31. The expansion of desert like conditions into areas where they did not previously exist is called desertification.
32. In some cases the loose soil is blown completely away, leaving a stony surface.
33. Desertification is accomplished primarily through the loss of stabilizing natural vegetation and the subsequent accelerated erosion of the soil by wind and water.
34. The impact of raindrops on the loose soil tends to transfer fine clay particles into the tiniest soil spaces, sealing them and producing a surface that allows very little water penetration.
35. The gradual drying of the soil caused by its diminished ability to absorb water results in the further loss of vegetation, so that a cycle of progressive surface deterioration is established.
36. In some regions, the increase in desert areas is occurring largely as the result of a trend toward drier climatic conditions.
37. The process may be accelerated in subsequent decades if global warming resulting from air pollution seriously increases.
38. The semiarid lands bordering the deserts exist in a delicate ecological balance and are limited in their potential to adjust to increased environmental pressures.
39. During the dry periods that are common phenomena along the desert margins, though, the pressure on the land is often far in excess of its diminished capacity, and desertification results.
40. Since the raising of most crops necessitates the prior removal of the natural vegetation, crop failures leave extensive tracts of land devoid of a plant cover and susceptible to wind and water erosion.
