The organic litter helped retain moisture for plant growth. Gradually the debris rotted and returned the nutrients to the soil. The roaming bison left the prairie to recover without further interference, allowing for lush and unrestrained growth. Putting fences across the land and stocking it with cattle creates a new sequence of grazing, which logically has a different effect on the land. This old material blocks sunlight, killing the new growth below.
Old vegetation stands for years, slowly decomposing through oxidation and weathering.
With fences to keep the cattle contained, the young plants are eaten repeatedly as grazing animals return without allowing the vegetation to recover. Burning the range can accelerate desertification, stealing vital organic matter from the soil and putting it into the atmosphere to contribute to global warming. Loss of organic matter also results in lack of soil structure, breaking down the granules or clumps of aggregated soil particles that allow air circulation and penetration of water and roots. Raindrops strike the exposed ground, pulverizing and separating the soil, just like you might find under the drip line of a house. The fine particles of silt, sand and clay dry to form a hard surface crust.