Holocene environmental changes derived from a montane pollen sequence in the KwaZulu-Natal midlands, South Africa.

Abstract

There is a limited understanding of the climatic history of summer rainfall regions of South Africa, especially the east coast, even though palaeo-research has become a popular technique used in southern Africa to determine past environmental and climatic changes. Sites such as wetlands and peatlands are ideal for palaeo-environmental research as they are of high organic content and enable pollen preservation. Dartmoor Vlei, situated at Mt. Gilboa, KwaZulu-Natal, is surrounded by Midlands Mistbelt grassland and in close proximity of the Karkloof Forest archipelago, rendering the site ideal for investigating grassland/forest dynamics. A minimally disturbed, 240 cm, organic rich sediment core was obtained from Dartmoor Vlei for analyses. A multi-proxy approach, viz. radiocarbon, charcoal, geochemical (carbon and nitrogen stable isotopes) and palynological analyses, was adopted to determine past environmental changes. Six samples were used for AMS radiocarbon dating, which indicates sediments date back ca. 12,200 cal yr BP at 144 cm. Environmental conditions at Dartmoor Vlei during the early Holocene are characterised by warmer, dry conditions, and arboreal pollen taxa are found in high concentrations between ca. 12,300 and 9000 cal yr BP. The mid-Holocene marks a period where systematic changes begin to occur at Dartmoor Vlei, as wetter conditions in accordance with the Holocene Altithermal are evident ca. 8000 cal yr BP. A period of locally drier conditions at ca. 6000 cal yr BP is followed by a decrease in arboreal taxa such as Podocarpus, Brassicaceae, Anacardiaceae and Celtis at ca. 5800 cal yr BP. The occurance of Zea mays in the record at ca. 1600 cal yr BP, the increase in fire intensity and frequency, and subsequent decrease in some arboreal taxa is a robust indication of anthropogenic activity in the KwaZulu-Natal Midlands region, attributed to Iron Age settlers. Arboreal and grassland pollen signals indicate the existence of a mosaic of montane and sub-alpine grassland and montane forests in the region of Dartmoor Vlei throughout the Holocene, and at present.