Graph of the Day: Transformation of the biosphere over 8000 years
12 September 2017 (UNCCD) – There is broad evidence to suggest that direct human alteration of terrestrial ecosystems by hunting, foraging, land clearing, agriculture, and other activities started about 12,000 years ago. Sometimes referred to as the “Neolithic Revolution,” agriculture slowly began to transform societies and the way in which people lived; traditional hunter-gatherer lifestyles were abandoned in favor of more permanent settlements and a reliable food supply. This transformation was particularly significant in some regions, which experienced long-term changes from forest clearing, increased frequency of fire, megafaunal extinctions, species invasions, and soil erosion.Beginning around 8,000 years ago, agricultural land use expanded in Mesopotamia and in the Fertile Crescent areas of southwest Asia; this was followed by growth in China, India, and Europe. Intensive land use patterns developed in India, especially on the Ganges plains; in China, along the lower Yellow and Yangtze rivers; in Africa, throughout the Sahel; and in South America, along the Andes. This agricultural expansion led to the development of more complex forms of societal organization. Fertile land and the domestication of wild food crop species allowed nomadic tribes to settle and form early towns and cities. The landscapes of the neo-tropical dry forests of South America, for instance, played a pivotal role in the emergence of pre-Colombian civilizations, such as the Incas. By approximately 6,000 years ago, agricultural expansion had spread across most continents, leading to the clearing of native vegetation and to the culling, or domestication, of herbivores. Native flora and fauna were replaced with intensive crop and livestock management practices as human populations grew and became denser. Starting around 1750, the transformation of land started to accelerate, and rapid land use change continues to be a dominant influence today.By the start of the Common Era (CE), up to 60 per cent of the land in Europe was being used by humans, albeit with significant fluctuations as some areas were periodically abandoned due to war, famine, and other events that affected human populations. By the Middle Ages (14th and 15th centuries), land use intensity in both Europe and China increased greatly following the development of cities and towns. During the same period, nearly 90 per cent of the indigenous peoples of the Americas died as a result of European contact, through slaughter and, principally, disease. This led to the massive regrowth of natural vegetation, especially of forests in the Amazon, Andes, Mesoamerica, and the western areas of North America. These pre-1700 land use changes were substantially smaller, more localized, and less intensive than those that came later but still transformed landscapes, e.g., from closed to open woodlands, altering soils, fire regimes, and regional patterns of biodiversity. In some cases, relatively small human populations are thought to have made widespread and profound ecological changes over 3,000 years ago.
