Describing a drowned Pleistocene ecosystem: Last Glacial Maximum vegetation reconstruction of the Palaeo-Agulhas Plain

Abstract

Pleistocene ecosystems provided the stage for modern human emergence. Terrestrial vegetation communities structure resources for human foragers, providing plant food, wood for fuel and tools, and fibre, as well as habitat for animal prey. The Pleistocene distribution of vegetation communities is seldom considered as a key constraint on hunter-gatherers foraging across the landscape. We used modern vegetation patterns along the Cape south coast to develop a rule-based model of the expected vegetation for a given soil type, precipitation regime and fire regime. We then applied this ruleset to present-day environmental conditions to test and validate the model. We also scaled the climate-vegetation ruleset to account for likely effects of low atmospheric [CO2] and lower temperature in the Last Glacial Maximum (LGM) on plant water use efficiency. The model was then used to postdict vegetation patterns for the LGM using palaeo-landscape reconstruction of geological substrata and soils, and palaeoclimate simulations. This palaeoscape comprised the extensive Palaeo-Agulhas Plain (PAP), which was exposed at lower sea levels during glacial periods. Our model predicts that the PAP was dominated by limestone fynbos in its southern part, and by shale grassland with cappings of dune fynbos-thicket mosaic in the north. Shale and sandstone fynbos were restricted to the western zone, which experienced a stronger winter rainfall regime during the LGM than at present. The entire PAP was dissected by broad and shallow floodplains supporting a mosaic of woodland and grassland on fertile, alluvial soils. This savanna-like vegetation, as well as shale grassland, are poorly represented in the modern landscape, and would have been capable of supporting the diverse megafauna typical of glacial periods. These Pleistocene periods would have presented a very different resource landscape for early modern human hunter-gatherers than the interglacial landscape such as is found in the Cape coastal lowlands today.