tree using non-destructive measurements (diameter, height), have been established for tropical African forests. At the stand level, the review highlights the spatial and temporal variations in biomass between forest types in Central and Eastern Africa. While biomass recovery after a disturbance (logging, for instance) is rather quick, a great deal of uncertainty still remains regarding the spatial variation in biomass, and there is no consensus on a regional biomass map. The quality of biomass mapping in tropical Africa strongly depends on the type of remotely-sensed data being used (optical, RADAR or LIDAR), and the allometric equation used to convert forest inventory data into biomass. Conclusions. Based on the lack of precision of the available allometric equations and forest inventory data and the large spatial scale involved, many uncertainties persist in relation to the estimation of the biomass and carbon stocks contained in African tropical forests. [less ▲]

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See detailHautes Valeurs de Conservation (HVC) dans les Unités Forestières d'Aménagement du Cameroun : concepts, choix et pratiques
Daïnou, Kasso ULg; Bracke, Charles; Vermeulen, Cédric ULg et al

Book published by Presses Agronomiques de Gembloux (2016)

Le système de certification FSC (Forest Stewardship Council) vise à promouvoir la gestion durable des forêts. Il repose sur un ensemble de normes dont une est particulièrement complexe à mettre en oeuvre ... [more ▼]

Le système de certification FSC (Forest Stewardship Council) vise à promouvoir la gestion durable des forêts. Il repose sur un ensemble de normes dont une est particulièrement complexe à mettre en oeuvre en Afrique Centrale, le principe 9 traitant des Hautes Valeurs de Conservation (HVC). Ce principe devrait être interprété aux échelons nationaux afin de prendre en compte les spécificités de chaque pays. Bien que des ouvrages aient déjà été élaborés par diverses organisations, aucun ne cible particulièrement les grandes concessions forestières. Au Cameroun, ces concessions ou Unités Forestières d’Aménagement (UFA), représentent pourtant 40 % du domaine forestier national. Le présent guide ambitionne de fournir aux acteurs de la gestion forestière au Cameroun les connaissances les plus pertinentes afin de leur permettre d’identifier, de gérer et de suivre les Hautes Valeurs de Conservation dans les UFA. Il se démarque des précédents guides par plusieurs points : (i) une revue bibliographique détaillée est fournie sur le sujet épineux de l’identification de chaque HVC, et l’opinion des auteurs y est mise en exergue; (ii) la démarche d’identification est appuyée par les références les plus pertinentes, évitant au gestionnaire de se disperser dans sa quête de documentation; (iii) sur la base de leur expérience, les auteurs proposent une série de menaces pouvant affecter les HVC, de mesures de gestion et d’indicateurs de suivi. L’approche développée se base sur des méthodes empiriques et pragmatiques d’une part et, d’autre part, sur des études scientifiques. Cet ouvrage devrait constituer une base intéressante pour une interprétation solide des HVC au Cameroun. De plus, bien que ciblant les UFA camerounaises, il pourrait inspirer d’autres acteurs forestiers œuvrant dans le Bassin du Congo. [less ▲]

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See detailHigh selfing rate, limited pollen dispersal and inbreeding depression in the emblematic African rain forest tree Baillonella toxisperma - Management implications
Duminil, Jérôme; Mendene Abessolo, D. T.; Ndiade Bourobou, D. et al

in Forest Ecology & Management (2016), 379

Mating system and gene flow are major influencing factors of species population dynamics and evolution. These factors are often not characterized in tropical tree species, yet they constitute basic ... [more ▼]

Mating system and gene flow are major influencing factors of species population dynamics and evolution. These factors are often not characterized in tropical tree species, yet they constitute basic information that must be considered to implement sustainable management practices. In particular, as logging implies a reduction of the density of congeneric mates, the connectivity through pollination between individuals has to be well characterized (selfing versus outcrossing rates, distances between mates). We conducted a genetic-based analysis (using 10 nuclear microsatellites) to determine the mating system and gene flow characteristics of an emblematic timber tree species from lowland rain forests of the Congo Basin, Baillonella toxisperma (Sapotaceae). The species, which is frequently exploited for its wood and for a number of non-timber forest products, naturally occurs at low densities (ca. 0.01–0.1 individuals/ha). It is supposedly an entomophilous species whose seeds are probably dispersed by mammals. We have shown that the species presents a mixed-mating system (about 20–40% of selfing depending on analysis method). However, the comparison of inbreeding parameters among cohorts suggests that inbred individuals die between seedling and mature tree stages. The mean pollen dispersal distance was relatively low for such a low-density population species (estimated to be 690 or 777 m depending on analysis method) and, together with a low mean number of pollen donors (NEP = 2.76), it suggests a pattern of nearest-neighbour mating where allo-pollen could be a limiting factor. However, B. toxisperma presents a relatively weak genetic structure (Sp statistic = 0.0095) indicative of long gene dispersal distance (rg = 3–5 km according to the assumed effective population density). Overall, this would indicate that gene flow occurs mainly by extensive seed dispersal in this species. These results suggest that mammals and local populations involved in the dispersal of the species play a key role by lowering biparental inbreeding effects. Sustainable population management might require assisted regeneration using unrelated planting material. [less ▲]

