A spatiotemporally explicit paleoenvironmental framework for the Middle Stone Age of eastern Africa.

Eastern Africa has played a prominent role in debates about human evolution and dispersal due to the presence of rich archaeological, palaeoanthropological and palaeoenvironmental records. However, substantial disconnects occur between the spatial and temporal resolutions of these data that complicate their integration. Here, we apply high-resolution climatic simulations of two key parameters, mean annual temperature and precipitation, and a biome model, to produce a highly refined characterisation of the environments inhabited during the eastern African Middle Stone Age. Occupations are typically found in sub-humid climates and landscapes dominated by or including tropical xerophytic shrubland. Marked expansions from these core landscapes include movement into hotter, low-altitude landscapes in Marine Isotope Stage 5 and cooler, high-altitude landscapes in Marine Isotope Stage 3, with the recurrent inhabitation of ecotones between open and forested habitats. Through our use of high-resolution climate models, we demonstrate a significant independent relationship between past precipitation and patterns of Middle Stone Age stone tool production modes overlooked by previous studies. Engagement with these models not only enables spatiotemporally explicit examination of climatic variability across Middle Stone Age occupations in eastern Africa but enables clearer characterisation of the habitats early human populations were adapted to, and how they changed through time.

Late Holocene environmental change and anthropogenic: Ecosystem interaction on the Laikipia Plateau, Kenya.

East African ecosystems have been shaped by long-term socio-ecological-environmental interactions. Although much previous work on human-environment interrelationships have emphasised the negative impacts of human interventions, a growing body of work shows that there have also often been strong beneficial connections between people and ecosystems, especially in savanna environments. However, limited information and understanding of past interactions between humans and ecosystems of periods longer than a century hampers effective management of contemporary environments. Here, we present a late Holocene study of pollen, fern spore, fungal spore, and charcoal analyses from radiocarbon-dated sediment sequences and assess this record against archaeological and historical data to describe socio-ecological changes on the Laikipia Plateau in Rift Valley Province, Kenya. The results suggest a landscape characterised by closed forests between 2268 years before present (cal year BP) and 1615 cal year BP when there was a significant change to a more open woodland/grassland mosaic that continues to prevail across the study area. Increased amounts of charcoal in the sediment are observed for this same period, becoming particularly common from around 900 cal year BP associated with fungal spores commonly linked to the presence of herbivores. It is likely these trends reflect changes in land use management as pastoral populations improved and extended pasture, using fire to eradicate disease-prone habitats. Implications for contemporary land use management are discussed in the light of these findings.

Increased ecological resource variability during a critical transition in hominin evolution.

Although climate change is considered to have been a large-scale driver of African human evolution, landscape-scale shifts in ecological resources that may have shaped novel hominin adaptations are rarely investigated. We use well-dated, high-resolution, drill-core datasets to understand ecological dynamics associated with a major adaptive transition in the archeological record ~24 km from the coring site. Outcrops preserve evidence of the replacement of Acheulean by Middle Stone Age (MSA) technological, cognitive, and social innovations between 500 and 300 thousand years (ka) ago, contemporaneous with large-scale taxonomic and adaptive turnover in mammal herbivores. Beginning ~400 ka ago, tectonic, hydrological, and ecological changes combined to disrupt a relatively stable resource base, prompting fluctuations of increasing magnitude in freshwater availability, grassland communities, and woody plant cover. Interaction of these factors offers a resource-oriented hypothesis for the evolutionary success of MSA adaptations, which likely contributed to the ecological flexibility typical of Homo sapiens foragers.

Late Holocene wetland transgression and 500 years of vegetation and fire variability in the semi-arid Amboseli landscape, southern Kenya.

The semi-arid Amboseli landscape, southern Kenya, is characterised by intermittent groundwater-fed wetlands that form sedimentary geoarchives recording past ecosystem changes. We present a 5000-year environmental history of a radiocarbon dated sediment core from Esambu Swamp adjacent to Amboseli National Park. Although radiocarbon dates suggest an unconformity or sedimentary gap that spans between 3800 and 500 cal year BP, the record provides a unique insight into the long-term ecosystem history and wetland processes, particularly the past 500 years. Climatic shifts, fire activity and recent anthropogenic activity drive changes in ecosystem composition. Prior to 3800 cal year BP the pollen data suggest semi-arid savanna ecosystem persisted near the wetland. The wetland transgressed at some time between 3800 and 500 cal year BP and it is difficult to constrain this timing further, and palustrine peaty sediments have accumulated since 400 cal year BP. Increased abundance of Afromontane forest taxa from adjacent highlands of Kilimanjaro and the Chyulu Hills and local arboreal taxa reflect changes in regional moisture budgets. Particularly transformative changes occurred in the last five centuries, associated with increased local biomass burning coeval with the arrival of Maa-speaking pastoralists and intensification of the ivory trade. Cereal crops occurred consistently from around 300 cal year BP, indicative of further anthropogenic activity. The study provides unique insight in Amboseli ecosystem history and the link between ecosystem drivers of change. Such long-term perspectives are crucial for future climate change and associated livelihood impacts, so that suitable responses to ensure sustainable management practices can be developed in an important conservation landscape.

Animal movements in the Kenya Rift and evidence for the earliest ambush hunting by hominins.

Animal movements in the Kenya Rift Valley today are influenced by a combination of topography and trace nutrient distribution. These patterns would have been the same in the past when hominins inhabited the area. We use this approach to create a landscape reconstruction of Olorgesailie, a key site in the East African Rift with abundant evidence of large-mammal butchery between ~1.2 and ~0.5 Ma BP. The site location in relation to limited animal routes through the area show that hominins were aware of animal movements and used the location for ambush hunting during the Lower to Middle Pleistocene. These features explain the importance of Olorgesailie as a preferred location of repeated hominin activity through multiple changes in climate and local environmental conditions, and provide insights into the cognitive and hunting abilities of Homo erectus while indicating that their activities at the site were aimed at hunting, rather than scavenging.

Nonlinear vegetation cover changes in the North Ethiopian Highlands: Evidence from the Lake Ashenge closed basin.

Vegetation cover changes in African drylands are often thought to result from population growth, social factors and aridification. Here we show that long-term vegetation proxy records can help disentangling these main driving factors. Taking the case of North Ethiopia, we performed an integrated investigation of land cover changes over the last four centuries around the endorheic Lake Ashenge, as derived from pollen analysis and repeat photography complemented with information from historical sources. Pollen and sediment analysis of radiocarbon-dated lake deposits shows a phase of environmental destabilization during the 18th century, after a more stable previous period. This is evidenced by decreases of tree pollen (Juniperus, Olea, Celtis, Podocarpus<5%), increases in Poaceae (>40%) and deposition of coarser silt lake sediments (>70%). Quantitative analysis of 30 repeated landscape photographs around the lake indicates a gradual decline of the vegetation cover since a relative maximum during the mid-19th Century. Vegetation cover declined sharply between the 1950s and the 1980s, but has since begun to recover. Overall, the data from around Lake Ashenge reveal a nonlinear pattern of deforestation and forest regrowth with several periods of vegetation cover change over the past four centuries. While there is forcing of regional drought and the regional land tenure system, the cyclic changes do not support a simplified focus on aridification or population growth.