Resumen de Reconstructing past vegetation and modern human foraging strategies on the south coast of south africa
South Africa continues to receive substantial attention from scholars researching modern human origins. The importance of this region lies in the many caves and rock shelters containing well preserved evidence of human activity, cultural material complexity and a growing number of early modern human fossils dating to the Middle Stone Age (MSA). South Africa also hosts the world's smallest floral kingdom, now called the Greater Cape Floristic Region (GCFR), with high species richness and endemism. We use phytoliths –amorphous silica particles that formed in epidermal cells of plants–in order to study the evolution of plant exploitation strategies by first modern humans and also to reconstruct the paleoenvironmental conditions on the south coast of South Africa. A second main aim is to understand the response of GCFR environments to glacial-interglacial cycles and rainfall shifts and its implication with the evolution of first modern humans that inhabited the south coast of South Africa during marine isotope stages (MIS) 5 to 3.
In paleoanthropological research, improving our capacity to reconstruct past climatic and environmental conditions can help us to shed light on survival strategies of hunter-gatherers. To do this, one must use actualistic studies of modern assemblages from extant habitats to develop analogies for the past and improve paleoenvironmental reconstructions. Accordingly, this thesis contemplates fossil and modern material: i) archaeological sediment samples from Pinnacle Point 5-6 site (PP5-6) located on the south coast of South Africa; ii) modern plants from the GCFR and susceptible to have been exploited by first modern humans inhabiting the south coast; iii) modern surface soil samples from different GCFR vegetation types of the south coast of South Africa.
The modern plant reference collection is the first quantitative and morphological study conducted with different plant types and plant parts (wood and leaves of trees and shrubs, leaves, bulb scale leaves and edible part of the bulb of geophytes, restios–Restionaceae and grasses–Poaceae) from the GCFR on the south coast of South Africa. We observed that grasses are the highest phytolith producers among plant types. We reported through thin sections and SEM that the characteristic restio phytoliths belong to and characterize the Restionaceae family and have been detected in the parenchyma sheath of the culms. Geophytes did not produce diagnostic phytolith morphotypes that can be used for taxonomic identification what might make difficult their identification in the fossil record.
The results of the modern surface soil samples showed that phytolith concentration relates mostly to vegetation types and the dominant vegetation rather than to the type of soils. More abundant phytoliths from Restionaceae and woody/shrubby vegetation are also noted from fynbos vegetation and grass phytoliths are a recurrent component in all the vegetation types in spite of being a minor component in the modern vegetation. The grass silica short cells (GSSCs) from these plants, however, suggest a mix of C3 and C4 grasses in most of the vegetation types with a major presence of the rondels ascribed to C3 grasses. The exceptions are riparian, coastal thicket and coastal forest vegetation, which are characterized by the dominance of C4 grass phytoliths.
The study of the modern plants and soils from the surrounding areas of Pinnacle Point were used as proxy for the reconstruction of past human foraging strategies and paleoenvironmental reconstruction through the phytolith record from PP5-6 site. The study of the archaeological sediment samples from this site indicated a wide range of plants used by first modern humans inhabiting the area including wood, leaves and fruits of trees and shrubs, grasses and restios. We reported for the first time the presence of restios in the South African archaeological record through the study of phytoliths. Changes in the plant and mineralogical component from MIS5 to 4 have been interpreted as the result of changes in the plant exploitation strategies. These changes are also associated to major changes observed in the cultural material that took place over MIS5 to 4 and that have also been link to climate shifts. From an environmental perspective, the combined study of modern plants and soils in comparison to the archaeological phytolith assemblage have been interpreted as indicative of the presence of a fynbos-thicket mosaic vegetation where C3 grasses dominated although C4 grasses were also well represented and this is also supported by previous archives recorded from the south coast.
