Iron Age landscape changes in the Benoué River Valley, Cameroon

The introduction of agriculture is known to have profoundly affected the ecological complexion of landscapes. In this study, a rapid transition from C3 to C4 vegetation is inferred from a shift to higher stable carbon ( ¹³C/ ¹²C) isotope ratios of soils and sediments in the Benoué River Valley and upland Fali Mountains in northern Cameroon. Landscape change is viewed from the perspective of two settlement mounds and adjacent floodplains, as well as a rock terrace agricultural field dating from 1100 cal yr BP to the recent past (<400 cal yr BP). Nitrogen ( ¹⁵N/ ¹⁴N) isotope ratios and soil micromorphology demonstrate variable uses of land adjacent to the mound sites. These results indicate that Early Iron Age settlement practices involved exploitation of C3 plants on soils with low δ ¹⁵N values, indicating wetter soils. Conversely, from the Late Iron Age (>700 cal yr BP) until recent times, high soil and sediment δ ¹³C and δ ¹⁵N values reflect more C4 biomass and anthropogenic organic matter in open, dry environments. The results suggest that Iron Age settlement practices profoundly changed landscapes in this part of West Africa through land clearance and/or utilization of C4 plants.