This section is based on of a worldwide assessment of soil degradation problems, the GLASOD project (ISRIC, 1991). Table 3 presents the main results for the eight countries of the region covered by the said project; the rest of the section is based on a sub-regional analysis for the same countries, using GLASOD data and complementing them with additional information (FAO, 1994).
3.1 Levels and types of degradation
At the global level, GLASOD found 15 percent of the land area to be degraded by human activities (around 1989).6/ For five countries in our group the proportion degraded is higher than this average, sometimes much higher.
The seriousness of degradation also must be taken into account. A handy way of doing this is to assign weighting coefficients to the percentages of Table 3; assigning 1 to lightly degraded areas, 2 to those moderately degraded and 3 to those strongly degraded, one sees that:
Areas with the most severe and extensive degradation comprise:
Soil erosion under the action of water (rain, streams and floods) is the main form of land degradation in the eight countries reviewed. According to the GLASOD assessment 83 million hectares (Mha) are affected, or 25% of the total area under crops and pastures.
Wind erosion affects 59 Mha--entirely in the dry zone, where 48% of the land under crops and pasture are thus affected (60% in Iran).7/
Chemical degradation, which accounts for 12 percent only of soil degradation at the global level, has a much higher impact in some of the countries reviewed here (Bangladesh and Sri Lanka in particular). This class of problems includes salinization, loss of soil fertility (nutrients, organic matter)8/ and pollution. Salinization, which is typical of irrigated areas, affects 42 Mha in the region (33 Mha in Iran, where more than half of all agricultural land is affected).
Finally, physical degradation has very little incidence here.9/
3.2 Causes of degradation and the role of population
If natural hazards are left aside, the causes of land degradation can be divided into direct and underlying causes. Direct causes are inappropriate land use and unsuitable land management practices, e.g. the cultivation of steep slopes without soil conservation measures. Underlying causes are the reasons why these inappropriate practices take place, e.g. the slopes may be cultivated because the landless poor need food, and conservation measures not taken because farmers lack security of tenure.
The GLASOD assessment addressed the direct causes of land degradation for each map unit, recognizing four causes:
Deforestation is a cause of degradation when the land that is cleared is steeply sloping or has shallow or easily erodible soils, and when clearance is not followed by good management. It is the dominant cause in six out of eight countries here (the exceptions are Iran and Afghanistan). According to the FAO Forest Resources Assessment 1990 project, these six countries have lost more than half a million hectares of forest area annually during 1980-1990 (FAO, 1994); the absolute annual losses, and remaining areas in 1990, were the following:
* Bangladesh: 38,000 ha lost(0.8 Mha remaining)
* Bhutan: 16,000 ha "( 2.8 Mha " )
* India: 339,000 ha "(51.7 Mha " )
* Nepal: 54,000 ha "(5.0 Mha " )
* Pakistan: 77,000 ha "( 1.9 Mha " )
* Sri Lanka: 27,000 ha "( 7.0 Mha " )
If absolute annual losses were to continue at the pace indicated here, the forests of Bangladesh would be entirely gone by 2011 and those of Pakistan by 2015.
Overcutting of vegetation occurs when people cut forests, woodlands and shrublands--to obtain timber, fuelwood and other products--at a pace exceeding the rate of natural regrowth. This is frequent in semi-arid environments, where fuelwood shortages are often severe. The phenomenon is significant in three countries here; it is the leading factor in Iran.
Overgrazing is the grazing of natural pastures at stocking intensities above the livestock carrying capacity; the resulting decrease in the vegetation cover is a leading cause of wind and water erosion. It is a significant factor in six countries, and by far the most important in Afghanistan.
Agricultural activities that can cause land degradation include shifting cultivation without adequate fallow periods, absence of soil conservation measures, cultivation of fragile or marginal lands, unbalanced fertilizer use, and a host of possible problems arising from faulty planning or management of irrigation. They are a major factor in Sri Lanka and the dominant one in Bangladesh.
The role of population factors in land degradation processes obviously occurs in the context of the underlying causes. In the region, in fact, it is indeed one of the two major basic causes of degradation along with land shortage, and land shortage itself ultimately is a consequence of continued population growth in the face of the finiteness of land resources. In the context of land shortage the growing population pressure, during 1980-1990, has led to decreases in the already small areas of agricultural land per person in six out of eight countries (14% for India and 22% for Pakistan).
Population pressure also operates through other mechanisms. Improper agricultural practices, for instance, occur only under constraints such as the saturation of good lands under population pressure which leads settlers to cultivate too shallow or too steep soils, plough fallow land before it has recovered its fertility, or attempt to obtain multiple crops by irrigating unsuitable soils.