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See detailQuelle histoire pour les forêts d'Afrique centrale ?
Morin-Rivat, Julie ULg

Scientific conference (2014, July 24)

Conférence grand public sur les indicateurs de perturbations climatiques et anthropiques dans les forêts d'Afrique centrale.

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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 ▲]

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See detailCharcoal records reveal past occurrences of perturbations in the forests of the Kisangani region(RDC): vegetation history of the semi-deciduous rainforest
Tshibamba Mukendi, John; Hubau, Wannes; Morin-Rivat, Julie ULg et al

Poster (2014, April 28)

Introduction. Past disturbances have modified the structure and the floristic composition of Central African rainforests. These perturbations represent a driving force for forest dynamics and they are ... [more ▼]

Introduction. Past disturbances have modified the structure and the floristic composition of Central African rainforests. These perturbations represent a driving force for forest dynamics and they are presumably at the origin of present-day forest mosaics. Fire is a prominent forest disturbance, leaving behind charcoal as a witness of past forest dynamics. The question arises whether quantification, dating and botanical identification of ancient charcoal fragments found in soil layers (pedoanthracology) allows a detailed reconstruction of forest history, including the possible occurrence of past disturbances. Material & methods. We organized pedoanthracological excavations in 6 regrowth sites and 48 sites of primary forests of Yangambi, Yoko, Masako and Kole in the Kisangani (RDC). We performed a detailed sampling in different vegetation types of a semi -deciduous rainforest (Yoko). Charcoal sampling was conducted in pit intervals of 10 cm. The charcoal was quantified whereby pottery fragments were also registered. A selection of charcoal fragments has been dated through AMS 14C measurement. Floristic identifications were conducted using. former protocols based on wood anatomy, which is largely preserved after charcoalification. Results. Charcoal was found in most pit intervals. The anthracomass in the soil of regrowth forests (secondary forests) is much higher than in the primary forest: 27,59 mg/kg for secondary forests et 2,53 mg/kg for primary forests. The specific soil anthracomass of the primary forest of the Yoko reserve is higher (7,7 mg/kg) than in Yangambi (1,9 mg/kg) , Masako (1,7 mg/kg) and Kole (0,8 mg/kg). No systematic differences have been found between soil charcoal content of the different forest type representing different forest histories. Gilbertiodendron dewevrei (De Wild.) J. Leonard forests showed surprisingly a higher concentration of soil charcoal. Discussion. Forest disturbances in the Kisangani region appear to be more recent than those in the Mayombe forest in Western RDC ( 3000-2000 calBP (Hubau, 2013)) and those of the Cameroon forest (2300-1300 calBP) (Morin-Rivat, J et al., 2014). Stratified charcoal conserved in the soil is a useful indicator of past forest disturbances. [less ▲]

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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 ▲]

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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

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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.

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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 ▲]

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See detailWood charcoal analysis: a relatively new tool for palaeoecology in tropical Africa
Morin-Rivat, Julie ULg; Biwole, Achille ULg; Bourland, Nils ULg et al

Scientific conference (2014, February 14)

This is an introduction about wood charcoal properties, collection and taxonomical identification in the framework of palaeoecological studies in Central Africa through examples of possible applications.

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See detailFrom wood charcoals to trees: pitfalls and successes of the taxonomic identification in tropical contexts
Morin-Rivat, Julie ULg; De Weerdt, Joëlle; Hubau, Wannes et al

Poster (2014, February 07)

So as to document the past history of tropical forests, several palaeoenvironmental proxies have been used. For instance, charcoals from soil deposits provide a local signal of the evolution of the ... [more ▼]

So as to document the past history of tropical forests, several palaeoenvironmental proxies have been used. For instance, charcoals from soil deposits provide a local signal of the evolution of the vegetation together with snapshots of human interactions with the environment. As charcoal analyses are rare in tropical contexts, here we aim at presenting the different aspects of charcoal studies through their pitfalls and successes as well as the needs for further research. Charcoal analysis (anthracology) is a discipline initially from archaeobotany that consists in the analysis of pieces of charred wood primarily found in archaeological contexts but also in natural soil layers. Its goal is to identified the species that burnt during the past through the observation of the charred wood structure. Indeed carbonization, as the incomplete combustion of the ligneous material, preserves the wood structure. The identifications obtained through microscopic observations allow assessing past uses of wood and human impacts on the forest landscape. However, issues typically tropical exist: difficulties related to fieldwork accessibility, to sampling, to soil processing so as to collect the charcoals, difficulties related to the taxonomic identification because of the huge number of species and of the limited number of anatomical descriptions. New developments are nonetheless emerging for Central Africa with original anatomical descriptions, identification protocols and visual keys. [less ▲]

