Abstract
Grasslands are one of the world’s most extensive terrestrial biomes and are central to the survival of herders, their livestock and diverse communities of large wild mammals1,2,3. In Africa, tropical soils are predominantly nutrient-limited4,5,6 but productive grassy patches in wooded grassland savannah ecosystems2,4 grow on fertile soils created by geologic and edaphic factors, megafauna, fire and termites4,5,6. Mobile pastoralists also create soil-fertility hotspots by penning their herds at night, which concentrates excrement—and thus nutrients—from grazing of the surrounding savannahs7,8,9,10,11. Historical anthropogenic hotspots produce high-quality forage, attract wildlife and increase spatial heterogeneity in African savannahs4,12,13,14,15. Archaeological research suggests this effect extends back at least 1,000 years16,17,18,19 but little is known about nutrient persistence at millennial scales. Here we use chemical, isotopic and sedimentary analyses to show high nutrient and 15N enrichment in on-site degraded dung deposits relative to off-site soils at five Pastoral Neolithic20 sites (radiocarbon dated to between 3,700 and 1,550 calibrated years before present (cal. bp)). This study demonstrates the longevity of nutrient hotspots and the long-term legacy of ancient herders, whose settlements enriched and diversified African savannah landscapes over three millennia.
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Acknowledgements
We thank the Kenya Ministry of Science and Technology for permission to conduct research (MOST 13/001/38C234, NCST RRI/12/BS011/38) and National Museums of Kenya for research affiliation, excavation licence and support. We are grateful to J. K. Mulwa and M. Mulwa, for site access at Lukenya and to A. Kabiru, J. M. Munyiri, N. Ole Simpai, H. Ole Saitabau and J. K. Ole Tumpuya for research assistance. Funding was received from Washington University in St Louis I-CARES and support from the Liu and the Kidder laboratories, the Nano Research Facility at Washington University, NSF Grant No. ECS-0335765 and the University of Illinois Environmental Isotope Paleobiogeochemistry Laboratory.
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Nature thanks N. Boivin, R. Conant, J. Lee-Thorp and the other anonymous reviewer(s) for their contribution to the peer review of this work.
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F.M. and S.H.A. designed the study; F.M., S.H.A., A.W. and S.G. collected field data, R.E.B.R., R.S.-G., S.G., M.S., S.A. and L.H. performed analyses. All authors discussed data and wrote the paper.
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Extended data figures and tables
Extended Data Fig. 1 On-site versus off-site sediment profiles for sampled locales.
a, On-site and off-site stratigraphy at Indapi Dapo. a1 depicts on-site stratigraphy: (1) modern topsoil, (2) light grey cultural horizon, (3) light yellow–brown cultural and dung horizon, (4) discontinuous harder trampled surface and (5) dark yellow–brown sterile sediments. a2 depicts off-site stratigraphy: (1) loamy modern topsoil, (2) brown silts with carbonate nodules and (3) rocky bedrock-derived sediment. b, On-site and off-site stratigraphy at Oloika 1. b1 depicts on-site stratigraphy: (1) modern topsoil, (2) pale grey cultural and dung horizon, (3) compacted cultural horizon with hard undulating calcium carbonate crust and (4) sterile oxidized palaeosol with manganese nodules. b2 depicts off-site stratigraphy: (1) light brown modern topsoil, (2) grey–brown sediment with carbonate nodules, (3) oxidized subsoil. c, On-site and off-site stratigraphy at Oloika 2. c1 depicts on-site stratigraphy: (1) modern topsoil, (2) pale grey cultural and dung horizon, (3) compacted calcium carbonate lens, (4) oxidized subsoil, (5) recent animal burrow and (6) oxidized subsoil pisolithic formation with manganese nodules. c2 depicts off-site stratigraphy: (1) light brown modern topsoil, (2) grey–brown sediment with carbonate nodules and (3) consolidated lighter grey soil with increasing carbonate nodules. d, On-site road-cut (GvJm48) and step-trench (GvJm44) stratigraphy, and off-site stratigraphy at GvJm44. d1 depicts the GvJm48 road-cut stratigraphy: (1) modern topsoil, (2) grey–brown silty loam, (3a, 3b, 3c) top, middle and bottom, respectively, of pale grey silty loam cultural and dung horizon, (4) pre-cultural loam palaeosol and (5) bedrock-derived weathered sediments. d2 depicts the GvJm44 step-trench stratigraphy: (1) modern topsoil, (2) dark yellow–brown clay grading to silty loam cultural horizon and (3) lower dark brown silty loam cultural horizon. d3 depicts off-site stratigraphy at GvJm44: (1) modern topsoil, (2) dark brown to red brown sandy loam (3) sandy loam.
