Holocene vegetation and climate records from Lake Sibaya, KwaZulu-Natal (South Africa)

The palynology of two overlapping Holocene cores from Lake Sibaya in KwaZulu-Natal elucidates the relationship between climate, vegetation and human impact in the region. By means of twenty-one AMS 14C dates, loss on ignition, and palynological results we established a composite profile. Pollen assemblages include elements of swamp forest (e.g. Rauvolfia, Macaranga), dune forest (e.g. Mimusops), mangrove vegetation (Bruguiera), palmveld (e.g. Phoenix) and bushveld (e.g. Spirostachys, Sclerocarya). Poaceae, aquatics and Cyperaceae are abundant, and fynbos elements like Ericaceae and Restionaceae are rare. Based on comparisons between palynological and archaeological/historical data, the radiocarbon dates seem to show an age error of 50–550 yr, which is probably due to a hardwater reservoir effect. Applying the mean of this error range to our age model suggests that the oldest sediments represent ~ 6750–7100 cal yr BP, that a > 5000 yr hiatus occurs ca. 253 cm depth, and that the upper 253 cm of the composite profile covers the period between ~ 1300–1500 cal yr BP (~ 450–650 AD, Early Iron Age), and 2004 AD. The Middle Holocene is characterized by high tree pollen values (especially Phoenix) suggesting warm humid conditions. The Early Iron Age is characterized by high Podocarpus percentages that indicate moist but possibly cooler climatic conditions. The upper part of the pollen sequence is characterized by the decrease of Podocarpus, Isoglossa and Celtis and a rise in Spirostachys. Increasing values of cereal pollen and algae might reflect human activity. Zea mays appears ~ 150–300 cal yr BP in the pollen sequence according to the radiocarbon chronology and both archaeological and historical evidence. The curve of Pinus pollen rises to 50–70% at the top of the diagram, reflecting the spread of pine plantations since the 1920's, and Poaceae values decrease. Stoebe and the introduction of neophytes like Ambrosia and Casuarina suggest recent human disturbance.