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 regions. In these areas, response rates are high and the environmental consequences of residues are not yet a problem. Hence these regions would benefit by using more agrochemicals. However, the growth in the use of chemicals tends to be concentrated precisely where they may be doing more overall harm than good.

3.3 Pressure on Forests
29. Forests are crucial for maintaining and improving the productivity of agricultural land. Yet agricultural expansion, a growing world timber trade, and woodfuel demand have destroyed much forest cover. Although this destruction has occurred worldwide, today the greatest challenge is in developing countries, particularly in tropical forests. (See Chapter 6.)

30. Growing populations and the decreasing availability of arable land lead poor farmers in these countries to seek new land in forests to grow more food. Some government policies encourage the conversion of forests to pastures and others encourage large resettlement schemes in forests. There is nothing inherently wrong with clearing forests for farming, provided that the land is the best there is for new farming, can support the numbers encouraged to settle upon it, and is not already serving a more useful function, such as watershed protection. But often forests are cleared without forethought or planning.

31. Deforestation most severely disrupts mountainous areas and upland watersheds and the ecosystems that depend on them. The uplands influence precipitation, and the state of their soil and vegetation systems influence how this precipitation is released into the streams and rivers and onto the croplands of the plains below. The growing numbers and growing severity of both floods and droughts in many parts of the world have been linked to the deforestation of upland watersheds.

3.4 Advancing Deserts
32. Some 29 per cent of the earth's land area suffers slight, moderate, or severe desertification; an additional 6 per cent is classified as extremely severely desertified. In 1984, the world's drylands supported some 850 million people, of whom 230 million were on lands affected by severe desertification.

33. The process of desertification affects almost every region of the globe, but it is most destructive in the drylands of South America, Asia, and Africa; for these three areas combined, 18.5 per cent (870 million hectares) of productive lands are severely desertified. Of the drylands in developing countries, Africa's Sudano-Sahelian zones and, to a lesser extent, some countries south of this zone suffer the most. In their arid and semi-arid lands are to be found 80 per cent of the moderately affected and 85 per cent of the severely affected people.

34. Land permanently degraded to desert-like conditions continues to grow at an annual rate of 6 million hectares. Each year, 21 million additional hectares provide no economic /…