Extended Data Fig. 2 Archaeological landscapes and stratigraphic sections.
a, Satellite image of GvJm44 and GvJm48, Lukenya (dry season). At GvJm48, a track exposes fine-grained grey midden deposits in an open grassy area. Redder sandy clays are exposed north and south of the site. b, Landscape and stratigraphic view of GvJm44, showing dark Neolithic midden sediment in cross section. Arrows indicate midden edges. Person standing atop the centre of the midden is about 165-cm tall. c, Dung layer at GvJm48. d, Open glades visible near the Ntuka River (dry season) at Ol Owarukeri (GvJh108), a large Elmenteitan (Pastoral Neolithic tradition dating to approximately 3,500–1,500 cal. bp) site with modern pastoralist settlement and two smaller Pastoral Neolithic sites, one with modern settlement. a, d, Imagery from Google Earth Pro, Digital Globe. b, c, Photographs by S.H.A., 1977–1978.
Extended Data Fig. 3 Sediment sample micromorphology.
a, Flatbed scan of a thin section representing off-site sediments (Oloika 1). b, Flatbed scan of a thin section representing on-site sediments (Oloika 1). Both scans are 6.2-cm wide. Note the colour and structure differences between on-site and off-site sediments. The reddish rounded particles are weathered local magmatic rock. c, Microphotograph of on-site sediments (Indapi Dapo) showing granular microstructure associated with large voids, which indicates severe bioturbation. Note the modern plant root (1) within the large void on the right. Scale bar, 1 mm; plane-polarized light. d, Microphotograph of on-site sediments (Indapi Dapo) showing black manganese-oxide florets (2), which indicate periods of water saturation. Scale bar, 1 mm; plane-polarized light. e, Microphotograph of on-site sediments (Oloika 2) that have been disaggregated (‘grain mount’) to enable clear observation of phytoliths and dung spherulites. Arrows point to several phytoliths of various types. Scale bar, 0.1 mm; plane-polarized light. f, Same view as in e, but in crossed-polarized light. Arrows point to a few dung spherulites.
Extended Data Fig. 5 Landscape of Nkuta showing 116 modern and 5 ancient pastoral settlements (bomas) visible in the study area.
Ole Pariata (1), Ol Owarukeri (GvJh108) (2), Oloika 1 (3), Oloika 2 (4) and Indapi Dapo (5). ArcGIS model with a base 30-m-resolution digital elevation derived from the Shuttle Radar Topography Mission.
Supplementary information
Supplementary Information
This file contains Supplementary Notes Parts A-H and Supplementary References.
Supplementary Table 1
Particle size, loss on ignition, magnetic susceptibility, ICPMS elemental, isotope, and FTIR data for on- and off-site sediment samples.
Supplementary Table 2
Summary of data from African anthropogenic hotspots.
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Marshall, F., Reid, R.E.B., Goldstein, S. et al. Ancient herders enriched and restructured African grasslands. Nature 561, 387–390 (2018). https://doi.org/10.1038/s41586-018-0456-9
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DOI: https://doi.org/10.1038/s41586-018-0456-9
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