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See detailUsing herbarium records to explore the ecological differentiation between closely‐related tree species in tropical Africa
Gorel, Anaïs ULg; Duminil; Doucet, Jean-Louis ULg et al

Poster (2016, June 20)

Background: Tree hypothesis are invoked to explain species distribution and evolutionary history of tree clades in tropical Africa: 1) The forest refuge hypothesis postulates that contractions of lowland ... [more ▼]

Background: Tree hypothesis are invoked to explain species distribution and evolutionary history of tree clades in tropical Africa: 1) The forest refuge hypothesis postulates that contractions of lowland forests during the climatic oscillations of the Pleistocene could have driven allopatric speciation between fragmented populations; 2) The ecological gradient hypothesis states that environmental gradients promote parapatric speciation; 3) The vanishing refuge hypothesis reconciles the two previous hypotheses and postulated a diversification process through climate-driven habitat fragmentation and exposure to new environments. Disentangling the respective influence of environmental and historical factors requires information on phylogeny, as well as information on geography and the environmental space used by species. In this study, we aimed to determine the environmental factors constraining the distribution of African tree species in order to explore ecological divergence and speciation processes. Method: We focused on three African Erythrophleum species (Fabaceae, Caesalpinioideae) that are economically and socially important, providing timber and non-timber resources. Erythrophleum ivorense, Erythrophleum suaveolens and Erythrophleum africanum also show contrasted distributions in Africa. To determine species climatic niche, we used a combination of species presence data gathered from 606 herbarium records and environmental factors (19 BIOCLIM variables). We used Species Distribution Models (SDM, MaxEnt algorithm) in combination with similarity metrics to quantify the degree of niche divergence between species. Results: We showed that the distribution of Erythrophleum species are substantially determined by climate (especially annual rainfall and temperature range) and support the ecological gradient hypothesis. Moreover, the main traits (e.g. wood density and leaf area) and growth rates previously reported among Erythrophleum species confirmed a differential adaptation to drought. Conclusion: Herbarium data provide valuable information on the distribution of species over the whole range. In tropical regions where extensive inventories data are extremely rare, herbarium records in combination with presence-only SDM offer opportunities to explore speciation processes. [less ▲]

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See detailInfluence of frugivore taxa on the generation of plant recruitment foci and on the composition of plant recruits’ communities
Trolliet, Franck ULg; Forget, Pierre-Michel; Doucet, Jean-Louis ULg et al

Conference (2016, June 20)

Frugivores can disperse seeds in a spatially contagious pattern and generate recruitment foci (e.g. under fruiting trees). This process is increasingly explored to understand the influence of frugivores ... [more ▼]

Frugivores can disperse seeds in a spatially contagious pattern and generate recruitment foci (e.g. under fruiting trees). This process is increasingly explored to understand the influence of frugivores on the spatial organization of plant communities, and can also serve as a method to efficiently monitor the consequences of animal extirpation. However, there is limited evidence contrasting the influence of different frugivores taxa on the creation of recruitment foci under fruiting trees, and, similarly, on the overall composition of plant communities. Here, we aimed (i) to compare the role of hornbills and primates in creating recruitment foci, and (ii) to investigate how the presence of hornbills, primates and elephants influence the overall composition of plant recruit’s community in an anthropized forest-savanna mosaic in DR Congo. We firstly compared the community of recruits (0.5-2 m high) in 25-m² plots below hornbill-dispersed trees (Staudtia kamerunensis, N=32), primate-dispersed trees (Dialium spp., N=26), and in control plots located below other tree species (N= 4900 m²). Secondly, we considered all plots to compare the community of recruits in five sites characterized by contrasted levels of hunting and housing different seed disperser communities. Our preliminary results indicate (i) communities of recruits below hornbill-dispersed trees are significantly more dense and richer than in control plots, unlike these below primate-dispersed trees. Also, (ii) recruits in sites less affected by hunting, housing more large frugivores, including elephants, tend to belong to species with longer seeds. We conclude that hornbills generate recruitment foci under fruiting trees, which can serve as an efficient tool to monitor the ecological consequences of their extirpation. Moreover, we discuss the potential influence of the different studied frugivore taxa and the risk of their extirpation from afro-tropical forests on the composition of plant recruits’ community. [less ▲]

