Christopher M Brierley, Katie Manning, Mark Maslin

The benefits of pastoralism for marginal, arid environments are often not appreciated. One notable past example of the human response to encroaching desertification comes from the regional climate deterioration after the most recent African Humid Period, which ended around 5,500 years ago. Recent evidence points to a population expansion in northern Africa prior to this, associated with the introduction of pastoralism. Here we consider the role, if any, of this population on the subsequent ecological collapse. Using a climate-vegetation model driven by global forcings, we estimate the natural length of the most recent African Humid Period (AHP). The model indicates that the system was most susceptible to collapse between 7-6 ka, which is at least 500 years before the observed collapse. Together with archaeological and ethnographic evidence from northern Africa, this suggests that the inclusion of increasing elements of pastoralism after 7 ka was an effective adaptation to the regional environmental changes. Pastoralism also appears to have slowed the deterioration caused by orbitally-driven climate change. This supports the view that modern pastoralism is not only sustainable, but beneficial for the management of the world’s dryland environments.