Reconstruction of ancient palm vegetation landscapes using a phytolith approach

Palms (Arecaceae) are a dominant feature of some landscapes in Africa and may provide different subsistence elements for humans such as construction materials, fabrics, fuel, food, medicine, and ornamentals. Palms have been identified through phytolith analyses in different localities and palaeoanthropological levels of Olduvai Gorge (northern Tanzania) dated to approximately 1.8 Ma. Thus, the presence of palms poses some interesting questions mostly related to the information they can provide in terms of ecological and vegetation reconstructions as well as the interaction between these plants and the possible use of them by hominins. We present here the study of modern soils from Serengeti National Park, Lake Eyasi and Lake Manyara, where palms are still present. The main goal is the reconstruction of palm landscapes and their interaction with other geographical factors (palaeolake, fresh water courses, etc.) through phytolith analyses and taking into account preservation conditions. Contrary to what was expected, characteristic palm phytoliths do not accumulate in the same amounts as observed in the palaeoanthropological samples from Olduvai Gorge. The short cell phytoliths of grasses, also common in the area, do not correspond to the grasses growing in the spots where the samples were collected. There are several reasons for these inconsistencies. Preservation of phytoliths is poor in disturbed areas, open grasslands and scarcely vegetated areas. Fresh watercourses may also influence in the number of phytoliths and preservation caused presumably by erosion and water transport. This study reaffirms the idea that the absence in the archaeological and palaeontological/palaeoecological record of some phytolith morphotypes it is not always related to their absence on the past. Most importantly, the presence of plant groups is very significant but the relative abundance is not easily interpreted because of preservation and disturbance.