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See detailHigh spatial resolution of late-Holocene human activities in the moist forests of central Africa using soil charcoal and charred botanical remains
Morin, Julie ULg; Biwolé, Achille; Gorel, Anaïs ULg et al

in Holocene (2016), 26(12), 1954-1967

Palaeoecological and archaeological studies have demonstrated that human populations have long inhabited the moist forests of central Africa. However, spatial and temporal patterns of human activities ... [more ▼]

Palaeoecological and archaeological studies have demonstrated that human populations have long inhabited the moist forests of central Africa. However, spatial and temporal patterns of human activities have hardly been investigated with satisfactory accuracy. In this study, we propose to characterize past human activities at local scale by using a systematic quantitative and qualitative methodology based on soil charcoal and charred botanical remains. A total of 88 equidistant test-pits were excavated along six transects in two contrasting forest types in southern Cameroon. Charred botanical remains were collected by water-sieving and sorted by type (wood charcoals, oil palm endocarps, and unidentified seeds). A total of 50 Accelerator Mass Spectrometry 14C dates were also obtained. Results showed that charred macroremains were found at multiple places in the forest, suggesting scattered human activities, which were distributed into two main periods (Phase A: 2300-1300 BP – Phase B: 580 BP to the present). Charred botanical remains indicated two types of land use: (i) domestic, with oil palm endocarps most often associated with potsherds (villages) and (ii) agricultural, with charcoal as probable remnant of slash-and-burn cultivation (fields). Oil palm endocarp abundance decreased with distance from the identified human settlements. Our methodology allowed documenting, at high resolution, the spatial and temporal patterns of human activities in central African moist forests and could be applied to other tropical contexts. [less ▲]

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See detailAssessment of fine scale population genetic diversity and regeneration in Congo basin logged forests
Evrard, Quentin ULg; Daïnou, Kasso ULg; Hardy, Olivier et al

Poster (2016, June)

Background In the Congo Basin most of the light-demanding timber tree species display a deficit of natural regeneration which is a major handicap for sustainable production and certification. Whilst the ... [more ▼]

Background In the Congo Basin most of the light-demanding timber tree species display a deficit of natural regeneration which is a major handicap for sustainable production and certification. Whilst the majority of scientists investigate abiotic and biotic factors explaining that pattern, we hypothesize that tree population density or individual spatial isolation may also affect the tree fitness through inbreeding. In this study, we integrate ecological and genetic approaches to characterize the regeneration potential of a set of priority timber species by (i) estimating pollen dispersal distances at various tree population densities, and (ii) evaluating the impact of increasing spatial isolation on mating characteristics and tree fitness. The ultimate goal is the proposal of minimum population density that prevents inbreeding consequences. Method This ongoing study focuses on 10 timber species (Pericopsis elata, Milicia excelsa, Baillonella toxisperma, Entandrophragma cylindricum, E. utile, E. angolense, E. candollei, Afzelia bipindensis, Erythrophleum suaveloens, Terminalia superba). The data collection was carried out in the logging concession granted to Pallisco in Cameroon. We established two 400-ha plots, where all individuals (DBH > 10 cm) of the target species were inventoried and mapped. A sample of leave or cambium was collected for each of these individuals, as well as for seedlings to characterize patterns of gene flow using genetic tools (nuclear microsatellites). Dispersal agents were identified by direct observations and camera traps. Germination success was characterized in nursery for seeds collected on trees under an increasing isolation gradient. Results Main dispersal agents (wind, bat, rodent) and predators (rodent) were identified for all the species. The gene flow and germination data is still being analyzed and the main results will be presented in the poster. Conclusion Our data will allow characterizing the reproductive biology of a set of important timber species from the Congo basin. These information will strengthen sustainable forest management and the application of certification by adjusting harvesting norms through the use of scientifically-relevant data. In particular, we will tentatively define a maximum distance to be maintained between two adults to allow a qualitative reproduction. [less ▲]

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See detailThe determinants of tropical forest deciduousness: disentangling the effects of rainfall and geology in central Africa
Ouedraogo, Dakis-Yaoba ULg; Fayolle, Adeline ULg; Gourlet-Fleury, Sylvie et al

in Journal of Ecology (2016)

1. Understanding the environmental determinants of forests deciduousness i.e. proportion of deciduous trees in a forest stand, is of great importance when predicting the impact of ongoing global climate ... [more ▼]

