Although these forests have dense vegetation and many trees, the underlying soils are very poor with almost all the nutrients being held in the vegetation. As of now, about 80% of the soils in the humid tropics are acidic and infertile. The problem is that once forests have been cut down, essential nutrients are washed out of the soil altogether, leading to soil erosion. Erosion is a process where the soil is carried away by water, rain water, wind, etc.
The trees in the forest also keep the soil under them fresh and healthy. When the trees are cut down, there are no trees to keep the soil in place, and it becomes a target for erosion. It dries and cracks under the sun's heat. Once the soil temperature exceeds 25 degrees celsius, delicate nutrient ingredients like nitrogen can be lost, further reducing the fertility of the remaining soil. Furthermore, rainfall washes the remaining nutrients into the rivers. This means that replanting trees will not necessarily help to solve the problems of deforestation: by the time the new trees have matured, the soil might be completely stripped of essential nutrients. The soil will eventually be too poor to support the growth of vegetation and the land will be useless. Soil erosion eventually results in large areas of unusable land.
