Many reasons including PH, Soil retention under weathering (tree roots hold soil, and reduce wind erosion from leaves too), preferred fertilizer mix (nitrogen f

Many reasons including PH, Soil retention under weathering (tree roots hold soil, and reduce wind erosion from leaves too), preferred fertilizer mix (nitrogen for example). This all said, there are plenty of farming techniques that can make the land productive, it's just not as simple as clear cut + plant.