Atlas Search:

AAAS > International




Peter H. Raven


  Natural resources
  Land use
  Waste and chemicals
  Atlas endnotes
Background sources
About the atlas
World map and   conversion tables


Flash version in EARTHscope

Order Print Copy





[Add] = Add preceding section to My Atlas
Use link at page bottom to add entire article

astures, which cover more than a quarter of the Earth's land surface, are facing pressures from the rapidly increasing demand for meat and from cultivators trying to convert them to croplands. Can these seemingly fragile lands be sustainably managed, or must they fall prey to human consumption?

Rainforest clearance

In Latin America in particular, rainforests are being cleared to make way for cattle pastures. In Brazil, for example, an estimated 70 percent of deforestation has been attributed to clearance for livestock. This often destroys soil fertility within a few years, forcing the abandonment of some areas and the clearance of more forest [8]. [Add]

The world's expanse of pastures -- grazing lands ranging from the Argentinian pampas and the arid scrublands of the Sahel, to the Mongolian grassland steppes and the rainfed grasslands of New Zealand -- remained almost stationary during the past three centuries. Increases in the less densely populated regions of tropical Africa and Latin America, often at the expense of forests, were matched by declines, each of around 20 percent, in Europe, Southeast Asia and North America, where increasing population densities forced a switch from grazing to more intensive cultivation and the feeding of animals using grains such as maize [1]. More recently however, parts of Asia, particularly China and Saudi Arabia, have seen substantial increases, accounting for much of the 9 percent rise in global pasture land over the last 25 years [2]. [Add]

Livestock and pollution
Livestock herds are large-scale producers of gas emissions. All animals emit carbon dioxide, while ruminants also produce another greenhouse gas, methane. A third gas responsible for global warming, nitrous oxide, is released from manure. Intensive "factory farming" has created an increasing waste problem. The Netherlands is being forced to reduce its pig production because of problems with disposing of slurry safely without polluting rivers or intensifying acid deposition problems through the evaporation of ammonia. [Add]
It is estimated that 73 percent of the world's grazing land has so deteriorated that it has lost at least 25 percent of its animal carrying capacity [3]. Traditional livestock herders are often demonized as the cause, but some researchers have defended the traditional techniques of pastoralists, saying that they have frequently been forced to occupy already degraded land -- unsuitable for cultivation because of its low and unreliable rains, poor drainage, extreme temperatures and rough terrain. Moreover, the policies of many developing world governments towards pastures can often be inappropriate, geared towards Western-style cattle grazing based on intensification, standardization and individual land ownership. This is very different from the indigenous and ecologically more viable methods of tropical rangeland management, based on diversity and migration across unfenced areas [4]. It has also been argued that rangeland vegetation and soils are far more resilient than once assumed, able to recover when the animals move on or the rains return [5]. [Add]

Livestock provide meat, dairy products, hides, tallow and other products. They are also the main source of motive power on more than 300 million hectares of cropland [6] and represent a form of capital for many rural families, realizable in hard times or as a dowry for a bride. Around the world grazing systems vary greatly. Even in rich developed countries large areas of land unsuitable for cultivation are grazed with little or no chemical inputs -- notably the hills and mountains of much of Europe, and the sheep pastures of southern South America, Central Asia, Australia and New Zealand. In such conditions, as well as in the tropics, livestock can improve biodiversity, soil and vegetation cover -- notably by removing and controlling the growth of "bush" that can trigger fires, and by dispersing seeds on their hooves and in their dung [7].

Manure from livestock is vital to land fertility in both natural and agricultural ecosystems, particularly where national and personal incomes are too low to allow the purchase of chemical fertilizers. While grazing and eating, ruminants in particular collect and concentrate nutrients and convert them into manure, which fertilizes the soil and maintains soil structure. In effect their digestive systems are speeding up the recycling of nutrients. In traditional farming systems, animals are often tethered on croplands, so helping sustain crop production.


[world pasture map]

[animal products]

[animals / grassland]

Studies in Africa have shown livestock-mediated nutrient recycling to be essential to maintaining croplands without large inputs of chemical fertilizer, and the value of livestock in fertilizing crops rises with increased population density. In the East African highlands, such as the Kiambu district of Kenya, where population density can exceed 500 people per square kilometer, livestock are vital parts of the cropping system [9]. In contrast, more intensively managed pastures, where artificial fertilizer is added to accelerate the growth of grass, may have an overall negative effect on the long-term health of the environment [10]. The nitrogen suppresses biodiversity and causes the glut that leads to eutrophication of rivers. [Add]

[Add to My Atlas]

Demand for meat, however, has outstripped available pastures, with the result that more and more livestock are fed on fodder crops. This is a global trend but applies particularly in the most densely populated countries. Between 1990 and 1995, four fifths of China's increase in grain consumption went to feed livestock. Worldwide, 40 percent of grain is grown to feed livestock. The main fodder is maize, the production of which, for the first time in history, edged ahead of wheat globally in the late 1990s. [Add]

The shortage of pastures has also helped change the kind of livestock being raised. The global population of cattle, which traditionally feed on pastures, is rising much less quickly than animals that eat from feedlots, such as pigs (now the world's largest meat source) and poultry, which also now exceeds beef production. But intensive livestock systems tend to reduce "barnyard biodiversity" in the same way that the green revolution in crops has reduced it amongst plants. Many traditional livestock breeds have disappeared. Of the 3 800 breeds of cattle, water buffalo, goats, pigs, sheep, horses and donkeys catalogued by the Food and Agriculture Organization, 16 percent have become extinct and a further 15 percent are rare [11]. [Add]

In Western countries, where population densities are often high and most land and livestock owners are dependent upon the major corporations that control food distribution networks, the intensification of livestock production is most marked. In developing countries, livestock owners are often the poor and politically marginalized [12], and grazing stocks of cattle, sheep and goats still occupy traditional pastures with no chemical inputs. But these pastoralists, too, are dependent on markets for a part of their income, and attempts to rear ever larger herds in fragile arid regions and on hillsides can lead to soil degradation and the specter of desertification.

Reviving traditional methods, most of which rely on a series of finely balanced factors including the ability to migrate across large areas of rangeland, herd sizes and the mix of animals being reared, will prove hard when demands on pastures from cultivators are growing and two thirds of the world's agricultural land is already given over to livestock pastures [13]. [Add]

[Add article to My Atlas] [Download article as PDF]

[Croplands] [Minerals]