Question

how does defforestation land the reduction of soil fertility

Answer 1

1) Logging and subsequently harvesting trees removes nutrients, like phosphates, from the system.
2) The removal of the vegetation that would also normally act as a protective cover and windbreak increases the raindrop impact and wind velocity, whilst simultaneously decreasing the humus content.
3) This accelerates soil erosion from wind and rain splash.
4) Reduced humus content means there is less infiltration and the soil is looser, and so is more easily eroded and removed from the area in runoff.
5) Removal of root systems reduces the root binding effect that gives the soil structure and holds it together.
6) A further impact of deforestation is the reduced evapotranspiration rate, leading to decreased humidity and therefore reduced regional rainfall – contributing to accelerated desertification.
7) These cumulative effects result in a reduction in the nutrient content of the soil and also in the depth of the layer of fertile topsoil.

Answer 2

Deforestation leads in soil eroison which futher leads in carrying away the humus layer of soil which is considered for fertility of soil. Thus deforestation leads in reduction of soil fertility.