How does the fertility of soil decreases due to deforestation?

Deforestation dramatically reduces soil fertility by disrupting the natural nutrient cycling processes that forests maintain. In healthy forests, fallen leaves, branches, fruits, and dead organisms decompose on the forest floor, continuously releasing nitrogen, phosphorus, potassium, and other essential nutrients back into the soil. Tree roots also help break down rocks and minerals, making nutrients accessible to plants. When trees are removed, this nutrient recycling system collapses—there is no longer a steady supply of organic matter to decompose and enrich the soil. Additionally, tree roots that once held soil particles together and prevented nutrient-rich topsoil from washing away are no longer present.

Without forest cover, exposed soil becomes vulnerable to erosion by wind and rain, which rapidly washes away the fertile topsoil layer that took centuries to form. Heavy rainfall directly strikes bare ground, compacting soil and reducing its ability to absorb water and nutrients. Soil temperatures also fluctuate more dramatically without the moderating canopy cover, killing beneficial microorganisms, earthworms, and fungi that help maintain soil structure and fertility. The soil gradually becomes hard, depleted, and less productive. In tropical regions, this degradation occurs particularly quickly because rainforest soils naturally depend heavily on constant organic matter inputs—once the forest is cleared, the thin fertile layer disappears within just a few growing seasons, leaving behind infertile, compacted earth unsuitable for sustained agriculture.