Past tree cover of the Congo Basin recovered by phytoliths and d 13 C along soil proﬁles L. Bremond * , S.C. Bodin, I. Bentaleb, C. Favier, S. Canal Institut des Sciences de l'Evolution e UMR5554, Universit e de Montpellier, CNRS, IRD, EPHE, Place Eug ene Bataillon, 34095 Montpellier cedex 05, France article info Article history: Available online xxx Keywords: Phytolith d 13 C Soil proﬁle Congo Basin Savanna Forest abstract The tropical moist forests (TMF) of the Congo Basin are extremely diverse in terms of structure and functional diversity. Previous paleoecological work suggests that these forests have experienced dra- matic changes over the last millennia, related to climate or humans. These disturbances still inﬂuence today's repartition of forests and savannas as well as species distributions. The objective of this study is to explore the sensitivity of phytolith assemblages, compared to the d 13 C of soil organic carbon (SOC), to reconstruct past tree cover of the present TMF. Large transects across different geological substrata and forest communities were explored. In total, 18 soil proﬁles were investigated for pedogenic features, and 53 radiocarbon dates from SOC and charcoals were obtained. Phytolith extractions from modern soils and along four soil proﬁles were performed. The d 13 C of SOC and phytolith assemblages were interpreted in terms of tree cover changes. One of the most interesting results highlighted by this study was the strong match between phytolith tree cover and the d 13 C signal; as it not only aids the interpretation of d 13 C soil signals, but also puts into question the transport behavior of phytoliths in soil by processes that are still poorly understood. The d 13 C SOC method has been successfully used to study major vegetation changes in Africa, but has never been previously constrained with another proxy of tree cover. This study conﬁrms the value of a multi-proxy approach to investigate past vegetation changes in African tropical moist forests, and shows that SOC d 13 C and phytolith signatures in soil proﬁles display the same dynamics and are complemen- tary. They suggest that the majority of the present forested sites never experienced a true savanna phase. © 2016 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction Biogeographical patterns of plant distribution in the tropical moist forests of the Congo Basin are currently linked to environ- mental conditions, speciﬁcally rainfall (Poorter et al., 2004), or soil and geological substrate (R ejou-M echain et al., 2008; Fayolle et al., 2012). However, large parts of the modern distribution still remain poorly explained, and it has been suggested that recent past changes in climate may explain discontinuities in species compo- sition across Africa. Also, Schwartz (1992) suggested that enclosed savannas were more extensive two or three thousand years ago, and that opening the forest would have facilitated the Bantu migration from north to south of the forest block. Later, Maley (2002) suggested that a major general and synchronous forest destruction occurred between 3000 and 2500 years BP, by considering pollen records from Lake Barombi Mbo (Maley and Brenac, 1998), Lake Ossa (Reynaud-Farrera et al., 1996) in west Cameroon, and lakes in the Congo (Elenga et al., 1994, 1996; Vincens et al., 1999); as well as the present distribution of two light-demanding pioneer trees abundant in the periphery and gaps of the rain forest: oil palm (Elaeis guineensis) and Okoum e (Aucoumea klaineana). This event, later called the ‘third millennium BP crisis of the central African rainforest’ was well recorded in several swamps and lakes from Atlantic Central Africa (Ngomanda et al., 2009b). However, given the spatial distribution of these re- cords, extrapolation across the entire Congo Basin would be prob- lematic. Also, several studies support the opinion that it was not a general deforestation event of the Inner Congo Basin, but the development of a mosaic of mature and secondary forests of pioneer trees (Neumann et al., 2012a, 2012b) due to an intensiﬁ- cation in seasonality. In another recent study, Thi eblemont et al. (2013) suggests that most of the surface of Gabon and western Congo were free of forest from c. 4000 to 2000 BP. However, this * Corresponding author. E-mail address: laurent.bremond@univ-montp2.fr (L. Bremond). Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint http://dx.doi.org/10.1016/j.quaint.2015.11.150 1040-6182/© 2016 Elsevier Ltd and INQUA. All rights reserved. Quaternary International xxx (2016) 1e11 Please cite this article in press as: Bremond, L., et al., Past tree cover of the Congo Basin recovered by phytoliths and d 13 C along soil proﬁles, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2015.11.150