Enhanced zoogeomorphological processes in North Africa in thehuman-impacted landscapes of the Anthropocene

Abstract

New zoogeomorphological features discovered in dryland landscapes of Northern Africa reflect human-animal agency since prehistory, and attest to complex, networked activities over great distances. We discuss the role of zoogeomorphology in shaping Earth's surface since the beginning of the Anthropocene, the timeframe when natural processes shifted and landscape evolution became more human-dominated. We focus on contexts in arid and semiarid lands of Northern Africa, which are metastable, sensitive ecosystems that are prone to modifications triggered by climatic and anthropogenically forced factors. Studying the geoarchaeological record in context of landscape impact and animal procurement by people throughout Antiquity is important for reconstructing domestication and husbandry of cattle, sheep, and goats in this region. Among the features we recognize in association with transhumance, pastoralism, and herding are trails, trackways, footholds, animal daybeds, stables, animal dwellings, rockshelters, game blinds, and monuments, to name a few. Related activities with landscape-scale impacts include herding, transport, corralling and browsing of cattle (Bos sp.), goats, and sheep (ovicaprines) as well as pasturage activities like cropping, fire-setting, and manuring. These activities were disturbances that affected surface processes like erosion and dust mobilization, as well as reduced vegetation and ecosystems productivity. In dryland Africa, and especially in the Sahara, intensive herding led to the alteration of the pristine aspects of bare rock surfaces and of the stone desert pavement (i.e., the hamada); many regions preserved evidence of middle-late Holocene animal daybeds, trampled areas, and barren tracks and trails. We suggest that human and herd animal activities affected geomorphic surfaces that affected slope stability, intensified erosion and dust mobilization, and enhanced dust export from the African continent offshore. We reinterpret the increased dust emission from North Africa during the mid-Holocene at the end of the African Humid Period, as has been interpreted from ocean cores; aridification of the Green Sahara followed the insolation-forced monsoonal maximum, and was exacerbated by human-animal activities across the Sahara and the Sahel. We argue that the spread of human activities and intensive husbandry of cattle, and caprines (goat and sheep) in this region significantly influenced the geomorphic stability, ecosystem and landscape sustainability in a comparable manner of overuse observed in present-day arid and marginal environments, where pastoral overgrazing pressure increases erosion processes and enhances dust mobilization. We suggest that human-animal activities have amplified dust generation from the North African continental interior since ~7 ka BP. This evidence of prehistoric human impacts on surface processes in North Africa supports arguments for an early beginning of the Anthropocene.