Once upon a time, the Sahara was green. There were vast lakes. Hippos and giraffe lived there, and large human populations of fishers foraged for food alongside the lakeshores. [...]
The stark difference between 10,000 years ago and now largely exists due to changing orbital conditions of the earth – the wobble of the earth on its axis and within its orbit relative to the sun. [...]
The most commonly accepted theory about this shift holds that devegetation of the landscape meant that more light reflected off the ground surface (a process known as albedo), helping to create the high-pressure ridge that dominates today’s Sahara.
But what caused the initial devegetation? That’s uncertain, in part because the area involved with studying the effects is so vast. But my recent paper presents evidence that areas where the Sahara dried out quickly happen to be the same areas where domesticated animals first appeared. At this time, where there is evidence to show it, we can see that the vegetation changes from grasslands into scrublands. [...]
If you remove the threat of predation, the prey behave differently. In Yellowstone National Park, the absence of predators is argued to have changed grazers’ habits. Prey felt more comfortable grazing alongside the exposed riverbanks, which increased the erosion in those areas. The re-introduction of wolves into the ecosystem completely shifted this dynamic and forests regenerated within several years. By altering the “fear-based ecology”, significant changes in landscape processes are known to follow.
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