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See detailImprove the characterization of tropical forests to improve management: policy brief
Gourlet-Fleury, Sylvie; Aleman, Julie; Bayol, Nicolas et al

Report (2014)

CoForChange has shown that management plans based on timber stock recovery are not enough to ensure the sustainability of these production forests. The variability of forest characteristics and their ... [more ▼]

CoForChange has shown that management plans based on timber stock recovery are not enough to ensure the sustainability of these production forests. The variability of forest characteristics and their different responses to disturbance should be considered in management decisions. [less ▲]

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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 detailRelation entre anatomie du bois et traits fonctionnels chez 584 espèces d'Afrique tropicale
Morin-Rivat, Julie ULg; Fayolle, Adeline ULg; Doucet, Jean-Louis ULg et al

Poster (2013, November 19)

Les différences anatomiques observées dans le bois ont souvent été mises en relation avec des adaptations évolutives et environnementales. Toutefois, les liens entre structure du bois et contraintes ... [more ▼]

Les différences anatomiques observées dans le bois ont souvent été mises en relation avec des adaptations évolutives et environnementales. Toutefois, les liens entre structure du bois et contraintes écologiques restent peu connus. En effet, peu d’études ont combiné les approches anatomique et fonctionnelle. De plus, nos connaissances sont très limitées pour les biomes à grande diversité spécifique, en particulier l’Afrique tropicale. Les récents développements relatifs aux traits fonctionnels des espèces du Bassin du Congo poussent à tester de nouvelles hypothèses sur ces essences. Objectifs : Montrer dans quelle mesure les caractères anatomiques d’espèces de la zone guinéo-congolaise sont associés à plusieurs traits fonctionnels majeurs. Nous avons croisé plusieurs bases de données : 1) InsideWood : anatomie du bois, codage binaire (1/0) des descriptions : présence/absence des 163 caractères de la liste IAWA et 2) CoForTraits : traits fonctionnels de 1236 espèces, utilisation de 5 groupes de traits impliqués dans la croissance, la survie et la reproduction des plantes : a) la phénologie foliaire, b) le tempérament, c) la dispersion des graines, d) la forme de vie et e) la densité du bois. Analyse des pourcentages d’occurrence des caractères anatomiques pour les 584 espèces communes aux deux bases. Analyse factorielle des correspondances (AFC) entre les caractères anatomiques et les espèces. Analyse taxonomique enracinée pour évaluer les relations entre les caractères anatomiques et les traits fonctionnels. Tests de la variance. Résultats : 131 caractères anatomiques présents et 13 absents. Les caractères absents ou rares représentent soit des variables quantitatives soit des caractères typiques des régions tempérées. Les caractères très fréquents sont tropicaux et/ou africains. Plusieurs caractères sont très variables (ex. les cernes de croissance). Les 4 premiers axes de l’AFC représentent 15,23% de la variation anatomique. Parmi les caractères fréquents (ex. ponctuations ornées) et peu fréquents (ex. perforations scalariformes, cellules en tuile), plusieurs représentent un signal taxonomique soit au niveau de la famille (ex. Malvaceae, Fabaceae), soit au niveau du genre (ex. Strombosia spp.) Certains caractères proviennent d’un héritage écologique. Il existe en effet une divergence fonctionnelle et anatomique entre a) les grands arbres émergents et les arbustes de sous-bois. Ces éléments peuvent être mis en relation avec les stratégies de croissance en hauteur, de compétition pour accéder à la lumière, de durée de vie, d’efficacité vs de sécurité de la conduction hydrique, de résistance à la sécheresse et de colonisation de l’espace. Notre étude montre que les caractères anatomiques du bois sont dans une certaine mesure liés aux traits fonctionnels impliqués dans la croissance, la survie et la reproduction des plantes. Notre approche peut être utilisée pour évaluer les stratégies des plantes dans des milieux tropicaux à forte diversité spécifique. [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 detailHow closely are Pericopsis elata (Fabaceae) patches linked to past human disturbances in South-Eastern Cameroon
Bourland, Nils ULg; Cerisier, François; Daïnou, Kasso ULg et al

Conference (2013, June 26)

Studies conducted in the Congo Basin forests concluded that soil parameters and large disturbances induced by human activities since 3000–2000 BP could be the main driver for the persistence of long lived ... [more ▼]