1. Understanding the environmental determinants of forests deciduousness i.e. proportion of deciduous trees in a forest stand, is of great importance when predicting the impact of ongoing global climate change on forests. In this study, we examine (i) how forest deciduousness varies in relation to rainfall and geology, and (ii) whether the influence of geology on deciduousness could be related to differences in soil fertility and water content between geological substrates. 2. The study was conducted in mixed moist semi-deciduous forests in the northern part of the Congo basin. We modelled the response of forest deciduousness to the severity of the dry season across four contrasting geological substrates (sandstone, alluvium, metamorphic and basic rocks). For this, we combined information on forest composition at genus level based on commercial forest inventories (62 624 0.5 ha plots scattered over 6 million of ha), leaf habit, and rainfall and geological maps. We further examined whether substrates differ in soil fertility and water-holding capacity using soil data from 37 pits in an area that was, at the time, relatively unexplored. 3. Forest deciduousness increased with the severity of the dry season, and this increase strongly varied with the geological substrate. Geology was found to be three times more important than the rainfall regime in explaining the total variation in deciduousness. The four substrates differed in soil properties, with higher fertility and water-holding capacity on metamorphic and basic rocks than on sandstone and alluvium. The increase in forest deciduousness was stronger on the substrates that formed resource-rich clay soils (metamorphic and basic rocks) than on substrates that formed resource-poor sandy soils (sandstone and alluvium). 4. Synthesis. We found evidence that tropical forest deciduousness is the result of both the competitive advantage of deciduous species in climates with high rainfall seasonality, and the persistence of evergreen species on resource-poor soils. Our findings offer a clear illustration of wellknown theoretical leaf carbon economy models, explaining the patterns in the dominance of evergreen versus deciduous species. And, this large-scale assessment of the interaction between climate and geology in determining forest deciduousness may help to improve future predictions of vegetation distribution under climate change scenarios. In central Africa, forest is likely to respond differently to variation in rainfall and/or evapotranspiration depending on the geological substrate. [less ▲]

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See detailWhat Are the Impacts of Deforestation on the Harvest of Non-Timber Forest Products in Central Africa?
Gillet, Pauline ULg; Vermeulen, Cédric ULg; Doucet, Jean-Louis ULg et al

in Forests (2016), 7(5),

The objective of the study is to evaluate the impact of forest transition on non-timber forest product (NTFP) harvesting in Central Africa. We analyze the evolution of several parameters, including ... [more ▼]

The objective of the study is to evaluate the impact of forest transition on non-timber forest product (NTFP) harvesting in Central Africa. We analyze the evolution of several parameters, including distance from NTFP harvest site to road, proportion of dietary intake and villagers’ incomes. The research is based on field surveys, participatory mapping and the geolocation of activities in three study sites representing different stages along the Mather’s forest transition curve: (i) intact forest; (ii) partially degraded forest; and (iii) small areas of degraded forest with plantations of useful trees. The results show that the maximum distance from harvest site to road is higher in Site 2 compared to Site 1 as a consequence of a lower availability of NTFPs; and that this distance is significantly lower in Site 3 due to a drastically smaller village territory. The diversity of bushmeat decreases as game evolves from large to small species, commensurate with the progression of forest transition. As a consequence, there is also a reduction in the proportion of these products represented both in household dietary intake and cash income. This analysis establishes a strong link between the Mather’s forest transition curve and a decline in the importance of NTFPs in village production and livelihoods. [less ▲]

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See detailEnrichment of Central African logged forests with high-value tree species: testing a new approach to regenerating degraded forests
Doucet, Jean-Louis ULg; Daïnou, Kasso ULg; Ligot, Gauthier ULg et al

in International Journal of Biodiversity Science, Ecosystem Services and Management (2016)

In natural forests of Central Africa, several studies indicate a dramatic decrease in commercial trees, including species of concern for conservation. Enrichment planting with these species will favor ... [more ▼]

In natural forests of Central Africa, several studies indicate a dramatic decrease in commercial trees, including species of concern for conservation. Enrichment planting with these species will favor both the long-term recovery of their populations and biodiversity conservation in logged forests. In this study, we analyzed the survival and growth of 23 species in plantations. Fourteen 0.2–1.1 ha mixed species plantations consisting of single-species 15 × 15 m blocks were studied for 5 years in a logging concession of southeastern Cameroon. The plantation design considered both species light requirements and sensitivity to damage by pests. To identify the best species for enrichment planting, we assessed both species performance and plantation costs. We also tested for relationships between species traits and species performance. Mean annual diameter growth increments ranged from 1.67 to 42.9 mm. No significant relationship was found between growth and survival. Herbivory by wild Bovidae was the main cause of mortality and should be carefully considered in rehabilitation efforts. We found a significant negative relationship between wood density and maximum growth rate. The other traits tested were not good predictors of species performance in plantations. The two best-performing species, Triplochiton scleroxylon and Terminalia superba, could reach the minimum cutting diameter during a 30-year cutting cycle. Costs were high and mechanized site preparation is suggested to reduce them. Widespread adoption of such plantations will only occur if financial incentives or national regulations for assuring regeneration are implemented. [less ▲]

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