References of "Gillet, Jean-François"
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See detailNew Evidence of Human Activities during the Holocene in the Lowland Forests of the Northern Congo Basin
Morin-Rivat, Julie ULg; Fayolle, Adeline ULg; Gillet, Jean-François et al

in Radiocarbon (2014), 56(1), 209-220

In the last decade, the myth of the pristine tropical forest has been seriously challenged. In central Africa, there is a growing body of evidence for past human settlements along the Atlantic forests ... [more ▼]

In the last decade, the myth of the pristine tropical forest has been seriously challenged. In central Africa, there is a growing body of evidence for past human settlements along the Atlantic forests, but very little information is available about human activities further inland. In this study, we aimed at determining the temporal and spatial patterns of human activities in an archaeologically unexplored area of 110,000 km² located in the northern Congo Basin and currently covered by dense forest. Fieldwork involving archaeology as well as archaeobotany was undertaken in 36 sites located in southeastern Cameroon and in the northern Republic of Congo. Evidence of past human activities through either artifacts or charred botanical remains was observed in all excavated test pits across the study area. The set of 43 radiocarbon dates extending from 15,000 BP to the present time showed a bimodal distribution in the Late Holocene which was interpreted as two phases of human expansion with an intermediate phase of depopulation. 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. This is in agreement with the population collapse already reported for central Africa. Following this, the 670–20 BP phase corresponds to a new period of human expansion known as the Late Iron Age. These results bring new and extensive evidence of human activities in the northern Congo Basin and support the established chronology for human history in central Africa. [less ▲]

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See detailDe la paléoécologie à l'écologie actuelle : 2000 ans d'interaction homme-milieu dans le nord du Bassin du Congo
Morin-Rivat, Julie ULg; Bentaleb, Ilham; Biwole, Achille ULg et al

Poster (2013, November 06)

La forêt tropicale africaine a longtemps été considérée comme vierge du passage de l’homme. Cependant, plusieurs études récentes en paléoécologie et archéologie ont démontré la présence d’activités ... [more ▼]

La forêt tropicale africaine a longtemps été considérée comme vierge du passage de l’homme. Cependant, plusieurs études récentes en paléoécologie et archéologie ont démontré la présence d’activités humaines anciennes à partir d’indices paléoenvironnementaux (i.e. pollens de plantes anthropophiles) et d’artefacts (i.e. tessons de céramique). Ces études sont toutefois trop rares en raison de difficultés de terrain pour repérer et accéder aux sites archéologiques (couvert végétale dense, absence de pistes). De grandes zones à l’intérieur des terres demeurent donc inexplorées. Par ailleurs, peu d’études se sont penchées sur la question de l’impact de ces activités anthropiques passées sur la structure et la composition de la végétation actuelle. Grâce à une approche multidisciplinaire à la frontière entre sciences humaines et sciences de l’environnement (archéologie, pédoanthracologie : charbons de bois des sols, écologie forestière), notre objectif est d’identifier des indices d’activités humaines anciennes, lesquels sont été mis en relation avec les patrons actuels de végétation. Nos trois zones d’étude sont localisées en forêt tropicale humide de type guinéo-congolais et sont réparties dans le sud-ouest et sud-est du Cameroun et le nord de la République du Congo. Le long d’une vingtaine de transects de plusieurs kilomètres, nous avons appliqué un protocole systématique de récolte de matériel archéologique et archéobotanique dans des fosses situées sur des parcelles d’inventaire botanique. Ceci nous a permis de récolter plus d’un millier d’échantillons contenant des macrorestes végétaux carbonisés ainsi que des artefacts inédits pour la région (pierre taillée et polie, tessons de céramique, scories de métallurgie) et d’inventorier la végétation dans l’environnement immédiat des découvertes. L’analyse spatiale et temporelle (chronologie relative et par datation radiocarbone) des macrorestes a permis d’identifier des villages entourés de probables champs agricoles (agriculture itinérante sur brûlis). Les 68 datations radiocarbones et les types céramiques obtenus suivent une chronologie archéologique en deux phases : un âge du Fer ancien entre 2300 et 1300 BP et un âge du Fer récent se poursuivant jusqu’à la période subactuelle, entre 670 et 20 BP. Entre ces deux phases d’occupation, les traces d’activités anthropiques sont rares. La première phase d’activités serait à mettre en relation avec une fragmentation de la forêt dense à la suite d’un épisode climatique aride autour de 2500 BP, permettant ainsi aux populations de pénétrer la forêt. Un épisode plus humide à partir de 800 BP, avec un retour d’un couvert plus dense, aurait fait reculer les populations humaines. Leur rétablissement dans les forêts se serait produit conjointement à des conditions plus sèches. Ces trois phases rejoignent la chronologie générale établie à l’échelle de l’Afrique centrale. Les premiers taxons identifiés parmi les macrorestes végétaux carbonisés, graines et charbons de bois, démontrent l’utilisation ancienne du palmier à huile et d’arbres fruitiers sauvages. Les espèces ligneuses identifiées sont présentes dans le cortège floristique actuel. L’identification taxonomique des charbons de bois devrait nous permettre de reconstituer l’environnement végétal au cours des deux derniers millénaires. Les différences observées dans les couverts forestiers passé et actuel en termes de composition floristique ainsi que la structure des peuplements actuels sont de bons indicateurs d’impacts récents de l’homme sur son milieu. [less ▲]

