Collapse of the Mapungubwe society: Vulnerability of pastoralism to increasing aridity

The Mapungubwe agro-pastoral society in the Limpopo valley, South Africa, persisted for 300 yrs before disappearing in about 1290 as a result of a decrease in mean annual rainfall ( MAR) from about 500 mm to the current 340 mm. The influence of rainfall changes and competition from wildlife on cattle and small stock populations was investigated ( agriculture was not) using the SAVANNA model. Six scenarios were compared for a 350 km(2) area (Venetia-Limpopo Nature Reserve) for a 280 yrs simulation period: livestock only, wildlife only, and wildlife plus livestock, for a climate of 'low' ( MAR 340 mm) versus 'high' ( MAR 480 mm) rainfall. High inter-annual variability in rainfall resulted in highly variable grass production, but production of woody plants was more stable. Extreme drought events of one or more years duration resulted in marked population declines of the grazers, cattle and zebra. Populations of mixed feeders or browsers, including kudu, small stock and impala, were comparatively stable, the latter two mentioned were in part stabilised by offtake. Cattle populations persisted under a high rainfall climate irrespective of wildlife, but became extinct within 120 yrs under a low rainfall climate when competing with wildlife, in particular zebra. The size of the persisting populations of cattle or small stock under low rainfall was about half that for the corresponding high rainfall scenario. Pastoralism based on cattle was apparently unviable once climate started changing, and small stock were probably insufficient for meeting societal needs. Although crop failure is a sufficient explanation for the disappearance of the Mapungubwe settlement, destabilization of pastoralism would have compounded food security. The recorded rapid onset of a dry climate is of portent for current-day pastoral societies in marginal environments.