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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 detailDeuxième mission de terrain dans la reserve de Yangambi
de Haulleville, Thalès ULg; Bogaert, Jan ULg; Beeckman, Hans

Scientific conference (2014, March 18)

Presentation of Thales de Haulleville's planned fieldwork during his second field mission.

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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 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 detailAbove-ground biomass and structure of 260 african tropical forests
Lewis, Simon L.; Sonké, Bonaventure; Sunderland, Terry et al

in Philosophical Transactions of the Royal Society B (2013), 368

We report above-ground biomass (AGB), basal area, stemdensity and wood mass density estimates from 260 sample plots (mean size: 1.2 ha) in intact closed-canopy tropical forests across 12 African countries ... [more ▼]

We report above-ground biomass (AGB), basal area, stemdensity and wood mass density estimates from 260 sample plots (mean size: 1.2 ha) in intact closed-canopy tropical forests across 12 African countries. Mean AGB is 395.7 Mg dry mass ha21 (95% CI: 14.3), substantially higher than Amazonian values, with the Congo Basin and contiguous forest region attaining AGB values (429 Mg ha21) similar to those of Bornean forests, and significantly greater than East or West African forests. AGB therefore appears generally higher in palaeo- comparedwithneotropical forests.However, mean stem density is low(426+11 stems ha21 greater than or equal to 100 mm diameter) compared with both Amazonian and Bornean forests (cf. approx. 600) and is the signature structural feature of African tropical forests. While spatial autocorrelation complicates analyses, AGB shows a positive relationship with rainfall in the driest nine months of the year, and an opposite association with the wettest three months of the year; a negative relationship with temperature; positive relationship with clay-rich soils; and negative relationshipswith C :Nratio (suggesting a positive soil phosphorus–AGB relationship), and soil fertility computed as the sum of base cations. The results indicate that AGB is mediated by both climate and soils, and suggest that the AGB of African closed-canopy tropical forests may be particularly sensitive to future precipitation and temperature changes. [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 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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See detailInvestigation of edge effect on wood density in recent tropical forest edges in Yangambi Man and Biosphere Reserve
de Haulleville, Thalès ULg; Bogaert, Jan ULg; Beeckman, Hans

Conference (2013, April)

Rapid development of lumbering activities in tropical forested areas has an important impact on carbon stocks and landscape configuration. Indeed, lumbering tend to fragment forest patches, extend edges ... [more ▼]

Rapid development of lumbering activities in tropical forested areas has an important impact on carbon stocks and landscape configuration. Indeed, lumbering tend to fragment forest patches, extend edges length, and expose core areas to non-forested ecosystems. These exposed core areas then undergo new constraints that can lead to a shift in their ecological features, called the edge effect. We investigate the possible presence of an edge effect on wood density in Yangambi reserve. Wood density (along with diameter and height) is a key feature for biomass estimations in tropical forests. Thus, fluctuations of wood density in forest edges could lead to incorrect estimations of carbon stocks. Ten 1ha plots were installed in core and recent (5 to 10 years) forest¿s edges. Trees were measured and wood samples were collected for density analysis. We focused on 2 main research questions: 1) Does the edge effect induce the emergence of species with a higher or lower wood density in edge area? 2) Does wood density differ amongst individuals of the same specie in core and in edge area? While the data is still being explored as we write, preliminary results seem to indicate that there is no significant difference between the overall mean wood density in edge and core plots. Density differences amongst species are still under exploration. If this behaviour still holds, this would imply that the fragmentation of a forested landscape has no short-term effect on the overall forest wood density and thus, no effect on biomass estimations. [less ▲]

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See detailStockage du Carbone dans les forêts de Yangambi (RDC)
de Haulleville, Thalès ULg; Kearsley, Elizabeth; Bogaert, Jan ULg et al

Scientific conference (2012, October 12)

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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 detailExploring ancient charcoal archives in Central Africa
Hubau, Wannes; Morin-Rivat, Julie ULg; Van den Bulcke, Jan et al

Conference (2012, July)

Fossil pollen and charcoal fragments are preserved in lake sediments, in forest soils and in ancient human settlements, were they can be accompanied by artifacts. As such, vegetation history is remarkably ... [more ▼]

Fossil pollen and charcoal fragments are preserved in lake sediments, in forest soils and in ancient human settlements, were they can be accompanied by artifacts. As such, vegetation history is remarkably well archived and sometimes closely linked to cultural history. Direct evidence for Central African vegetation history has been mainly derived from pollen analysis, while the charcoal archive remains hardly explored. However, analysis of charred wood remains has proven worthwhile for palaeovegetation reconstructions in temperate and arid regions. One of the main challenges for charcoal identification in tropical regions is species diversity. Therefore we developed and present a transparent charcoal identification protocol within an umbrella database of species names and metadata, compiled from the on-line database of wood-anatomical descriptions (InsideWood), the database of the world’s largest reference collection of Central African wood specimens (RMCA, Tervuren, Belgium) and inventory and indicator species lists. We applied the protocol on radiocarbon dated charcoal collections sampled in the Mayumbe forest (Bas-Congo, DRCongo), in human settlements along the Aruwimi and Lomami rivers (Province Orientale, DRCongo), along the Sangha river (Sangha department, Republic of the Congo) and in Pallisco logging concessions (East Province of Cameroon). First charcoal identification results are promising and sometimes seem to be taxonomically more precise than pollen identification. However, next to opportunities, we also present some pitfalls when exploring ancient charcoal archives. [less ▲]

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See detailCurrent Pericopsis elata (Fabaceae) patches in southeastern Cameroon: remnants of a long and rich Human-rainforest relationship?
Bourland, Nils ULg; Cerisier, François; Livingstone Smith, Alexandre et al

Poster (2012, June 23)

Pericopsis elata is one of the most valuable African timber species. This IUCN Red Listed tree suffers from a lack of regeneration, thus its current presence provokes questioning. Our work aimed at ... [more ▼]

Pericopsis elata is one of the most valuable African timber species. This IUCN Red Listed tree suffers from a lack of regeneration, thus its current presence provokes questioning. Our work aimed at understanding its origins so as to help securing its future. This study, lead away from engineering works, was conducted in four different sites located within the natural distribution area of the species and taking into account the different growing conditions were the species occurs. Our observations are based on an analysis of charcoal elements and pottery fragments discovered in subsurface layers of soils as well as current botanical and pedological surveys. Evidence of past human activities we found led to the assumption that this part of the Congo Basin was much more inhabited than previously thought. Some of the results obtained for P. elata could apply for other long lived light demanding species growing in the same environment [less ▲]

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