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See detailImpacts of past Human disturbances on present-day tree species assembly in a tropical forest of South-East Cameroon
Vleminckx, Jason; Doucet, Jean-Louis ULg; Daïnou, Kasso ULg et al

Poster (2013, November 06)

Many evidence have been found for intensive past Human presence in the forests of Central Africa, notably widespread charcoal occurrence in the soil. Forest clearing for slash-and-burn agriculture may ... [more ▼]

Many evidence have been found for intensive past Human presence in the forests of Central Africa, notably widespread charcoal occurrence in the soil. Forest clearing for slash-and-burn agriculture may have favored the competitiveness of light-demanding species (LD) to the detriment of shade-bearer species (SB). Hypothesis: Positive correlation between abundance of charcoal in the soil (proxy for past Human clearing) and abundance of LD.Mostly “young” charcoals were thought to reflect past Human disturbances that would have shaped present-day species assembly. However, CAI 0-20cm and CAI 20-100cm were highly correlated with each other (r-Pearson = 0.55; P<0.001) and both displayed positive correlations with Non-Pioneer LD abundance (significant with a classic test) and negative correlations with SB abundance. Although this observation is coherent with our hypothesis, significance disappeared when correcting for spatial autocorrelation [4], even after removing small-diameter trees potentially too young to be linked with last Human disturbances (not shown). Correlation of CAI between the two soil layers => Humans found appropriate conditions for settlement in the same area at different periods? Absence of significant correlation in ❸ (i) Last Human disturbances are too old to detect any signal on present-day tree species assembly. (ii) Human impact is weak compared to other factors (soil properties, dispersal limitation,…) (iii) Local scale heterogeneity of LD abundance is weak compared to landscape scale. Parallel large scale gradients in the abundance of Non-Pioneer LD and charcoal abundance (proxy for past slash-and-burn activities) were observed, but a causal link cannot be established so far. [less ▲]

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See detailAnalyzing soil charcoals to assess the naturalness of tropical forest
Morin-Rivat, Julie ULg; Gorel, Anaïs-Pasiphaé; Daïnou, Kasso ULg et al

Conference (2013, June 26)

For conservation biology and sustainable management, the natural character of tropical forest is a crucial issue. Its assessment is usually based on ecological proxies such as forest composition and ... [more ▼]

For conservation biology and sustainable management, the natural character of tropical forest is a crucial issue. Its assessment is usually based on ecological proxies such as forest composition and structure. However the estimation made on this basis only considers short term processes at a local scale. In contrast the long term processes are appraised by palaeoecological proxies (such as pollen) at a regional scale. So as to assess the degree of naturalness of tropical ecosystems in a conservation perspective it is important to combine a long temporal scale as well as a fine resolution spatial scale. Such approaches using palaeoecological proxies have been recently tested in temperate Europe but little in tropical ecosystems. Nonetheless the long term preservation of the palaeoecological material and its broad presence in the environment are necessary conditions to fulfill. In this perspective soil charcoal appears to meet these requirements. In this paper we aimed at assessing the naturalness of tropical forest using soil charcoal from southeastern Cameroon. Fieldwork involving as well archaeology as botany was undertaken at 53 sites. We quantified charcoal in soil samples by layers of 10 cm taken from pits located in the center of plots of botanical inventory. Spatial projections were performed using statistics together with multivariate analyses. Radiocarbon dating allowed interpreting the temporal framework. Results showed 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. These practices shaped the forest over time which cannot be considered as natural anymore. This underlines the potential input of the use of palaeoecological material in conservation biology and sustainable management issues. Charcoal fragments are under taxonomical identification and may provide new insights on the long term history of forest composition. [less ▲]

