This is not new. In 1938, Walter Lowdermilk, a senior official in the Soil Conservation Service of the USDA, traveled abroad to look at lands that had been cultivated for thousands of years, seeking to learn how these older civilizations had coped with soil erosion. He found that some had managed their land well, maintaining its fertility over long stretches of history, and were thriving. Others had failed to do so and left only remnants of their illustrious pasts.
In a section of his report titled "The Hundred Dead Cities," he described a site in northern
Wind and water erosion take a toll. The latter can be seen in the silting of reservoirs and in satellite photographs of muddy, silt-laden rivers flowing into the sea. Pakistan’s two large reservoirs, Mangla and Tarbela, which store Indus River water for the country’s vast irrigation network, are losing roughly 1 percent of their storage capacity each year as they fill with silt from deforested watersheds.
Ethiopia, a mountainous country with highly erodible soils, is losing close to 2 billion tons of topsoil a year, washed away by rain. This is one reason
Soil erosion from the deterioration of grasslands is widespread. The world’s steadily growing herds of cattle and flocks of sheep and goats forage on the two-fifths of the earth's land surface that is too dry, too steeply sloping, or not fertile enough to sustain crop production. This area supports most of the world’s 3.3 billion cattle, sheep, and goats, all ruminants with complex digestive systems that enable them to digest roughage, converting it into beef, mutton, and milk.
An estimated 200 million people make their living as pastoralists, tending cattle, sheep, and goats. Since most land is held in common in pastoral societies, overgrazing is difficult to control. As a result, half of the world’s grasslands are degraded. The problem is highly visible throughout Africa, the Middle East, Central Asia, and northwest
Nigeria, Africa's most populous country, is losing 351,000 hectares (867,000 acres) of rangeland and cropland to desertification each year. While
Iran, with 73 million people, illustrates the pressures facing the
Soil erosion often results from the demand-driven expansion of cultivation onto marginal land. Over the last century or so there were massive cropland expansions in two countries -- the
During the late 19th century, millions of Americans pushed westward, homesteading on the
The second major expansion came in the
A third massive cropland expansion is now taking place in the Brazilian Amazon Basin and in the cerrado, a savannah-like region bordering the basin on its south side. Land in the cerrado, like that in the U.S. and Soviet expansion, is vulnerable to soil erosion. This cropland expansion is pushing cattle ranchers into the Amazon forests, where ecologists are convinced that continuing to clear the area of trees will end in disaster. Reporter Geoffrey Lean, summarizing the findings of a 2006 Brazilian scientific symposium in London’s Independent, notes that the alternative to a rainforest in the Amazon would be “dry savannah at best, desert at worst.”
Civilization depends on fertile soils. Ultimately, the health of the people cannot be separated from the health of the land. Conserving and rebuilding soils will be covered in the next Plan B 4.0 Book Byte.
Adapted from Chapter 2, “Population Pressure: Land and Water” in Lester R. Brown, Plan B 4.0: Mobilizing to Save Civilization.