托福閱讀真題 Desert formation (6)
Paragraph 5: There is little doubt, however, that desertification in most areas primarily from human activities rather than natural processes. The semiarid lands bordering the desert exist in a delicate ecological balance and are limited in their potential to adjust to increased environmental pressures. Expanding populations are subjecting the land to increasing pressures to provide them with food and fuel. In wet periods, the land may be able to respond to these stresses. During the dry period that are common phenomena along the desert margins, though, the pressure on the land is often far in excess if its diminished capacity, and desertification results.