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See detailImpacts of past Human disturbances on present day tree species assembly in the tropical forests of South-East Cameroon
Vleminckx, Jason; Doucet, Jean-Louis ULg; Daïnou, Kasso ULg et al

Poster (2013, June 25)

Non-random spatial distribution of trees is the result of both neutral and deterministic factors. Neutral models suggest that species within a community are equally competitive, with spatial structures ... [more ▼]

Non-random spatial distribution of trees is the result of both neutral and deterministic factors. Neutral models suggest that species within a community are equally competitive, with spatial structures mainly due to dispersal limitation. Deterministic (or non-neutral) models consider species assemblages as the result of what we name “induced spatial dependence”, where forcing (explanatory) variables shape diversity organization. However, deterministic models have often included habitat variables only, without considering human disturbance which we know enhances the competitive advantage of heliophytic (light-demanding) species and therefore the floristic composition of phytocenoses. Based on charcoal abundance in the soil (used as an indicator of anthropogenic perturbation), species abundance, and environmental data from a forest of south-east Cameroon, we applied modern variation partitioning methods to assess the relative impact of human disturbance on floristic patterns, controlling for purely spatial and habitat effects. Significant signals of human influence have been found so far, and a new collection of data should establish with a better precision the importance of the anthropogenic impact on tree species assemblages. [less ▲]

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See detailWest Central African peoples: Survey of radiocarbon dates over the past 5000 years
Oslisly, Richard; Bentaleb, Ilham; Favier, Charly et al

in Radiocarbon (2013), 55(2-3), 1377-1382

Tracing human history in west central Africa suffers from a scarcity of historical data and archaeological remains. In order to provide new insight into this problem, we reviewed 733 radiocarbon dates of ... [more ▼]

Tracing human history in west central Africa suffers from a scarcity of historical data and archaeological remains. In order to provide new insight into this problem, we reviewed 733 radiocarbon dates of archaeological sites from the end of the Late Stone Age, Neolithic Stage, and Early and Late Iron Age in Cameroon, Gabon, Central African Republic, Equatorial Guinea, Republic of the Congo, and the western Democratic Republic of Congo. This review provides a spatiotemporal framework of human settlement in the forest biome. Beyond the well-known initial spread of Iron Age populations through central African forests from 2500 cal BP, it depicts the geographical patterns and links with the cultural evolution of the successive phases of human expansion from 5000 to 3000 cal BP and then from 3000 to 1600 cal BP, of the interland depopulation from 1350 to 850 cal BP, and of recolonization up to 500 cal BP. [less ▲]

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See detailTree allometry in Central Africa: Testing the validity of pantropical multi-species allometric equations for estimating biomass and carbon stocks
Fayolle, Adeline ULg; Doucet, Jean-Louis ULg; Gillet, Jean-François et al

in Forest Ecology & Management (2013), (305), 29-37

There is a lot of uncertainty in the amount and spatial variations of above-ground biomass in Africa, partly because very few allometric equations are available. The aim of this study was to assess the ... [more ▼]

