Reconstructing past vegetation and modern human foraging strategies on the south coast of South Africa

Abstract

[eng] The importance of South Africa 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 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 the Upper Pleistocene. 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 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. From an environmental perspective, the changes observed in the phytolith record from Pinnacle Point deposits are indicative of vegetation movements accordingly to climate changes and sea level fluctuations, in a continuous regional mosaic of habitats.

[spa] Este trabajo de tesis tiene el objetivo último de conocer las estrategias de explotación de recursos vegetales de las poblaciones de primeros humanos modernos, así como la reconstrucción de la vegetación y el clima existente durante el Pleistoceno Medio y el Pleistoceno Final a través del estudio de fitolitos de los depósitos arqueológicos del abrigo rocoso de Pinnacle Point 5-6 (PP5-6). Para ello realizamos u Realiamos estudios actualísticos de plantas y suelos modernos como base análoga de nuestro estudio. Del estudio de plantas modernos dos son los principales resultados que se obtuvieron: i) a través de secciones delgadas y microscopio electrónico de barrido se caracterizó fitolitos diagnósticos de la familia Restionaceae (restios) en la vaina del parénquima de los tallos y ii) los geófitos no producen morfotipos diagnósticos que pudieran ser utilizados para su identificación taxonómica. Los resultados de los suelos mostraron que la concentración de fitolitos se relaciona principalmente con el tipo de vegetación y las plantan que ellos dominan. Los fitolitos característicos de restios dominan en la vegetación de tipo fynbos. Las células cortas de gramíneas (GSSC) sugieren una mezcla de gramíneas de tipo C3 y C4 en la mayoría de los tipos de vegetación. Las excepciones son la vegetación riparia y de coastal thicket donde gramíneas C4 dominan. El estudio de las muestras de sedimentos arqueológicos de PP5-6 indicó una amplia gama de plantas utilizadas por los habitantes de PP5-6. Identificamos por primera vez la presencia de restios en el registro arqueológico sudafricano a través del estudio de fitolitos. Desde una perspectiva ambiental, los cambios observados en el registro de fitolitos de los depósitos de Pinnacle Point son indicativos de los movimientos de vegetación en consecuencia a los cambios climáticos y las fluctuaciones del nivel del mar, en un mosaico regional continuo de hábitats.