The Advance of Agriculture and the Retreat of Wilderness
People began to cultivate crop plants about 11,500 years ago in Southwest Asia and more recently in every other part of the populated world. At first, the early crops faced severe competition from wild plants, but in time the farmers overcame them, at least partially. It was not only their chosen plant species that the farmers were domesticating; they were also domesticating their soils. In those parts of the world where the land has been farmed for thousands of years little evidence remains about the effect of domesticating the soil, but the history of arable farming in the United States offers a recent, and very dramatic, example of soil domestication.
Originally, the North American Great Plains were covered by temperate grassland—the prairies. Prairie grasses were the predominant plants, some of them growing as tussocks. The tussocks slowed the wind close to ground level and the mats of grass roots, some extending to a considerable depth, bound the soil particles together. The plants secured the surface soil from erosion in a windy and fairly dry climate.
Farmers began migrating onto the plains in large numbers around the middle of the 19th century, many drawn there by the Homestead Act of 1862, which offered a free plot of land to anyone willing to live on it and farm it. The farmers burnt off the prairie grasses and plowed the land. Plowing was hard work, because the soil naturally formed clods that baked rock-hard in the hot summer sunshine. These had to be broken up in order to produce a fine texture suitable for sowing with arable crops. The work became easier after about 1915, when tractors began to appear. Between 1910 and 1919 the area of arable farmland on the prairies more than doubled. Little by little the work grew less arduous and yields increased. The farmers were succeeding in “taming” the prairie soils.
Then, the economic depression of the 1930s forced farmers to intensify production in order to maintain their incomes, just as a series of years with above-average rainfall came to an end. A prolonged drought destroyed crops. In previous droughts the roots of the prairie grasses and the hard clods of earth had prevented erosion, but the fine-textured farm soils had no such protection. The soil simply blew away.
This is an extreme example, but everywhere in the world, farming the land involves clearing the natural vegetation and progressively altering the character of the soil. Over most of lowland Europe, for instance, the temperate forest was the original natural vegetation. Except in the far north, where the climate is too cold for arable farming, farmers cleared almost all of that forest centuries ago. The landscapes of Europe are beautiful, but they are the product of agriculture.
The total land area of the world is approximately 50.40 million square miles (130.58 million km2). Of that total, almost 44 percent is farmed either with arable crops, perennial crops, or permanent pasture. Today, most people live in urban areas, and the expansion into the countryside of housing, commercial development, and roads is highly visible. Understandably, people fear that this poses a serious threat to biodiversity. Globally, however, urban areas occupy a mere 1.5 percent of the land area. It is not urban expansion that threatens biodiversity, but the expansion of agriculture.
During the 21st century, the predicted increase in the size of the human population means that food production must increase substantially. Every available technology will have to be applied if the increased output is to be achieved without destroying even more areas of natural habitat and reducing biodiversity. From the point of view of preserving biodiversity, the greenest type of farming is that which produces the highest yields from the smallest area of land while using agricultural chemicals efficiently to minimize both cost and pollution.