Paper No. 101-5
Presentation Time: 9:10 AM
CHANGING VIEWS ON THE EVOLUTION OF THE PLANT COMMUNITY ALONG THE SOUTH AFRICAN SOUTH-WEST COAST DURING THE PLIO-PLEISTOCENE
The Mio-Pliocene transition ushered in a period of global climatic change, with conditions becoming progressively cooler and drier. This shift in climate profoundly affected plant, and ultimately animal communities. Most significantly, C4 grasses began to expand at the expense of previously abundant C3 plants, particularly woodland and forest taxa. In Africa, the shift to C4 grass-dominated ecosystems coincided with the proliferation of open-adapted grazing ungulates, as well as the evolution of the hominin lineage. While C4 grass expansion was extensive, some ecosystems were less affected than others. The effect that post-Miocene climatic shifts had on these C3 enclaves is unclear. Stable isotope analyses of ungulate enamel carbonate from Plio-Pleistocene fossil sites situated along the South African south-west coast indicate that this region was one such enclave. Today this coast is still dominated by C3 vegetation - mainly a mix of low-growing shrub, succulent and geophyte species of the strandveld, renosterveld and coastal fynbos plant communities. Floral diversity is high; however grass (mainly C3 taxa) and trees are rare, resulting in a contemporary animal community with very low levels of ungulate biomass and diversity. Fossil evidence indicates significantly greater ungulate diversity during the Plio-Pleistocene, and thus by implication, a considerably more productive plant community. It has long been believed that the region’s contemporary plant community structure developed relatively recently, at the onset of the Holocene. Prior to this however, it was hypothesized that a fynbos shrubland/C3 grassland mosaic, which originally replaced local forests/woodlands during the early Pliocene, dominated the region. Recent evidence relating to fossil ungulate diets suggests that the situation might have been much more complicated than originally thought. We summarize this evidence and propose that the loss of forest/woodland vegetation was much more gradual than previously suggested. A shrubland/C3 grassland mosaic only became prominent towards the late Pleistocene. Furthermore, the regional plant community was likely most productive during the early to middle Pleistocene, when shrublands/C3 grasslands were already established, however, forest/woodland vegetation still persisted.