If not eaten, they decompose and the organic matter is returned to the soil, which is vital in terms of keeping the soil nutrient-rich. Dead trees also decompose over time, and return their nutrients to the soil. The shade keeps the harsh sunlight from penetrating the ground, allowing it to maintain an appropriate moisture level. The tree trunk and canopy also protect the soil from harsh winds. Trees maintain soil fertility when nutrients drawn up by their roots are recycled into the top layers of the soil by leaf decomposition.
Trees also help keep the soil in place by means of their strong root systems.
This, as well as a tree's protective canopy, prevent soil erosion, which can have some very serious consequences. A half-hour thunderstorm in tropical forests can produce forty times more rain than the average northeastern U.S. thunderstorm. Therefore, these heavy downpours wash away more soil than anywhere else in the world. When it rains on slopes, hills or mountains that have been deforested, the rainwater will run off, carrying with it much of the topsoil from the hills. But it takes one hundred years for nature to produce just one inch of topsoil, which holds the nutrients needed for plant regeneration.