Early anthropogenic impact on Western Central African rainforests 2,600 y ago

Abstract

A potential human footprint on Western Central African rainforests before the Common Era has become the focus of an ongoing controversy. Between 3,000 y ago and 2,000 y ago, regional pollen sequences indicate a replacement of mature rainforests by a forest-savannah mosaic including pioneer trees. Although some studies suggested an anthropogenic influence on this forest fragmentation, current interpretations based on pollen data attribute the ''rainforest crisis'' to climate change toward a drier, more seasonal climate. A rigorous test of this hypothesis, however, requires climate proxies independent of vegetation changes. Here we resolve this controversy through a continuous 10,500-y record of both vegetation and hydrological changes from Lake Barombi in Southwest Cameroon based on changes in carbon and hydrogen isotope compositions of plant waxes. [Formula: see text]C-inferred vegetation changes confirm a prominent and abrupt appearance of C plants in the Lake Barombi catchment, at 2,600 calendar years before AD 1950 (cal y BP), followed by an equally sudden return to rainforest vegetation at 2,020 cal y BP. [Formula: see text]D values from the same plant wax compounds, however, show no simultaneous hydrological change. Based on the combination of these data with a comprehensive regional archaeological database we provide evidence that humans triggered the rainforest fragmentation 2,600 y ago. Our findings suggest that technological developments, including agricultural practices and iron metallurgy, possibly related to the large-scale Bantu expansion, significantly impacted the ecosystems before the Common Era.

Tropical monodominant forest resilience to climate change in Central Africa: A Gilbertiodendron dewevrei forest pollen record over the past 2,700 years

“…The timing of the fire events at sites between 10 and 1,000 km apart suggests that fires were localized rather than indicating any major regional fires in the last 3,000 years (Hart, Hart, Dechamps, Fournier, & Atahols, ; Hubau et al., ; Morin‐Rivat et al., ; Tovar et al., ). Lastly, discoveries of archaeological remains across Central Africa indicate a widespread human presence over the last several millennia in the rainforest, potentially impacting forest structure and composition through slash‐and‐burn agriculture (Bayon et al., ; Garcin et al., ; Morin‐Rivat et al., ).…”

Vegetation state changes in the course of shrub encroachment in an African savanna since about 1850 CE and their potential drivers

“…This technique enables the reconstruction of tropical plant diversity at high taxonomic resolution (Boessenkool et al, 2014;Bremond et al, 2017). Further, fire dynamics and its impact on savanna vegetation can be reconstructed from sedimentary charcoal (Colombaroli, van der Plas, Rucina, & Verschuren, 2018;Gillson & Ekblom, 2009), while carbon (δ 13 C) and deuterium (δD) isotope compositions of plant-wax n-alkanes can be used to reconstruct vegetation structure and hydrological variability (Garcin et al, 2018;Miller et al, 2019;Walther & Neumann, 2011). In addition, grain-size analyses of lake sediments are useful to reconstruct sediment mobility in savanna landscapes and to identify soil erosion (Walther & Neumann, 2011).…”

Untitled

“…10), pearl-millet farming in the Central African forests had expanded to several more sites in southern Cameroon, including Abang Minko'o and Mintyaminyoumin-even as far as Boso-Njafo in the Inner Congo Basin, which is beyond our study area (Eggert et al 2006;Kahlheber, Eggert, Seidensticker and Wotzka 2014;Neumann, Boeston et al 2012a). Several studies have documented an increase in population in tropical Africa at this time (Garcin, Deschamps et al 2018a;Morin-Rivat, Biwole et al 2016;Morin-Rivat, Fayolle et al 2014;Wotzka 2006). Also by this time, proto-Bantu language speaking farmers had expanded out of West Africa, bringing both their language and crop set towards the east and south 1 3 of the continent (Bostoen, Grollemund and Muluwa 2013;Grollemund et al 2015;Russell, Silva and Steel 2014).…”