My best guess is that the development of forest root structures, combined with microbial, animal, and insect action, makes the soil more porous and absorbent. This allows rainfall to be captured and "reclaimed" by the soil, with excess trickling down into the aquifer. Simultaneously, the dense canopy provides shade to slow the effects of evaporation.
By contrast, a barren soil would become hard and compacted, and much of the rainfall would simply wash away or be lost to evaporation.
Again, this is one man's educated guess. I'm no expert, and it's quite possible I'm way off the mark.
By contrast, a barren soil would become hard and compacted, and much of the rainfall would simply wash away or be lost to evaporation.
Again, this is one man's educated guess. I'm no expert, and it's quite possible I'm way off the mark.