There is a lot of uncertainty in the amount and spatial variations of above-ground biomass in Africa, partly because very few allometric equations are available. The aim of this study was to assess the validity of using pan-tropical multispecies allometric equations developed by Chave et al. (2005) for estimating the above-ground biomass of trees in Central Africa and/or to develop site-specific equations. The study was conducted in lowland tropical forests of South-eastern Cameroon, at the edge between evergreen and semi-evergreen forests. Data of above-ground woody biomass were obtained from destructive sampling of 138 trees belonging to 47 taxa across a huge range of diameter (5.30–192.50 cm) and wood specific gravity (0.284–1.152 g cm 3). A set of local site-specific multi- and single-species models relating above-ground biomass to tree diameter and wood specific gravity were fitted to the data. The best model was selected using information criterion. Both tree diameter and wood specific gravity were important predictor to consider for the estimation of above-ground biomass at tree scale. Single-species models were not necessarily better than multi-species models including wood specific gravity as a predictor. The best local multi-species model had the same structure and parameters as the pan-tropical equation developed by Chave et al. (2005) for moist forests. The estimates from the pan-tropical multi-species equation were nearly as good as those of the local multi-species equation. Using wood specific gravity from the global data base only slightly increased the estimation errors, because for the study taxa wood specific gravity was highly correlated to wood specific gravity from the global data base. In this study, we showed that the pantropical multi-species allometric equation developped for moist forests can be used to produce accurate estimates of biomass and carbon stocks from diameter measurement in forest inventory and wood specific gravity from global data base at species level. These findings are especially timely given the urgent need to quantify biomass and carbon stocks in the tropics, and given the spatial extent of moist forests in Central Africa. [less ▲]

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See detailContribution of new radiocarbon dates to track the impact of past anthropogenic disturbances on current vegetation in Central Africa
Morin-Rivat, Julie ULg; Gillet, Jean-François; Bourland, Nils ULg et al

Poster (2012, July)

Introduction: Understanding current Central Africa vegetation patterns faces the scarcity of data about their past evolution. However, a growing hypothesis suggests that past human activities could have ... [more ▼]

Introduction: Understanding current Central Africa vegetation patterns faces the scarcity of data about their past evolution. However, a growing hypothesis suggests that past human activities could have had a substantial influence on vegetation (Van Gemerden et al. 2003, Brncic et al. 2009). Indeed, by creating large openings (fig. 1), they might have triggered the expansion of light-demanding species currently suffering from a lack of regeneration. This lack of saplings could have been caused by the change in land use since colonization with the sedentarization of shifting cultivators. Aim of the study: To investigate the potential relationship between past anthropogenic disturbances and present vegetation. Material & methods: Fieldworks combining anthracological and ecological approaches have been undertaken in Northern Congo and South-Eastern Cameroon (fig. 2). We excavated thirty 150-200 cm deep pits under different forest covers and vegetation types to identify evidences of past human presence (i.e potsherds, fig. 3, slags from metallurgy, anthropogenic pieces of charcoals and anthropophilous charred seeds). Charcoals and seeds (oil palm Elaeis guineensis, fig. 4, Canarium schweinfurthii) in combination with artifacts have been dated. Results: A set of 38 new radiocarbon dates ranging from 15,200 cal BP to present time have been obtained. They confirm the existence of important past fire events in a region where natural ones seldom occur. Together with artifacts, our findings support the few already available dates documenting evidences of past human activities in Central African rainforests. On the 36 most recent dates (fig. 5), the majority belongs to the 2,300-1,400 cal BP period (61%). The whole semi-deciduous forest zone is concerned by this period of intense disturbances with a high rate of fragmentation. It follows the last great arid phase ca. 2,500 cal BP and might be linked to the iron workers expansion. Another pool of dates between 650 and 250 cal BP (33%) associated with potsherds might be correlated to a dry phase contemporary to the Little Ice Age in Europe. That last group of dates points out the potential positive impact of anthropogenic disturbances connected to a dry climatic event on light-demanding species populations. Indeed, this is consistent with the fact that most of current light-demanding trees have a higher number of stems around 100 cm dbh. Conclusion: Our multidisciplinary approach allowed new insights into the link between human history and vegetation dynamics in Central Africa. Further investigations should be conducted to go deeper into the understanding of the evolution of Central African rainforests and to improve the management of currently logged light-demanding species resulting from the LIA period. Thirty new dates from sixteen soil profiles are forthcoming. References: Brncic T., Willis M., K. J., Harris D. J., Telfer M. W. & Bailey M. W. 2009. Fire and climate change impacts on lowland forest composition in northern Congo during the last 2580 years from palaeoecological analyses of a seasonally flooded swamp. The Holocene, 19, 79-89. Reimer P. J., Baillie M. G. L., Bard E., Bayliss A., Beck J. W., Blackwell P. G., Bronk Ramsey C., Buck C. E., Burr G. S., Edwards R. L., Friedrich M., Grootes P. M., Guilderson T. P., Hajdas I., Heaton T. J., Hogg A. G., Hughen K. A., Kaiser K. F., Kromer B., McCormac F. G., Manning S. W., Reimer R. W., Richards D. A., Southon J.R., Talamo S., Turney C. S. M., van der Plicht J., & Weyhenmeyer, C. E. 2009. IntCal09 and Marine09 radiocarbon age calibration curves, 0-50,000 years cal BP. Radiocarbon, 51(4), 1111-1150. Van Gemerden B. S., Olff H., Parren M. P. E, Bongers F. 2003. The pristine rain forest? Remnants of historical human impacts on current tree species composition and diversity. Journal of Biogeography, 30, 1381-1390. [less ▲]

