Climatic and cultural changes in the west Congo Basin forests over the past 5000 years

Abstract

Central Africa includes the world's second largest rainforest block. The ecology of the region remains poorly understood, as does its vegetation and archaeological history. However, over the past 20 years, multidisciplinary scientific programmes have enhanced knowledge of old human presence and palaeoenvironments in the forestry block of Central Africa. This first regional synthesis documents significant cultural changes over the past five millennia and describes how they are linked to climate. It is now well documented that climatic conditions in the African tropics underwent significant changes throughout this period and here we demonstrate that corresponding shifts in human demography have had a strong influence on the forests. The most influential event was the decline of the strong African monsoon in the Late Holocene, resulting in serious disturbance of the forest block around 3500 BP. During the same period, populations from the north settled in the forest zone; they mastered new technologies such as pottery and fabrication of polished stone tools, and seem to have practised agriculture. The opening up of forests from 2500 BP favoured the arrival of metallurgist populations that impacted the forest. During this long period (2500–1400 BP), a remarkable increase of archaeological sites is an indication of a demographic explosion of metallurgist populations. Paradoxically, we have found evidence of pearl millet (Pennisetum glaucum) cultivation in the forest around 2200 BP, implying a more arid context. While Early Iron Age sites (prior to 1400 BP) and recent pre-colonial sites (two to eight centuries BP) are abundant, the period between 1600 and 1000 BP is characterized by a sharp decrease in human settlements, with a population crash between 1300 and 1000 BP over a large part of Central Africa. It is only in the eleventh century that new populations of metallurgists settled into the forest block. In this paper, we analyse the spatial and temporal distribution of 328 archaeological sites that have been reliably radiocarbon dated. The results allow us to piece together changes in the relationships between human populations and the environments in which they lived. On this basis, we discuss interactions between humans, climate and vegetation during the past five millennia and the implications of the absence of people from the landscape over three centuries. We go on to discuss modern vegetation patterns and African forest conservation in the light of these events.

New Evidence of Human Activities During the Holocene in the Lowland Forests of the Northern Congo Basin

“…Oslisly (2001) postulated that a widespread epidemic disease could be at the origin of this hiatus. Such a hypothesis is still debated (Clist, reported by Wotzka 2006), although historical sources related major outbreaks of trypanosomiasis at the end of the 19th century (Sautter 1966;Oslisly et al 2013a). Wotzka (2006) added that a lack of any human evidence may reflect differential destructive taphonomic processes, i.e.…”

“…stone tools, potsherds, and iron slags) and charred botanical remains (e.g. charcoals and endocarps) constitute valuable witnesses of human history in the forests (van Gemerden et al 2003;Wotzka 2006;Brncic et al 2007;Höhn and Neumann 2012;Logan and D'Andrea 2012;Neumann et al 2012a;Gillet and Doucet 2013;Oslisly et al 2013a). …”

Increasing human dominance of tropical forests

“…Archaeological remains indicate some intensively cultivated areas, including anthropogenic soil creation in Africa and Amazonia (18), and more commonly, extensively cultivated areas associated with ancient empires (Maya, Khmer), forest kingdoms (West Africa), concentrated resources (Southern Amazonia near rivers (17)), and technological innovation (western Congo basin, 2,500-1,400 BP (19)). These were always a small fraction of total forest area.…”

Drought Effects on Photosynthesis and Implications of Photoassimilate Distribution in 11C-Labeled Leaves in the African Tropical Tree Species Maesopsis eminii Engl.

“…These effects have gained increasing attention [2][3][4][5][6][7][8][9][10] as the biome represents 15% of worldwide forests, and dominates inter-annual carbon cycling with 50% [11,12]. Concerned stakeholders are calling for investigative studies on the impact of climate change on carbon cycling processes in this terrestrial ecosystem [11][12][13][14].…”