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.
Highlights
An ongoing and key question in paleoenvironmental research concerns the relative contribution that prehistoric anthropogenic processes played in the formation of contemporary vegetation communities
Paleoenvironmental research conducted over the last three decades in central Africa clearly shows that the Holocene epoch ushered in a period of highly volatile climatic fluctuations that were geographically widespread and influenced forest vegetation distribution and composition [1,2,3,4,5,6,7]
Surveys identifying unique botanical features and biotic communities, including the presence of monodominant forests, the prevalence of light-demanding and long-lived trees, low species diversity, forest-savanna mosaics, and endemic species led many to infer a long history of anthropogenic disturbance in the Central African rainforest [16, 17, 18,19,20,21,22,23]
Summary
An ongoing and key question in paleoenvironmental research concerns the relative contribution that prehistoric anthropogenic processes played in the formation of contemporary vegetation communities. Questions about the timing, scale and scope of prehistoric anthropogenic impacts on the Central African rainforest have persisted for more than a century [8,9,10,11,12,13,14,15,16,17]. Despite the introduction of imported iron and metal objects during the historic period, the use and production of indigenously produced raw iron and objects continued and in some areas reached peak production levels [56] well into the 19th century and persisted into the ethnographic record [26, 57]. Despite the clear cultural, sociopolitical, and spiritual importance of iron, its role in shaping vegetation communities in the Central Africa forest is generally presumed to be negligible [13, 58]
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