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See detailForest anomalies and human occupation in Central Africa during the last two millennia
Livingstone Smith, Alexandre; Beeckman, Hans; Cerisier, François et al

Conference (2012, June 23)

Central African rainforests are no longer considered as pristine, but as the outcome of a long history of changes due mainly to climatic variation. For the later part of the Holocene it has been ... [more ▼]

Central African rainforests are no longer considered as pristine, but as the outcome of a long history of changes due mainly to climatic variation. For the later part of the Holocene it has been hypothesised that climate changes together with human activities triggered modifications in terms of distribution and botanical composition. While developing a research project to explore the mechanisms of forest change, new research avenues for the archaeology of rainforests became apparent. In this paper, we outline the results of this approach, implemented on a forest concession (Cameroon). We introduce our methodology based on the analysis of botanical inventories (focused on large trees of human linked species and light demanding species), coupled to systematic core boring and test pits. A sampling strategy for the collection of charcoal and its identification is developed and archaeological remains found in association are analyzed at the Royal Museum for Central Africa. [less ▲]

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See detailPerturbations récentes dans le Bassin du Congo : Contribution de l’anthracologie à une restitution paléoenvironnementale
Morin-Rivat, Julie ULg; Hubau, Wannes; Gillet, Jean-François et al

Poster (2012, May 22)

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See detailPredicting alpha diversity of African rain forests: models based on climate and satellite-derived data do not perform better than a purely spatial model
Parmentier, Ingrid; Harrigan, Ryan J.; Buermann, Wolfgang et al

in Journal of Biogeography (2011), 38(6), 1164-1176

Aim Our aim was to evaluate the extent to which we can predict and map tree alpha diversity across broad spatial scales either by using climate and remote sensing data or by exploiting spatial ... [more ▼]

Aim Our aim was to evaluate the extent to which we can predict and map tree alpha diversity across broad spatial scales either by using climate and remote sensing data or by exploiting spatial autocorrelation patterns. Location Tropical rain forest, West Africa and Atlantic Central Africa. Methods Alpha diversity estimates were compiled for trees with diameter at breast height ‡ 10 cm in 573 inventory plots. Linear regression (ordinary least squares, OLS) and random forest (RF) statistical techniques were used to project alpha diversity estimates at unsampled locations using climate data and remote sensing data [Moderate Resolution Imaging Spectroradiometer (MODIS), normalized difference vegetation index (NDVI), Quick Scatterometer (QSCAT), tree cover, elevation]. The prediction reliabilities of OLS and RF models were evaluated using a novel approach and compared to that of a kriging model based on geographic location alone. Results The predictive power of the kriging model was comparable to that of OLS and RF models based on climatic and remote sensing data. The three models provided congruent predictions of alpha diversity in well-sampled areas but not in poorly inventoried locations. The reliability of the predictions of all three models declined markedly with distance from points with inventory data, becoming very low at distances > 50 km. According to inventory data, Atlantic Central African forests display a higher mean alpha diversity than do West African forests. Main conclusions The lower tree alpha diversity in West Africa than in Atlantic Central Africa may reflect a richer regional species pool in the latter. Our results emphasize and illustrate the need to test model predictions in a spatially explicit manner. Good OLS or RF model predictions from inventory data at short distance largely result from the strong spatial autocorrelation displayed by both the alpha diversity and the predictive variables rather than necessarily from causal relationships. Our results suggest that alpha diversity is driven by history rather than by the contemporary environment. Given the low predictive power of models, we call for a major effort to broaden the geographical extent and intensity of forest assessments to expand our knowledge of African rain forest diversity. [less ▲]

