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The human did not accelerate the decline of the "Green Sahara" and may have succeeded in delaying the onset of the Sahara desert by about 500 years, according to a new study conducted by UCL.
The study by a team of geographers and archaeologists from UCL and King's College London, published in Nature Communicationssuggests that the first pastoralists in North Africa combined in-depth knowledge of the environment with newly domesticated species to cope with the long-term drought trend.
The first pastoralists in North Africa are thought to have developed complex methods for efficiently managing sparse vegetation and relatively dry, low fertility soils.
Dr. Chris Brierley (UCL Geography), lead author, said, "The possibility that humans may have had a stabilizing influence on the environment has important consequences. We challenge the common thesis that past interactions between humans and the environment must always be those of over-exploitation and degradation.
"The fact that societies practicing" pastoralism "have persisted in this region for so long and have invested both economically and ideologically in the local landscape is not conducive to the overexploitation scenario. Our study shows that human population growth and sustainable pastoralism have not accelerated – and perhaps even delayed – the decline of the 'Green Sahara'. "
About 8,000 years ago, the Sahara was not a desert, but a vibrant ecosystem that supported hunter-gatherers and fishermen. The "Green Sahara" – a familiar term from the humid African period – was the period during which North Africa became much wetter than today thanks to a series of monsoons.
As the Earth's orbit changed, the rain began to decrease and vegetation began to die. About 5,500 years ago, the Sahara ecosystem is in permanent decline towards the desert that we know today.
Pastoralism (nomadic or semi-nomadic cattle herders) developed in the Sahara about 1000 years before this collapse. Previous studies have blamed the collapse of the "green Sahara" for these nomads who have often been marginalized in history, but these latest studies refute this myth.
The study uses a new climate-vegetation model to determine if the end of the African humid period has occurred earlier than expected. The model records variables such as vegetation and rainfall, as well as other processes such as the amount of energy coming from the sun and the amount of carbon dioxide in the atmosphere.
The model found that the "Green Sahara" should have collapsed earlier than in the past. This suggests that pastoralists have lasted longer than expected and that the techniques they have used have helped them adapt to environmental changes.
Dr. Brierley added, "The places where pastors last longer are those where there are the most resources. It is a good adaptation to climate change that is taking place at the time. There is now work on what we can learn from nomadic pastoralists, such as selective grazing strategies, that can be applied to sustainable adaptation to desertification that we expect from future climate change.
Dr. Katie Manning (King's College London) concluded: "Despite the largely inhospitable conditions of the Sahara today, it is not difficult to find evidence of human occupation for 11,000 years. Thousands of rock art sites illustrate a lush environment, big game hunting and breeding. The spread of domestic animals across the Sahara has occurred at a time of increasing climatic instability, yet these pastoral populations have flourished.
"It is likely that the strategies used by traditional pastoralists, such as seasonal movements and selective grazing, have also been used by these early pastoralists, helping to maintain an otherwise degraded ecosystem."
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