But a new report by AG's Land and Water Development Division (AGL) warns that population pressure, accompanied by rising demand for food, fuel and construction materials, is placing progressively more intense pressure on the region's natural resources. It estimates that soil erosion, acidification, loss of organic matter, compaction, nutrient impoverishment and salinization have reduced productivity on more than 3 million sq km of farmland, while almost 800,000 sq km of drylands are threatened by desertification due to overgrazing, overexploitation of vegetation for domestic use, deforestation and inappropriate irrigation methods.
While the overall cultivable land area could be expanded more than fourfold from the present 1.7 million sq km, most of the potentially cultivable land is of marginal quality and its utilization would entail high social, economic and environmental risks. Other lands that are not being used for cultivation are covered by tropical forests, whose conservation is vital to global ecological stability and biodiversity. Although little more than 4% of cultivable lands are irrigated, possibilities of expanding the irrigated area are limited and competition for water for domestic consumption and industry is increasing.
Different agro-environments. AGL says that sustainable development in Latin America and the Caribbean will be possible only when problems of land degradation and desertification are overcome, and land is used and managed in a way that is socially and economically acceptable to all sectors of society and does not cause environmental deterioration. Its report divides the region into several clearly differentiated agro-environments with specific potentials and limitations.
Insidious processes of soil erosion in densely populated steeplands is progressively reducing local people's capacity to meet even their subsistence food needs. Average daily food intake in these zones is below the regional average of 2,673 kcal/person. Soil erosion is also forcing large numbers of small-scale farmers to migrate to cities or to forested areas in the lowland tropics which constitute the agricultural frontier in many Andean countries. As in many other mountainous environments of the world, soil erosion is becoming the most pressing environmental problem in these areas.
Dryland areas constitute approximately 15% of Latin America and are found in a great variety of landscapes, ranging from the Pacific coastal zone and Chaco plains to the semi-arid Pampa grasslands. About one-third of these areas is threatened by desertification. Within the dryland zones are important irrigated areas, which provide more than 50% of total food production in Mexico and produce a significant proportion of the agricultural exports of Chile and Brazil. The productivity of many irrigated areas is in danger because of poor quality water and diminishing water supplies - an estimated 10% to 15% of irrigated land in arid zones are degraded by waterlogging and salinity.
The conversion of forested land to cropland and pastures is most rapid in the humid tropics. The creation of croplands has led to loss of soil organic matter, accelerated erosion and increased sediment loads in rivers and lakes. It has also given rise to losses of important plant and animal species due to direct destruction and to changes in their habitats. In the Amazonian region in particular, new settlers have been allowed to extract timber and establish crops or pastures. However, the nature of the soils, vegetation and climate and restricted land use suitability have seldom been taken into account. In some areas, especially those with high rainfall, transformation of the natural ecosystem has caused pronounced land degradation and loss of productive capacity. It is estimated that more than 800,000 sq km of forest in the Amazon have been felled due to the combined effects of population pressure, poverty and the commercial exploitation of cattle, timber and minerals.
Grazing lands include subtropical and temperate grasslands in the south of the continent, seasonal pastures of the high altitude Andean regions, and tropical savannahs and pastures of the Amazon basin. Overgrazing is the main cause of degradation of natural pastures, resulting in a rapid decline in productivity. In large watersheds this can result in damage such as gully erosion and contaminated water supplies in lower-lying areas of the catchment. Many of the soils under cultivated pastures are of low fertility and pasture productivity generally diminishes with time due to poor management. In the Andean highlands, the risks of deterioration are accentuated by steep topography and the short length of growing periods. Under these conditions, water and wind erosion can severely damage soil, cause sediment accumulation in river channels and reservoirs, and lead to flooding, waterlogging and salinization.
Wetlands occupy 11% of the region and are most common in Central America, the southern cone, the north of Bolivia, southeast Brazil and Mexico. Their principal limitations are lack of drainage and a high risk of flooding. Although soils are very varied in terms of texture and acidity, the majority are well supplied with nutrients and can be very productive if adequately drained and protected from flooding. The potential effects of drainage on the hydrology of the surrounding land and on the environment, including plant and animal diversity, need to be considered before such conversion.
The acid savannahs, consisting predominantly of low shrubs and tough grasses with a 4-6 month dry season and an annual rainfall of 1,200-2,000 mm, occur mainly in the vast Cerrado region of Brazil where they occupy 1.1 million sq km of rolling landscape. The soils are physically good, deep, well drained and easy to plough, but suffer from very low chemical fertility due to high acidity, low nutrient content and very high aluminium saturation. However, with good management - including considerable quantities of fertilizers and lime - acid savannahs can become very productive. However, the application of fertilizers and lime is very costly and, alone, not sufficient to sustain yields. Soils are very susceptible to erosion and if management practices do not ensure an adequate soil cover and provide effective conservation, erosion can rapidly degrade the soils until they are abandoned.
Small island environments
In the Caribbean, the small proportion of agriculturally suitable land provides few opportunities for production and leads to an intensive use of the limited areas available. Due to the population pressure, these limitations have become even more serious on almost all of the Caribbean islands, both large and small, with the possible exception of the Dominican Republic and Cuba, where agro-ecological conditions are more similar to those of continent.
Published November 1998