It takes considerable time for fertile soil to cover the surface of mountain. Many ingredients and some other factors are also required. First rocks must be broken down by wind and rain to pieces to become the base of soil. Fertile soil must include water and air inside. Having those in the base of soil several organisms such as plants, micro fungi and bacteria work together. The secretion of bacteria makes a small lump of a particle in the base of soil. Earthworms are also important. They eat soil and excrete feces of which form are small lumps as well. Then roots of plants and micro fungi connect these small lumps to each other to become a large lump. Both small and large lumps create many gaps among them. These gaps are able to hold air and water. Besides inside of each small lump there are cavities in which air and water stay. On such fertile soil trees and other large plants can easily spread their roots to use water and air inside.

It is also necessary for fertile soil that many kinds of animals and plants live simultaneously in the basic of soil. Organic matters such as fallen leaves and twigs are almost impossible to be decomposed, but insects such as termites and fungi are able to break those organic matters into leaf mold which is known as natural fertilizer. Fungi give minerals such as phosphoric acid and nitric acid to plants and get organic matters such as carbohydrates instead through the roots of plants. This activity also accumulates minerals and organic matters in the soil. Not only feces but also carcass of animals are decomposed by insects and bacteria and become natural fertilizer such as calcium and irons for plants and fungi.