Does soil degradation happen quickly?
Yes, many tropical soils are quite fragile, so that their condition can change markedly in a matter of months. Natural disturbances (D 11) such as a single heavy downpour, sudden rise in river level or severe windstorm can remove a lot of unprotected soil within a few hours. How much soil? When tropical land is completely cleared, the power of rain and wind to remove soil is not just increased a little, nor is it doubled or trebled. For savanna it is about a hundred times greater. For dense tropical forest it is around a thousand times more (D 23, D 70). Why then has land been allowed to become degraded? For many reasons, including: • lack of understanding of tropical ecosystems (D 10–16, D 60) and so introducing inappropriate techniques (D 16); • felling trees for timber without replacing them (D 24, D 36); • over-emphasis on large-scale, single-storey, pure plantations (D 2, D 30, D 50–54); • increasing human populations (D 3, D 5); • social problems related to land tenure (D 4); • s