Studies conducted in the Congo Basin forests concluded that soil parameters and large disturbances induced by human activities since 3000–2000 BP could be the main driver for the persistence of long lived light-demanding tall tree species. Today most of the timber species belong to this group, among them Pericopsis elata (Fabaceae). Like many other light-demanding trees, this species suffers from important regeneration problems. While the conditions for its establishment must have been met in the past, they obviously have become unfavourable. Because of ongoing logging activities and a natural decline of its populations, this species is recorded in both the IUCN Red List and the CITES Appendix II listings. Our goal was to investigate the roles of both pedological and anthropogenic factors in the persistence of forest patches characterized by this clustered species. Soil surveys, botanical inventories and anthracological excavations were conducted in three different forest sites located in south-eastern Cameroon. P. elata patches (3.3-14.7 ha) were studied and compared to their close surroundings. No statistical differences were observed between the results of botanical inventories conducted inside and outside the patches (Morisita-Horn indices from 0.69-0.77). Soils only differed in Fe content, but otherwise no significant differences could be observed. Charcoal is widespread and abundant in study sites, mostly inside the patches. Charcoal radiocarbon dating (2,150-195 BP) was consistent with decoration techniques of archaeological materials that we discovered. The average age of P. elata individuals coincides with fire events that occurred in a region where fires rarely occur naturally. We present evidence of past anthropogenic disturbances (human settlement, slash-and-burn cultivation) in the Congolese mixed moist semi-evergreen forest in south-eastern Cameroon. We discuss the potential influence of our findings on the management of light-demanding tall trees populations in a context of logging activities. [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 detailLife history traits related to hydraulic functioning in 211 African tropical woody species
Morin-Rivat, Julie ULg; Fayolle, Adeline ULg; Doucet, Jean-Louis ULg et al

Poster (2013, June 06)

In the context of global change understanding the interactions between plant ecology and plant physiology remains a crucial issue. In this study we aimed at analyzing the vascular characteristics involved ... [more ▼]

In the context of global change understanding the interactions between plant ecology and plant physiology remains a crucial issue. In this study we aimed at analyzing the vascular characteristics involved in the ecological traits of woody species from the northern Congo Basin. We crosschecked three databases: the botanical inventories (857 spp.) and the database of life history traits (464 spp.) produced during the CoForChange project, and the anatomical database Inside Wood (761 spp. and genera for tropical Africa). A total of 211 shared species was obtained. We performed correspondence analyses between the tangential diameter of the vessel lumina (40-43), the number of vessels per mm² (46-50) and five life history traits: leaf phenology, light requirement, seed dispersal, tree size and wood density. Species were distributed along a gradient from species with numerous small vessels to species with few large vessels. This distribution was correlated to a gradient in leaf phenology and light requirement: from evergreen shade-tolerant species to deciduous non-pioneer and pioneer light-demanding species. Dispersal followed this distribution in a lesser extent: from zoochoria to autochoria via anemochoria. Finally, a gradient in size was observed, from small shrubs to tall trees, as well as a gradient in wood density, from dense to light woods. We conclude that the ecological traits of the African tropical woody species are closely related to their hydraulic functioning. The strategies adopted by plants regarding light and water availability can thus be deduced from their vascular characteristics. On this basis we anticipate that climate change will foster light-demanding tree species as better competitors than shade-tolerant species, especially as drought stress is concerned. Further research is needed to increase the input of wood anatomy in explaining the life history traits in African tropical species. [less ▲]

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See detailEcological wood anatomy of 155 African tropical hardwoods
Beeckman, Hans; Fayolle, Adeline ULg; Doucet, Jean-Louis ULg et al

Conference (2013, April 19)

In this study we aimed at identifying the anatomical characters expressing life history traits of woody species from the northern Congo Basin. We crosschecked three databases: the botanical inventories ... [more ▼]

In this study we aimed at identifying the anatomical characters expressing life history traits of woody species from the northern Congo Basin. We crosschecked three databases: the botanical inventories produced during the CoForChange project (857 spp.), the database of life history traits established by the CIRAD (France) and GxABT (Belgium) (464 spp.), and the anatomical database Inside Wood (761 spp. and genera for tropical Africa). A total of 155 shared species was obtained. We performed correspondence analyses between the anatomical characters and two main groups of traits: leaf phenology and light-requirement. Results showed: (i) that wood anatomy is involved in leaf phenology and light-requirement in a significant way (7.56% of the variance on axe1), (ii) that evergreenness was correlated to IAWA characters 14 to 18 (scalariform perforation plates, e.g. Olacaceae) and deciduousness to characters 118 to 122 (storied structures, e.g. Malvaceae and Meliaceae), (iii) that pioneer (P) and non-pioneer light-demanding (NPLD) species showed similar traits but were different from shade-tolerant (ST) species, (iv) that deciduous and evergreen species showed separate distributions, and (v) that wood anatomy validated the well documented strong correlation between evergreen species and ST species, with an inversion of the tendency for deciduous species correlated to P and NPLD species. We conclude that anatomical characters can be used as indicators of life history traits in species-rich biomes. Further investigations are needed to increase the input of wood anatomy in explaining the life history traits in African tropical species. [less ▲]

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