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See detailEtat actuel de la sécondarisation de la forêt en périphérie nord de la Réserve de biosphère du Dja (Sud-est Cameroun) : influences des facteurs anthropiques passés et des éléphants
Nguenang, Guy-Merlin; Nkongmeneck, Bernard Aloys; Gillet, Jean-François et al

in International Journal of Biological and Chemical Sciences (2010), 4(5), 1766-1781

Plusieurs études récentes révèlent une proportion importante de formations secondaires au sein des forêts tropicales africaines. La présente étude a pour but, de caractériser les différents faciès de ... [more ▼]

Plusieurs études récentes révèlent une proportion importante de formations secondaires au sein des forêts tropicales africaines. La présente étude a pour but, de caractériser les différents faciès de végétation de la forêt du Dja (Sud-est Cameroun) en ressortant l’état et les causes de sa secondarisation. L’étude a été menée dans deux sites en périphérie nord de la Réserve de biosphère du Dja, l’un situé hors de la Réserve (Mimpala) et l’autre à l’intérieur (Dingué). Un total de 104 km de transects a été parcouru. La caractérisation de la végétation a été faite le long de transects en relevant les différents faciès de végétation traversés. Les marques visibles d’anciennes présences humaines et les réseaux de pistes d’éléphants rencontrés ont été comptabilisés. Les chiffres révèlent une prédominance des formations secondarisées aussi bien dans le site situé à l’extérieur de la Réserve, que dans celui se trouvant dans la Réserve: soit respectivement 52% et 58%. Notre étude permet de montrer que l’état actuel de la secondarisation de la forêt du Dja est fortement lié à l’action anthropique traditionnelle dans un passé plus ou moins récent et à celle des éléphants. [less ▲]

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See detailThe origin of the forests in the North of the Congo Republic: an anthraco-pedological contribution.
Gillet, Jean-François; Beeckman, H.; Doucet, Jean-Louis ULg

in Damblon, F.; Court-Picon, M. (Eds.) Geological survey of Belgium professional papers N. 303-2008/1 (2008)

The vegetation of the Sangha region in the North of the Congo Republic is composed of a mosaic of forest formations including semi-deciduous humid dense forests characterized by Ulmaceae and Sterculiaceae ... [more ▼]

The vegetation of the Sangha region in the North of the Congo Republic is composed of a mosaic of forest formations including semi-deciduous humid dense forests characterized by Ulmaceae and Sterculiaceae, evergreen forests with Gilbertiodendron dewevrei and woodland with Marantaceae. Palynological analyses proved that this region witnessed an arid phase 2500 years ago. This was associated with an important reduction of the forest cover and an equal extension of savannahs that could have facilitated the migrations of the Bantou people and the propagation of the shifting cultivation agriculture in the whole region which is, still at the moment, sparsely populated. In order to verify climatic and anthropological influences on the present composition of the forest vegetation, a pedological investigation has been set up in the region of Pokola (1.5° N; 16.5 °E) comprising 43 drillings and 12 pits along a gradient covering the different forest types. Charcoal has been found in 84% of the cores in all the forest formations especially between 30 cm and 60 cm depth. Charred oil palm seeds (Elaeis guineensis), often a culture accompanying species, have been found in 60% of the pits. C14 analysis revealed dates between 600 and 2200 years BP. Pedological analyses showed the association between semi-deciduous humid dense forest and red ferralsols, between Marantaceae woodlands and ochre ferralsols (poorer than the former) and between Gilbertiodendron dewevrei stands and pseudogleys and gleysols. The identification of the botanical taxon of charcoal fragments from tropical regions deals with important limitations due to scarce reference collections that are far from being complete. Therefore it is crucial to combine a thorough knowledge of the different vegetation types and their character species with a wood anatomical study. Given the hypothesised strong influence of man induced perturbations and past climatic changes, these results emphasize the importance of edaphic factors in differentiating the forest stands in the North of the Congo Republic. They also permit a better understanding of a potential evolution of the forests in this region driven by the actual climatic changes. [less ▲]

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