On Intensive Late Holocene Iron Mining and Production in the Northern Congo Basin and the Environmental Consequences Associated with Metallurgy in Central Africa

Abstract

An ongoing question in paleoenvironmental reconstructions of the central African rainforest concerns the role that prehistoric metallurgy played in shaping forest vegetation. Here we report evidence of intensive iron-ore mining and smelting in forested regions of the northern Congo Basin dating to the late Holocene. Volumetric estimates on extracted iron-ore and associated slag mounds from prehistoric sites in the southern Central African Republic suggest large-scale iron production on par with other archaeological and historically-known iron fabrication areas. These data document the first evidence of intensive iron mining and production spanning approximately 90 years prior to colonial occupation (circa AD 1889) and during an interval of time that is poorly represented in the archaeological record. Additional site areas pre-dating these remains by 3-4 centuries reflect an earlier period of iron production on a smaller scale. Microbotanical evidence from a sediment core collected from an adjacent riparian trap shows a reduction in shade-demanding trees in concert with an increase in light-demanding species spanning the time interval associated with iron intensification. This shift occurs during the same time interval when many portions of the Central African witnessed forest transgressions associated with a return to moister and more humid conditions beginning 500-100 years ago. Although data presented here do not demonstrate that iron smelting activities caused widespread vegetation change in Central Africa, we argue that intense mining and smelting can have localized and potentially regional impacts on vegetation communities. These data further demonstrate the high value of pairing archeological and paleoenvironmental analyses to reconstruct regional-scale forest histories.

Present-day central African forest is a legacy of the 19th century human history

“…The volume of charcoal used and, by extension, the associated deforestation, should have been important for feeding the furnaces, as shown by Pinçon (1990). However, the debate is still alive about estimating the volume of wood needed for metallurgy (Lupo et al, 2015), compared to the volume of trees logged for shifting agriculture (Goucher, 1981). …”

“…The pollen of naturally grown oil palms and pioneer trees became rare or absent. In southeastern Cameroon and in the CAR, pollen, phytoliths, soil charcoal and δ 13 C values indicate little disturbance during the past 100–150 years, with the recolonization of the savannas by forest trees (Runge et al, 2014; Lupo et al, 2015). The anthropogenic burning persisted, as indicated by charcoal particles found in sites located along rivers (Brnčić et al, 2007, 2009; Tovar et al, 2014), which might document either the colluvium of charcoals downslope or the concentration of human activities on the riverbanks.…”

“…We documented the paleoenvironmental changes in the SRI for the last 1000 years (Supplementary file 5) (Laraque et al, 1998; DeMenocal et al, 2000; Runge and Fimbel, 2001; Harris, 2002; Runge and Nguimalet, 2005; Brnčić et al, 2007, 2009 ;Neumer et al, 2008; Runge, 2008; Sangen et al, 2011; Sangen, 2012; Aleman et al, 2013; Runge et al, 2014; Tovar et al, 2014; Lupo et al, 2015). We acquired paleoenvironmental data from 34 sites, either terra firme , swamp, lake or marine sites, that provided data on the past climate (SSTs and atmospheric dust signal), vegetation (phytoliths, δ 13 C, pollen) and anthropogenic disturbances (charcoal influxes, alluvial discharges through grain size and chemical elements analyses).…”

“…We used 63 uncalibrated traditional and accelerator mass spectrometry (AMS) radiocarbon dates and two optically stimulated luminescence (OSL) dates from 52 archaeological sites and punctual discoveries that covered the last 1000 years (Supplementary file 6) (Fay, 1997; Lanfranchi et al, 1998; Brnčić, 2003; Moga, 2008; Meyer et al, 2009; Oslisly et al, 2013b; Morin-Rivat et al, 2014, 2016 ;Lupo et al, 2015). A total of 22 published dates from 21 sites in Cameroon, 15 dates from 13 sites in the Republic of the Congo, and 28 dates from 18 sites in the Central African Republic were acquired.…”

The Role of Metallurgy in Transforming Global Forests.

“…The high volume of charcoal required to smelt metals from ores has meant that for centuries, the development and intensification of metal production has been linked to reductions in forest cover, environmental decline and associated socio-economic change: [Hoover and Hoover 1950: 8] Echoing Agricola s observations of sixteenth century Bohemia, the degrading impact of metal production industries on local and regional forest environments has more recently been invoked in archaeological research contexts around the globe (e.g . Muntz 1960;Voss 1988;Okafor 1993;Haaland 1980Haaland , 1985Bayon et al 2012a;Lupo et al 2015). However, a methodical and rigorous demonstration of the triggers of environmental degradation is often not attempted in these cases (Wagner 2013), with instead a heavy burden of proof placed on observed correlations between archaeological evidence for industrial activity and palaeoenvironmental proxies for environmental decline.…”