Contribution of new radiocarbon dates to track the impact of past anthropogenic disturbances on current vegetation in Central Africa

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 ▲]

Documenting the past anthropogenic disturbances in the African tropical forest: back from a fieldwork in Cameroon

Conference given outside the academic context (2012)

Fieldwork in Cameroon. Excavation of pits to collect charcoals and artifacts. Botanical inventories.

Ancient macro-charcoals analysis as a tool to restitute the past history of African tropical forests

Scientific conference (2012, May 22)

Anthracology: past disturbances and vegetation evolution

in CoForChange - Newsletter (2012)

One of CoForChange aims is to highlight the relationship between human settlement and plant distribution. Recent studies show that anthropogenic disturbances have had an impact on vegetation, including ... [more ▼]

One of CoForChange aims is to highlight the relationship between human settlement and plant distribution. Recent studies show that anthropogenic disturbances have had an impact on vegetation, including enabling the expansion of light-demanding species (see Newsl. No 4). To contribute to this analysis in a context of deep scarcity of anthracological data in Africa, we have been studying the charcoals from nine soil pits of the CoForChange project as part of a Master’s. The objective was to understand past and present species composition of the forests in relation with past disturbances. Two anthracological protocols of identification were tested: 1) at species level, by describing the anatomical characteristics of charcoals, by carrying investigations with InsideWood online database, and by comparing anatomical data at XylariumTervuren; 2) at community level, by searching for statistical relationships between ecological traits of species and wood anatomy. The results show that the taxonomic diversity is greater in Marantaceae forests than in lowland forests. Three identifications were obtained from 48 described taxa: Gilbertiodendron dewevrei under G. dewevrei monodominant forest (GIB1 at 40 cm depth, 1510 ± 30 years cal. BP), Millettia drastica and Pterocarpus soyauxii inMarantaceae open forests (F9 at 40 cm, 1200 ± 30 cal. BP). Our hypothesis is that monodominant stands of G. dewevrei are relatively stable. With regard to P. soyauxii, the proportion of this lightdemanding species seems to be decreasing over time (at levels from 20 to 40 cm) for the benefit of Marantaceae. Another result highlights the absence of Triplochiton scleroxylon under T. scleroxylon, which may confirm the hypothesis of the recent settlement of this species. Results on the relationship between wood anatomy and functional traits are still preliminary, and further research will be conducted through a PhD programme. The on-going developments of anthracology in tropical Africa will help to identify a larger number of collected samples, and thus to understand better the evolution of tropical forests. [less ▲]

Le site Néolithique final de Labarthe 2 à Argelos (Pyrénées Atlantiques) : une occupation temporaire ?

in Perrin, Thomas; Sénépart, Ingrid; Thirault, Eric (Eds.) Actes des 9ème Rencontres Méridionales de Préhistoire récente, St-Goerges-de-Didonne (17), 08 et 09 octobre 2010 (2012)

In the Luy de France valley at Labarthe-Argelos (Pyrénées-Atlantiques), a rescue excavation was carried out during spring 2009 on a surface of 2200 m2. The entire Final Neolithic remains were recovered ... [more ▼]

In the Luy de France valley at Labarthe-Argelos (Pyrénées-Atlantiques), a rescue excavation was carried out during spring 2009 on a surface of 2200 m2. The entire Final Neolithic remains were recovered from one single soil unit within the colluvium sequence at bottom of the slope. Nine hearths have been studied (see contribution of B. Nicolle, this volume), the pottery and lithic objects have been positioned in the stratigraphy and a delimitated area with abundant pottery sherds has been identified in close proximity to a small hearth. The pottery assemblage can be assigned to the Final Neolithic sequence of south-western France, within the third millennium. It forms, however, an original facies and contributes to fill an information gap in the Northern Pyrenean region. The lithic artefacts were made on flint and quartzite. Two radiocarbon dates consistent with the data assemblage stemming from the excavation place these occupations between 2600 and 2400 BC cal. The field data attribute Labarthe 2 to a series of small sites exhibiting subtle features not very deeply anchored into the ground that are known in the Bearn and the Landes regions. They are interpreted by a variety of hypotheses: stops during pastoral displacements, crossing points of the valley, places for specific activities (fishing, hunting?), etc. Their location, at the foot of a spur dominating the confluence may also be complementary of a possible settlement on top of the spur. [less ▲]